Comparative analysis of encephalization in mammals reveals relaxed constraints on anthropoid primate and cetacean brain scaling

Evolutionary lability of food caching behaviour in mammals

Food hoarding provides animals access to resources during periods of scarcity. Studies on mammalian caching indicate associations with brain size, seasonality and diet but are biased to a subset of rodents. Whether the behaviour is generalizable at other taxonomic scales and/or is influenced by other ecological factors is less understood. Population density may influence food caching due to food competition or pilferage, but this remains untested in a comparative framework. Using phylogenetic analyses, we assessed the role of morphology (body and brain size), climate, diet breadth and population density on food caching behaviour evolution at multiple taxonomic scales. We also used a long-term dataset on caching behaviour of red squirrels (Tamiasciurus fremonti) to test key factors (climate and population density) on hoarding intensity. Consistent with previous smaller scale studies, we found the mammalian ancestral state for food caching was larderhoarding, and scatterhoarding was derived. Caching strategy was strongly associated with brain size, population density and climate. Mammals with larger brains and hippocampal volumes were more likely to scatterhoard, and species living at higher population densities and in colder climates were more likely to larderhoard. Finer-scale analyses within families, sub-families and tribes indicated that the behaviour is evolutionary labile. Brain size in family Sciuridae and tribe Marmotini was larger in scatterhoarders, but not in other tribes. Scatterhoarding in tribe Marmotini was more likely in species with lower population densities while scatterhoarding in tribe Sciurini was associated with warmer climates. Red squirrel larderhoarding intensity was positively related to population density but not climate, implicating food competition or pilferage as an important mechanism mediating caching behaviour. Our results are consistent with previous smaller-scale studies on food caching and indicate the evolutionary patterns of mammalian food caching are broadly generalizable. Given the lability of caching behaviour as evidenced by the variability of our results at finer phylogenetic scales, comparative analyses must consider taxonomic scale. Applying our results to conservation could prove useful as changes in population density or climate may select for different food caching strategies and thus can inform management of threatened and endangered species and their habitats.

Smarter foragers do not forage smarter: a test of the diet hypothesis for brain expansion

A leading hypothesis for the evolution of large brains in humans and other species is that a feedback loop exists whereby intelligent animals forage more efficiently, which results in increased energy intake that fuels the growth and maintenance of large brains. We test this hypothesis for the first time with high-resolution tracking data from four sympatric, frugivorous rainforest mammal species (42 individuals) and drone-based maps of their predominant feeding trees. We found no evidence that larger-brained primates had more efficient foraging paths than smaller brained procyonids. This refutes a key assumption of the fruit-diet hypothesis for brain evolution, suggesting that other factors such as temporal cognition, extractive foraging or sociality have been more important for brain evolution.

Tempo and mode of gene expression evolution in the brain across primates

Primate evolution has led to a remarkable diversity of behavioral specializations and pronounced brain size variation among species (Barton, 2012; DeCasien and Higham, 2019; Powell et al., 2017). Gene expression provides a promising opportunity for studying the molecular basis of brain evolution, but it has been explored in very few primate species to date (e.g. Khaitovich et al., 2005; Khrameeva et al., 2020; Ma et al., 2022; Somel et al., 2009). To understand the landscape of gene expression evolution across the primate lineage, we generated and analyzed RNA-seq data from four brain regions in an unprecedented eighteen species. Here, we show a remarkable level of variation in gene expression among hominid species, including humans and chimpanzees, despite their relatively recent divergence time from other primates. We found that individual genes display a wide range of expression dynamics across evolutionary time reflective of the diverse selection pressures acting on genes within primate brain tissue. Using our samples that represent a 190-fold difference in primate brain size, we identified genes with variation in expression most correlated with brain size. Our study extensively broadens the phylogenetic context of what is known about the molecular evolution of the brain across primates and identifies novel candidate genes for the study of genetic regulation of brain evolution.

Report on the brain of the monk seal (Monachus monachus, Hermann, 1779)

The Mediterranean monk seal (Monachus monachus, Hermann, 1779) is an endangered species of pinniped endemic to few areas of the Mediterranean Sea. Extensive hunting and poaching over the last two centuries have rendered it a rare sight, scattered mainly in the Aegean Sea and the western coast of North Africa. In a rare event, a female monk seal calf stranded and died in southern Italy (Brindisi, Puglia). During due necropsy, the brain was extracted and fixed. The present report is the first of a monk seal brain. The features reported are remarkably typical of a true seal brain, with some specific characteristics. The brain cortical circonvolutions, main fissures and the external parts are described, and an EQ was calculated. Overall, this carnivore adapted to aquatic life shares some aspects of its neuroanatomy and physiology with other seemingly distant aquatic mammals.

CEGA: a method for inferring natural selection by comparative population genomic analysis across species

We developed maximum likelihood method for detecting positive selection or balancing selection using multilocus or genomic polymorphism and divergence data from two species. The method is especially useful for investigating natural selection in noncoding regions. Simulations demonstrate that the method outperforms existing methods in detecting both positive and balancing selection. We apply the method to population genomic data from human and chimpanzee. The list of genes identified under selection in the noncoding regions is prominently enriched in pathways related to the brain and nervous system. Therefore, our method will serve as a useful tool for comparative population genomic analysis.

Island biogeography theory and the gut: why taller people tend to harbor more diverse gut microbiomes

Prior work has shown a positive scaling relationship between vertebrate body size and gut microbiome alpha-diversity. This observation mirrors commonly observed species area relationships (SAR) in many other ecosystems. Here, we show a similar scaling relationship between human height and gut microbiome alpha-diversity across two large, independent cohorts, controlling for a wide range of relevant covariates, such as body mass index, age, sex, and bowel movement frequency. Island Biogeography Theory (IBT), which predicts that larger islands tend to harbor greater species diversity through neutral demographic processes, provides a simple mechanism for these positive SARs. Using an individual-based model of IBT adapted to the gut, we demonstrate that increasing the length of a flow-through ecosystem is associated with increased species diversity. We delve into the possible clinical implications of these SARs in the American Gut Cohort. Consistent with prior observations that lower alpha-diversity is a risk factor for Clostridioides difficile infection (CDI), we found that individuals who reported a history of CDI were shorter than those who did not and that this relationship appeared to be mediated by alpha-diversity. We also observed that vegetable consumption mitigated this risk increase, also by mediation through alpha-diversity. In summary, we find that body size and gut microbiome diversity show a robust positive association, that this macroecological scaling relationship is related to CDI risk, and that greater vegetable intake can mitigate this effect.

Regulatory and coding sequences of TRNP1 co-evolve with brain size and cortical folding in mammals

Brain size and cortical folding have increased and decreased recurrently during mammalian evolution. Identifying genetic elements whose sequence or functional properties co-evolve with these traits can provide unique information on evolutionary and developmental mechanisms. A good candidate for such a comparative approach is TRNP1, as it controls proliferation of neural progenitors in mice and ferrets. Here, we investigate the contribution of both regulatory and coding sequences of TRNP1 to brain size and cortical folding in over 30 mammals. We find that the rate of TRNP1 protein evolution (ω) significantly correlates with brain size, slightly less with cortical folding and much less with body size. This brain correlation is stronger than for >95% of random control proteins. This co-evolution is likely affecting TRNP1 activity, as we find that TRNP1 from species with larger brains and more cortical folding induce higher proliferation rates in neural stem cells. Furthermore, we compare the activity of putative cis-regulatory elements (CREs) of TRNP1 in a massively parallel reporter assay and identify one CRE that likely co-evolves with cortical folding in Old World monkeys and apes. Our analyses indicate that coding and regulatory changes that increased TRNP1 activity were positively selected either as a cause or a consequence of increases in brain size and cortical folding. They also provide an example how phylogenetic approaches can inform biological mechanisms, especially when combined with molecular phenotypes across several species.

