Comparative analyses of longevity and senescence reveal variable survival benefits of living in zoos across mammals

Ecological Realism Accelerates Epigenetic Aging in Mice

The aging of mammalian epigenomes fundamentally alters cellular functions, and such changes are the focus of many healthspan and lifespan studies. However, studies of this process typically use mouse models living under standardized laboratory conditions and neglect the impact of variation in social, physical, microbial, and other aspects of the living environment on age-related changes. We examined differences in age-associated methylation changes between traditionally laboratory-reared mice from Jackson Laboratory and "rewilded" C57BL/6J mice, which lived in an outdoor field environment at Cornell University with enhanced ecological realism. Systematic analysis of age-associated methylation dynamics in the liver indicates a genomic region-conditioned, faster epigenetic aging rate in mice living in the field than those living in the lab, implicating perturbed 3D genome conformation and liver function. Altered epigenetic aging rates were more pronounced in sites that gain methylation with age, including sites enriched for transcription factor binding related to DNA repair. These observations underscore the overlooked role of the social and physical environment in epigenetic aging with implications for both basic and applied aging research.

Maximum lifespan and brain size in mammals are associated with gene family size expansion related to immune system functions

Mammals exhibit an unusual variation in their maximum lifespan potential, measured as the longest recorded longevity of any individual in a species. Evidence suggests that lifespan increases follow expansion in brain size relative to body mass. Here, we found significant gene family size expansions associated with maximum lifespan potential and relative brain size but not in gestation time, age of sexual maturity, and body mass in 46 mammalian species. Extended lifespan is associated with expanding gene families enriched in immune system functions. Our results suggest an association between gene duplication in immune-related gene families and the evolution of longer lifespans in mammals. These findings explore the genomic features linked with the evolution of lifespan in mammals and its association with life story and morphological traits.

Does death drive the scaling of life?

The magnitude of many kinds of biological structures and processes scale with organismal size, often in regular ways that can be described by power functions. Traditionally, many of these "biological scaling" relationships have been explained based on internal geometric, physical, and energetic constraints according to universal natural laws, such as the "surface law" and "3/4-power law". However, during the last three decades it has become increasingly apparent that biological scaling relationships vary greatly in response to various external (environmental) factors. In this review, I propose and provide several lines of evidence supporting a new ecological perspective that I call the "mortality theory of ecology" (MorTE). According to this viewpoint, mortality imposes time limits on the growth, development, and reproduction of organisms. Accordingly, small, vulnerable organisms subject to high mortality due to predation and other environmental hazards have evolved faster, shorter lives than larger, more protected organisms. A MorTE also includes various corollary, size-related internal and external causative factors (e.g. intraspecific resource competition, geometric surface area to volume effects on resource supply/transport and the protection of internal tissues from environmental hazards, internal homeostatic regulatory systems, incidence of pathogens and parasites, etc.) that impact the scaling of life. A mortality-centred approach successfully predicts the ranges of body-mass scaling slopes observed for many kinds of biological and ecological traits. Furthermore, I argue that mortality rate should be considered the ultimate (evolutionary) driver of the scaling of life, that is expressed in the context of other proximate (functional) drivers such as information-based biological regulation and spatial (geometric) and energetic (metabolic) constraints.

No evidence for Peto's paradox in terrestrial vertebrates

Larger, longer-lived species are expected to have a higher cancer prevalence compared to smaller, shorter-lived species owing to the greater number of cell divisions that occur during their lifespan. Yet, to date, no evidence has been found to support this expectation, and no association has been found between cancer prevalence and body size across species-a phenomenon known as Peto's paradox. Specifically, while anticancer mechanisms have been identified for individual species, wider phylogenetic evidence has remained elusive. Here, we show that there is no evidence for Peto's paradox across amphibians, birds, mammals, and squamate reptiles: Larger species do in fact have a higher cancer prevalence compared to smaller species. Moreover, we demonstrate that the accumulation of repeated instances of accelerated body size evolution in mammals and birds is associated with a reduction in the prevalence of neoplasia and malignancy, suggesting that increased rates of body size evolution are associated with the evolution of improved cellular growth control. These results represent empirical evidence showing that larger body size is related to higher cancer prevalence, thus rejecting Peto's paradox, and demonstrating the importance of heterogenous routes of body size evolution in shaping anticancer defenses.

A Macaque Model for the Effects of Hybridization on Body Size

OBJECTIVES

Genomics research has uncovered recurrent hybridization between hominin species, yet its morphological impact remains understudied. Non-human primate research has suggested a morphological signature of hybrid ancestry, which could be used to identify hybrids in the hominin fossil record. This pattern may include extreme size, heightened variation, and markers of developmental instability, but factors affecting these characteristics are poorly understood. Studies of non-mammalian taxa suggest that extreme morphology is more likely in early-generation hybrids and with a greater parental distance. To understand hybridization in hominins, therefore, we must use appropriate proxy taxa.

MATERIALS AND METHODS

Here, we use Chinese × Indian Macaca mulatta hybrids with a comparable divergence time in generations to Homo sapiens/Neanderthals and wide variation in admixture. Measuring limb lengths, body length, and weight, we investigate the relationship between admixture and size/variation.

RESULTS

Compared to previous work with more phylogenetically distant primate taxa and a focus on early generation hybrids, we found no evidence of a relationship between admixture and extreme large size, nor with increased size variation. Hybrids in our sample are relatively small but within the range of variation of the smaller parental taxon.

CONCLUSIONS

Our results suggest that hybridization between closely related taxa, such as Neanderthals and H. sapiens, may lead to more subtle morphological patterns than previously anticipated. It will be necessary, however, to better understand the factors governing primate hybrid morphology before we can produce robust inferences on how hybridization has affected hominin evolution.

Prenatal sex determination illuminates the unusual adult sex ratio of a group-living lemur

Most mammals, including humans, exhibit even or slightly male-biased birth sex ratios (BSRs) and female-biased adult sex ratios (ASRs) much later in life due to higher male mortality rates. The group-living primates of Madagascar are unusual in this respect because they lack female-biased ASRs, but it is unknown whether this is the result of skewed BSRs or sex-specific disappearance patterns. Using long-term demographic data from wild red-fronted lemurs (Eulemur rufifrons), we analysed their sex ratio dynamics across the lifespan. We assessed BSR via prenatal sex determination using maternal faecal oestrogen metabolite measurements during late pregnancy, confirming a visually determined equal sex ratio three months after birth, and indicating no early sex-specific mortality. Demographic analyses additionally disclosed higher female disappearance within the first 8 years of age, likely associated with reproductive effort early in life. Thereby, adult male survival had the greatest positive effect on the ASR. Our study offers a rare perspective on the dynamics of age- and sex-specific disappearance in a wild primate population, whose sex-reversed patterns may also contribute to a more general understanding of the mechanisms generating sex-biased mortality.

