Habitat use affects morphological diversification in dragon lizards

Diadromy Drives Elevated Rates of Trait Evolution and Ecomorphological Convergence in Clupeiformes (Herring, Shad, and Anchovies)

AbstractMigration can have a profound influence on rates and patterns of phenotypic evolution. Diadromy is the migration between marine and freshwater habitats for feeding and reproduction that can require individuals to travel tens to thousands of kilometers. The high energetic demands of diadromy are predicted to select for ecomorphological traits that maximize swimming and locomotor efficiency. Intraspecific studies have shown repeated instances of divergence among diadromous and nondiadromous populations in locomotor and foraging traits, which suggests that at a macroevolutionary scale diadromous lineages may experience convergent evolution onto one or multiple adaptive optima. We tested for differences in rates and patterns of phenotypic evolution among diadromous and nondiadromous lineages in Clupeiformes, a clade that has evolved diadromy more than 10 times. Our results show that diadromous clupeiforms show convergent evolution for some locomotor traits and faster rates of evolution, which we propose are adaptive responses to the locomotor demands of migration. We also find evidence that diadromous lineages show convergence into multiple regions of multivariate trait space and suggest that these respective trait spaces are associated with differences in migration and trophic ecology. However, not all locomotor traits and no trophic traits show evidence of convergence or elevated rates of evolution associated with diadromy. Our results show that long-distance migration influences the tempo and patterns of phenotypic evolution at macroevolutionary scales, but there is not a single diadromous syndrome.

Female lizards (Eremias argus) reverse Bergmann's rule across altitude

The evolution of body size within and among species is predicted to be influenced by multifarious environmental factors. However, the specific drivers of body size variation have remained difficult to understand because of the wide range of proximate factors that covary with ectotherm body sizes across populations with varying local environmental conditions. Here, we used female Eremias argus lizards collected from different populations across their wide range in China, and constructed linear mixed models to assess how climatic conditions and/or available resources at different altitudes shape the geographical patterns of lizard body size across altitude. Lizard populations showed significant differences in body size across altitudes. Furthermore, we found that climatic and seasonal changes along the altitudinal gradient also explained variations in body size among populations. Specifically, body size decreased with colder and drier environmental conditions at high altitudes, reversing Bergmann's rule. Limited resources at high altitudes, measured by the low vegetative index, may also constrain body size. Therefore, our study demonstrates that multifarious environmental factors could strongly influence the intraspecific variation in organisms' body size.

Ecological and life-history drivers of avian skull evolution

One of the most famous examples of adaptive radiation is that of the Galápagos finches, where skull morphology, particularly the beak, varies with feeding ecology. Yet increasingly studies are questioning the strength of this correlation between feeding ecology and morphology in relation to the entire neornithine radiation, suggesting that other factors also significantly affect skull evolution. Here, we broaden this debate to assess the influence of a range of ecological and life-history factors, specifically habitat density, migration, and developmental mode, in shaping avian skull evolution. Using 3D geometric morphometric data to robustly quantify skull shape for 354 extant species spanning avian diversity, we fitted flexible phylogenetic regressions and estimated evolutionary rates for each of these factors across the full data set. The results support a highly significant relationship between skull shape and both habitat density and migration, but not developmental mode. We further found heterogenous rates of evolution between different character states within habitat density, migration, and developmental mode, with rapid skull evolution in species that occupy dense habitats, are migratory, or are precocial. These patterns demonstrate that diverse factors affect the tempo and mode of avian phenotypic evolution and that skull evolution in birds is not simply a reflection of feeding ecology.

Ecology, sexual dimorphism, and jumping evolution in anurans

Sexual dimorphism (SD) is a common feature of animals, and selection for sexually dimorphic traits may affect both functional morphological traits and organismal performance. Trait evolution through natural selection can also vary across environments. However, whether the evolution of organismal performance is distinct between the sexes is rarely tested in a phylogenetic comparative context. Anurans commonly exhibit sexual size dimorphism, which may affect jumping performance given the effects of body size on locomotion. They also live in a wide variety of microhabitats. Yet the relationships among dimorphism, performance, and ecology remain underexamined in anurans. Here, we explore relationships between microhabitat use, body size, and jumping performance in males and females to determine the drivers of dimorphic patterns in jumping performance. Using methods for predicting jumping performance through anatomical measurements, we describe how fecundity selection and natural selection associated with body size and microhabitat have likely shaped female jumping performance. We found that the magnitude of sexual size dimorphism (where females are about 14% larger than males) was much lower than dimorphism in muscle volume, where females had 42% more muscle than males (after accounting for body size). Despite these sometimes-large averages, phylogenetic t-tests failed to show the statistical significance of SD for any variable, indicating sexually dimorphic species tend to be closely related. While SD of jumping performance did not vary among microhabitats, we found female jumping velocity and energy differed across microhabitats. Overall, our findings indicate that differences in sex-specific reproductive roles, size, jumping-related morphology, and performance are all important determinants in how selection has led to the incredible ecophenotypic diversity of anurans.