Innovative problem-solving in a small, wild canid

Innovation - the ability to solve problems in a novel way - is not only associated with cognitive abilities and relative brain size, but also by noncognitive traits, such as personality and motivation. We used a novel foraging task with three access options to determine how neophobia, exploration, and persistence influence innovation in 12 habituated bat-eared foxes (Otocyon megalotis) in the Kalahari Desert. Bat-eared foxes offer a unique system to understand cognition as they have the smallest relative brain size of measured canids and a specialized, termite-based diet, yet have displayed foraging innovations. Interestingly, most of our individuals solved the task at least once and six individuals solved the task in every trial. Neophobia did not influence success on the first trial, but both exploration and persistence influenced success across all trials. Those individuals that solved the puzzle over multiple trials became faster over time, suggesting that they learned how to open the box more efficiently. We found some variation in the method to open the puzzle box with six individuals solving the puzzle using two methods and one individual using all three methods. This is the first study to show innovation in a novel foraging task in wild bat-eared foxes.

Gradistics: An underappreciated dimension in evolutionary space

The growth of complexity is an unsolved and underappreciated problem. We consider possible causes of this growth, hypotheses testing, molecular mechanisms, complexity measures, cases of simplification, and significance for biomedicine. We focus on a general ability of regulation, which is based on the growing information storage and processing capacities, as the main proxy of complexity. Natural selection is indifferent to complexity. However, complexification can be inferred from the same first principle, on which natural selection is founded. Natural selection depends on potentially unlimited reproduction under limited environmental conditions. Because of the demographic pressure, the simple ecological niches become fulfilled and diversified (due to species splitting and divergence). Diversification increases complexity of biocenoses. After the filling and diversification of simple niches, the more complex niches can arise. This is the 'atomic orbitals' (AO) model. Complexity has many shortcomings but it has an advantage. This advantage is ability to regulatory adaptation, including behavioral, formed in the evolution by means of genetic adaptation. Regulatory adaptation is much faster than genetic one because it is based on the information previously accumulated via genetic adaptation and learning. Regulatory adaptation further increases complexity of biocenoses. This is the 'regulatory advantage' (RA) model. The comparison of both models allows testable predictions. We focus on the animal evolution because of the appearance of higher regulatory level (nervous system), which is absent in other lineages, and relevance to humans (including biomedical aspects).

Evolution of Longevity as a Species-Specific Trait in Mammals

From the evolutionary point of view, the priority problem for an individual is not longevity, but adaptation to the environment associated with the need for survival, food supply, and reproduction. We see two main vectors in the evolution of mammals. One is a short lifespan and numerous offspring ensuring reproductive success (r-strategy). The other one is development of valuable skills in order compete successfully (K-strategy). Species with the K-strategy should develop and enhance specific systems (anti-aging programs) aimed at increasing the reliability and adaptability, including lifespan. These systems are signaling cascades that provide cell repair and antioxidant defense. Hence, any arbitrarily selected long-living species should be characterized by manifestation to a different extent of the longevity-favoring traits (e.g., body size, brain development, sociality, activity of body repair and antioxidant defense systems, resistance to xenobiotics and tumor formation, presence of neotenic traits). Hereafter, we will call a set of such traits as the gerontological success of a species. Longevity is not equivalent to the evolutionary or reproductive success. This difference between these phenomena reaches its peak in mammals due to the development of endothermy and cephalization associated with the cerebral cortex expansion, which leads to the upregulated production of oxidative radicals by the mitochondria (and, consequently, accelerated aging), increase in the number of non-dividing differentiated cells, accumulation of the age-related damage in these cells, and development of neurodegenerative diseases. The article presents mathematical indicators used to assess the predisposition to longevity in different species (including the standard mortality rate and basal metabolic rate, as well as their derivatives). The properties of the evolution of mammals (including the differences between modern mammals and their ancestral forms) are also discussed.

Layered habitats: An evolutionary model for present-day recreational needs

Urbanisation and lifestyle-related illnesses increase globally. This highlights the need to shape modern human habitats to support basic recreational needs, promoting such things as physical activity and restoration of high stress levels and cognitive fatigue. Previous research suggests eight perceived qualities in the outdoor environment, described as eight perceived sensory dimensions, as universally meaningful to people in this regard. However quite extensively studied in relation to various health and wellbeing outcomes, human sensitivity and appreciation for these qualities has not yet been explicitly analysed from an evolutionary perspective. This paper investigates their possible evolutionary roots and suggests an order for their development. This is linked with empirical findings on their relative capacity to support restoration of stress and cognitive fatigue. Qualities of earlier origin are suggested to correspond to older, more fundamental adaptations. Each subsequently developed quality implies an increased complexity of our environmental relations, associated with higher demands on more recently developed capacities. The proposed model thus links the more restorative Serene, Sheltered, Natural, and Cohesive perceived sensory dimensions with earlier stages of our development while the more demanding Diverse, Open, Cultural, and Social qualities are associated with more recent transitions. It might be of relevance when shaping modern human habitats from a health-promoting perspective, and have applications in the planning and design of, e.g., health care settings, rehabilitation gardens, urban green areas, recreational forests or other similar outdoor environments.

The large numbers of minicolumns in the primary visual cortex of humans, chimpanzees and gorillas are related to high visual acuity

Minicolumns are thought to be a fundamental neural unit in the neocortex and their replication may have formed the basis of the rapid cortical expansion that occurred during primate evolution. We sought evidence of minicolumns in the primary visual cortex (V-1) of three great apes, three rodents and representatives from three other mammalian orders: Eulipotyphla (European hedgehog), Artiodactyla (domestic pig) and Carnivora (ferret). Minicolumns, identified by the presence of a long bundle of radial, myelinated fibers stretching from layer III to the white matter of silver-stained sections, were found in the human, chimpanzee, gorilla and guinea pig V-1. Shorter bundles confined to one or two layers were found in the other species but represent modules rather than minicolumns. The inter-bundle distance, and hence density of minicolumns, varied systematically both within a local area that might represent a hypercolumn but also across the whole visual field. The distance between all bundles had a similar range for human, chimpanzee, gorilla, ferret and guinea pig: most bundles were 20-45 μm apart. By contrast, the space between bundles was greater for the hedgehog and pig (20-140 μm). The mean density of minicolumns was greater in tangential sections of the gorilla and chimpanzee (1,243-1,287 bundles/mm2) than in human (314-422 bundles/mm2) or guinea pig (643 bundles/mm2). The minicolumnar bundles did not form a hexagonal lattice but were arranged in thin curving and branched bands separated by thicker bands of neuropil/somata. Estimates of the total number of modules/minicolumns within V-1 were strongly correlated with visual acuity.