Cancer Prevalence across Vertebrates

Cancer is pervasive across multicellular species, but what explains the differences in cancer prevalence across species? Using 16,049 necropsy records for 292 species spanning three clades of tetrapods (amphibians, sauropsids, and mammals), we found that neoplasia and malignancy prevalence increases with adult mass (contrary to Peto's paradox) and somatic mutation rate but decreases with gestation time. The relationship between adult mass and malignancy prevalence was only apparent when we controlled for gestation time. Evolution of cancer susceptibility appears to have undergone sudden shifts followed by stabilizing selection. Outliers for neoplasia prevalence include the common porpoise (<1.3%), the Rodrigues fruit bat (<1.6%), the black-footed penguin (<0.4%), ferrets (63%), and opossums (35%). Discovering why some species have particularly high or low levels of cancer may lead to a better understanding of cancer syndromes and novel strategies for the management and prevention of cancer. Significance: Evolution has discovered mechanisms for suppressing cancer in a wide variety of species. By analyzing veterinary necropsy records, we can identify species with exceptionally high or low cancer prevalence. Discovering the mechanisms of cancer susceptibility and resistance may help improve cancer prevention and explain cancer syndromes. See related commentary by Metzger, p. 14.

Indirect evidence of an early mating advantage in wild cooperatively breeding male banded mongooses

Promiscuous females reduce male reproductive control. Males can attempt to monopolise access to these females, but distractions and sneaky rivals mean extra copulations cannot always be blocked. By mating first, males can obtain a headstart in sperm competition, but this may be negated by sperm storage and cryptic female choice mechanisms. We carry out an indirect rare test of an early mating advantage in a population of free-living wild animals. Using Bayesian GLMM analysis of a long-term life history database spanning 17 years, we show that banded mongoose males who interacted with females in earlier days of oestrus had a higher chance of siring their offspring compared with later rivals. An early mating advantage would intensify initial male-male competition and hence selection for male choice, as any initial mistake identifying preferred mating partners could see paternity lost to rivals.

Gene expression comparisons between captive and wild shrew brains reveal captivity effects

Compared with their free-ranging counterparts, wild animals in captivity experience different conditions with lasting physiological and behavioural effects. Although shifts in gene expression are expected to occur upstream of these phenotypes, we found no previous gene expression comparisons of captive versus free-ranging mammals. We assessed gene expression profiles of three brain regions (cortex, olfactory bulb and hippocampus) of wild shrews (Sorex araneus) compared with shrews kept in captivity for two months and undertook sample dropout to examine robustness given limited sample sizes. Consistent with captivity effects, we found hundreds of differentially expressed genes in all three brain regions, 104 overlapping across all three, that enriched pathways associated with neurodegenerative disease, oxidative phosphorylation and genes encoding ribosomal proteins. In the shrew, transcriptomic changes detected under captivity resemble responses in several human pathologies, including major depressive disorder and neurodegeneration. While interpretations of individual genes are tempered by small sample sizes, we propose captivity influences brain gene expression and function and can confound analyses of natural processes in wild individuals under captive conditions.

Key Concepts for Enhancing Zoo Animal Welfare: Coping, Comfort, Choice, Control, Challenge, and Compassion

Zoo animal welfare is subject to increasing scrutiny by many audiences. Although zoo husbandry and management techniques have progressed, common welfare issues are still apparent. To encourage further improvements, converting theoretical welfare definition into practical application is key. This paper evaluates a familiar definition to form a baseline for practical welfare assessment that benefits animals and zoo operations. If we consider coping and comfort as measurable indicators, plus choice and control to cement autonomy for the animal, achieving positive welfare is more likely. Providing positive cognitive challenge results in improvements to behavioral diversity. When husbandry is ecologically relevant, this welfare-friendly approach evolves into husbandry-based evidence, further justifying approaches to animal care. The human element of husbandry (e.g., development and training of personnel) impacts on welfare, necessitating a compassionate approach to daily operations. Compassion - for animal and human wellbeing - ultimately embeds welfare as a core zoo goal. The unique environment of the zoo, with its mix of wild species, human workforce and visitors, coupled with the amount we still must learn about species' husbandry needs emphasizes continual development of welfare approaches.

Wild capuchin monkeys as a model system for investigating the social and ecological determinants of ageing

Studying biological ageing in animal models can circumvent some of the confounds exhibited by studies of human ageing. Ageing research in non-human primates has provided invaluable insights into human lifespan and healthspan. Yet data on patterns of ageing from wild primates remain relatively scarce, centred around a few populations of catarrhine species. Here, we introduce the white-faced capuchin, a long-lived platyrrhine primate, as a promising new model system for ageing research. Like humans, capuchins are highly social, omnivorous generalists, whose healthspan and lifespan relative to body size exceed that of other non-human primate model species. We review recent insights from capuchin ageing biology and outline our expanding, integrative research programme that combines metrics of the social and physical environments with physical, physiological and molecular hallmarks of ageing across the natural life courses of multiple longitudinally tracked individuals. By increasing the taxonomic breadth of well-studied primate ageing models, we generate new insights, increase the comparative value of existing datasets to geroscience and work towards the collective goal of developing accurate, non-invasive and reliable biomarkers with high potential for standardization across field sites and species, enhancing the translatability of primate studies.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

Usefulness of noninvasive blood pressure measurement in captive Red Panda (Ailurus fulgens)

The red panda (Ailurus fulgens) can be found in zoos around the world, and various behavioral restraint procedures are used as part of their health care. Wild animals that are kept in zoos, including red pandas, are known to have a longer life span than those in the wild. Therefore, the health management of aging animals is considered especially important for zoos that maintain many precious wild animals. Blood pressure measurement is important for determining cardiovascular dynamics, however there are no reports of blood pressure measurements performed in red pandas without anesthesia. In this study, we measured blood pressure in four red pandas, over 4 years to establish a blood pressure measurement method using behavioral restraints. As a result, the blood pressure of red pandas was found to be similar to that of dogs and cats. In addition, in one case of red panda that evaluated high blood pressure during the measurement period, we added the antihypertensive drug and showed good effect for improvement of hypertension on long- term monitoring. Blood pressure values obtained using noninvasive methods were useful for red pandas. Moreover, these data were considered important for animal welfare.

Amyloid-Beta, Tau, and Microglial Activation in Aged Felid Brains

Alzheimer's disease (AD) and its associated pathology have been primarily identified in humans, who have relatively large brains and long lifespans. To expand what is known about aging and neurodegeneration across mammalian species, we characterized amyloid-beta (Aβ) and tau lesions in five species of aged felids (n = 9; cheetah, clouded leopard, African lion, serval, Siberian tiger). We performed immunohistochemistry to detect Aβ40 and Aβ42 in plaques and vessels and hyperphosphorylated tau in the temporal lobe gyrus sylvius and in the CA1 and CA3 subfields of the hippocampus. We also quantified the densities and morphological types of microglia expressing IBA1. We found that diffuse Aβ42 plaques, but not dense-core plaques, were present more frequently in the temporal cortex and tended to be more common than Aβ40 plaques across species. Conversely, vascular Aβ was labeled more consistently with Aβ40 for each species on average. Although all individuals showed some degree of Aβ40 and/or Aβ42 immunoreactivity, only the cheetahs and clouded leopards exhibited intraneuronal hyperphosphorylated tau (i.e., pretangles), which was more common in the hippocampus. Reactive, intermediate microglia were significantly associated with total Aβ40 vessel area and pretangle load in the hippocampus. This study demonstrates the co-occurrence of Aβ and tau pathology in two felid species, cheetahs and clouded leopards. Overall, these results provide an initial view of the manifestation of Aβ and tau pathology in aged, large-brained felids, which can be compared with markers of neurodegeneration across different taxa, including domestic cats, nonhuman primates, and humans.