Evolutionary relationships among the snakelike pygopodid lizards: a review of phylogenetic studies of an enigmatic Australian adaptive radiation

Here, I review phylogenetic studies of the lizard family Pygopodidae, a group of 47 extant species that diversified in Australia and New Guinea. The goal of this study was to examine published phylogenetic and phylogenomic hypotheses on pygopodids to identify the strengths and weaknesses in our understanding of their phylogeny. Many parts of the pygopodid family tree are well established by multiple independent tree inferences including: (1) all multispecies genera (i.e., Aprasia, Delma, Lialis, Pletholax, and Pygopus) are monophyletic groups; (2) the root of the pygopodid tree is located along the branch leading to the Delma clade, thus showing that Delma is the sister group to all other pygopodid genera; (3) the Aprasia repens group, Delma tincta group, and several other groups of closely related species are demonstrated to be monophyletic entities; and (4) the monotypic Paradelma orientalis is the sister lineage to the Pygopus clade. Based on accumulated phylogenetic evidence, two taxonomic recommendations are given: Paradelma merits generic status rather than being subsumed into Pygopus as some earlier studies had suggested, and the monotypic Aclys concinna should be recognized as a member of Delma (following current practice) until future studies clarify its placement inside or outside the Delma clade. One chronic problem with phylogenetic studies of pygopodids, which has limited the explanatory power of many tree hypotheses, concerns the undersampling of known species. Although the continual addition of newly described species, especially over the past two decades, has been a major reason for these taxon sampling gaps, deficits in species sampling for ingroups and/or outgroups in several studies of pygopodid species complexes has confounded the testing of some ingroup monophyly hypotheses. Ancient hybridization between non-sister lineages may also be confounding attempts to recover the relationships among pygopodids using molecular data. Indeed, such a phenomenon can explain at least five cases of mito-nuclear discordance and conflicts among trees based on nuclear DNA datasets. Another problem has been the lack of consensus on the relationships among most pygopodid genera, an issue that may stem from rapid diversification of these lineages early in the group's history. Despite current weaknesses in our understanding of pygopodid phylogeny, enough evidence exists to clarify many major and minor structural parts of their family tree. Accordingly, a composite tree for the Pygopodidae was able to be synthesized. This novel tree hypothesis contains all recognized pygopodid species and reveals that about half of the clades are corroborated by multiple independent tree hypotheses, while the remaining clades have less empirical support.

Can Morphology Predict the Conservation Status of Iguanian Lizards?

The integrity of regional and local biological diversity is under siege as a result of multiple anthropogenic threats. The conversion of habitats, such as rain forests, into agricultural ecosystems, reduces the area available to support species populations. Rising temperatures and altered rainfall patterns lead to additional challenges for species. The ability of conservation biologists to ascertain the threats to a species requires data on changes in distribution, abundance, life history, and ecology. The International Union for the Conservation of Nature (IUCN) uses these data to appraise the extinction risk for a species. However, many species remain data deficient (DD) or unassessed. Here, I use 14 morphological traits related to locomotor function, habitat, and feeding to predict the threat status of over 400 species of lizards in the infraorder Iguania. Morphological traits are an ideal proxy for making inferences about a species' risk of extinction. Patterns of morphological covariation have a known association with habitat use, foraging behavior, and physiological performance across multiple taxa. Results from phylogenetic general linear models revealed that limb lengths as well as head characters predicted extinction risk. In addition, I used an artificial neural network (ANN) technique to generate a classification function based on the morphological traits of species with an assigned IUCN threat status. The network approach identified eight morphological traits as predictors of extinction risk, which included head and limb characters. The best supported model had a classification accuracy of 87.4%. Moreover, the ANN model predicted >18% of DD/not assessed species were at risk of extinction. The predicted assessments were supported by other sources of threat status, for example, Convention on International Trade in Endangered Species appendices. Because of the functional link between morphology, performance, and ecology, an ecomorphological approach may be a useful tool for rapid assessment of DD or poorly known species.