Socioecological complexity in primate groups and its cognitive correlates

Characterizing non-human primate social complexity and its cognitive bases has proved challenging. Using principal component analyses, we show that primate social, ecological and reproductive behaviours condense into two components: socioecological complexity (including most social and ecological variables) and reproductive cooperation (comprising mainly a suite of behaviours associated with pairbonded monogamy). We contextualize these results using a meta-analysis of 44 published analyses of primate brain evolution. These studies yield two main consistent results: cognition, sociality and cooperative behaviours are associated with absolute brain volume, neocortex size and neocortex ratio, whereas diet composition and life history are consistently associated with relative brain size. We use a path analysis to evaluate the causal relationships among these variables, demonstrating that social group size is predicted by the neocortex, whereas ecological traits are predicted by the volume of brain structures other than the neocortex. That a range of social and technical behaviours covary, and are correlated with social group size and brain size, suggests that primate cognition has evolved along a continuum resulting in an increasingly flexible, domain-general capacity to solve a range of socioecological challenges culminating in a capacity for, and reliance on, innovation and social information use in the great apes and humans. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

The impact of environmental factors on the evolution of brain size in carnivorans

The reasons why some animals have developed larger brains has long been a subject of debate. Yet, it remains unclear which selective pressures may favour the encephalization and how it may act during evolution at different taxonomic scales. Here we studied the patterns and tempo of brain evolution within the order Carnivora and present large-scale comparative analysis of the effect of ecological, environmental, social, and physiological variables on relative brain size in a sample of 174 extant carnivoran species. We found a complex pattern of brain size change between carnivoran families with differences in both the rate and diversity of encephalization. Our findings suggest that during carnivorans’ evolution, a trade-off have occurred between the cognitive advantages of acquiring a relatively large brain allowing to adapt to specific environments, and the metabolic costs of the brain which may constitute a disadvantage when facing the need to colonize new environments.

The brain size of carnivores has evolved to balance a trade-off between increased cognitive function and increased metabolic cost.

The impact of environmental factors on the evolution of brain size in carnivorans

The reasons why some animals have developed larger brains has long been a subject of debate. Yet, it remains unclear which selective pressures may favour the encephalization and how it may act during evolution at different taxonomic scales. Here we studied the patterns and tempo of brain evolution within the order Carnivora and present large-scale comparative analysis of the effect of ecological, environmental, social, and physiological variables on relative brain size in a sample of 174 extant carnivoran species. We found a complex pattern of brain size change between carnivoran families with differences in both the rate and diversity of encephalization. Our findings suggest that during carnivorans' evolution, a trade-off have occurred between the cognitive advantages of acquiring a relatively large brain allowing to adapt to specific environments, and the metabolic costs of the brain which may constitute a disadvantage when facing the need to colonize new environments.

AnimalTraits - a curated animal trait database for body mass, metabolic rate and brain size

Trait databases have become important resources for large-scale comparative studies in ecology and evolution. Here we introduce the AnimalTraits database, a curated database of body mass, metabolic rate and brain size, in standardised units, for terrestrial animals. The database has broad taxonomic breadth, including tetrapods, arthropods, molluscs and annelids from almost 2000 species and 1000 genera. All data recorded in the database are sourced from their original empirical publication, and the original metrics and measurements are included with each record. This allows for subsequent data transformations as required. We have included rich metadata to allow users to filter the dataset. The additional R scripts we provide will assist researchers with aggregating standardised observations into species-level trait values. Our goals are to provide this resource without restrictions, to keep the AnimalTraits database current, and to grow the number of relevant traits in the future.

Measurement(s)	metabolic rate quantification • body mass • brain size
Technology Type(s)	metabolic rate measurement • body mass quantification • brain mass brain volume

Evolutionary and ecological patterns of scatter- and larder-hoarding behaviours in rodents

Scatter- and larder hoarding are the primary strategies of food-hoarding animals and have important implications for plant-animal interactions and plant recruitment. However, their origins and influencing factors have not been fully investigated across a wide range of taxa. Our systematic literature search amassed data for 183 seed-hoarding rodent species worldwide and tested relationships of seed-hoarding behaviours with phylogenetic signal, functional traits and environmental factors. We found that the evolution of hoarding strategies was not random in phylogeny, and scatter hoarding originated independently multiple times from larder hoarding. Rodents with higher encephalisation quotient (relative brain size), omnivorous diet (related to dependence on seeds) and inhabiting lower latitudes were disproportionately likely to scatter hoard. Despite body mass's potential relationship with competition through food defence, it was associated with food-hoarding strategy only in a few families. Our results show the need to study the community and ecological context of food-hoarding behaviours.

Beyond the beak: Brain size and allometry in avian craniofacial evolution

Birds exhibit an enormous variety of beak shapes. Such remarkable variation, however, has distracted research from other important aspects of their skull evolution, the nature of which has been little explored. Key aspects of avian skull variation appear to be qualitatively similar to those of mammals, encompassing variation in the degree of cranial vaulting, cranial base flexure, and the proportions and orientations of the occipital and facial regions. The evolution of these traits has been studied intensively in mammals under the Spatial Packing Hypothesis (SPH), an architectural constraint so-called because the general anatomical organization and development of such skull parts makes them evolve predictably in response to changes in relative brain size. Such SPH predictions account for the different appearances of skull configurations across species, either in having longer or shorter faces, and caudally or ventrally oriented occiputs, respectively. This pattern has been morphometrically and experimentally proven in mammals but has not been examined in birds or other tetrapods, and so its generality remains unknown. We explored the SPH in an interspecific sample of birds using three-dimensional geometric morphometrics. Our results show that the dominant trend of evolutionary variation in the skull of crown-group birds can be predicted by the SPH, involving concomitant changes in the face, the cranial vault and the basicranium, and with striking similarities to craniofacial variation among mammals. Although craniofacial variation is significantly affected by allometry, these allometric effects are independent of the influence of the SPH on skull morphology, as are any effects of volumetric encephalization. Our results, therefore, validate the hypothesis that a general architectural constraint underlies skull homoplasy evolution of cranial morphology among avian clades, and possibly between birds and mammals, but they downplay encephalization and allometry as the only factors involved.

Evolution of prefrontal cortex

Subdivisions of the prefrontal cortex (PFC) evolved at different times. Agranular parts of the PFC emerged in early mammals, and rodents, primates, and other modern mammals share them by inheritance. These are limbic areas and include the agranular orbital cortex and agranular medial frontal cortex (areas 24, 32, and 25). Rodent research provides valuable insights into the structure, functions, and development of these shared areas, but it contributes less to parts of the PFC that are specific to primates, namely, the granular, isocortical PFC that dominates the frontal lobe in humans. The first granular PFC areas evolved either in early primates or in the last common ancestor of primates and tree shrews. Additional granular PFC areas emerged in the primate stem lineage, as represented by modern strepsirrhines. Other granular PFC areas evolved in simians, the group that includes apes, humans, and monkeys. In general, PFC accreted new areas along a roughly posterior to anterior trajectory during primate evolution. A major expansion of the granular PFC occurred in humans in concert with other association areas, with modifications of corticocortical connectivity and gene expression, although current evidence does not support the addition of a large number of new, human-specific PFC areas.