Noninvasive, epigenetic age estimation in an elasmobranch, the cownose ray (Rhinoptera bonasus)

Age data are essential for estimating life history parameters and are thus critical for population assessment, management, and conservation. Traditional vertebrae-based age estimation in elasmobranchs can be costly, time intensive, of low accuracy, and is by necessity lethal. Herein, epigenetic clocks were developed for an elasmobranch, the cownose ray (Rhinoptera bonasus), using aquarium-born individuals (n = 42) with known dates of birth (age range: 7-7,878 days or 0-21 years) and two tissue types (fin clips and whole blood) that can be sampled in a relatively non-invasive manner. Enzymatically-converted restriction site-associated DNA sequencing (ECrad-seq) was used to identify CpG sites that exhibited age-correlated DNA methylation. The epigenetic clocks developed were highly accurate (mean absolute error, MAE, < 0.75 years) and precise (R2 > 0.98). Age-associated CpG sites were identified across tissues, and a multi-tissue clock was also highly accurate (MAE < 1 year) and precise (R2 = 0.97). Using the developed fin clip clock, three wild-caught individuals of unknown age but managed in aquariums for > 22 years were predicted to be 22.10-23.49 years old. Overall, the results have important implications for future epigenetic clock development and noninvasive age estimation in elasmobranchs.

Larger Than Life? Body Mass Records of Zoo-Managed Giant Anteaters (Myrmecophaga tridactyla)

It has been suggested repeatedly that zoo-kept giant anteaters (Myrmecophaga tridactyla) have higher body masses than their free-ranging conspecifics. Here, we assess this hypothesis by comparing body mass data of 184 female and 173 male individuals kept in zoos to published and unpublished data of free-ranging animals (n = 215). In zoos, the average adult body mass of all individuals was 45.9 ± 9.6 kg (range 19.2-72.6 kg), whereas body mass for free-ranging specimens was 33.0 ± 2.3 kg (21-45.5 kg). Among those zoo animals in which a sufficient number of subsequent intra-annual measures had been taken, we assessed visually whether regular, annual fluctuations in body mass were evident. We observed regular, likely seasonal, cycles in body mass, which (i) may be plausibly attributed to ambient temperature changes that affect the body temperature of anteaters, and (ii) would likely not have occurred if the animals were affected by obesity. Additionally, we explain our hypothesis that in the case of giant anteaters, the discrepancy in body mass between natural habitats and zoos most likely is not indicative of a generally obese population in zoos, as is typically concluded in the case of similar comparisons in primates, but represents an unleashing of the full growth potential of the species by conditions of optimal energy and nutrient provision. Future recording of not only body mass but also body dimensions is recommended to better compare the body condition of free-ranging and zoo-managed individuals.

Early-life glucocorticoids accelerate lymphocyte count senescence in roe deer

Immunosenescence corresponds to the progressive decline of immune functions with increasing age. Although it is critical to understand what modulates such a decline, the ecological and physiological drivers of immunosenescence remain poorly understood in the wild. Among them, the level of glucocorticoids (GCs) during early life are good candidates to modulate immunosenescence patterns because these hormones can have long-term consequences on individual physiology. Indeed, GCs act as regulators of energy allocation to ensure allostasis, are part of the stress response triggered by unpredictable events and have immunosuppressive effects when chronically elevated. We used longitudinal data collected over two decades in two populations of roe deer (Capreolus capreolus) to test whether higher baseline GC levels measured within the first year of life were associated with a more pronounced immunosenescence and parasite susceptibility. We first assessed immunosenescence trajectories in these populations facing contrasting environmental conditions. Then, we found that juvenile GC levels can modulate lymphocyte trajectory. Lymphocyte depletion was accelerated late in life when GCs were elevated early in life. Although the exact mechanism remains to be elucidated, it could involve a role of GCs on thymic characteristics. In addition, elevated GC levels in juveniles were associated with a higher abundance of lung parasites during adulthood for individuals born during bad years, suggesting short-term negative effects of GCs on juvenile immunity, having in turn long-lasting consequences on adult parasite load, depending on juvenile environmental conditions. These findings offer promising research directions in assessing the carry-over consequences of GCs on life-history traits in the wild.

Monitoring the world-oldest zoo-housed male giant panda (Ailuropoda melanoleuca): A case-study on pathway utilization

Habitat use monitoring is necessary for a comprehensive understanding of the biological and psychological requirements of animals under human care, facilitating improved exhibit designs and promoting animal welfare. Current studies focused on the space use of the exhibit while limited studies examined the pathway use of the zoo-housed animals. This study aimed to investigate the habitat use of An An, the world-oldest male giant panda (Ailuropoda melanoleuca) at Ocean Park Hong Kong using a pathway utilization monitoring method. The result showed uneven utilization of pathways favoring the upper area near his den over the lower area which required longer walking in the hilly exhibit. Moreover, the comparisons of walking directions showed a preference for gentle slopes during uphill movement and a favor for steep slopes during downhill movement. Our study also compared the walking distance between uphill and downhill movements and the results showed that An An walked longer distances heading upward than moving downward due to his choice of pathways. Our results are in line with the findings in the wild population, showing a preference for gentle slopes, especially in uphill movement. Our study demonstrated the value of the pathway monitoring technique. Due to its easy and time-effective use, this technique can be incorporated into the care teams' operation, providing valuable information on daily activity (e.g. accessing the walking ability of the aged animals by investigating the pathway use and walking distance) and habitat use. Consequently, the pathway monitoring technique can help improve exhibit designs promoting welfare.

Epigenetic aging studies of pair bonding in prairie voles

The quality of romantic relationships can predict health consequences related to aging. DNA methylation-based biomarkers of aging accurately estimate chronological age. We developed several highly accurate epigenetic aging clocks, based on highly conserved mammalian CpGs, for the socially monogamous prairie vole (Microtus ochrogaster). In addition, our dual-species human-vole clock accurately measured relative age and illustrates high species conservation of epigenetic aging effects. Next, we assessed how pair bonding impacts epigenetic aging. We did not find evidence that pair-bonded voles exhibit accelerated or decelerated epigenetic aging effects in blood, ear, liver, or brain tissue. Our epigenome wide association study identified CpGs in five genes strongly associated with pair bonding: Foxp4, Phf2, Mms22l, Foxb1, and Eif1ad. Overall, we present accurate DNA methylation-based estimators of age for a species of great interest to researchers studying monogamy in animals. We did not find any evidence that sex-naive animals age differently from pair-bonded animals.