Ecological Opportunity from Innovation, not Islands, Drove the Anole Lizard Adaptive Radiation

Islands are thought to facilitate adaptive radiation by providing release from competition and predation. Anole lizards are considered a classic example of this phenomenon: different ecological specialists ('ecomorphs') evolved in the Caribbean Greater Antilles (Cuba, Hispaniola, Jamaica, and Puerto Rico), resulting in convergent assemblages that are not observed in mainland Latin America. Yet, the role of islands in facilitating adaptive radiation is more often implied than directly tested, leaving uncertain the role of biogeography in stimulating diversification. Here, we assess the proposed "island effect" on anole diversification using Bayesian phylogenetic comparative methods that explicitly incorporate rate heterogeneity across the tree and demonstrate two cases of would-be false positives. We discovered that rates of speciation and morphological evolution of island and mainland anoles are equivalent, implying that islands provide no special context for exceptionally rapid diversification. Likewise, rates of evolution were equivalent between island anoles that arose via in situ versus dispersal-based mechanisms, and we found no evidence for island-specific rates of speciation or morphological evolution. Nonetheless, the origin of Anolis is characterized by a speciation pulse that slowed over time - a classic signature of waning ecological opportunity. Our findings cast doubt on the notion that islands catalyzed the anole adaptive radiation and instead point to a key innovation, adhesive toe pads, which facilitated the exploitation of many arboreal niches sparsely utilized by other iguanian lizards. The selective pressures responsible for arboreal niche diversification differ between islands and the mainland, but the tempo of diversification driven by these discordant processes is indistinguishable.

Size, microhabitat, and loss of larval feeding drive cranial diversification in frogs

Habitat is one of the most important factors shaping organismal morphology, but it may vary across life history stages. Ontogenetic shifts in ecology may introduce antagonistic selection that constrains adult phenotype, particularly with ecologically distinct developmental phases such as the free-living, feeding larval stage of many frogs (Lissamphibia: Anura). We test the relative influences of developmental and ecological factors on the diversification of adult skull morphology with a detailed analysis of 15 individual cranial regions across 173 anuran species, representing every extant family. Skull size, adult microhabitat, larval feeding, and ossification timing are all significant factors shaping aspects of cranial evolution in frogs, with late-ossifying elements showing the greatest disparity and fastest evolutionary rates. Size and microhabitat show the strongest effects on cranial shape, and we identify a "large size-wide skull" pattern of anuran, and possibly amphibian, evolutionary allometry. Fossorial and aquatic microhabitats occupy distinct regions of morphospace and display fast evolution and high disparity. Taxa with and without feeding larvae do not notably differ in cranial morphology. However, loss of an actively feeding larval stage is associated with higher evolutionary rates and disparity, suggesting that functional pressures experienced earlier in ontogeny significantly impact adult morphological evolution.

Spawning substrate shift associated with the evolution of a female sexual characteristic in a family of fishes

Because ‘primary’ sexual characteristics (i.e. those directly associated with reproduction) can be extremely variable, evolve quickly, and can be impacted by both natural and sexual selection, they are often considered excellent model systems in which to study evolution. Here, we explore the evolution of the anal sheath, a trait hypothesized to facilitate the release and proper placement of eggs on the spawning substrate, and its relationship to spawning habitat and maximum body size in a family of fish (Fundulidae). In addition to using phylogenetically informed statistics to determine the role of preferred spawning habitat and maximum body size on the evolution of anal sheath length, we reconstruct the evolutionary history of the anal sheath and preferred spawning habitat. We then test for significant phylogenetic signal and evolutionary rate shifts in the size of the anal sheath and the preferred spawning habitat. Our results indicate that preferred spawning habitat, and not maximum body length, significantly influences anal sheath size, which is associated with a significant phylogenetic signal, and an evolutionary rate similar to that of preferred spawning substrate. We discuss these results in terms of potential evolutionary mechanisms driving anal sheath length.

Accelerated Brain Shape Evolution Is Associated with Rapid Diversification in an Avian Radiation

AbstractNiche expansion is a critical step in the speciation process. Large brains linked to improved cognitive ability may enable species to expand their niches and forage in new ways, thereby promoting speciation. Despite considerable work on ecological divergence in brain size and its importance in speciation, relatively little is known about how brain shape relates to behavioral, ecological, and taxonomic diversity at macroevolutionary scales. This is due in part to inherent challenges with quantifying brain shape across many species. Here we present a novel, semiautomated approach for rapidly phenotyping brain shape using semilandmarks derived from X-ray computed microtomography scans. We then test its utility by parsing evolutionary trends within a diverse radiation of birds: kingfishers (Aves: Alcedinidae). Multivariate comparative analyses reveal that rates of brain shape evolution (but not beak shape) are positively correlated with lineage diversification rates. Distinct brain shapes are further associated with changes in body size and foraging behavior, suggesting both allometric and ecological constraints on brain shape evolution. These results are in line with the idea of brains acting as a "master regulator" of critical processes governing speciation, such as dispersal, foraging behavior, and dietary niche.