High Encephalization in a Fossil Rorqual Illuminates Baleen Whale Brain Evolution

Baleen whales are considered underencephalized mammals due to their reduced brain size with respect to their body size (encephalization quotient [EQ] << 1). Despite their low EQ, mysticetes exhibit complex behavioral patterns in terms of motor abilities, vocal repertoire, and cultural learning. Very scarce information is available about the morphological evolution of the brain in this group; this makes it difficult to investigate the historical changes in brain shape and size in order to relate the origin of the complex mysticete behavioral repertoire to the evolution of specific neural substrates. Here, the first description of the virtual endocast of a fossil balaenopterid species, Marzanoptera tersillae from the Italian Pliocene, reveals an EQ of around 3, which is exceptional for baleen whales. The endocast showed a morphologically different organization of the brain in this fossil whale as the cerebral hemispheres are anteroposteriorly shortened, the cerebellum lacks the posteromedial expansion of the cerebellar hemispheres, and the cerebellar vermis is unusually reduced. The comparative reductions of the cerebral and cerebellar hemispheres suggest that the motor behavior of M. tersillae probably was less sophisticated than that exhibited by the extant rorqual and humpback species. The presence of an EQ value in this fossil species that is around 10 times higher than that of extant mysticetes opens new questions about brain evolution and provides new, invaluable information about the evolutionary path of morphological and size change in the brain of baleen whales.

Cranial Anatomical Integration and Disparity Among Bones Discriminate Between Primates and Non-primate Mammals

The primate skull hosts a unique combination of anatomical features among mammals, such as a short face, wide orbits, and big braincase. Together with a trend to fuse bones in late development, these features define the anatomical organization of the skull of primates—which bones articulate to each other and the pattern this creates. Here, I quantified the anatomical organization of the skull of 17 primates and 15 non-primate mammals using anatomical network analysis to assess how the skulls of primates have diverged from those of other mammals, and whether their anatomical differences coevolved with brain size. Results show that primates have a greater anatomical integration of their skulls and a greater disparity among bones than other non-primate mammals. Brain size seems to contribute in part to this difference, but its true effect could not be conclusively proven. This supports the hypothesis that primates have a distinct anatomical organization of the skull, but whether this is related to their larger brains remains an open question.

Exceptionally Steep Brain-Body Evolutionary Allometry Underlies the Unique Encephalization of Osteoglossiformes

Brain-body static allometry, which is the relationship between brain size and body size within species, is thought to reflect developmental and genetic constraints. Existing evidence suggests that the evolution of large brain size without accompanying changes in body size (that is, encephalization) may occur when this constraint is relaxed. Teleost fish species are generally characterized by having close-fitting brain-body static allometries, leading to strong allometric constraints and small relative brain sizes. However, one order of teleost, Osteoglossiformes, underwent extreme encephalization, and its mechanistic bases are unknown. Here, I used a dataset and phylogeny encompassing 859 teleost species to demonstrate that the encephalization of Osteoglossiformes occurred through an increase in the slope of evolutionary (among-species) brain-body allometry. The slope is virtually isometric (1.03 ± 0.09 SE), making it one of the steepest evolutionary brain-body allometric slopes reported to date, and it deviates significantly from the evolutionary brain-body allometric slopes of other clades of teleost. Examination of the relationship between static allometric parameters (intercepts and slopes) and evolutionary allometry revealed that the dramatic steepening of the evolutionary allometric slope in Osteoglossiformes was a combined result of evolution in the slopes and intercepts of static allometry. These results suggest that the evolution of static allometry, which likely has been driven by evolutionary changes in the rate and timing of brain development, has facilitated the unique encephalization of Osteoglossiformes.

The pattern of brain-size change in the early evolution of cetaceans

Most authors have identified two rapid increases in relative brain size (encephalization quotient, EQ) in cetacean evolution: first at the origin of the modern suborders (odontocetes and mysticetes) around the Eocene-Oligocene transition, and a second at the origin of the delphinoid odontocetes during the middle Miocene. We explore how methods used to estimate brain and body mass alter this perceived timing and rate of cetacean EQ evolution. We provide new data on modern mammals (mysticetes, odontocetes, and terrestrial artiodactyls) and show that brain mass and endocranial volume scale allometrically, and that endocranial volume is not a direct proxy for brain mass. We demonstrate that inconsistencies in the methods used to estimate body size across the Eocene-Oligocene boundary have caused a spurious pattern in earlier relative brain size studies. Instead, we employ a single method, using occipital condyle width as a skeletal proxy for body mass using a new dataset of extant cetaceans, to clarify this pattern. We suggest that cetacean relative brain size is most accurately portrayed using EQs based on the scaling coefficients as observed in the closely related terrestrial artiodactyls. Finally, we include additional data for an Eocene whale, raising the sample size of Eocene archaeocetes to seven. Our analysis of fossil cetacean EQ is different from previous works which had shown that a sudden increase in EQ coincided with the origin of odontocetes at the Eocene-Oligocene boundary. Instead, our data show that brain size increased at the origin of basilosaurids, 5 million years before the Eocene-Oligocene transition, and we do not observe a significant increase in relative brain size at the origin of odontocetes.

Comparative anatomy of the encephalon of new world primates with emphasis for the Sapajus sp

Studies about the anatomy of the New World Primates are scarce, mainly comparative neuroanatomy, then a morphological comparative analysis about the tropical Primates were performed and a effort was made for an Old World Primates and modern humans relationship for the obtained data; plus, comments about behavior e and allometry were performed to try link the high cognition and abilities of the Sapajus with the neuroanatomical results, however, despite the deep neuroanatomic data obtained, we do not found an intrinsic relation to explain that.

Total energy expenditure of bottlenose dolphins (Tursiops truncatus) of different ages

Marine mammals are thought to have an energetically expensive lifestyle because endothermy is costly in marine environments. However, measurements of total energy expenditure (TEE; kcal day-1) are available only for a limited number of marine mammals, because large body size and inaccessible habitats make TEE measurements expensive and difficult to obtain for many taxa. We measured TEE in 10 adult common bottlenose dolphins (Tursiops truncatus) living in natural seawater lagoons at two facilities (Dolphin Research Center and Dolphin Quest) using the doubly labeled water method. We assessed the relative effects of body mass, age and physical activity on TEE. We also examined whether TEE of bottlenose dolphins, and more generally of marine mammals, differs from that expected for their body mass compared with other eutherian mammals, using phylogenetic least squares (PGLS) regressions. There were no differences in body mass or TEE (unadjusted TEE and TEE adjusted for fat-free mass) between dolphins from the two facilities. Our results show that adjusted TEE decreased and fat mass increased with age. Different measures of activity were not related to age, body fat or adjusted TEE. Both PGLS and the non-phylogenetic linear regression indicate that marine mammals have an elevated TEE compared with that of terrestrial mammals. However, bottlenose dolphins expended 17.1% less energy than other marine mammals of similar body mass. The two oldest dolphins (>40 years) showed a lower TEE, similar to the decline in TEE seen in older humans. To our knowledge, this is the first study to show an age-related metabolic decline in a large non-human mammal.

The genomics of ecological flexibility, large brains, and long lives in capuchin monkeys revealed with fecalFACS

Surviving challenging environments, living long lives, and engaging in complex cognitive processes are hallmark human characteristics. Similar traits have evolved in parallel in capuchin monkeys, but their genetic underpinnings remain unexplored. We developed and annotated a reference assembly for white-faced capuchin monkeys to explore the evolution of these phenotypes. By comparing populations of capuchins inhabiting rainforest versus dry forests with seasonal droughts, we detected selection in genes associated with kidney function, muscular wasting, and metabolism, suggesting adaptation to periodic resource scarcity. When comparing capuchins to other mammals, we identified evidence of selection in multiple genes implicated in longevity and brain development. Our research was facilitated by our method to generate high- and low-coverage genomes from noninvasive biomaterials.

