Mean age at menarche and climate variables on a global scale

OBJECTIVES

Cross-population variation in age at menarche is related to many factors. The purpose of this study was to examine climate variables in relation to mean age at menarche among 87 modern human populations. We hypothesized a later age at menarche among populations living in areas with high precipitation variability, heavy seasonal rainfall, and high temperatures year-round due to water-borne diseases and periods of resource scarcity.

METHODS

Using a comparative dataset, we examined geospatial distribution and climate variables in relation to age at menarche for 87 modern human populations.

RESULTS

We found the strongest predictor of a later age at menarche was higher fertility followed by a later mean age at death. In addition, higher annual rainfall, higher precipitation seasonality, and lower annual mean temperature were moderate predictors of age at menarche.

CONCLUSIONS

We propose that later ages at menarche in countries with high fertility may be a life-history strategy developed in response to climatic conditions that have resulted in higher immunological load. In these conditions, females may prioritize growth rather than reproduction. Shifts in climate and global population growth may change the future biological landscape of age at menarche.

Variation in human functional eccrine gland density and its implications for the evolution of human sweating

OBJECTIVES

We aim to test three questions regarding human eccrine sweat gland density, which is highly derived yet poorly understood. First, is variation in functional eccrine gland density ("FED") explained by childhood climate, suggesting phenotypic plasticity? Second, is variation in FED explained by genetic similarity (a proxy for "geographic ancestry"), implying divergent evolutionary pathways in this trait of ancestral populations? Third, what is the relationship between FED and sweat production?

MATERIALS AND METHODS

To test questions one and two, we measured FED in 68 volunteers aged 18-39 with varied childhood climate regimes and geographic ancestries. To test question three, we compared sweat production to FED in our n = 68 sample. In addition, we examined the relationship between FED and whole-body sweat loss during cycling in warm conditions using a sample of eight heat-acclimated endurance athletes.

RESULTS

Interindividual variation in six-site FED was more than twofold, ranging from 60.9 to 132.7 glands/cm² . Variation in FED was best explained by body surface area and limb circumferences (negative associations) and poorly explained by childhood climatic conditions and genetic similarity. Pilocarpine-induced sweat production was unrelated to FED while whole-body sweat loss during cycling was significantly, though modestly, associated with FED.

DISCUSSION

We hypothesize that gland-level phenotypic plasticity, rather than changes in eccrine gland density, was sufficient to permit thermal adaptation to novel environments as humans colonized the globe. Future research should measure effects of FED in dehydrated states and the relationship between FED and salt loss, and control for effects of microclimate to rule out phenotypic plasticity effects.

Differential habitat use by sympatric species of mouse lemurs across a mangrove–dry forest habitat gradient

Understanding the mechanisms by which similar species coexist in sympatry is a major driver of ecological research. Niche partitioning and ecological plasticity can facilitate spatial and habitat use overlap between generalist and specialist species. Mouse lemurs (Microcebus spp.) are a highly speciose group of small primates that are endemic to the forests of Madagascar. In northwestern Madagascar, the relatively widespread M. murinus occurs sympatrically with the microendemic M. ravelobensis. We investigated spatial distributions and densities of these two species across a mangrove–dry forest habitat gradient in Mariarano commune. We used capture-mark-recapture techniques and nocturnal line transect surveys along six transects during June and July 2017. Spatial capture-recapture and distance sampling models were used to estimate lemur densities across habitat types. The congeners displayed differential patterns of spatial distribution and densities. Microcebus murinus was found in similar densities across all habitat types, while M. ravelobensis was found at much higher densities in dry forests compared with mangroves. This suggests that the generalist M. murinus uses a wider array of habitats more evenly than the specialist M. ravelobensis. Our study provides empirical evidence of how cryptic lemur species differ in their habitat use and distribution across an environmental gradient and provides new insights into their ecology in an understudied habitat. Lemurs are one of the most threatened groups of mammals in the world, and understanding how these species are distributed across different forest types is crucial for planning and implementing conservation measures to protect lemur habitat.

