While the lifespan advantage of small body size and mixed breed status has been documented repeatedly, evidence for an effect of genetic diversity across dog breeds is equivocal. We hypothesized that this might be due to a strong right-censoring bias in available breed-specific lifespan estimates where early-dying dogs from birth cohorts that have not died off completely at the time of data collection are sampled disproportionately, especially in breeds with rapidly growing populations. We took advantage of data on owner reported lifespan and cause of death from a large public database to quantify the effect of size and genetic diversity (heterozygosity) on mortality patterns across 118 breeds based on more than 40,000 dogs. After documenting and removing the right-censoring bias from the breed-specific lifespan estimates by including only completed birth cohorts in our analyses, we show that small size and genetic diversity are both linked to a significant increase in mean lifespan across breeds. To better understand the proximate mechanisms underlying these patterns, we then investigated two major mortality causes in dogs — the cumulative pathophysiologies of old age and cancer. Old age lifespan, as well as the percentage of old age mortality, decreased with increasing body size and increased with increasing genetic diversity. The lifespan of dogs dying of cancer followed the same patterns, but while large size significantly increased proportional cancer mortality, we could not detect a significant signal for lowered cancer mortality with increasing diversity. Our findings suggest that outcross programs will be beneficial for breed health and longevity. They also emphasize the need for high-quality mortality data for veterinary epidemiology as well as for developing the dog as a translational model for human geroscience.

The life histories and population dynamics of chameleons remain poorly known, most likely due to practical challenges related to their cryptic nature. However, several studies have indicated that some of these reptiles have unusually brief life histories. Specifically, one Madagascan chameleon ( Furcifer labordi ) was found to have an annual life cycle characterized by population-wide survival of the austral winter in the egg stage; a unique life history among tetrapods. In this study, we compare the life history of F. labordi with two locally sympatric congeners ( F. cf. nicosiai and F. oustaleti ) in Kirindy forest, western Madagascar, to determine how these species adjust their life histories to a highly seasonal and unpredictable climate. We found differences in lifespan, timing of hatching, growth rates, survival, reproductive rates, adult body size, and roosting heights among all three species. Moreover, two species exhibited relatively short lifespans: 6-9 months in F. labordi and 16-18 months in F. cf. nicosiai . In contrast, F. oustaleti is perennial and large-sized juveniles and adults aestivate during the dry season, but survival rates of adults seemed relatively low. Strikingly, the annual cohort of F. labordi was already adult when hatchlings of F. oustaleti and subsequently F. cf. nicosiai emerged. Our study suggests the co-existence of three different life histories with seasonal adjustment that might be related to the partitioning of overall food availability and contributes valuable life history data on enigmatic chameleon species.

Life history theory predicts that species with shorter lifespan should show higher investments into growth and reproduction at the expense of immune defenses. Labord's chameleon (Furcifer labordi) is the tetrapod with the shortest known life span. To investigate to which extent immunosenescence influences the die-off of these chameleons when they are only about 6 months old, we examined the gastrointestinal-, blood- and ectoparasite burden in F. labordi in Kirindy Forest (western Madagascar) and compared them with sympatric and longer living F. cf. nicosiai. Moreover, we included data from wild F. labordi that were singly housed under ambient conditions with daily food and water supply. Gastrointestinal parasite prevalence of wild F. labordi increased dramatically during the last 3 months of their lives, which include the reproductive period. Furcifer cf. nicosiai was found to have a belated increase in gastrointestinal parasites compared to F. labordi. In F. cf. nicosiai higher prevalence of blood parasites were found, which probably result from the longer exposure to the arthropod intermediate host. Both species showed infestations with ectoparasites, which peaked in the rainy season but disappeared towards the dry season. Male F. labordi showed a significantly higher prevalence of gastrointestinal - and ectoparasites and higher intensities of coccidians and ectoparasites than females. Males of F. cf. nicosiai exhibited higher prevalence of blood- and ectoparasites, as well as higher intensities in ectoparasites. Caged individuals of both sexes showed delayed senescence, reduced parasite burden and lived longer than their wild conspecifics. Overall, the increase in the prevalence in gastrointestinal - and blood parasites towards the disappearance of the wild population of F. labordi indicates that this species invests comparatively less energy in efficient immune system function, supporting the prediction of life history theory.