Habitat preference and diversification rates in a speciose lineage of diving beetles

The long-term geological stability of aquatic habitats has been demonstrated to be a determinant in the evolution of macroinvertebrate fauna, with species in running (lotic) waters having lower dispersal abilities, smaller ranges and higher gene flow between populations than species in standing (lentic) environments. Lotic species have been hypothesized to be more specialised, but the diversification dynamics of both habitat types have not been studied in detail. Using a speciose lineage of water beetles we test here whether diversification rates are related to the habitat preference of the species and its consequences on turnover, which we expect to be higher for lotic taxa. Moreover, we tested whether life in lotic environments is acting as an evolutionary dead-end as it is considered an ecological specialisation. We built a comprehensive molecular phylogeny with 473 terminals representing 421 of the 689 known species of the tribe Hydroporini (Coleoptera, Dytiscidae), using a combination of sequences from four mitochondrial and two nuclear genes plus 69 mitogenomes obtained with NGS. We found a general pattern of gradual acceleration of diversification rate with time, with 2-3 significant diversification shifts. However, habitat is not the main factor driving diversification in Hydroporini based on SecSSE analyses. The most recent common ancestor of Hydroporini was reconstructed as a lotic species, with multiple shifts to lentic environments. Most frequent transitions were estimated from lentic and lotic habitats to the category "both", followed by transitions from lotic to lentic and lentic to lotic respectively, although with very similar rates. Contrary to expectations, we found little evidence for differences in diversification dynamics between habitats, with lotic environments clearly not acting as evolutionary dead-ends in Hydroporini.

Phylogenetic patterns and ontogenetic origins of limb length variation in ecologically diverse lacertine lizards

Limb length is intrinsically linked to function and, ultimately, fitness. Thus, it can co-evolve with habitat structure, as exemplified by tropical lizards in highly heterogeneous environments. But does lizard limb length respond in a similar manner during adaptive diversification in temperate zones? Here, we examine variation in habitat preference and limb length in lacertine lizards from the Palaearctic. We tested the following three hypotheses: (1) species of the Lacertini tribe descended from a generalist ancestor and subsequently underwent habitat specialization; (2) specialized ecological roles are associated with relative limb length in extant species; and (3) interspecific differences in limb length emerge in embryonic development. Our comparisons supported an ancestral ‘rocky’ or ‘generalist’ habitat preference, and phenotype–habitat associations were particularly supported when examining size-adjusted forelimb length in 69 species that represented all known Lacertini genera. Moreover, we revealed an elevated interlimb ratio in high-vegetation species, which might be linked to climbing performance in species with relatively longer forelimbs. Furthermore, embryonic limb variation was detected solely against an Eremiadini outgroup species. Instead, hind limb length differences within Lacertini originated in post-hatching ontogeny. The mechanisms that modulate limb growth are likely to be limited in Lacertini, because adaptive morphological change might mirror historical contingency and the ecological context wherein this clade diversified.

A Bayesian Approach for Inferring the Impact of a Discrete Character on Rates of Continuous-Character Evolution in the Presence of Background-Rate Variation

Understanding how and why rates of character evolution vary across the Tree of Life is central to many evolutionary questions; for example, does the trophic apparatus (a set of continuous characters) evolve at a higher rate in fish lineages that dwell in reef versus nonreef habitats (a discrete character)? Existing approaches for inferring the relationship between a discrete character and rates of continuous-character evolution rely on comparing a null model (in which rates of continuous-character evolution are constant across lineages) to an alternative model (in which rates of continuous-character evolution depend on the state of the discrete character under consideration). However, these approaches are susceptible to a "straw-man" effect: the influence of the discrete character is inflated because the null model is extremely unrealistic. Here, we describe MuSSCRat, a Bayesian approach for inferring the impact of a discrete trait on rates of continuous-character evolution in the presence of alternative sources of rate variation ("background-rate variation"). We demonstrate by simulation that our method is able to reliably infer the degree of state-dependent rate variation, and show that ignoring background-rate variation leads to biased inferences regarding the degree of state-dependent rate variation in grunts (the fish group Haemulidae). [Bayesian phylogenetic comparative methods; continuous-character evolution; data augmentation; discrete-character evolution.].

Body shape diversification along the benthic-pelagic axis in marine fishes

Colonization of novel habitats can result in marked phenotypic responses to the new environment that include changes in body shape and opportunities for further morphological diversification. Fishes have repeatedly transitioned along the benthic-pelagic axis, with varying degrees of association with the substrate. Previous work focusing on individual lineages shows that these transitions are accompanied by highly predictable changes in body form. Here, we generalize expectations drawn from this literature to study the effects of habitat on body shape diversification across 3344 marine teleost fishes. We compare rates and patterns of evolution in eight linear measurements of body shape among fishes that live in pelagic, demersal and benthic habitats. While average body shape differs between habitats, these differences are subtle compared with the high diversity of shapes found within each habitat. Benthic living increases the rate of body shape evolution and has led to numerous lineages evolving extreme body shapes, including both exceptionally wide bodies and highly elongate, eel-like forms. By contrast, we find that benthic living is associated with the slowest diversification of structures associated with feeding. Though we find that habitat can serve as an impetus for predictable trait changes, we also highlight the diversity of responses in marine teleosts to opportunities presented by major habitats.