Prevalence and Risk Factors of Bone and Dental Lesions in Neotropical Deer

Bone and dental lesions have been documented in various deer species globally, affecting the efficiency of ingestion and digestion, consequently influencing their general health and leading to a decline in survival and reproductive performance. The present study aimed to characterize bone and dental lesions in the dry skulls of individual deer, estimate the prevalence of these lesions, and assess potential risk factors associated with the development of bone and dental alterations. This study assessed bone and dental lesions in 180 dry skulls of eleven neotropical deer species, originating from both captivity and wildlife conditions, through direct visual inspection. A high prevalence of bone and dental lesions was observed in all analyzed species. Dental calculus was the most common alteration (96.7%), followed by dental wear (71.1%). Animal age positively correlated with most bone and dental alterations, indicating that older animals showed more lesions. Additionally, the prevalence of these alterations was similar between sexes. Moreover, all lesions were more common in captive-bred animals, likely attributed to their older age and a less diverse diet. Blastocerus dichotomus and Mazama americana were most affected by bone resorption and dental trauma and had the highest dental calculus prevalence, along with Subulo gouazoubira and Passalites nemorivagus. All eleven species evaluated in the present study were susceptible to the occurrence of bone and dental lesions. Therefore, monitoring oral health and diet in captivity are fundamental practices for the conservation of these species.

Pulmonary acinar adenocarcinoma in a captive lioness (Panthera leo)

Neoplasms in wild felids are more frequently observed in captive animals, of which clinicopathological features of pulmonary tumors are not commonly described. This study aimed to describe the clinical and pathological aspects of a case of diffuse pulmonary acinar adenocarcinoma in a 23-year-old, captive lioness with clinical history of dyspnea, progressive weight loss and inappetence. At necropsy, the lungs were mildly pale, moderately firm, and the pleural surface was diffusely irregular with multifocal to coalescent, grey to white areas. No masses or superficial nodules were detected, but, on the cut surface, there were numerous, spherical, firm, white to yellow areas up to 0.5 cm in diameter affecting all pulmonary lobes. Histologically, in the lungs, there were extensive, non-delineated areas of neoplastic proliferation of columnar, ciliated epithelial cells arranged in irregular tubuloacinar structures. Immunohistochemical analysis revealed immunolabeling of neoplastic cells for pan-cytokeratin and thyroid transcription factor-1. Napsin-A exhibited only scarce and scattered immunolabeling in the neoplastic cells. The gross, histologic and immunohistochemical findings confirmed the final diagnosis of primary diffuse pulmonary adenocarcinoma.

Tumor and Tumor-like Lesions in Red Foxes (Vulpes vulpes) from Croatia

The red fox, found on all continents except Antarctica, occupies diverse habitats. In Croatia, it is an indigenous wild species with a population density of 0.7 animals per square kilometer. While tumors in wild animals from the Canidae family are scarce, the true prevalence and diversity of tumors are likely underestimated due to limited research. So far, a limited number of tumors have been observed among the red fox population, either in their natural habitat or in captivity. As part of the National Rabies Control Program, we examined 1890 red fox carcasses over a four-year period. Our focus was on identifying abnormalities on the skin and internal organs that suggest potential neoplastic proliferation. Five red foxes, three males and two females, were found to have growths resembling potential tumors. Their age distribution spanned from 2 to 7 years. Microscopic investigation revealed two collagenous hamartomas, two Meibomian gland adenomas, and one intra-abdominal teratoma within a cryptorchid testis. This retrospective study aims to provide a comprehensive description of tumor and tumor-like lesions observed in free-range red foxes from Croatia, marking the first research of its kind in Croatia.

Putting zoo animal cancer into perspective

As part of a comparative research agenda that promises insights that help extend the human lifespan and combat cancer, cancer prevalence in zoo animals has received recent attention. Here, we want to draw attention to a principle of cancer research that was introduced into the zoo world as early on as 1933, but that seems to have gone somewhat forgotten: Cancer is mainly a disease of old age, and therefore studies aiming at identifying taxa that are particularly susceptible or resistant to cancer must control for whether the respective zoo populations are 'old.' In a comparative context, 'old age' cannot be measured in absolute terms (e.g., years), but only in relation to a species' maximum lifespan: Species that achieve, across zoos, a higher mean lifespan as a percent of their maximum lifespan are 'older.' When applying this metric to former as well as more recently published data on cancer prevalence, it appears that those species that become relatively old in zoos-in particular, the carnivores-have a relatively high cancer prevalence. Any improvement in animal husbandry-which reduces premature deaths-should, by default, lead to more cancer. Cancer in zoo animals, like any other old-age condition, might therefore be embraced as a proxy for good husbandry. Rather than following a sensationalist approach that dramatizes disease and death per se, zoos should be clear about what their husbandry goals are, what relative longevities they want to achieve for which species, and what old-age diseases they should therefore expect: in the end, one has to die of something.

Getting to the Meat of It: The Effects of a Captive Diet upon the Skull Morphology of the Lion and Tiger

Zoo animals are crucial for conserving and potentially re-introducing species to the wild, yet it is known that the morphology of captive animals differs from that of wild animals. It is important to know how and why zoo and wild animal morphology differs to better care for captive animals and enhance their survival in reintroductions, and to understand how plasticity may influence morphology, which is supposedly indicative of evolutionary relationships. Using museum collections, we took 56 morphological measurements of skulls and mandibles from 617 captive and wild lions and tigers, reflecting each species' recent historical range. Linear morphometrics were used to identify differences in size and shape. Skull size does not differ between captive and wild lions and tigers, but skull and mandible shape does. Differences occur in regions associated with biting, indicating that diet has influenced forces acting upon the skull and mandible. The diets of captive big cats used in this study predominantly consisted of whole or partial carcasses, which closely resemble the mechanical properties of wild diets. Thus, we speculate that the additional impacts of killing, manipulating and consuming large prey in the wild have driven differentiation between captive and wild big cats.

Quality-of-Life Assessments in Zoo Animals: Not Just for the Aged and Charismatic

Zoos should aim to provide all of their animals with a good quality of life (QoL) throughout all life stages. In parallel with the evolution of QoL assessment questionnaires and tools in human and domestic animal settings, in recent times, some individual zoos and zoo industry associations have incorporated such instruments into their animal management practices. This has been conducted predominantly to inform, monitor, and document end-of-life decision-making for large, charismatic mammals. There is scope to expand the use of these tools to improve their utility, validity, reliability, and value to an animal welfare program. Assessment of QoL is a complex task given that the notion being measured is abstract and self-determined, and the design and purpose of the tools to do this require careful consideration. This review explores the QoL concept as it applies to animals, the assessment indications and methodologies relevant to a zoo setting, and the importance of considering QoL at any life stage across species. An overview of current thinking and the applications and limitations of QoL evaluation of captive wild animals is offered to promote and aid facility practice reviews and to help direct future innovations that leverage concurrent and converging advances in zoo animal welfare science.