Mid-Cenozoic climate change, extinction, and faunal turnover in Madagascar, and their bearing on the evolution of lemurs

Background

Was there a mid-Cenozoic vertebrate extinction and recovery event in Madagascar and, if so, what are its implications for the evolution of lemurs? The near lack of an early and mid-Cenozoic fossil record on Madagascar has inhibited direct testing of any such hypotheses. We compare the terrestrial vertebrate fauna of Madagascar in the Holocene to that of early Cenozoic continental Africa to shed light on the probability of a major mid-Cenozoic lemur extinction event, followed by an “adaptive radiation” or recovery. We also use multiple analytic approaches to test competing models of lemur diversification and the null hypothesis that no unusual mid-Cenozoic extinction of lemurs occurred.

Results

Comparisons of the terrestrial vertebrate faunas of the early Cenozoic on continental Africa and Holocene on Madagascar support the inference that Madagascar suffered a major mid-Cenozoic extinction event. Evolutionary modeling offers some corroboration, although the level of support varies by phylogeny and model used. Using the lemur phylogeny and divergence dates generated by Kistler and colleagues, RPANDA and TESS offer moderate support for the occurrence of unusual extinction at or near the Eocene-Oligocene (E-O) boundary (34 Ma). TreePar, operating under the condition of obligate mass extinction, found peak diversification at 31 Ma, and low probability of survival of prior lineages. Extinction at the E-O boundary received greater support than other candidate extinctions or the null hypothesis of no major extinction. Using the lemur phylogeny and divergence dates generated by Herrera & Dàvalos, evidence for large-scale extinction diminishes and its most likely timing shifts to before 40 Ma, which fails to conform to global expectations.

Conclusions

While support for large-scale mid-Cenozoic lemur extinction on Madagascar based on phylogenetic modeling is inconclusive, the African fossil record does provide indirect support. Furthermore, a major extinction and recovery of lemuriforms during the Eocene-Oligocene transition (EOT) would coincide with other major vertebrate extinctions in North America, Europe, and Africa. It would suggest that Madagascar’s lemurs were impacted by the climate shift from “greenhouse” to “ice-house” conditions that occurred at that time. This could, in turn, help to explain some of the peculiar characteristics of the lemuriform clade.

Does facial hair greying in chimpanzees provide a salient progressive cue of aging?

The greying of human head hair is arguably the most salient marker of human aging. In wild mammal populations, greying can change with life history or environmental factors (e.g., sexual maturity in silverback gorillas). Yet, whether humans are unique in our pattern of age-related hair depigmentation is unclear. We examined the relationship between pigmentation loss in facial hair (greying) to age, population, and sex in wild and captive chimpanzees (Pan troglodytes). Digital facial photographs representing three chimpanzee populations (N = 145; ages 1–60 years) were scored for hair greying on a scale of one [~100% pigmented] to six [~0% pigmented]. Our data suggest that chimpanzee head and facial hair generally greys with age prior to mid-life (~30 years old), but afterwards, greying ceases to increase incrementally. Our results highlight that chimpanzee pigmentation likely exhibits substantial variation between populations, and that both 'grey' and pigmented phenotypes exist across various age classes. Thus, chimpanzee facial hair greying is unlikely a progressive indicator of age beyond mid-life, and thus facial greying in chimpanzees seems different from the pattern observed in humans. Whether this reflects neutral differences in senescence, or potential differences in selection pressures (e.g. related to conspecific communication), is unclear and worthy of more detailed examination across populations and taxa.

Sexual selection in the Kinda baboon

Due to wide variation in the presence and degree of expression of a diverse suite of sexually-selected traits, the tribe Papionini represents an outstanding model for understanding how variation in sexual selection pressures and mechanisms leads to trait evolution. Here, we discuss the particular value of Papio as a model genus for studies of sexual selection, emphasizing the presence of multiple mating systems, and differences in the expression of sexually-selected traits among closely-related species. We draw particular attention to the Kinda baboon (Papio kindae), a comparatively less-studied baboon species, by providing a primer to Kinda baboon morphology, genetics, physiology, and behavior. Based on observations of large group sizes, combined with low degrees of sexual dimorphism and large relative testis size relative to other baboon species, we test the hypothesis that Kinda baboons have evolved under reduced direct, and increased indirect, male-male competition. We present the first long-term data on wild Kinda baboons in Zambia. Kinda baboon females show seasonal peaks in births and reproductive receptivity, and males exhibit a queing-rather than contest-based dominance acquisition with long alpha-male tenure lengths. We finish by making a number of explicit testable predictions about Kinda baboon sexual signals and behaviors, and suggest that Kinda baboons have potential to offer new insights into the selective environments that may have been experienced during homininization.