Habitat transitions alter the adaptive landscape and shape phenotypic evolution in needlefishes (Belonidae)

Habitat occupancy can have a profound influence on macroevolutionary dynamics, and a switch in major habitat type may alter the evolutionary trajectory of a lineage. In this study, we investigate how evolutionary transitions between marine and freshwater habitats affect macroevolutionary adaptive landscapes, using needlefishes (Belonidae) as a model system. We examined the evolution of body shape and size in marine and freshwater needlefishes and tested for phenotypic change in response to transitions between habitats. Using micro-computed tomographic (µCT) scanning and geometric morphometrics, we quantified body shape, size, and vertebral counts of 31 belonid species. We then examined the pattern and tempo of body shape and size evolution using phylogenetic comparative methods. Our results show that transitions from marine to freshwater habitats have altered the adaptive landscape for needlefishes and expanded morphospace relative to marine taxa. We provide further evidence that freshwater taxa attain reduced sizes either through dwarfism (as inferred from axial skeletal reduction) or through developmental truncation (as inferred from axial skeletal loss). We propose that transitions to freshwater habitats produce morphological novelty in response to novel prey resources and changes in locomotor demands. We find that repeated invasions of different habitats have prompted predictable changes in morphology.

Cranial integration in the fire salamander, Salamandra salamandra (Caudata: Salamandridae)

Phenotypic integration and modularity are concepts that represent the pattern of connectivity of morphological structures within an organism. Integration describes the coordinated variation of traits, and analyses of these relationships among traits often reveals the presence of modules, sets of traits that are highly integrated but relatively independent of other traits. Phenotypic integration and modularity have been studied at both the evolutionary and static level across a variety of clades, although most studies thus far are focused on amniotes, and especially mammals. Using a high-dimensional geometric morphometric approach, we investigated the pattern of cranial integration and modularity of the Italian fire salamander (Salamandra salamandra giglioli). We recovered a highly modular pattern, but this pattern did not support either entirely developmental or functional hypotheses of cranial organisation, possibly reflecting complex interactions amongst multiple influencing factors. We found that size had no significant effect on cranial shape, and that morphological variance of individual modules had no significant relationship with degree of within-module integration. The pattern of cranial integration in the fire salamander is similar to that previously recovered for caecilians, with highly integrated jaw suspensorium and occipital regions, suggesting possible conservation of patterns across lissamphibians.

The Evolution of a Single Toe in Horses: Causes, Consequences, and the Way Forward

Horses are a classic example of macroevolution in three major traits-large body size, tall-crowned teeth (hypsodonty), and a single toe (monodactyly)-but how and why monodactyly evolved is still poorly understood. Existing hypotheses usually connect digit reduction in horses to the spread and eventual dominance of open-habitat grasslands, which took over from forests during the Cenozoic; digit reduction has been argued to be an adaptation for speed, locomotor economy, stability, and/or increased body size. In this review, we assess the evidence for these (not necessarily mutually exclusive) hypotheses from a variety of related fields, including paleoecology, phylogenetic comparative methods, and biomechanics. Convergent evolution of digit reduction, including in litopterns and artiodactyls, is also considered. We find it unlikely that a single evolutionary driver was responsible for the evolution of monodactyly, because changes in body size, foot posture, habitat, and substrate are frequently found to influence one another (and to connect to broader potential drivers, such as changing climate). We conclude with suggestions for future research to help untangle the complex dynamics of this remarkable morphological change in extinct horses. A path forward should combine regional paleoecology studies, quantitative biomechanical work, and make use of convergence and modern analogs to estimate the relative contributions of potential evolutionary drivers for digit reduction.