Cutaneous apocrine gland neoplasia in 16 captive African wild dogs (Lycaon pictus)

This retrospective study documents the occurrence of single and multiple cutaneous apocrine gland tumours (CATs) on the dorsal midline of 16 captive African wild dogs (AWDs, Lycaon pictus) derived from 161 submissions to diagnostic laboratories in South Africa, France and Germany between 1997 and 2022. Animals included in the study came from zoological institutions in South Africa (n = 2), France (n = 5) and Germany (n = 1) and ranged from 5 to 14 years of age. Fifteen affected animals were female (94%) and one was male. CATs presented as raised, hairless, multilobular, grey firm masses, consistently located along the dorsal midline. Apart from a single cutaneous apocrine adenoma and a cystadenoma occurring concurrently with two non-cystic adenocarcinomas, neoplasms were consistent with malignant cutaneous apocrine adenocarcinomas with lymphatic spread and visceral metastases. Advanced age and female sex were identified as risk factors. A genetic component or association with the increasing use of GnRH agonist contraceptives was suspected but could not be established. This study highlights the need for close clinical monitoring of AWDs over the age of 5 years for the development of CATs along the dorsal midline and supports early surgical intervention. More research is needed to determine the role of inbreeding, endocrine changes and husbandry factors that may play a role in the development of CATs on the dorsal midline of AWDs.

Historical development of the survivorship of zoo rhinoceroses-A comparative historical analysis

Zoo animal husbandry is a skill that should be developing constantly. In theory, this should lead to an improvement of zoo animal survivorship over time. Additionally, it has been suggested that species that are at a comparatively higher risk of extinction in their natural habitats (in situ) might also be more difficult to keep under zoo conditions (ex situ). Here, we assessed these questions for three zoo-managed rhinoceros species with different extinction risk status allocated by the IUCN: the "critically endangered" black rhino (Diceros bicornis), the "vulnerable" greater one-horned (GOH) rhino (Rhinoceros unicornis), and the "near threatened" white rhino (Ceratotherium simum). Comparing zoo animals ≥1 year of age, the black rhino had the lowest and the white rhino the highest survivorship, in congruence with their extinction risk status. Historically, the survivorship of both black and white rhino in zoos improved significantly over time, whereas that of GOH rhino stagnated. Juvenile mortality was generally low and decreased even further in black and white rhinos over time. Together with the development of population pyramids, this shows increasing competence of the global zoo community to sustain all three species. Compared to the continuously expanding zoo population of GOH and white rhinos, the zoo-managed black rhino population has stagnated in numbers in recent years. Zoos do not only contribute to conservation by propagating ex situ populations, but also by increasing species-specific husbandry skills. We recommend detailed research to understand specific factors responsible for the stagnation but also the general improvement of survivorship of zoo-managed rhinos.

Do mammals have menopause?

Semantics and lack of data have clouded our understanding about menopause in non-human mammals. The traditional definition of menopause based on the last menstrual bleed is limited and hinders cross-species comparison. Here, we redefine it as the permanent cessation of ovulation and show menopause to be widespread across mammalian orders.

The welfare problems of wide-ranging Carnivora reflect naturally itinerant lifestyles

Carnivora with naturally small home ranges readily adjust to the evolutionarily new environment of captivity, but wider-ranging species seem prone to stress. Understanding why would advance both collection planning and enclosure design. We therefore investigated which aspects of wide-ranging lifestyles are key. We identified eight correlates of home range size (reflecting energetic needs, movement, intra-specific interactions, and itinerant lifestyles). We systematically assessed whether these correlates predict welfare better than range size per se, using data on captive juvenile mortality (from 13 518 individuals across 42 species) and stereotypic route-tracing (456 individuals, 27 species). Naturally itinerant lifestyles (quantified via ratios of daily to annual travel distances) were found to confer risk, predicting greater captive juvenile losses and stereotypic time-budgets. This finding advances our understanding of the evolutionary basis for welfare problems in captive Carnivora, helping explain why naturally sedentary species (e.g. American mink) may breed even in intensive farm conditions, while others (e.g. polar bears, giant pandas) can struggle even in modern zoos and conservation breeding centres. Naturally itinerant lifestyles involve decision-making, and strategic shifts between locations, suggesting that supplying more novelty, cognitive challenge and/or opportunities for control will be effective ways to meet these animals' welfare needs in captivity.

Ageing without senescence: A critical absence in social gerontology?

This paper addresses the absence of the term 'senescence' in recent social science literature on ageing. The significance of this omission is considered in light of the emerging standpoint of gero-science, which argues that the central processes defining ageing are concerned with the rising probability of functional decline, development of degenerative disease and death. From this perspective, the separation of ageing and senescence sustains the myth that there exist forms of ageing that are exempt from senescence. The persistence of this myth underlies ageing studies, the sociology of later life and most social gerontology. While there have been undoubted benefits arising from this bracketing out of senescence, the argument of this paper is that the continuing advances associated with this standpoint are outweighed by the need to seriously engage with the consequences of contemporary societal ageing and the centrality of the processes of senescence in establishing an adequate understanding of ageing, its correlates and contingencies and its personal and social consequences.

Losing the forest for the tree? On the wisdom of subpopulation management

Animal habitats are changing around the world in many ways, presenting challenges to the survival of species. Zoo animal populations are also challenged by small population sizes and limited genetic diversity. Some ex situ populations are managed as subpopulations based on presumed subspecies or geographic locality and related concerns over genetic purity or taxonomic integrity. However, these decisions can accelerate the loss of genetic diversity and increase the likelihood of population extinction. Here I challenge the wisdom of subpopulation management, pointing out significant concerns in the literature with delineation of species, subspecies, and evolutionarily significant units. I also review literature demonstrating the value of gene flow for preserving adaptive potential, the often-misunderstood role of hybridization in evolution, and the likely overstated concerns about outbreeding depression, and preservation of local adaptations. I argue that the most effective way to manage animal populations for the long term be they in human care, in the wild, or if a captive population is being managed for reintroduction, is to manage for maximum genetic diversity rather than managing subpopulations focusing on taxonomic integrity, genetic purity, or geographic locale because selection in the future, rather than the past, will determine what genotypes and phenotypes are the most fit. Several case studies are presented to challenge the wisdom of subpopulation management and stimulate thinking about the preservation of genomes rather than species, subspecies, or lineages because those units evolved in habitats that are likely very different from those habitats today and in the future.

Behaviour, Furnishing and Vertical Space Use of Captive Callimico (Callimico goeldii): Implications for Welfare

Provision of optimal captive care should be supported by species-specific evidence. Callimico (Callimico goeldii) is a small South American callitrichid primate. This study sought to address gaps in species-specific knowledge and captive management research by examining differences in callimico behaviour across multiple collections, investigating vertical enclosure use and a possible association between specific behaviours and vertical zones. Observational research was conducted at five European Association of Zoos and Aquaria (EAZA) organisations, in exhibits that were visually divided into four vertical zones. Instantaneous scan sampling was used to record behaviour and location of callimico over a six-day period at each collection, exceeding 160 observational hours. Significant differences were observed in foraging between collections and were much lower than the recommendations in Best Practice Guidelines, although near-wild levels were recorded in one enclosure. At an average height of 2 m, callimico utilized a similar vertical space across very different enclosures, regardless of overall available height, reflective of their natural ecology. The association between whole food items and increased foraging time, horizontal branches and locomotion and deep substrate and diversity of behaviours, offers further species-specific evidence of how the callimico use their captive environment. Our findings complement current EAZA guidelines to support species appropriate care for callimico and makes specific recommendations for further research.