Diversity and evolution of human eccrine sweat gland density

The human eccrine sweat gland is central to the evolution of the human genus, permitting an enormous thermoregulatory sweating capacity that was essential to the human niche of high physical activity in open, hot, semi-arid environments. Despite a century of research inventorying the structure and function of eccrine glands and the physiological responses of human heat acclimation, we do not have a clear understanding of how intraspecific differences in eccrine density affect thermoregulation. Similarly, existing data does not comprehensively catalogue modern human diversity in this trait, nor do we understand the relative influences of evolutionary forces and phenotypic plasticity in shaping this diversity.

Effects of Environmental Stress on Primate Populations

Environmental stress on primate populations can take many forms. Abiotic factors, such as temperature and precipitation, may directly influence the behavior of primates owing to physiological demands of thermoregulation or through indirect influences on vegetation that primates rely on for food. These effects can also scale up to the macro scale, impacting primate distributions and evolution. Primates also encounter stress during interactions within and between species (i.e., biotic interactions). For example, selective pressure from male-perpetrated infanticide can drive the development of female counterstrategies and can impact life-history traits. Predation on primates can modify group size, ranging behavior, and habitat use. Finally, humans have influenced primate populations for millennia. More recently, hunting, habitat disturbance, disease, and climate change have increased in frequency and severity with detrimental impacts on primate populations worldwide. These effects and recent evidence from camera traps emphasize the importance of maintaining protected areas for conserving primate populations.

Ecological niche modeling of the genus Papio

OBJECTIVE

Ecological niche modeling (ENM) has been used to assess how abiotic variables influence species distributions and diversity. Baboons are broadly distributed throughout Africa, yet the degree of climatic specialization is largely unexplored for individual taxa. Also, the influence of climate on baboon phylogenetic divergence is unknown. In this study, we constructed ENMs to investigate how niches vary across Papio species to understand how climatic variables have influenced their biogeography and mode of speciation.

MATERIALS AND METHODS

We used Maxent to generate ENMs by collating locality data for six Papio species and climate information from WorldClim. In addition, we examined the degree of niche overlap among all possible pairs of taxa, which can provide insight into patterns of species diversity. Lastly, we conducted a Mantel test to assess the relationship between niche overlap and estimated time since divergence.

RESULTS

Our models performed moderately to extremely well, with a mean area under the curve value of 0.868. The species with the best models include P. papio and P. kindae, whereas P. hamadryas had the poorest models. We found that most species pairs exhibited significantly different niches. Lastly, we found no significant correlation between niche overlap and divergence times.

DISCUSSION

Niche models had good predictive power, which indicates Papio species distributions are correlated with climatic variables to varying degrees. Significantly little niche overlap and incomplete geographic boundaries suggests these models generally support a parapatric speciation scenario for the genus Papio.

The evolution of eccrine sweat glands in human and nonhuman primates

Sweating is an unusual thermoregulatory strategy for most mammals, yet is critical for humans. This trait is commonly hypothesized to result from human ancestors moving from a forest to a warmer and drier open environment. As soft tissue traits do not typically fossilize, this idea has been difficult to test. Therefore, we used a comparative approach to examine 15 eccrine gland traits from 35 primate species. For each trait we measured phylogenetic signal, tested three evolutionary models to explain trait variation, and used phylogenetic models to examine how traits varied in response to climate variables. Phylogenetic signal in traits varied substantially, with the two traits exhibiting the highest values being gland distribution on the body and percent eccrine vs. apocrine glands on the body. Variation in most traits was best explained by an Ornstein-Uhlenbeck model suggesting the importance of natural selection. Two traits were strongly predicted by climate. First, species with high eccrine gland glycogen content were associated with habitats exhibiting warm temperatures and low rainfall. Second, species with increased capillarization were associated with high temperature. Glycogen is a primary energy substrate powering sweat production and sodium reabsorption in the eccrine gland, and increased capillarization permits greater oxygen, glucose and electrolyte delivery. Thus, our results are evidence of natural selection for increased sweating capacity in primate species with body surface eccrine glands living in hot and dry climates. We suggest that selection for increased glycogen content and capillarization may have been part of initial increases in hominin thermoregulatory sweating capacity.