Ecological flexibility, extended lifespans, and large brains have long intrigued evolutionary biologists, and comparative genomics offers an efficient and effective tool for generating new insights into the evolution of such traits. Studies of capuchin monkeys are particularly well situated to shed light on the selective pressures and genetic underpinnings of local adaptation to diverse habitats, longevity, and brain development. Distributed widely across Central and South America, they are inventive and extractive foragers, known for their sensorimotor intelligence. Capuchins have among the largest relative brain size of any monkey and a lifespan that exceeds 50 y, despite their small (3 to 5 kg) body size. We assemble and annotate a de novo reference genome for Cebus imitator. Through high-depth sequencing of DNA derived from blood, various tissues, and feces via fluorescence-activated cell sorting (fecalFACS) to isolate monkey epithelial cells, we compared genomes of capuchin populations from tropical dry forests and lowland rainforests and identified population divergence in genes involved in water balance, kidney function, and metabolism. Through a comparative genomics approach spanning a wide diversity of mammals, we identified genes under positive selection associated with longevity and brain development. Additionally, we provide a technological advancement in the use of noninvasive genomics for studies of free-ranging mammals. Our intra- and interspecific comparative study of capuchin genomics provides insights into processes underlying local adaptation to diverse and physiologically challenging environments, as well as the molecular basis of brain evolution and longevity.

A Farewell to the Encephalization Quotient: A New Brain Size Measure for Comparative Primate Cognition

Both absolute and relative brain sizes vary greatly among and within the major vertebrate lineages. Scientists have long debated how larger brains in primates and hominins translate into greater cognitive performance, and in particular how to control for the relationship between the noncognitive functions of the brain and body size. One solution to this problem is to establish the slope of cognitive equivalence, i.e., the line connecting organisms with an identical bauplan but different body sizes. The original approach to estimate this slope through intraspecific regressions was abandoned after it became clear that it generated slopes that were too low by an unknown margin due to estimation error. Here, we revisit this method. We control for the error problem by focusing on highly dimorphic primate species with large sample sizes and fitting a line through the mean values for adult females and males. We obtain the best estimate for the slope of circa 0.27, a value much lower than those constructed using all mammal species and close to the value expected based on the genetic correlation between brain size and body size. We also find that the estimate of cognitive brain size based on cognitive equivalence fits empirical cognitive studies better than the encephalization quotient, which should therefore be avoided in future studies on primates and presumably mammals and birds in general. The use of residuals from the line of cognitive equivalence may change conclusions concerning the cognitive abilities of extant and extinct primate species, including hominins.

A drastic shift in the energetic landscape of toothed whale sperm cells

Mammalian spermatozoa are a notable example of metabolic compartmentalization.¹ Energy in the form of ATP production, vital for motility, capacitation, and fertilization, is subcellularly separated in sperm cells. While glycolysis provides a local, rapid, and low-yielding input of ATP along the flagellum fibrous sheath, oxidative phosphorylation (OXPHOS), far more efficient over a longer time frame, is concentrated in the midpiece mitochondria.² The relative weight of glycolysis and OXPHOS pathways in sperm function is variable among species and sensitive to oxygen and substrate availability.^3-5 Besides partitioning energy production, sperm cell energetics display an additional singularity: the occurrence of sperm-specific gene duplicates and alternative spliced variants, with conserved function but structurally bound to the flagellar fibrous sheath.^6,7 The wider selective forces driving the compartmentalization and adaptability of this energy system in mammalian species remain largely unknown, much like the impact of ecosystem resource availability (e.g., carbohydrates, fatty acids, and proteins) and dietary adaptations in reproductive physiology traits.⁸ Here, we investigated the Cetacea, an iconic group of fully aquatic and carnivorous marine mammals, evolutionarily related to extant terrestrial herbivores.⁹ In this lineage, episodes of profound trait remodeling have been accompanied by clear genomic signatures.^10-14 We show that toothed whales exhibit impaired sperm glycolysis, due to gene and exon erosion, and demonstrate that dolphin spermatozoa motility depends on endogenous fatty acid β-oxidation, but not carbohydrates. Such unique energetic rewiring substantiates the observation of large mitochondria in toothed whale spermatozoa and emphasizes the radical physiological reorganization imposed by the transition to a carbohydrate-depleted marine environment.

Developmental Differences in Neocortex Neurogenesis and Maturation Between the Altricial Dwarf Rabbit and Precocial Guinea Pig

Mammals are born on a precocial-altricial continuum. Altricial species produce helpless neonates with closed distant organs incapable of locomotion, whereas precocial species give birth to well-developed young that possess sophisticated sensory and locomotor capabilities. Previous studies suggest that distinct patterns of cortex development differ between precocial and altricial species. This study compares patterns of neocortex neurogenesis and maturation in the precocial guinea pig and altricial dwarf rabbit, both belonging to the taxon of Glires. We show that the principal order of neurodevelopmental events is preserved in the neocortex of both species. Moreover, we show that neurogenesis starts at a later postconceptional day and takes longer in absolute gestational days in the precocial than the altricial neocortex. Intriguingly, our data indicate that the dwarf rabbit neocortex contains a higher abundance of highly proliferative basal progenitors than the guinea pig, which might underlie its higher encephalization quotient, demonstrating that the amount of neuron production is determined by complex regulation of multiple factors. Furthermore, we show that the guinea pig neocortex exhibits a higher maturation status at birth, thus providing evidence for the notions that precocial species might have acquired the morphological machinery required to attain their high functional state at birth and that brain expansion in the precocial newborn is mainly due to prenatally initiating processes of gliogenesis and neuron differentiation instead of increased neurogenesis. Together, this study reveals important insights into the timing and cellular differences that regulate mammalian brain growth and maturation and provides a better understanding of the evolution of mammalian altriciality and presociality.

Functional ecological convergence between the thylacine and small prey-focused canids

BACKGROUND

Morphological convergence is a fundamental aspect of evolution, allowing for inference of the biology and ecology of extinct species by comparison with the form and function of living species as analogues. The thylacine (Thylacinus cynocephalus), the iconic recently extinct marsupial, is considered a classic example of convergent evolution with the distantly related placental wolf or dog, though almost nothing is actually known regarding its ecology. This lack of data leads to questions regarding the degree of convergence with, and the similarity of, the functional ecology of the thylacine and the wolf/dog. Here, we examined the cranium of the thylacine using 3D geometric morphometrics and two quantitative tests of convergence to more precisely determine convergent analogues, within a phylogenetically informed dataset of 56 comparative species across 12 families of marsupial and placental faunivorous mammals. Using this dataset, we investigated patterns of correlation between cranial shape and diet, phylogeny, and relative prey size across these terrestrial faunivores.

RESULTS

We find a correlation between cranial, facial, and neurocranial shape and the ratio of prey-to-predator body mass, though neurocranial shape may not correlate with prey size within marsupials. The thylacine was found to group with predators that routinely take prey smaller than 45% of their own body mass, not with predators that take subequal-sized or larger prey. Both convergence tests find significant levels of convergence between the thylacine and the African jackals and South American 'foxes', with lesser support for the coyote and red fox. We find little support for convergence between the thylacine and the wolf or dog.