The evolution of early-life telomere length, pace-of-life and telomere-chromosome length dynamics in birds

Telomeres, the short DNA sequences that protect chromosome ends, are an ancient molecular structure, which is highly conserved across most eukaryotes. Species differ in their telomere lengths, but the causes of this variation are not well understood. Here, we demonstrate that mean early-life telomere length is an evolutionary labile trait across 57 bird species (representing 35 families in 12 orders) with the greatest trait diversity found among passerines. Among these species, telomeres are significantly shorter in fast-lived than in slow-lived species, suggesting that telomere length may have evolved to mediate trade-offs between physiological requirements underlying the diversity of pace-of-life strategies in birds. This association was attenuated when excluding studies that may include interstitial telomeres in the estimation of mean telomere length. Curiously, within some species, larger individual chromosome size predicts longer telomere lengths on that chromosome, leading to the hypothesis that telomere length also covaries with chromosome length across species. We show that longer mean chromosome length or genome size tends to be associated with longer mean early-life telomere length (measured across all chromosomes) within a phylogenetic framework constituting up to 31 bird species. These associations were strengthened when excluding highly influential outliers. However, sensitivity analyses suggested that they were susceptible to sample size effects and not robust to the exclusion of studies that may include interstitial telomeres. Combined, our analyses generalize patterns previously found within a few species and provide potential adaptive explanations for the 10-fold variation in telomere lengths observed among birds.

The influence of immune challenges on the mean and variance in reproductive investment: a meta-analysis of the terminal investment hypothesis

Finding the optimal balance between survival and reproduction is a central puzzle in life-history theory. The terminal investment hypothesis predicts that when individuals encounter a survival threat that compromises future reproductive potential, they will increase immediate reproductive investment to maximise fitness. Despite decades of research on the terminal investment hypothesis, findings remain mixed. We examined the terminal investment hypothesis with a meta-analysis of studies that measured reproductive investment of multicellular iteroparous animals after a non-lethal immune challenge. We had two main aims. The first was to investigate whether individuals, on average, increase reproductive investment in response to an immune threat, as predicted by the terminal investment hypothesis. We also examined whether such responses vary adaptively on factors associated with the amount of reproductive opportunities left (residual reproductive value) in the individuals, as predicted by the terminal investment hypothesis. The second was to provide a quantitative test of a novel prediction based on the dynamic threshold model: that an immune threat increases between-individual variance in reproductive investment. Our results provided some support for our hypotheses. Older individuals, who are expected to have lower residual reproductive values, showed stronger mean terminal investment response than younger individuals. In terms of variance, individuals showed a divergence in responses, leading to an increase in variance. This increase in variance was especially amplified in longer-living species, which was consistent with our prediction that individuals in longer-living species should respond with greater individual variation due to increased phenotypic plasticity. We find little statistical evidence of publication bias. Together, our results highlight the need for a more nuanced view on the terminal investment hypothesis and a greater focus on the factors that drive individual responses.

Demography and epidemiology of captive former biomedical research chimpanzees (Pan troglodytes) 1: Survival and mortality

Accurate and up-to-date data on longevity and mortality are essential for describing, analyzing, and managing animal populations in captivity. We assembled a comprehensive demography data set and analyzed survival and mortality patterns in a population of captive former biomedical research chimpanzees. The study synthesized over 51,000 life-years of demographic data collected on 2349 individuals between 1923 and 2014. Our goal was to assess the population's current age-sex composition, estimate rates of survivorship, mortality and life expectancy, and compare findings with other chimpanzee populations of interest. Results indicated an increasingly geriatric contemporary population declining in size. The median life expectancy (MLE) of the entire population was 32.6 years (males 29.1, females 36.1). For chimpanzees who reached 1 year of age, the MLE increased to 34.9 years (males 31.0, females 38.8). Survival probability was influenced by both sex and birth type. Females exhibited greater survivorship than males (β₁  = -0.34, z = -5.74, p < 0.001) and wild-born individuals exhibited greater survivorship than captive-born individuals (β₂  = -0.55, z = -5.89, p < 0.001). There was also a seasonal trend in mortality, wherein more individuals died during the winter months (December-February) compared with other seasons. Analyses of life expectancy over time showed continual increases in both median age of living individuals and median age at death, suggesting that these chimpanzees have yet to reach their full aging potential in a postresearch environment. As they continue to age, ongoing monitoring and analysis of demographic changes will be necessary for science-based population and program management until extinction occurs some decades in the future.

Sex differences in adult lifespan and aging rate across mammals: a test of the 'Mother Curse hypothesis'

In many animal species, including humans, males have shorter lifespan and show faster survival aging than females. This differential increase in mortality between sexes could result from the accumulation of deleterious mutations in the mitochondrial genome of males due to the maternal mode of mtDNA inheritance. To date, empirical evidence supporting the existence of this mechanism - called the Mother Curse hypothesis - remains largely limited to a few study cases in humans and Drosophila. In this study, we tested whether the Mother Curse hypothesis accounts for sex differences in lifespan and aging rate across 128 populations of mammals (60 and 68 populations studied in wild and captive conditions, respectively) encompassing 104 species. We found that adult lifespan decreases with increasing mtDNA neutral substitution rate in both sexes in a similar way in the wild - but not in captivity. Moreover, the aging rate marginally increased with neutral substitution rate in males and females in the wild. Overall, these results indicate that the Mother Curse hypothesis is not supported across mammals. We further discuss the implication of these findings for our understanding of the evolution of sex differences in mortality and aging.

Raising offspring increases ageing: Differences in senescence among three populations of a long-lived seabird, the Atlantic puffin

Actuarial senescence, the decline of survival with age, is well documented in the wild. Rates of senescence vary widely between taxa, to some extent also between sexes, with the fastest life histories showing the highest rates of senescence. Few studies have investigated differences in senescence among populations of the same species, although such variation is expected from population-level differences in environmental conditions, leading to differences in vital rates and thus life histories. We predict that, within species, populations differing in productivity (suggesting different paces of life) should experience different rates of senescence, but with little or no sexual difference in senescence within populations of monogamous, monomorphic species where the sexes share breeding duties. We compared rates of actuarial senescence among three contrasting populations of the Atlantic puffin Fratercula arctica. The dataset comprised 31 years (1990-2020) of parallel capture-mark-recapture data from three breeding colonies, Isle of May (North Sea), Røst (Norwegian Sea) and Hornøya (Barents Sea), showing contrasting productivities (i.e. annual breeding success) and population trends. We used time elapsed since first capture as a proxy for bird age, and productivity and the winter North Atlantic Oscillation Index (wNAO) as proxies for the environmental conditions experienced by the populations within and outside the breeding season, respectively. In accordance with our predictions, we found that senescence rates differed among the study populations, with no evidence for sexual differences. There was no evidence for an effect of wNAO, but the population with the lowest productivity, Røst, showed the lowest rate of senescence. As a consequence, the negative effect of senescence on the population growth rate (λ) was up to 3-5 times smaller on Røst (Δλ = -0.009) than on the two other colonies. Our findings suggest that environmentally induced differences in senescence rates among populations of a species should be accounted for when predicting effects of climate variation and change on species persistence. There is thus a need for more detailed information on how both actuarial and reproductive senescence influence vital rates of populations of the same species, calling for large-scale comparative studies.