Strong influence of palaeoclimate on the structure of modern African mammal communities

Ecological research often assumes that species are adapted to their current climatic environments. However, climate fluctuations over geologic timescales have influenced species dispersal and extinction, which in turn may affect community structure. Modern community structure is likely to be the product of both palaeoclimate and modern climate, with the relative degrees of influence of past and present climates unknown. Here, we assessed the influence of climate at different time periods on the phylogenetic and functional trait structure of 203 African mammal communities. We found that the climate of the mid-Holocene (approx. 6000 years ago) and Last Glacial Maximum (approx. 22 000 years ago) were frequently better predictors of community structure than modern climate for mammals overall, carnivorans and ungulates. Primate communities were more strongly influenced by modern climate than palaeoclimate. Overall, community structure of African mammals appears to be related to the ecological flexibility of the groups considered here and the regions of continental Africa that they occupy. Our results indicate that the future redistribution, expansion and contraction of particular biomes due to human activity, such as climate and land-use change, will differentially affect mammal groups that vary in their sensitivity to environmental change.

Behavioral thermoregulation in Lemur catta: The significance of sunning and huddling behaviors

Regulation of body temperature poses significant problems for organisms that inhabit environments with extreme and seasonally fluctuating ambient temperatures. To help alleviate the energetic costs of autonomic responses, these organisms often thermoregulate through behavioral mechanisms. Among primates, lemurs in Madagascar experience uncharacteristically seasonal and unpredictable climates relative to other primate-rich regions. Malagasy primates are physiologically flexible, but different species use different mechanisms to influence their body temperatures. Lemur catta, the ring-tailed lemur, experiences particularly acute diurnal temperature fluctuations in its mostly open-canopy habitat in south and southwest Madagascar. Ring-tailed lemurs are also atypical among lemurs in that they appear to use both sun basking postures and huddling to maintain body temperature when ambient temperatures are cold. To our knowledge, however, no one has systematically tested whether these behaviors function in thermoregulation. We present evidence that ring-tailed lemurs use these postures as behavioral thermoregulation strategies, and that different environmental variables are associated with the use of each posture. Major predictors of sunning included ambient temperature, time of day, and season. Specifically, L. catta consistently assumed sunning postures early after daybreak when ambient temperatures were <13°C, and ceased sunning around 10:00a.m., after ambient temperatures approached 26°C. Sunning occurred more often during austral winter months. Huddling was associated with time of day, but not with ambient temperature or season. We conclude that L. catta tend to sun, rather than huddle, under cold weather conditions when sunning is possible. However, both sunning and huddling are important behavioral adaptations of L. catta that augment chemical thermoregulation and the absence of a dynamic, insulating pelage. Sunning and huddling help to account for the great ecological flexibility of the species, but these adaptations may be insufficient in the face of future changes in protective vegetation and temperature. Am. J. Primatol. 78:745-754, 2016. © 2016 Wiley Periodicals, Inc.

Climate and species richness predict the phylogenetic structure of African mammal communities

We have little knowledge of how climatic variation (and by proxy, habitat variation) influences the phylogenetic structure of tropical communities. Here, we quantified the phylogenetic structure of mammal communities in Africa to investigate how community structure varies with respect to climate and species richness variation across the continent. In addition, we investigated how phylogenetic patterns vary across carnivores, primates, and ungulates. We predicted that climate would differentially affect the structure of communities from different clades due to between-clade biological variation. We examined 203 communities using two metrics, the net relatedness (NRI) and nearest taxon (NTI) indices. We used simultaneous autoregressive models to predict community phylogenetic structure from climate variables and species richness. We found that most individual communities exhibited a phylogenetic structure consistent with a null model, but both climate and species richness significantly predicted variation in community phylogenetic metrics. Using NTI, species rich communities were composed of more distantly related taxa for all mammal communities, as well as for communities of carnivorans or ungulates. Temperature seasonality predicted the phylogenetic structure of mammal, carnivoran, and ungulate communities, and annual rainfall predicted primate community structure. Additional climate variables related to temperature and rainfall also predicted the phylogenetic structure of ungulate communities. We suggest that both past interspecific competition and habitat filtering have shaped variation in tropical mammal communities. The significant effect of climatic factors on community structure has important implications for the diversity of mammal communities given current models of future climate change.