An integrative phylogenomic approach illuminates the evolutionary history of Old World tree frogs (Anura: Rhacophoridae)

Rhacophoridae are one of the most speciose and ecologically diverse families of amphibians. Resolution of their evolutionary relationships is key to understanding the accumulation of biodiversity, yet previous hypotheses based on Sanger sequencing exhibit much discordance amongst generic relationships. This conflict precludes the making of sound macroevolutionary conclusions. Herein, we conduct the first phylogenomic study using broad-scale sampling and sequences of 352 nuclear DNA loci obtained using anchored hybrid enrichment targeted sequencing. The robust time-calibrated phylogenetic hypothesis clarifies several long-disputed relationships and facilitates the testing of evolutionary hypotheses on spatiotemporal diversification and reproductive modes. The major extant lineages of Rhacophoridae appear to have radiated in mainland Asia, and the spatiotemporal process corresponds with several common accumulations of biodiversity in Asia. Analyses do not detect any case of "Out of Himalaya" in Rhacophoridae. All transitions of reproductive modes appear to have evolved in an ordered, gradual sequence associated with gaining independence of standing water for larval development. The different reproductive modes are phylogenetically conserved and the completion of their transitions appear to have occurred over a period of ~30 Ma, which does not fit a pattern of a rapid burst of diversification. Innovations in reproductive modes associate statistically with the uneven distribution of species-richness between clades, where higher diversification is linked to increased terrestrial modes of reproduction. These results strengthen the hypothesis that breeding innovations drive diversification by providing new opportunities for ecological release and dispersion.

A Bayesian extension of phylogenetic generalized least squares: Incorporating uncertainty in the comparative study of trait relationships and evolutionary rates

Phylogenetic comparative methods use tree topology, branch lengths, and models of phenotypic change to take into account nonindependence in statistical analysis. However, these methods normally assume that trees and models are known without error. Approaches relying on evolutionary regimes also assume specific distributions of character states across a tree, which often result from ancestral state reconstructions that are subject to uncertainty. Several methods have been proposed to deal with some of these sources of uncertainty, but approaches accounting for all of them are less common. Here, we show how Bayesian statistics facilitates this task while relaxing the homogeneous rate assumption of the well-known phylogenetic generalized least squares (PGLS) framework. This Bayesian formulation allows uncertainty about phylogeny, evolutionary regimes, or other statistical parameters to be taken into account for studies as simple as testing for coevolution in two traits or as complex as testing whether bursts of phenotypic change are associated with evolutionary shifts in intertrait correlations. A mixture of validation approaches indicates that the approach has good inferential properties and predictive performance. We provide suggestions for implementation and show its usefulness by exploring the coevolution of ankle posture and forefoot proportions in Carnivora.

The other side of the Sahulian coin: biogeography and evolution of Melanesian forest dragons (Agamidae)

New Guinea has been considered both as a refuge for mesic rainforest-associated lineages that contracted in response to the late Cenozoic aridification of Australia and as a centre of biotic diversification and radiation since the mid-Miocene or earlier. Here, we estimate the diversity and a phylogeny for the Australo-Papuan forest dragons (Sauria: Agamidae; ~20 species) in order to examine the following: (1) whether New Guinea and/or proto-Papuan Islands may have been a biogeographical refuge or a source for diversity in Australia; (2) whether mesic rainforest environments are ancestral to the entire radiation, as may be predicted by the New Guinea refuge hypothesis; and (3) more broadly, how agamid ecological diversity varies across the contrasting environments of Australia and New Guinea. Patterns of lineage distribution and diversity suggest that extinction in Australia, and colonization and radiation on proto-Papuan islands, have both shaped the extant diversity and distribution of forest dragons since the mid-Miocene. The ancestral biome for all Australo-Papuan agamids is ambiguous. Both rainforest and arid-adapted radiations probably started in the early Miocene. However, despite deep-lineage diversity in New Guinea rainforest habitats, overall species and ecological diversity is low when compared with more arid areas, with terrestrial taxa being strikingly absent.

Systematics of Clupeiformes and testing for ecological limits on species richness in a trans-marine/freshwater clade

ABSTRACT Clupeiformes (herring, sardines, shad, anchovies and allies) are a globally distributed clade with nearly 400 marine, freshwater, and diadromous species. Although best known as filter feeding fishes that form large schools, this group occupies a diverse array of trophic guilds and habitats. Theory suggests that species richness in clades is modulated by ecological limits, which results in diversity-dependent clade growth, a pattern that most clades exhibit. As a trans-marine/freshwater clade that has undergone repeated transitions between marine and freshwaters, Clupeiformes are an excellent system for investigating the interplay between ecological diversity and macroevolutionary dynamics. In this study we review the systematics of Clupeiformes and explore discordance in phylogenetic relationships and divergence times between mitochondrial and nuclear loci. We then use comparative methods to test whether ecological limits regulate diversity in Clupeiformes. We find discordance in phylogenetic relationships at various taxonomic scales, but also considerable agreement between genomes. Our results suggest that trans-marine/freshwater clades are able to circumvent ecological limits on clade growth at regional, but not on local scales. Our study demonstrates that phylogenies are a critical link between ecology and macroevolutionary dynamics, and suggests habitat transitions can play a key role in shaping diversity patterns, particularly in the neotropics.