Inbreeding poses a real or potential threat to nearly every species of conservation concern. Inbreeding leads to loss of diversity at the individual level, which can cause inbreeding depression, and at the population level, which can hinder ability to respond to a changing environment. In closed populations such as endangered species and ex situ breeding programs, some degree of inbreeding is inevitable. It is therefore vital to understand how different patterns of breeding and inbreeding can affect fitness in real animals. Domestic dogs provide an excellent model, showing dramatic variation in degree of inbreeding and in lifespan, an important aspect of fitness that is known to be impacted by inbreeding in other species. There is a strong negative correlation between body size and lifespan in dogs, but it is unknown whether the higher rate of aging in large dogs is due to body size per se or some other factor associated with large size. We used dense genome-wide SNP array data to calculate average inbreeding for over 100 dog breeds based on autozygous segment length and found that large breeds tend to have higher coefficients of inbreeding than small breeds. We then used data from the Veterinary medical Database and other published sources to estimate life expectancies for pure and mixed breed dogs. When controlling for size, variation in inbreeding was not associated with life expectancy across breeds. When comparing mixed versus purebred dogs, however, mixed breed dogs lived about 1.2 years longer on average than size-matched purebred dogs. Furthermore, individual pedigree coefficients of inbreeding and lifespans for over 9000 golden retrievers showed that inbreeding does negatively impact lifespan at the individual level. Registration data from the American Kennel Club suggest that the molecular inbreeding patterns observed in purebred dogs result from specific breeding practices and/or founder effects and not the current population size. Our results suggest that recent inbreeding, as reflected in variation within a breed, is more likely to affect fitness than historic inbreeding, as reflected in variation among breeds. Our results also indicate that occasional outcrosses, as in mixed breed dogs, can have a substantial positive effect on fitness.

Among tetrapods, the current record holder for shortest lifespan is Labord’s chameleon, Furcifer labordi . These reptiles from the arid southwest of Madagascar have a reported lifespan of 4–5 months during the annual rainy season and spend the majority of their life (8–9 months) as a developing embryo. This semelparous, annual life history is unique among tetrapods, but only one population (Ranobe) in the southernmost distribution range has been studied. We therefore investigated the potential for environmentally-dependent variability in lifespan in a population in Kirindy Forest, which has a much longer warm rainy season. While no adults were found after March in Ranobe, the disappearance of adults was delayed by several months in Kirindy. Our data also revealed sex-biased mortality, suggesting that females have a longevity advantage. Furthermore, we found that, after an unusually long previous rainy season, one female was capable of surviving until a second breeding season. Keeping F. labordi in cages under ambient conditions demonstrated that also males can also survive until the next season of activity under these conditions. Our study therefore revealed considerable variability in the extreme life history of this tetrapod that is linked to variation in ecological factors.

Genes of the major histocompatibility complex (MHC) play a central role in adaptive immune responses of vertebrates. They exhibit remarkable polymorphism, often crossing species boundaries with similar alleles or allelic motifs shared across species. This pattern may reflect parallel parasite-mediated selective pressures, either favouring the long maintenance of ancestral MHC allelic lineages across successive speciation events by balancing selection ("trans-species polymorphism"), or alternatively favouring the independent emergence of functionally similar alleles post-speciation via convergent evolution. Here, we investigate the origins of MHC similarity across several species of dwarf and mouse lemurs (Cheirogaleidae). We examined MHC class II variation in two highly polymorphic loci (DRB, DQB) and evaluated the overlap of gut-parasite communities in four sympatric lemurs. We tested for parasite-MHC associations across species to determine whether similar parasite pressures may select for similar MHC alleles in different species. Next, we integrated our MHC data with those previously obtained from other Cheirogaleidae to investigate the relative contribution of convergent evolution and co-ancestry to shared MHC polymorphism by contrasting patterns of codon usage at functional vs. neutral sites. Our results indicate that parasites shared across species may select for functionally similar MHC alleles, implying that the dynamics of MHC-parasite co-evolution should be envisaged at the community level. We further show that balancing selection maintaining trans-species polymorphism, rather than convergent evolution, is the primary mechanism explaining shared MHC sequence motifs between species that diverged up to 30 million years ago.