Phylogenetic signal in primate behaviour, ecology and life history

Examining biological diversity in an explicitly evolutionary context has been the subject of research for several decades, yet relatively recent advances in analytical techniques and the increasing availability of species-level phylogenies, have enabled scientists to ask new questions. One such approach is to quantify phylogenetic signal to determine how trait variation is correlated with the phylogenetic relatedness of species. When phylogenetic signal is high, closely related species exhibit similar traits, and this biological similarity decreases as the evolutionary distance between species increases. Here, we first review the concept of phylogenetic signal and suggest how to measure and interpret phylogenetic signal in species traits. Second, we quantified phylogenetic signal in primates for 31 variables, including body mass, brain size, life-history, sexual selection, social organization, diet, activity budget, ranging patterns and climatic variables. We found that phylogenetic signal varies extensively across and even within trait categories. The highest values are exhibited by brain size and body mass, moderate values are found in the degree of territoriality and canine size dimorphism, while low values are displayed by most of the remaining variables. Our results have important implications for the evolution of behaviour and ecology in primates and other vertebrates.

Did trichromatic color vision and red hair color coevolve in primates?

Reddish pelage and red hair ornaments have evolved many times, independently, during primate evolution. It is generally assumed that these red-coat phenotypes, like red skin phenotypes, play a role in sociosexual signaling and, thus evolved in tandem with conspecific color vision. This study examines the phylogenetic distribution of color vision and pelage coloration across the primate order to ask: (1) did red pelage and trichromacy coevolve; or (2) did trichromacy evolve first, and then subsequently red pelage evolved as an exaptation? We collected quantitative, color-corrected photographic color data for 142 museum research skins from 92 species representing 41 genera spanning all major primate lineages. For each species, we quantified the ratio of Red/Green values (from a RGB color model) at 20 anatomical landmarks. For these same species, we compiled data on color vision type (routine trichromatic, polymorphic, routine dichromatic, monochromatic) and data on variables that potentially covary with visual system (VS) and coloration, including activity pattern and body mass dimorphism (proxy for sexual selection). We also considered whether the long-term storage of research skins might influence coloration. Therefore, we included the time since the specimen was collected as an additional predictor. Analyzing the data with phylogenetic generalized least squares models, we found that the amount of red hair present in primates is associated with differences in VSs, but not in the direction expected. Surprisingly, trichromatic primate species generally exhibited less red hair compared to red-green colorblind species. Thus, our results do not support the general assumption that color vision and red pelage coloration are a coevolutionary product of sociosexual signaling in primates. In addition, we did not find an effect of activity pattern, body mass dimorphism, or time since collection on the redness of primate hair. Our results have important implications for the evolution of primate coloration and visual systems.

Eye shape and the nocturnal bottleneck of mammals

Most vertebrate groups exhibit eye shapes that vary predictably with activity pattern. Nocturnal vertebrates typically have large corneas relative to eye size as an adaptation for increased visual sensitivity. Conversely, diurnal vertebrates generally demonstrate smaller corneas relative to eye size as an adaptation for increased visual acuity. By contrast, several studies have concluded that many mammals exhibit typical nocturnal eye shapes, regardless of activity pattern. However, a recent study has argued that new statistical methods allow eye shape to accurately predict activity patterns of mammals, including cathemeral species (animals that are equally likely to be awake and active at any time of day or night). Here, we conduct a detailed analysis of eye shape and activity pattern in mammals, using a broad comparative sample of 266 species. We find that the eye shapes of cathemeral mammals completely overlap with nocturnal and diurnal species. Additionally, most diurnal and cathemeral mammals have eye shapes that are most similar to those of nocturnal birds and lizards. The only mammalian clade that diverges from this pattern is anthropoids, which have convergently evolved eye shapes similar to those of diurnal birds and lizards. Our results provide additional evidence for a nocturnal 'bottleneck' in the early evolution of crown mammals.