CONCLUSIONS

Our study finds little support for a wolf/dog-like functional ecology in the thylacine, with it instead being most similar to mid-sized canids such as African jackals and South American 'foxes' that mainly take prey less than half their size. This work suggests that concepts of convergence should extend beyond superficial similarity, and broader comparisons can lead to false interpretations of functional ecology. The thylacine was a predator of small to mid-sized prey, not a big-game specialist like the placental wolf.

Optimal Values of Body Composition for the Lowest Risk of Failure in Tabata Training's Effects in Adolescents: A Pilot Study

Background

The optimal body mass index (BMI) and fat mass index (FMI) values for a positive change or the lowest risk of no positive change after high-intensity interval training (HIIT) using the Tabata protocol remain unclear. This study is aimed at establishing these optimal BMI and FMI values for the lowest risk of failure of aerobic performance in adolescents.

Methods

A 10-week HIIT programme was introduced into the physical education of 73 students. BMI was calculated using height and weight. Bioelectrical impedance analysis measured body fat, and the InBody apparatus generated the FMI. Based on BMI and FMI, the participants were divided into four groups. Pre- and post-HIIT intervention analyses were carried out using the Harvard step test, which was used to determine the physical efficiency index (PEI).

Results

The Youden index confirmed that the risk of no positive effects in PEI was the lowest for the second BMI interval (19.01-22.00 kg/m²) and FMI Q₂₋₃ (7.96-8.91 kg/m²). The optimal BMI value for the lowest risk of no change in PEI was 20.60 kg/m², and the optimal FMI value was 8.84 kg/m².

Conclusion

A comparison of the two indices shows that FMI had stronger effects on PEI than BMI. In addition, the model obtained for FMI had higher accuracy. Identifying at-risk individuals, those in need of improving health-related fitness (H-RF), and those with a low risk of poor H-RF allows for efficient planning of individual intervention services and training programmes.

Quantification of Fetal Gyrogenesis in the Third Trimester. A Novel Algorithm for Evaluating Fetal Sulci Development

BACKGROUND AND PURPOSE

The fetal brain changes significantly throughout gestation. From a smooth (lissencephalic) cortex, it transforms into its convolved (gyrencephalic) state. Despite its importance, the diagnosis of delay in brain gyrogenesis is a challenge for many sonographers. This study presents a novel semiautomatic image processing algorithm for simple quantification of sagittal sulci maturation in the third trimester.

METHODS

Mid-sagittal fetal brain ultrasound images were obtained during routine third trimester scans. Fetal brain sulci length measurements were performed using a novel semiautomatic image processing algorithm followed by manual measurements. Correlations between the total length of the sulci, gestational age, and fetal biometry were examined.

RESULTS

The study included 64 patients. A significant positive linear correlation was found between total sulci length and gestational age (r = .658 for automated measurement, r = .7 for manual measurement, P < .0001). A similar relationship was found comparing total sulci length and fetal head circumference (r = .694 for automated measurement, r = .74 for manual measurement; P < .0001). A significant correlation was observed between automated and manual measurements (r = .947).

CONCLUSIONS

We found that fetal gyrogenesis is linear throughout the third trimester of pregnancy. The use of a computer algorithm to measure fetal sulci can be used as a simple prenatal screening test for delayed gyral maturation of the fetal brain.

The influence of domestication, insularity and sociality on the tempo and mode of brain size evolution in mammals

The ability to develop complex social bonds and an increased capacity for behavioural flexibility in novel environments have both been forwarded as selective forces favouring the evolution of a large brain in mammals. However, large brains are energetically expensive, and in circumstances in which selective pressures are relaxed, e.g. on islands, smaller brains are selected for. Similar reasoning has been offered to explain the reduction of brain size in domestic species relative to their wild relatives. Herein, we assess the effect of domestication, insularity and sociality on brain size evolution at the macroevolutionary scale. Our results are based on analyses of a 426-taxon tree, including both wild species and domestic breeds. We further develop the phylogenetic ridge regression comparative method (RRphylo) to work with discrete variables and compare the rates (tempo) and direction (mode) of brain size evolution among categories within each of three factors (sociality, insularity and domestication). The common assertion that domestication increases the rate of brain size evolution holds true. The same does not apply to insularity. We also find support for the suggested but previously untested hypothesis that species living in medium-sized groups exhibit faster rates of brain size evolution than either solitary or herding taxa.

Ranging Ecology: The View from Above

Animals use a variety of strategies to navigate their world, but few are thought to have detailed mental maps of their landscapes. New research with our closest relatives suggests chimpanzees may use cognitive maps to find the most energy efficient routes.

Digital Endocasting in Comparative Canine Brain Morphology

Computed tomography (CT) is one of the most useful techniques for digitizing bone structures and making endocranial models from the neurocranium. The resulting digital endocasts reflect the morphology of the brain and the associated structures. Our first aim was to document the methodology behind creating detailed digital endocasts of canine skulls. We created digital endocasts of the skulls of 24 different dog breeds and 4 wild canids for visualization and teaching purposes. We used CT scanning with 0.323 mm × 0.322 mm × 0.6 mm resolution. The imaging data were segmented with 3D Slicer software and refined with Autodesk Meshmixer. Images were visualized in 3D Slicer and surface models were converted to 3D PDFs to provide easier interactive access, and 3D prints were also generated for visualization purposes. Our second aim was to analyze how skull length and width relate to the surface areas of the prepiriform rhinencephalic, prefrontal, and non-prefrontal cerebral convexity areas of the endocasts. The rhinencephalic area ratio decreased with a larger skull index. Our results open the possibility to analyze the relationship between the skull and brain morphology, and to link certain features to behavior, and cognition in dogs.

An integrative understanding of comparative cognition: lessons from human brain evolution

A comprehensive understanding of animal cognition requires the integration of studies on behavior, electrophysiology, neuroanatomy, development, and genomics. Although studies of comparative cognition are receiving increasing attention from organismal biologists, most current studies focus on the comparison of behaviors and anatomical structures to understand their adaptative values. However, to understand the most potentially complex cognitive program of the human brain a greater synthesis of a multitude of disciplines is needed. In this review, we start with extensive neuroanatomic comparisons between humans and other primates. One likely specialization of the human brain is the expansion of neocortex, especially in regions for high-order cognition (e.g., prefrontal cortex). We then discuss how such an expansion can be linked to heterochrony of the brain developmental program, resulting in a greater number of neurons and enhanced computational capacity. Furthermore, alteration of gene expression in the human brain has been associated with positive selection in DNA sequences of gene regulatory regions. These results not only imply that genes associated with brain development are a major factor in the evolution of cognition, but also that high-quality whole-genome sequencing and gene manipulation techniques are needed for an integrative and functional understanding of comparative cognition in non-model organisms.

A natural endocast of an early Miocene odontocete and its implications in cetacean brain evolution

The natural endocast Museo di Geologia e Paleontologia of the Università degli Studi di Torino (MGPT)-PU 13873 is described and analyzed in order to interpret its taxonomic affinities and its potential significance on our understanding of cetacean brain evolution. The endocast is from the early Miocene of Piedmont (between ca. 19 and 16 million years ago), Northwestern Italy, and shows a number of plesiomorphic characters. These include: scarcely rounded cerebral hemispheres, cerebellum exposed in dorsal view with little superimposition by the cerebral hemispheres, short temporal lobe, and long sylvian fissure. The distance between the hypophysis and the rostral pons is particularly high, as it was determined by the calculus of the hypothalamus quotient, suggesting that the development of a deep interpeduncular fossa was not as advanced as in living odontocetes. The encephalization quotient (EQ) of MGPT-PU 13873 is ~1.81; therefore, this specimen shows an EQ in line with other fossil whales of the same geological age (early Miocene). Comparative analysis shows that there is a critical lack of data from the late Miocene and Pliocene that prevents us to fully understand the recent evolution of the EQ diversity in whales. Moreover, the past diversity of brain size and shape in mysticetes is virtually unknown. All these observations point to the need of additional efforts to uncover evolutionary patterns and processes on cetacean brain evolution.