Life history and cancer in birds: clutch size predicts cancer

Cancer is a disease that affects nearly all multicellular life, including birds. However, little is known about what factors explain the variance in cancer prevalence among species. Litter size is positively correlated with cancer prevalence in managed species of mammals, and larger body size, but not incubation or nestling period, is linked to tumor prevalence in wild birds. Also, birds that produce more elaborate sexual traits are expected to have fewer resources for cancer defenses and thus higher cancer prevalence. In this study, we examined whether cancer prevalence is associated with a wide variety of life history traits (clutch size, incubation length, body mass, lifespan, and the extent of sexual dimorphism) across 108 species of managed birds in 25 different zoological facilities, sanctuaries, and veterinary clinics. We found that clutch size was positively correlated with cancer and neoplasia (both benign and malignant) prevalence, even after controlling for body mass. Cancer prevalence was not associated with incubation length, body mass, lifespan, or sexual dimorphism. The positive correlations of clutch size with cancer prevalence and neoplasia prevalence suggest that there may be life-history trade-offs between reproductive investment and somatic maintenance (in the form of cancer prevention mechanisms) in managed birds.

Life span, growth, senescence and island syndrome: Accounting for imperfect detection and continuous growth

Small vertebrates on islands are expected to attain a larger body size, and a greater survival than their mainland counterparts. Comparative studies have questioned whether lizards exhibit this set of adaptations, referred to as the 'island syndrome'. We collected data on 730 individuals the endemic Lilford's lizard Podarcis lilfordi throughout a 10-year period on a small island of the Balearic archipelago (Spain). We coupled a growth function with a capture-mark-recapture model to simultaneously estimate size- and sex-dependent growth rate and survival. To put our results into a wider context, we conducted a systematic review of growth, life span and age at maturity in different Podarcis species comparing insular and mainland populations. We found a low average growth coefficient (0.56 and 0.41 year^-1 for males and females to reach an asymptotic size of 72.3 and 65.6 mm respectively), a high annual survival probability of 0.81 and 0.79 in males and females, and a large variability between individuals in growth parameters. Survival probability decreased with body size in both sexes, indicating a senescence pattern typical of long-lived species or in populations with a low extrinsic mortality. Assuming a constant survival after sexual maturity, at about 2 years old, the average life span was 6.18 years in males and 8.99 in females. The oldest animal was a male last captured at an estimated age of ≥13 years and still alive at the end of the study. Our results agree with the predictions of the 'island syndrome' for survival, life span and growth parameters. A comparative analysis of these values across 29 populations of 16 different species of Podarcis indicated that insular lizards grow slower and live longer than their mainland counterparts. However, our data differed from other island populations of the same species, suggesting that island-specific characteristics play an additional role to isolation. Within this study we developed an analytical approach to study the body size-dependent survival of small reptiles. We discuss its applicability to contrast hypotheses on senescence in different sexes of this species, and provide the code used to integrate the growth and capture-mark-recapture models.

Stress in wildlife: comparison of the stress response among domestic, captive, and free-ranging animals

The stress response, which involves joint activity of the nervous and endocrine systems, is one of the basic adaptive mechanisms that ensures the survival of the individual. The activation of the sympathetic nervous system, the sympathetic-adrenal-medullary axis, and the hypothalamic-pituitary-adrenal axis enables organisms to respond to endogenous and exogenous challenges. Repeated short-term stress leads to long-term stress, which disrupts physiological homeostasis. Unlike domestic animals, wild animals are not protected from environmental and weather influences or treated for diseases. In addition, climate change, habitat fragmentation and loss, and urban stressors (such as light, noise and chemical pollution; xenobiotics; traffic; and buildings) affect individual wildlife and populations. In this review, we have attempted to depict the magnitude of the stress response in wildlife and related domestic animals as well as in captive and free-ranging animals. The intensity of the stress response can be estimated by determining the concentration of glucocorticoids in body fluids, tissues, and excreta. A comparison of results from different studies suggests that domestic animals have lower fecal and hair glucocorticoid concentrations than related wild animals. Additionally, fecal and hair glucocorticoid concentrations in captive animals are higher than in free-ranging animals of the same species. As there are limited data on this topic, we cannot draw definitive conclusions about glucocorticoid concentration and stress response. Further studies are needed to clarify these issues.

Ex situ breeding programs benefit from science-based cooperative management

Science-based management confers a variety of benefits to wildlife populations that are cooperatively managed by zoos and aquariums, including those managed through the Association of Zoos and Aquariums. Briefly, when management strategies are successful, they result in reproductively robust populations that better retain genetic diversity and limit inbreeding than unmanaged populations. Although the benefits of demographic and genetic management have been well documented throughout both the scientific and popular literature, it has also been established that the majority of managed populations in zoos and aquariums are not meeting the minimum criteria believed to convey long-term biological viability. For most of these populations, an inability to meet viability criteria is not an inherent failure of how cooperative management is implemented. Furthermore, in recent years, we have perceived that the need to meet specific viability goals sometimes has obscured the benefits that these populations receive from rigorous, science-based management. To better clarify the conversation surrounding population viability in zoos and aquariums, we seek to decouple viability measures and how they predict population persistence from the benefits conferred to populations through science-based management. A primary goal of population management is to facilitate the persistence of priority species for longer than would be expected if no such management were implemented. Although current viability measures and future projections of viability are important tools for assessing the likelihood of population persistence, they are not indicators of which populations may most benefit from science-based management. Here, we review the history and purpose of applying science-based management to zoo and aquarium populations, describe measures of population viability and caution against confusing those measures of viability with population management goals or long-term population sustainability, and clearly articulate the benefits conferred to zoo and aquarium populations by science-based management.

Primary Ovarian Leiomyoma in a White Tiger (Panthera tigris)

Ovarian leiomyomas are very rare in domestic cats and occasionally mentioned in studies reporting general pathological findings and neoplasm occurrence in non-domestic large felids. This report describes a case of ovarian leiomyoma in a 22-year-old white tiger (Panthera tiger), treated with deslorelin implants, detailing pathological and immunohistochemical characteristics. Gross examination revealed a markedly enlarged, firm, whitish right ovary with a multinodular appearance. On a cut surface, multiple brown-fluid-filled cysts interspersed with solid grey-to-white areas were observed. On histopathological examination, the ovary was enlarged and replaced by a densely cellular neoplasm composed of spindle cells arranged in fascicles, or occasionally in a herringbone pattern, embedded in a large stroma of collagenous connective tissue. Neoplastic cells showed mild nuclear atypia and pleomorphism and low mitotic rate. Immunohistochemistry confirmed smooth muscle origin of the neoplasm, and cells were positive for vimentin, alpha-smooth muscle actin, desmin, and caldesmon. A low rate (<1%) of Ki-67-positive cells was observed. Although rare, ovarian leiomyoma should be considered when a mass is present in the ovary of a tiger with reproductive failure. Because cancer of the reproductive system impacts on species conservation by affecting reproduction, regular health monitoring is warranted to support wildlife conservation. Finally, the adverse effects associated with long-term treatment with synthetic GnRH analogues as contraceptives in non-domestic felids are worthy of future investigation.