Host longevity and parasite species richness in mammals

Hosts and parasites co-evolve, with each lineage exerting selective pressures on the other. Thus, parasites may influence host life-history characteristics, such as longevity, and simultaneously host life-history may influence parasite diversity. If parasite burden causes increased mortality, we expect a negative association between host longevity and parasite species richness. Alternatively, if long-lived species represent a more stable environment for parasite establishment, host longevity and parasite species richness may show a positive association. We tested these two opposing predictions in carnivores, primates and terrestrial ungulates using phylogenetic comparative methods and controlling for the potentially confounding effects of sampling effort and body mass. We also tested whether increased host longevity is associated with increased immunity, using white blood cell counts as a proxy for immune investment. Our analyses revealed weak relationships between parasite species richness and longevity. We found a significant negative relationship between longevity and parasite species richness for ungulates, but no significant associations in carnivores or primates. We also found no evidence for a relationship between immune investment and host longevity in any of our three groups. Our results suggest that greater parasite burden is linked to higher host mortality in ungulates. Thus, shorter-lived ungulates may be more vulnerable to disease outbreaks, which has implications for ungulate conservation, and may be applicable to other short-lived mammals.

RUNX2 tandem repeats and the evolution of facial length in placental mammals

Background

When simple sequence repeats are integrated into functional genes, they can potentially act as evolutionary ‘tuning knobs’, supplying abundant genetic variation with minimal risk of pleiotropic deleterious effects. The genetic basis of variation in facial shape and length represents a possible example of this phenomenon. Runt-related transcription factor 2 (RUNX2), which is involved in osteoblast differentiation, contains a functionally-important tandem repeat of glutamine and alanine amino acids. The ratio of glutamines to alanines (the QA ratio) in this protein seemingly influences the regulation of bone development. Notably, in domestic breeds of dog, and in carnivorans in general, the ratio of glutamines to alanines is strongly correlated with facial length.

Results

In this study we examine whether this correlation holds true across placental mammals, particularly those mammals for which facial length is highly variable and related to adaptive behavior and lifestyle (e.g., primates, afrotherians, xenarthrans). We obtained relative facial length measurements and RUNX2 sequences for 41 mammalian species representing 12 orders. Using both a phylogenetic generalized least squares model and a recently-developed Bayesian comparative method, we tested for a correlation between genetic and morphometric data while controlling for phylogeny, evolutionary rates, and divergence times. Non-carnivoran taxa generally had substantially lower glutamine-alanine ratios than carnivorans (primates and xenarthrans with means of 1.34 and 1.25, respectively, compared to a mean of 3.1 for carnivorans), and we found no correlation between RUNX2 sequence and face length across placental mammals.

Conclusions

Results of our diverse comparative phylogenetic analyses indicate that QA ratio does not consistently correlate with face length across the 41 mammalian taxa considered. Thus, although RUNX2 might function as a ‘tuning knob’ modifying face length in carnivorans, this relationship is not conserved across mammals in general.

Comment on "Nocturnality in dinosaurs inferred from scleral ring and orbit morphology"

Schmitz and Motani (Reports, 6 May 2011, p. 705) claimed to definitively reconstruct activity patterns of Mesozoic archosaurs using the anatomy of the orbit and scleral ring. However, we find serious flaws in the data, methods, and interpretations of this study. Accordingly, it is not yet possible to reconstruct the activity patterns of most fossil archosaurs with a high degree of confidence.