BACKGROUND:Glucocorticoid hormones are known to play a key role in mediating a cascade of physiological responses to social and ecological stressors and can therefore influence animals' behaviour and ultimately fitness. Yet, how glucocorticoid levels are associated with reproductive success or survival in a natural setting has received little empirical attention so far. Here, we examined links between survival and levels of glucocorticoid in a small, short-lived primate, the grey mouse lemur (Microcebus murinus), using for the first time an indicator of long-term stress load (hair cortisol concentration). Using a capture-mark-recapture modelling approach, we assessed the effect of stress on survival in a broad context (semi-annual rates), but also under a specific period of high energetic demands during the reproductive season. We further assessed the power of other commonly used health indicators (body condition and parasitism) in predicting survival outcomes relative to the effect of long-term stress.RESULTS:We found that high levels of hair cortisol were associated with reduced survival probabilities both at the semi-annual scale and over the reproductive season. Additionally, very good body condition (measured as scaled mass index) was related to increased survival at the semi-annual scale, but not during the breeding season. In contrast, variation in parasitism failed to predict survival.CONCLUSION:Altogether, our results indicate that long-term increased glucocorticoid levels can be related to survival and hence population dynamics, and suggest differential strength of selection acting on glucocorticoids, body condition, and parasite infection.

Inbreeding depression may be common in nature, reflecting either the failure of inbreeding avoidance strategies or inbreeding tolerance when avoidance is costly. The combined assessment of inbreeding risk, avoidance and depression is therefore fundamental to evaluate the inbreeding strategy of a population, that is how individuals respond to the risk of inbreeding. Here, we use the demographic and genetic monitoring of 10 generations of wild grey mouse lemurs (Microcebus murinus), small primates from Madagascar with overlapping generations, to examine their inbreeding strategy. Grey mouse lemurs have retained ancestral mammalian traits, including solitary lifestyle, polygynandry and male‐biased dispersal, and may therefore offer a representative example of the inbreeding strategy of solitary mammals. The occurrence of close kin among candidate mates was frequent in young females (~37%, most often the father) and uncommon in young males (~6%) due to male‐biased dispersal. However, close kin consistently represented a tiny fraction of candidate mates (< 1%) across age and sex categories. Mating biases favouring partners with intermediate relatedness were detectable in yearling females and adult males, possibly partly caused by avoidance of daughter–father matings. Finally, inbreeding depression, assessed as the effect of heterozygosity on survival, was undetectable using a capture–mark–recapture study. Overall, these results indicate that sex‐biased dispersal is a primary inbreeding avoidance mechanism at the population level, and mating biases represent an additional strategy that may mitigate residual inbreeding costs at the individual level. Combined, these mechanisms explain the rarity of inbreeding and the lack of detectable inbreeding depression in this large, genetically diverse population.