Brain gyrification in wild and domestic canids: Has domestication changed the gyrification index in domestic dogs?

Over the last 15 years, research on canid cognition has revealed that domestic dogs possess a surprising array of complex sociocognitive skills pointing to the possibility that the domestication process might have uniquely altered their brains; however, we know very little about how evolutionary processes (natural or artificial) might have modified underlying neural structure to support species-specific behaviors. Evaluating the degree of cortical folding (i.e., gyrification) within canids may prove useful, as this parameter is linked to functional variation of the cerebral cortex. Using quantitative magnetic resonance imaging to investigate the impact of domestication on the canine cortical surface, we compared the gyrification index (GI) in 19 carnivore species, including six wild canid and 13 domestic dog individuals. We also explored correlations between global and local GI with brain mass, cortical thickness, white and gray matter volume and surface area. Our results indicated that GI values for domestic dogs are largely consistent with what would be expected for a canid of their given brain mass, although more variable than that observed in wild canids. We also found that GI in canids is positively correlated with cortical surface area, cortical thickness and total cortical gray matter volumes. While we found no evidence of global differences in GI between domestic and wild canids, certain regional differences in gyrification were observed.

Bias and Misrepresentation of Science Undermines Productive Discourse on Animal Welfare Policy: A Case Study

Simple Summary

Creating good animal welfare-related laws, regulations, and policies depends on accurate knowledge. To that end, scientific reviews that explain and contextualize the relevant research can be powerful tools for informing decision-makers, assuming these reviews represent the state of the scientific knowledge accurately and objectively. In this commentary, we examine the major flaws, biases, and misrepresentations of the scientific literature in one such recent review regarding the welfare and care of captive killer whales. Such pervasive problems, in this or any review, make it impossible to determine the true state of knowledge of the relevant issues, and can ultimately result in misinformed, arbitrary, or even harmful decisions about animals and their care.

Abstract

Reliable scientific knowledge is crucial for informing legislative, regulatory, and policy decisions in a variety of areas. To that end, scientific reviews of topical issues can be invaluable tools for informing productive discourse and decision-making, assuming these reviews represent the target body of scientific knowledge as completely, accurately, and objectively as possible. Unfortunately, not all reviews live up to this standard. As a case in point, Marino et al.’s review regarding the welfare of killer whales in captivity contains methodological flaws and misrepresentations of the scientific literature, including problematic referencing, overinterpretation of the data, misleading word choice, and biased argumentation. These errors and misrepresentations undermine the authors’ conclusions and make it impossible to determine the true state of knowledge of the relevant issues. To achieve the goal of properly informing public discourse and policy on this and other issues, it is imperative that scientists and science communicators strive for higher standards of analysis, argumentation, and objectivity, in order to clearly communicate what is known, what is not known, what conclusions are supported by the data, and where we are lacking the data necessary to draw reliable conclusions.

Small Tropical Mammals Can Take the Heat: High Upper Limits of Thermoneutrality in a Bornean Treeshrew

Tropical ectotherms are generally believed to be more vulnerable to global heating than temperate species. Currently, however, we have insufficient knowledge of the thermoregulatory physiology of equatorial tropical mammals, particularly of small diurnal mammals, to enable similar predictions. In this study, we measured the resting metabolic rates (via oxygen consumption) of wild-caught lesser treeshrews (Tupaia minor, order Scandentia) over a range of ambient temperatures. We predicted that, similar to other treeshrews, T. minor would exhibit more flexibility in body temperature regulation and a wider thermoneutral zone compared with other small mammals because these thermoregulatory traits provide both energy and water savings at high ambient temperatures. Basal metabolic rate was on average 1.03±0.10 mL O₂ h^-1 g^-1, which is within the range predicted for a 65-g mammal. We calculated the lower critical temperature of the thermoneutral zone at 31.0°C (95% confidence interval: 29.3°-32.7°C), but using metabolic rates alone, we could not determine the upper critical temperature at ambient temperatures as high as 36°C. The thermoregulatory characteristics of lesser treeshrews provide a means of saving energy and water at temperatures well in excess of their current environmental temperatures. Our research highlights the knowledge gaps in our understanding of the energetics of mammals living in high-temperature environments, specifically in the equatorial tropics, and questions the purported lack of variance in the upper critical temperatures of the thermoneutral zone in mammals, emphasizing the importance of further research in the tropics.

Mosaic evolution, preadaptation, and the evolution of evolvability in apes

A major goal in postsynthesis evolutionary biology has been to better understand how complex interactions between traits drive movement along and facilitate the formation of distinct evolutionary pathways. I present analyses of a character matrix sampled across the haplorrhine skeleton that revealed several modules of characters displaying distinct patterns in macroevolutionary disparity. Comparison of these patterns to those in neurological development showed that early ape evolution was characterized by an intense regime of evolutionary and developmental flexibility. Shifting and reduced constraint in apes was met with episodic bursts in phenotypic innovation that built a wide array of functional diversity over a foundation of shared developmental and anatomical structure. Shifts in modularity drove dramatic evolutionary changes across the ape body plan in two distinct ways: (1) an episode of relaxed integration early in hominoid evolution coincided with bursts in evolutionary rate across multiple character suites; (2) the formation of two new trait modules along the branch leading to chimps and humans preceded rapid and dramatic evolutionary shifts in the carpus and pelvis. Changes to the structure of evolutionary mosaicism may correspond to enhanced evolvability that has a "preadaptive" effect by catalyzing later episodes of dramatic morphological remodeling.

The evolution of self-medication behaviour in mammals

Self-medication behaviour is the use of natural materials or chemical substances to manipulate behaviour or alter the body’s response to parasites or pathogens. Self-medication can be preventive, performed before an individual becomes infected or diseased, and/or therapeutic, performed after an individual becomes infected or diseased. We summarized all available reports of self-medication in mammals and reconstructed its evolution. We found that reports of self-medication were restricted to eutherian mammals and evolved at least four times independently. Self-medication was most commonly reported in primates. Detailed analyses of primates suggest that self-medication is a life-history trait associated with body size, absolute brain size and longevity, but we found no support for the hypothesis that self-medication evolved to reduce the costs of social living. Large, longer-lived species might thus benefit uniquely from self-medication.

Automatic generation of evolutionary hypotheses using mixed Gaussian phylogenetic models

Phylogenetic comparative methods (PCMs) are used to study the evolution of various biological species, ranging from microorganisms to animals and plants. These methods combine trait measurements, such as body masses measured in a set of species, with the species’ phylogenetic tree, to quantify the trait’s evolution along the tree. Here, we show that current PCMs fail to reproduce the patterns of evolution of brain and body mass in mammals, because they use mathematical models that cannot represent the heterogeneity of the evolutionary processes acting in different lineages of the tree. As a solution, we propose mixed Gaussian phylogenetic models allowing one to infer changes in the type and magnitude of evolutionary forces occurring on specific branches of the tree.