Testing Bergmann's rule and the resource seasonality hypothesis in Malagasy primates using GIS-based climate data

We tested four major hypotheses on the ecological aspects of body mass variation in extant Malagasy strepsirrhines: thermoregulation, resource seasonality/scarcity, resource quality, and primary productivity. These biogeographic hypotheses focus on the ecological aspects of body mass variation, largely ignoring the role of phylogeny for explaining body mass variation within lineages. We tested the independent effects of climate and resource-related variables on variation in body mass among Malagasy primates using recently developed comparative methods that account for phylogenetic history and spatial autocorrelation. We extracted data on lemur body mass and climate variables for a total of 43 species from 39 sites. Climatic data were obtained from the WorldClim database, which is based on climate data from weather stations compiled around the world. Using generalized linear models that incorporate parameters to account for phylogenetic and spatial autocorrelation, we found that diet and climate variables were weak predictors of lemur body mass. Moreover, there was a strong phylogenetic effect relative to the effects of space on lemur body mass in all models. Thus, we failed to find support for any of the four hypotheses on patterns of geography and body mass in extant strepsirrhines. Our results indicate that body mass has been conserved since early in the evolutionary history of each genus, while species diversified into different environmental niches. Our findings are in contrast to some previous studies that have suggested resource and climate related effects on body mass, though these studies have examined this question at different taxonomic and/or geographic scales.

Does geography or ecology best explain 'cultural' variation among chimpanzee communities?

Much attention has been paid to geographic variation in chimpanzee behavior, but few studies have applied quantitative techniques to explain this variation. Here, we apply methods typically utilized in macroecology to explain variation in the putative cultural traits of chimpanzees. We analyzed published data containing 39 behavioral traits from nine chimpanzee communities. We used a canonical correspondence analysis to examine the relative importance of environmental characteristics and geography, which may be a proxy for inter-community gene flow and/or social transmission, for explaining geographic variation in chimpanzee behavior. We found that geography, and longitude in particular, was the best predictor of behavioral variation. Chimpanzee communities in close longitudinal proximity to each other exhibit similar behavioral repertoires, independent of local ecological factors. No ecological variables were significantly related to behavioral variation. These results support the idea that inter-community dispersal patterns have played a major role in structuring behavioral variation. We cannot be certain whether behavioral variation has a genetic basis, is the result of innovation and diffusion, or a combination of the two.

Retinogeniculostriate pathway components scale with orbit convergence only in primates and not in other mammals

Studies of the relative sizes of brain components in mammals suggest that areas responsible for sensory processing, including visual processing, are correlated with aspects of ecology, especially activity pattern. Some studies suggest that primate orbit convergence and binocular vision are correlated with the overall size of the brain as well as components of the visual pathway, such as the lateral geniculate nucleus. However, the question remains whether components of the visual pathway are correlated with orbit convergence and binocular visual field overlap in nonprimate mammals. Here, we examine the relationship between orbit convergence and the volumes of components of the visual pathway (optic tract, dorsal lateral geniculate nucleus and primary visual cortex). Data on orbit orientation are combined with those on overall brain volume as well as brain component volumes in a taxonomically diverse sample of mammals. Our results demonstrate that nonprimate mammals scale isometrically for component volumes along the visual pathway, whereas primates display negatively allometric relationships. However, only among primates is higher orbit convergence correlated with volumetrically larger lateral geniculate nuclei and visual cortices. Diurnal primates exhibit statistically larger visual pathway components when compared to nocturnal primates. Nonprimate mammals do not display activity pattern differences with the single exception of optic tract sizes. We conclude that binocular vision was a much stronger factor in the evolution of the visual system in primates than in other mammals.

Species co-occurrence patterns and dietary resource competition in primates

Diamond (Assembly of species communities. In: Cody ML, Diamond JM, editors. Ecology and evolution of communities. Cambridge: Belknap. p 342-444 (1975)) argued that interspecific competition between species occupying similar niches results in a nonrandom pattern of species distributions. In particular, some species pairs may never be found in the same community due to competitive exclusion. Rigorous analytical methods have been developed to investigate the possible role that interspecific competition has on the evolution of communities. Many studies that have implemented these methods have shown support for Diamond's assembly rules, yet there are numerous exceptions. We build on this previous research by examining the co-occurrence patterns of primate species in 109 communities from across the world. We used EcoSim to calculate a checkerboard (C) score for each region. The C score provides a measure of the proportion of species pairs that do not co-occur in a set of communities. High C scores indicate that species are nonrandomly distributed throughout a region, and interspecific competition may be driving patterns of competitive exclusion. We conducted two sets of analyses. One included all primate species per region, and the second analysis assigned each species to one of four dietary guilds: frugivores, folivores, insectivores, and frugivore-insectivores. Using all species per region, we found significantly high C scores in 9 of 10 regions examined. For frugivores, we found significantly high-C scores in more than 50% of regions. In contrast, only 23% of regions exhibited significantly high-C scores for folivores. Our results suggest that communities are nonrandomly structured and may be the result of greater levels of interspecific competition between frugivores compared to folivores.