Environmental determinism, and not interspecific competition, drives morphological variability in Australasian warblers (Acanthizidae)

Interspecific competition is thought to play a key role in determining the coexistence of closely related species within adaptive radiations. Competition for ecological resources can lead to different outcomes from character displacement to, ultimately, competitive exclusion. Accordingly, divergent natural selection should disfavor those species that are the most similar to their competitor in resource use, thereby increasing morphological disparity. Here, we examined ecomorphological variability within an Australo‐Papuan bird radiation, the Acanthizidae, which include both allopatric and sympatric complexes. In addition, we investigated whether morphological similarities between species are related to environmental factors at fine scale (foraging niche) and/or large scale (climate). Contrary to that predicted by the competition hypothesis, we did not find a significant correlation between the morphological similarities found between species and their degree of range overlap. Comparative modeling based on both a priori and data‐driven identification of selective regimes suggested that foraging niche is a poor predictor of morphological variability in acanthizids. By contrast, our results indicate that climatic conditions were an important factor in the formation of morphological variation. We found a significant negative correlation between species scores for PC1 (positively associated to tarsus length and tail length) and both temperature and precipitation, whereas PC2 (positively associated to bill length and wing length) correlated positively with precipitation. In addition, we found that species inhabiting the same region are closer to each other in morphospace than to species outside that region regardless of genus to which they belong or its foraging strategy. Our results indicate that the conservative body form of acanthizids is one that can work under a wide variety of environments (an all‐purpose morphology), and the observed interspecific similarity is probably driven by the common response to environment.

Mechanical sensitivity and the dynamics of evolutionary rate shifts in biomechanical systems

The influence of biophysical relationships on rates of morphological evolution is a cornerstone of evolutionary theory. Mechanical sensitivity-the correlation strength between mechanical output and the system's underlying morphological components-is thought to impact the evolutionary dynamics of form-function relationships, yet has rarely been examined. Here, we compare the evolutionary rates of the mechanical components of the four-bar linkage system in the raptorial appendage of mantis shrimp (Order Stomatopoda). This system's mechanical output (kinematic transmission (KT)) is highly sensitive to variation in its output link, and less sensitive to its input and coupler links. We found that differential mechanical sensitivity is associated with variation in evolutionary rate: KT and the output link exhibit faster rates of evolution than the input and coupler links to which KT is less sensitive. Furthermore, for KT and, to a lesser extent, the output link, rates of evolution were faster in 'spearing' stomatopods than 'smashers', indicating that mechanical sensitivity may influence trait-dependent diversification. Our results suggest that mechanical sensitivity can impact morphological evolution and guide the process of phenotypic diversification. The connection between mechanical sensitivity and evolutionary rates provides a window into the interaction between physical rules and the evolutionary dynamics of morphological diversification.

Rates of morphological evolution, asymmetry and morphological integration of shell shape in scallops

Background

Rates of morphological evolution vary across different taxonomic groups, and this has been proposed as one of the main drivers for the great diversity of organisms on Earth. Of the extrinsic factors pertaining to this variation, ecological hypotheses feature prominently in observed differences in phenotypic evolutionary rates across lineages. But complex organisms are inherently modular, comprising distinct body parts that can be differentially affected by external selective pressures. Thus, the evolution of trait covariation and integration in modular systems may also play a prominent role in shaping patterns of phenotypic diversity. Here we investigate the role ecological diversity plays in morphological integration, and the tempo of shell shape evolution and of directional asymmetry in bivalved scallops.

Results

Overall, the shape of both valves and the magnitude of asymmetry of the whole shell (difference in shape between valves) are traits that are evolving fast in ecomorphs under strong selective pressures (gliders, recessers and nestling), compared to low rates observed in other ecomorphs (byssal-attaching, free-living and cementing). Given that different parts of an organism can be under different selective pressures from the environment, we also examined the degree of evolutionary integration between the valves as it relates to ecological shifts. We find that evolutionary morphological integration is consistent and surprisingly high across species, indicating that while the left and right valves of a scallop shell are diversifying in accordance with ecomorphology, they are doing so in a concerted fashion.

Conclusions

Our study on scallops adds another strong piece of evidence that ecological shifts play an important role in the tempo and mode of morphological evolution. Strong selective pressures from the environment, inferred from the repeated evolution of distinct ecomorphs, have influenced the rate of morphological evolution in valve shape and the magnitude of asymmetry between valves. Our observation that morphological integration of the valves making up the shell is consistently strong suggests tight developmental pathways are responsible for the concerted evolution of these structures while environmental pressures are driving whole shell shape. Finally, our study shows that directional asymmetry in shell shape among species is an important aspect of scallop macroevolution.