Genes of the Major Histocompatibility Complex (MHC) play a central role in adaptive immune responses of vertebrates. They exhibit remarkable polymorphism, often crossing species boundaries with similar alleles or allelic motifs shared across species. This pattern may reflect parallel parasitemediated selective pressures, either favouring the long maintenance of ancestral MHC allelic lineages across successive speciation events by balancing selection (‘trans-species polymorphism’), or alternatively favouring the independent emergence of functionally similar alleles post-speciation via convergent evolution. Here we investigate the origins of MHC similarity across several species of dwarf and mouse lemurs (Cheirogaleidae). We examined MHC class II variation in two highly polymorphic loci (DRB, DQB) and evaluated the overlap of gut-parasite communities in four sympatric lemurs. We tested for parasite-MHC associations across species to determine whether similar parasite pressures may select for similar MHC alleles in different species. Next, we integrated our MHC data with those previously obtained from other Cheirogaleidae to investigate the relative contribution of convergent evolution and co-ancestry to shared MHC polymorphism by contrasting patterns of codon usage at functional versus neutral sites. Our results indicate that parasites shared across species may select for functionally similar MHC alleles, implying that the dynamics of MHC-parasite co-evolution should be envisaged at the community level. We further show that balancing selection maintaining trans-species polymorphism, rather than convergent evolution, is the primary mechanism explaining shared MHC sequence motifs between species that diverged up to 30 million years ago.

Understanding how animals react to human-induced changes in their environment is a key question in conservation biology. Owing to their potential correlation with fitness, several physiological parameters are commonly used to assess the effect of habitat disturbance on animals' general health status. Here, we studied how two lemur species, the fat-tailed dwarf lemur (Cheirogaleus medius) and the grey mouse lemur (Microcebus murinus), respond to changing environmental conditions by comparing their stress levels (measured as hair cortisol concentration), parasitism and general body condition across four habitats ordered along a gradient of human disturbance at Kirindy Forest, Western Madagascar. These two species previously revealed contrasting responses to human disturbance; whereas M. murinus is known as a resilient species, C. medius is rarely encountered in highly disturbed habitats. However, neither hair cortisol concentrations nor parasitism patterns (prevalence, parasite species richness and rate of multiple infections) and body condition varied across the gradient of anthropogenic disturbance. Our results indicate that the effect of anthropogenic activities at Kirindy Forest is not reflected in the general health status of both species, which may have developed a range of behavioural adaptations to deal with suboptimal conditions. Nonetheless, a difference in relative density among sites suggests that the carrying capacity of disturbed habitat is lower, and both species respond differently to environmental changes, with C. medius being more negatively affected. Thus, even for behaviourally flexible species, extended habitat deterioration could hamper long-term viability of populations.

Chronic stress [i.e. long-term elevation of glucocorticoid (GC) levels] and aging have similar, negative effects on the functioning of an organism. Aged individuals’ declining ability to regulate GC levels may therefore impair their ability to cope with stress, as found in humans. The coping of aged animals with long-term natural stressors is virtually unstudied, even though the ability to respond appropriately to stressors is likely integral to the reproduction and survival of wild animals. To assess the effect of age on coping with naturally fluctuating energetic demands, we measured stress hormone output via GC metabolites in faecal samples (fGCM) of wild grey mouse lemurs ( Microcebus murinus ) in different ecological seasons. Aged individuals were expected to exhibit elevated fGCM levels under energetically demanding conditions. In line with this prediction, we found a positive age effect in the dry season, when food and water availability are low and mating takes place, suggesting impaired coping of aged wild animals. The age effect was significantly stronger in females, the longer-lived sex. Body mass of males but not females correlated positively with fGCM in the dry season. Age or body mass did not influence fGCM significantly in the rainy season. The sex- and season-specific predictors of fGCM may reflect the differential investment of males and females into reproduction and longevity. A review of prior research indicates contradictory aging patterns in GC regulation across and even within species. The context of sampling may influence the likelihood of detecting senescent declines in GC functioning.