Phylogenetic comparative methods are widely used to understand and quantify the evolution of phenotypic traits, based on phylogenetic trees and trait measurements of extant species. Such analyses depend crucially on the underlying model. Gaussian phylogenetic models like Brownian motion and Ornstein–Uhlenbeck processes are the workhorses of modeling continuous-trait evolution. However, these models fit poorly to big trees, because they neglect the heterogeneity of the evolutionary process in different lineages of the tree. Previous works have addressed this issue by introducing shifts in the evolutionary model occurring at inferred points in the tree. However, for computational reasons, in all current implementations, these shifts are “intramodel,” meaning that they allow jumps in 1 or 2 model parameters, keeping all other parameters “global” for the entire tree. There is no biological reason to restrict a shift to a single model parameter or, even, to a single type of model. Mixed Gaussian phylogenetic models (MGPMs) incorporate the idea of jointly inferring different types of Gaussian models associated with different parts of the tree. Here, we propose an approximate maximum-likelihood method for fitting MGPMs to comparative data comprising possibly incomplete measurements for several traits from extant and extinct phylogenetically linked species. We applied the method to the largest published tree of mammal species with body- and brain-mass measurements, showing strong statistical support for an MGPM with 12 distinct evolutionary regimes. Based on this result, we state a hypothesis for the evolution of the brain–body-mass allometry over the past 160 million y.

Intraspecific Energetic Trade-Offs and Costs of Encephalization Vary from Interspecific Relationships in Three Species of Mormyrid Electric Fishes

The evolution of increased encephalization comes with an energetic cost. Across species, this cost may be paid for by an increase in metabolic rate or by energetic trade-offs between the brain and other energy-expensive tissues. However, it remains unclear whether these solutions to deal with the energetic requirements of an enlarged brain are related to direct physiological constraints or other evolved co-adaptations. We studied the highly encephalized mormyrid fishes, which have extensive species diversity in relative brain size. We previously found a correlation between resting metabolic rate and relative brain size across species; however, it is unknown how this interspecific relationship evolved. To address this issue, we measured intraspecific variation in relative brain size, the sizes of other organs, metabolic rate, and hypoxia tolerance to determine if intraspecific relationships between brain size and organismal energetics are similar to interspecific relationships. We found that 3 species of mormyrids with varying degrees of encephalization had no intraspecific relationships between relative brain size and relative metabolic rate or relative sizes of other organs, and only 1 species had a relationship between relative brain size and hypoxia tolerance. These species-specific differences suggest that the interspecific relationship between metabolic rate and relative brain size is not the result of direct physiological constraints or strong stabilizing selection, but is instead due to other species level co-adaptations. We conclude that variation within species must be considered when determining the energetic costs and trade-offs underlying the evolution of extreme encephalization.

The modular organization of the cerebral cortex: Evolutionary significance and possible links to neurodevelopmental conditions

The recognition of discernible anatomical regularities that appear to self-organize during development makes apparent the modular organization of the cerebral cortex. The metabolic cost engendered in sustaining interneuronal communications has emphasized the viability of short connections among neighboring neurons. This pattern of connectivity establishes a microcircuit which is repeated in parallel throughout the cerebral cortex. This canonical circuit is contained within the smallest module of information processing of the cerebral cortex; one which Vernon Mountcastle called the minicolumn. Plasticity within the brain is accounted, in part, by the presence of weak linkages that allow minicolumns to process information from a variety of sources and to quickly adapt to environmental exigencies without a need for genetic change. Recent research suggests that interlaminar correlated firing between minicolumns during the decision phase of target selection provides for the emergence of some executive functions. Bottlenecks of information processing within this modular minicolumnar organization may account for a variety of mental disorders observed in neurodevelopmental conditions.

Memory for own behaviour in pinnipeds

Pinnipeds are aquatic predators feeding on a vast range of prey, and their social behaviour differs greatly between species (from extreme polygyny in some sea lions to monogamy in some true seals). It has been hypothesised that the foraging and social complexity of their lifestyle should drive the evolution of their cognitive abilities. To investigate how aware pinnipeds are of their own behaviour, a grey seal (Halichoerus grypus), two harbour seals (Phoca vitulina) and four South American sea lions (Otaria flavescens) were trained to repeat their own behaviour on command. Three already trained behaviours were used, and the animal was asked to repeat the behaviour twice to ensure that the animal recalled its own behaviour and not the command given for the previous behaviour. All three species could recall their own behaviour significantly better than by chance. The duration for which the animals could recall their behaviour was tested using a staircase paradigm. A delay was implemented between the completion of the behaviour and the command to repeat it. The delay was increased after correct responses and decreased after incorrect responses. The performance of all species fell towards chance level after 12-18 s, with no significant difference between species. These results indicate that sea lions and true seals are aware of their own behaviour and that true seals have similar short-term memory abilities. It also shows that pinnipeds have less developed short-term memory abilities compared to other aquatic predators, such as the bottlenose dolphin. The complexity of pinniped foraging and social behaviour does not seem to have driven the evolution of short-term memory abilities in these animals but might have contributed to their ability to recall their own behaviour.

Prenatal developmental sequence of the skull of minke whales and its implications for the evolution of mysticetes and the teeth-to-baleen transition

Baleen whales (Mysticeti) have an extraordinary fossil record documenting the transition from toothed raptorial taxa to modern species that bear baleen plates, keratinous bristles employed in filter-feeding. Remnants of their toothed ancestry can be found in their ontogeny, as they still develop tooth germs in utero. Understanding the developmental transition from teeth to baleen and the associated skull modifications in prenatal specimens of extant species can enhance our understanding of the evolutionary history of this lineage by using ontogeny as a relative proxy of the evolutionary changes observed in the fossil record. Although at present very little information is available on prenatal development of baleen whales, especially regarding tooth resorption and baleen formation, due to a lack of specimens. Here I present the first detailed description of prenatal specimens of minke whales (Balaenoptera acutorostrata and Balaenoptera bonaerensis), focusing on the skull anatomy and tooth germ development, resorption, and baleen growth. The ontogenetic sequence described consists of 10 specimens of both minke whale species, from the earliest fetal stages to full term. The internal skull anatomy of the specimens was visualized using traditional and iodine-enhanced computed tomography scanning. These high-quality data allow detailed description of skull development both qualitatively and quantitatively using three-dimensional landmark analysis. I report distinctive external anatomical changes and the presence of a denser tissue medial to the tooth germs in specimens from the final portion of gestation, which can be interpreted as the first signs of baleen formation (baleen rudiments). Tooth germs are only completely resorbed just before the eruption of the baleen from the gums, and they are still present for a brief period with baleen rudiments. Skull shape development is characterized by progressive elongation of the rostrum relative to the braincase and by the relative anterior movement of the supraoccipital shield, contributing to a defining feature of cetaceans, telescoping. These data aid the interpretation of fossil morphologies, especially of those extinct taxa where there is no direct evidence of presence of baleen, even if caution is needed when comparing prenatal extant specimens with adult fossils. The ontogeny of other mysticete species needs to be analyzed before drawing definitive conclusions about the influence of development on the evolution of this group. Nonetheless, this work is the first step towards a deeper understanding of the most distinctive patterns in prenatal skull development of baleen whales, and of the anatomical changes that accompany the transition from tooth germs to baleen. It also presents comprehensive hypotheses to explain the influence of developmental processes on the evolution of skull morphology and feeding adaptations of mysticetes.