Electronic supplementary material

The online version of this article (10.1186/s12862-017-1098-5) contains supplementary material, which is available to authorized users.

Shift from slow- to fast-water habitats accelerates lineage and phenotype evolution in a clade of Neotropical suckermouth catfishes (Loricariidae: Hypoptopomatinae)

Identifying habitat characteristics that accelerate organismal evolution is essential to understanding both the origins of life on Earth and the ecosystem properties that are most critical to maintaining life into the future. Searching for these characteristics on a large scale has only recently become possible via advances in phylogenetic reconstruction, time-calibration, and comparative analyses. In this study, we combine these tools with habitat and phenotype data for 105 species in a clade of Neotropical suckermouth catfishes commonly known as cascudinhos. Our goal was to determine whether riverine mesohabitats defined by different flow rates (i.e., pools vs. rapids) and substrates (plants vs. rocks) have affected rates of cascudinho cladogenesis and morphological diversification. In contrast to predictions based on general theory related to life in fast-flowing, rocky riverine habitats, Neoplecostomini lineages associated with these habitats exhibited increased body size, head shape diversity, and lineage and phenotype diversification rates. These findings are consistent with a growing understanding of river rapids as incubators of biological diversification and specialization. They also highlight the urgent need to conserve rapids habitats throughout the major rivers of the world.

Adaptive evolution in locomotor performance: How selective pressures and functional relationships produce diversity

Despite the complexity of nature, most comparative studies of phenotypic evolution consider selective pressures in isolation. When competing pressures operate on the same system, it is commonly expected that trade-offs will occur that will limit the evolution of phenotypic diversity, however, it is possible that interactions among selective pressures may promote diversity instead. We explored the evolution of locomotor performance in lizards in relation to possible selective pressures using the Ornstein-Uhlenbeck process. Here, we show that a combination of selection based on foraging mode and predator escape is required to explain variation in performance phenotypes. Surprisingly, habitat use contributed little explanatory power. We find that it is possible to evolve very different abilities in performance which were previously thought to be tightly correlated, supporting a growing literature that explores the many-to-one mapping of morphological design. Although we generally find the expected trade-off between maximal exertion and speed, this relationship surprisingly disappears when species experience selection for both performance types. We conclude that functional integration need not limit adaptive potential, and that an integrative approach considering multiple major influences on a phenotype allows a more complete understanding of adaptation and the evolution of diversity.

Molecular phylogeny of Harpactorini (Insecta: Reduviidae): correlation of novel predation strategy with accelerated evolution of predatory leg morphology

Much research and discussion have focused on the effects of key innovations on lineage diversification, whereas little has been done to investigate their role in morphological evolution using phylogenetic approaches. Here we present the first comprehensive molecular phylogeny of the Harpactorini (Insecta: Reduviidae), the largest assassin bug tribe, sampling 229 terminal taxa and using five gene segments (28S D2, D3-D5, 16S, COI, and Deformed). Employing comparative phylogenetic methods, we demonstrate the correlation of a putative key innovation, the sticky trap predation strategy, with accelerated rates of morphological evolution of the predatory fore leg in assassin bugs. We show that bugs exhibiting sticky trap predation have evolved more slender and longer fore femora than non-sticky bugs. Using phylogenetically independent contrast analyses, we document correlated evolution between femoral thickness and length. We argue that the novel sticky trap predation strategy may allow sticky bugs to alleviate functional constraints on the fore femur and thus to attain a higher rate of evolution than other Harpactorini or Reduviidae. We discuss the possibility that sticky bugs represent a case of adaptive radiation. We also test historical supra-generic groups within the Harpactorini, and show that most of them are not monophyletic. We confirm the paraphyly of Harpactorini with respect to Rhaphidosomini.

Morphological disparity opposes latitudinal diversity gradient in lacertid lizards

While global variation in taxonomic diversity is strongly linked to latitude, the extent to which morphological disparity follows geographical gradients is less well known. We estimated patterns of lineage diversification, morphological disparity and rates of phenotypic evolution in the Old World lizard family Lacertidae, which displays a nearly inverse latitudinal diversity gradient with decreasing species richness towards the tropics. We found that lacertids exhibit relatively constant rates of lineage accumulation over time, although the majority of morphological variation appears to have originated during recent divergence events, resulting in increased partitioning of disparity within subclades. Among subclades, tropical arboreal taxa exhibited the fastest rates of shape change while temperate European taxa were the slowest, resulting in an inverse relationship between latitudinal diversity and rates of phenotypic evolution. This pattern demonstrates a compelling counterexample to the ecological opportunity theory of diversification, suggesting an uncoupling of the processes generating species diversity and morphological differentiation across spatial scales.