OBJECTIVES:Health, disease, and immune function are key areas of research in studies of ecology and evolution, but work on free-ranging primates has been inhibited by a lack of direct noninvasive measures of condition. Here, we evaluate the potential usefulness of noninvasive measurement of three biomarkers, the acute-phase proteins C-reactive protein (CRP) and haptoglobin, and neopterin, a by-product of macrophage activity.MATERIALS AND METHODS:We took advantage of veterinary checks on captive rhesus (24) and long-tailed (3) macaques at the German Primate Center (DPZ) to analyze serum marker measures, before measuring concentrations in feces and urine, and evaluating relationships between matched serum, urine, and fecal concentrations. In a second study, we monitored excretion of these markers in response to simian immunodeficiency virus (SIV) infection and surgical tissue trauma, undertaken for a separate study.RESULTS:We found that each biomarker could be measured in each matrix. Serum and urinary concentrations of neopterin were strongly and significantly correlated, but neither haptoglobin nor CRP concentrations in excreta proxied circulating serum concentrations. Our infection study confirmed that urinary neopterin, in particular, is a reliable marker of viral infection in macaques, but also indicated the potential of urinary and fecal CRP and haptoglobin as indicators of inflammation.DISCUSSION:We highlight the potential of noninvasive markers of immune function, especially of urinary neopterin, which correlates strongly with serum neopterin, and is highly responsive to infection.

INTRODUCTION:Immunosenescence (deteriorating immune function at old age) affects humans and laboratory animals, but little is known about immunosenescence in natural populations despite its potential importance for population and disease dynamics and individual fitness. Although life histories and immune system profiles often differ between the sexes, sex-specific effects of aging on health are rarely studied in the wild. Life history theory predicts that due to their shorter lifespan and higher investment into reproduction at the expense of immune defences, males might experience accelerated immunosenescence. We tested this hypothesis by examining sex-specific age trajectories of endoparasite burden (helminth prevalence and morphotype richness measured via fecal egg counts), an indicator of overall health, in wild gray mouse lemurs (Microcebus murinus). To account for potential interactions between seasonality and host sex or age we examined the predictors of parasite burdens separately for the dry and rainy season.RESULTS:Contrary to the prediction of immunosenescence, parasite prevalence and morphotype richness decreased at old age in the dry season, indicating acquired immunity by older animals. This pattern was primarily caused by within-individual decline in parasite loads rather than the earlier mortality of highly parasitized individuals. With the exception of an increasing cestode prevalence in males from yearlings to prime age in the rainy season, no evidence was found of male-biased ageing in parasite resistance. Besides this sex*age interaction, host age was uncorrelated with rainy season parasite loads. Seasonality did not affect the overall parasite loads but seasonal patterns were found in the predictors of parasite prevalence and morphotype richness.CONCLUSIONS:These results provide rare information about the age-related patterns of health in a wild vertebrate population and suggest improvement rather than senescence in the ability to resist helminth infections at old age. Overall, males appear not to suffer from earlier immunosenescence relative to females. This may partially reflect the earlier mortality of males, which can render senescence difficult to detect. While helminth infections are not strongly associated with survival in wild gray mouse lemurs, parasite load may, however, reflect overall good phenotypic quality of long-lived individuals, and is a potential correlate of fitness.

Dogs, Canis familiaris, and other domestic species are more skilled than great apes at following human communicative gestures in object choice tasks. Several hypotheses differentially emphasizing the role of domestication, socialization and experience have been put forward to account for this discrepancy. Recently, it has been suggested that the performance gap between apes and domestic species could be due instead to inconsistent methodologies across studies. Apes have generally been tested with the containers directly in front of them, and the experimenter performing the communicative cue behind the containers (central set-up). In contrast, domestic animals are usually placed at a larger distance with the human experimenter performing the cue in their direct line of sight and the containers peripheral on both sides of the experimenter (peripheral set-up). The distraction hypothesis posits that the close proximity of the food-associated containers in the central set-up proves too distracting for the test subjects, leading to an indiscriminate choice behaviour. Consistent with this idea, great apes are able to solve the peripheral version of the object choice task. To evaluate the distraction hypothesis further, we tested domestic dogs and cats, Felis catus, in the central as well as the peripheral set-up. As predicted, dogs' performance dropped significantly when tested in the central version of the task compared with the peripheral one. Cats performed as well as dogs in the peripheral version, but, intriguingly, their success levels did not decline significantly in the central version. We speculate that this might be due to cats cuing into the movement part of the pointing gesture. These findings partly support the distraction hypothesis and add to the evidence that domestic species do not necessarily have superior skills in reading human communicative cues.