Evidence for reproductive senescence across ray-finned fishes: A review

The origin, incidence, and consequences of reproductive senescence vary greatly across the tree of life. In vertebrates, research on reproductive senescence has been mainly focused on mammals and birds, demonstrating that its variation is largely linked to critical life history traits, such as growth patterns, juvenile, and adult mortality, and reproductive strategy. Fishes represent half of the vertebrate taxonomic diversity and display remarkable variation in life history. Based on a thorough literature review, we summarize current evidence on reproductive senescence in ray-finned fishes (Actinopterygii). While survival and physiological senescence are acknowledged in fish, their potential age-related reproductive decline has often been disregarded due to the prevalence of indeterminate growth. We demonstrate that age-related reproductive decline is reported across fish phylogeny, environments, and traits. An important point of our review is that the incidence of reproductive senescence in a species depends on both the number of studies for that species and the coverage of its maximum lifespan by the study. Reproductive senescence was documented for one-third of the studied fish species, with females suffering an age-related decline in reproductive traits less often than males or both parents combined. Neither parental care nor migratory strategy corresponded with the occurrence of reproductive senescence in fish. The traits that were affected by reproductive senescence most often were sex-specific, with pre-mating and mating categories of traits declining in females and sperm quality and quantity in males. We also demonstrate that reproductive senescence can be buffered by indeterminate growth. We provide rich evidence of reproductive senescence across ray-finned fishes, but we highlight the need for better data on age-related reproduction in fishes.

Variable rate of ageing within species: insights from Darwin’s frogs

Actuarial senescence, the increase in adult mortality risk with increasing age, is a widespread phenomenon across the animal kingdom. Although between-species variation in the rate of increase in mortality as organisms age (i.e. ageing rate) is now well documented, the occurrence of variation in ageing rate within a given species remains much more debatable. We evaluated the level of within-species variation in ageing rate in four populations of the southern Darwin’s frog (Rhinoderma darwinii) from Chile. Our results revealed strong among-population variation in ageing rates, and these were correlated with the population-specific generation time. A higher ageing rate occurred in populations where individuals exhibited a faster pace of life. Our results, along with recent studies in evolutionarily distant amphibian species, indicate that there can be substantial within-species variation in the rate of ageing, highlighting amphibians as emerging models to study the patterns and mechanisms of intraspecific variation in ageing rate.

Is Aging an Inevitable Characteristic of Organic Life or an Evolutionary Adaptation?

Aging is an evolutionary paradox. Several hypotheses have been proposed to explain it, but none fully explains all the biochemical and ecologic data accumulated over decades of research. We suggest that senescence is a primitive immune strategy which acts to protect an individual's kin from chronic infections. Older organisms are exposed to pathogens for a longer period of time and have a higher likelihood of acquiring infectious diseases. Accordingly, the parasitic load in aged individuals is higher than in younger ones. Given that the probability of pathogen transmission is higher within the kin, the inclusive fitness cost of infection might exceed the benefit of living longer. In this case, programmed lifespan termination might be an evolutionarily stable strategy. Here, we discuss the classical evolutionary hypotheses of aging and compare them with the pathogen control hypothesis, discuss the consistency of these hypotheses with existing empirical data, and present a revised conceptual framework to understand the evolution of aging.

On the comparative biology of mammalian telomeres: Telomere length co-evolves with body mass, lifespan and cancer risk

Telomeres, the short repetitive DNA sequences that cap the ends of linear chromosomes, shorten during cell division and are implicated in senescence in most species. Telomerase can rebuild telomeres but is repressed in many mammals that exhibit replicative senescence, presumably as a tumour suppression mechanism. It is therefore important to understand the co-evolution of telomere biology and life-history traits that has shaped the diversity of senescence patterns across species. Gomes et al. previously produced a large data set on telomere length (TL), telomerase activity, body mass and lifespan among 57 mammal species. We re-analysed their data using the same phylogenetic multiple regressions and with several additional analyses to test the robustness of the findings. We found substantial inconsistencies in our results compared to Gomes et al.'s. Consistent with Gomes et al. we found an inverse association between TL and lifespan. Contrary to the analyses in Gomes et al., we found a generally robust inverse association between TL and mass, and only weak nonrobust evidence for an association between telomerase activity and mass. These results suggest that shorter TL may have been selected for in larger and longer lived species, probably as a mechanism to suppress cancer. We support this hypothesis by showing that longer telomeres predict higher cancer risk across 22 species. Furthermore, we find that domesticated species have longer telomeres. Our results call into question past interpretations of the co-evolution of telomere biology and life-history traits and stress the need for careful attention to model construction.

Maximum longevity and juvenile mortality in zoo-housed mangabeys

Little is known about the biology of grey-cheeked and black crested mangabeys (Lophocebus albigena and Lophocebus aterrimus, respectively). As these primates face threats in the wild, well-monitored zoo-housed populations with up to date registries are becoming increasingly valuable to acquire species knowledge and to support conservation efforts. We used international studbooks to extract demographic and genetic information on 519 mangabeys to investigate how life history and parent-related variables influence maximum longevity and juvenile mortality. Generalized linear mixed models, as well as survival analyses, were applied. Results showed that females lived significantly longer than males, which is not uncommon in primates. Furthermore, our results indicated that the maximum longevity is lower for individuals living in European zoos versus individuals from North American zoos, which may be due to a combination of environmental differences and potential founder effects. We also show that the maternal maximum longevity is positively related to the maximum longevity of the offspring, which may be explained by the inheritance of "good genes". However, the age of the mother at the moment of birth was negatively related to the maximum longevity of the offspring, which contradicts literature that states that, in primates, more experienced and thus older mothers will raise their offspring better than less experienced mothers. Instead, it is more likely that an "optimal age range" exists for breeding mothers. Our study provides insights into the population biology of captive mangabeys and may be helpful for identifying future research priorities to optimize primate health and welfare directly ex situ, and indirectly in situ.

Triparental ageing in a laboratory population of an insect with maternal care

Parental age at reproduction influences offspring size and survival by affecting prenatal and postnatal conditions in a wide variety of species, including humans. However, most investigations into this manifestation of ageing focus upon maternal age effects; the effects of paternal age and interactions between maternal and paternal age are often neglected. Furthermore, even when maternal age effects are studied, pre- and post-natal effects are often confounded. Using a cross-fostered experimental design, we investigated the joint effects of pre-natal paternal and maternal and post-natal maternal ages on five traits related to offspring outcomes in a laboratory population of a species of burying beetle, Nicrophorus vespilloides. We found a significant positive effect of the age of the egg producer on larval survival to dispersal. We found more statistical evidence for interaction effects, which acted on larval survival and egg length. Both interaction effects were negative and involved the age of the egg-producer, indicating that age-related pre-natal maternal improvements were mitigated by increasing age in fathers and foster mothers. These results agree with an early study that found little evidence for maternal senescence, but it emphasizes that parental age interactions may be an important contributor to ageing patterns. We discuss how the peculiar life history of this species may promote selection to resist the evolution of parental age effects, and how this might have influenced our ability to detect senescence.