Classic theories of ageing consider extrinsic mortality (EM) a major factor in shaping longevity and ageing, yet most studies of functional ageing focus on species with low EM. This bias may cause overestimation of the influence of senescent declines in performance over condition-dependent mortality on demographic processes across taxa. To simultaneously investigate the roles of functional senescence (FS) and intrinsic, extrinsic and condition-dependent mortality in a species with a high predation risk in nature, we compared age trajectories of body mass (BM) in wild and captive grey mouse lemurs ( Microcebus murinus ) using longitudinal data (853 individuals followed through adulthood). We found evidence of non-random mortality in both settings. In captivity, the oldest animals showed senescence in their ability to regain lost BM, whereas no evidence of FS was found in the wild. Overall, captive animals lived longer, but a reversed sex bias in lifespan was observed between wild and captive populations. We suggest that even moderately condition-dependent EM may lead to negligible FS in the wild. While high EM may act to reduce the average lifespan, this evolutionary process may be counteracted by the increased fitness of the long-lived, high-quality individuals.

Muscle strength reflects physical functioning, declines at old age and predicts health and survival in humans and laboratory animals. Age-associated muscle deterioration causes loss of strength and may impair fitness of wild animals. However, the effects of age and life-history characteristics on muscle strength in wild animals are unknown. We investigated environment- and sex-specific patterns of physical functioning by measuring grip strength in wild and captive gray mouse lemurs. We expected more pronounced strength senescence in captivity due to condition-dependent, extrinsic mortality found in nature. Males were predicted to be stronger but potentially experience more severe senescence than females as predicted by life history theory. We found similar senescent declines in captive males and females as well as wild females, whereas wild males showed little decline, presumably due to their early mortality. Captive animals were generally weaker and showed earlier declines than wild animals. Unexpectedly, females tended to be stronger than males, especially in the reproductive season. Universal intrinsic mechanisms (e.g. sarcopenia) likely cause the similar patterns of strength loss across settings. The female advantage in muscle strength merits further study; it may follow higher reproductive investment by males, or be an adaptation associated with female social dominance.

Reliable measurements of physiological stress are increasingly needed for eco-physiological research and for species conservation or management. Stress can be estimated by quantifying plasma glucocorticoid levels, but when this is not feasible, glucocorticoid metabolites are often measured from feces (FGCM). However, evidence is accumulating on the sensitivity of FGCM measurements to various nuisance factors. Careful species- and context-specific validations are therefore necessary to confirm the biological relevance and specificity of the method. The goals of this study were to: (1) establish and validate sampling methods and an enzymeimmunoassay to measure FGCM in the gray mouse lemur (Microcebus murinus); (2) explore causes of variability in the FGCM measurements, and; (3) assess the consequences of capturing and handling for free-living individuals by quantifying their stress responses via repeated fecal sampling within capture sessions. We further assessed the influence of different handling protocols and the animals' previous capture experience on the magnitude of the physiological response. Our validations identified the group-specific measurement of 11ß-hydroxyetiocholanolone as the most suitable assay for monitoring adrenocortical activity. The sample water content and the animal's age were found to significantly influence baseline FGCM-levels. Most captured animals exhibited a post-capture FGCM-elevation but its magnitude was not related to the handling protocol or capture experience. We found no evidence for long-term consequences of routine capturing on the animals' stress physiology. Hence the described methods can be employed to measure physiological stress in mouse lemurs in an effective and relatively non-invasive way.