The climatic niche diversity of malagasy primates: a phylogenetic perspective

BACKGROUND

Numerous researchers have posited that there should be a strong negative relationship between the evolutionary distance among species and their ecological similarity. Alternative evidence suggests that members of adaptive radiations should display no relationship between divergence time and ecological similarity because rapid evolution results in near-simultaneous speciation early in the clade's history. In this paper, we performed the first investigation of ecological diversity in a phylogenetic context using a mammalian adaptive radiation, the Malagasy primates.

METHODOLOGY/PRINCIPAL FINDINGS

We collected data for 43 extant species including: 1) 1064 species by locality samples, 2) GIS climate data for each sampling locality, and 3) the phylogenetic relationships of the species. We calculated the niche space of each species by summarizing the climatic variation at localities of known occurrence. Climate data from all species occurrences at all sites were entered into a principal components analysis. We calculated the mean value of the first two PCA axes, representing rainfall and temperature diversity, for each species. We calculated the K statistic using the Physig program for Matlab to examine how well the climatic niche space of species was correlated with phylogeny.

CONCLUSIONS/SIGNIFICANCE

We found that there was little relationship between the phylogenetic distance of Malagasy primates and their rainfall and temperature niche space, i.e., closely related species tend to occupy different climatic niches. Furthermore, several species from different genera converged on a similar climatic niche. These results have important implications for the evolution of ecological diversity, and the long-term survival of these endangered species.

Is group size related to longevity in mammals?

Life-history theory predicts that reduced extrinsic risk of mortality should increase species longevity over evolutionary time. Increasing group size should reduce an individual's risk of predation, and consequently reduce its extrinsic risk of mortality. Therefore, we should expect a relationship between group size and maximum longevity across species, while controlling for well-known correlates of longevity. We tested this hypothesis using a dataset of 253 mammal species and phylogenetic comparative methods. We found that group size was a poor predictor of maximum longevity across all mammals, as well as within primates and rodents. We found a weak but significant group-size effect on artiodactyl longevity, but in a negative direction. Body mass was consistently the best predictor of maximum longevity, which may be owing to lower predation risk and/or lower basal metabolic rates for large species. Artiodactyls living in large groups may exhibit higher rates of extrinsic mortality because of being more conspicuous to predators in open habitats, resulting in shorter lifespans.

Environmental and geographic correlates of the taxonomic structure of primate communities

Previous research has shown that both environmental and historical factors influence the taxonomic structure of animal communities; yet, the relative importance of these effects is not known for primates. Environmental characteristics shape the possible niches in a community, providing suitable habitats for some species and not others. Therefore, communities found in similar environments should display similar species compositions. Additionally, geography may be viewed as a surrogate for historical processes. For instance, as the geographic distance between communities increases, dispersal between sites is more limited, and the probability of historical vicariance increases. Therefore, communities in close proximity to each other should exhibit similar species compositions. The geographic location, environmental characteristics, and species composition of 168 primate communities were gathered from the literature. Canonical correspondence analyses were conducted to examine the relative effects of geographic distance and environmental variables on the taxonomic structure of communities. In addition, UPGMA cluster analyses were conducted to better visualize the taxonomic similarity of communities. Spatial variables were significant predictors of community structure in all regions. Rainfall patterns explained African, Malagasy, and Neotropical community structure. In addition, maximum temperature was also correlated with community structure in Madagascar and the Neotropics. No climatic variables predicted Asian community structure. These results demonstrate that both historical and environmental factors play a significant role in structuring modern primate communities; yet, the importance of environmental factors depend on the region in question.

Examining the extinction risk of specialized folivores: a comparative study of Colobine monkeys

Species extinctions are nonrandom with some taxa appearing to possess traits that increase their extinction risk. In this study, eight predictors of extinction risk were used as independent variables to predict the IUCN category of a subfamily of specialized folivorous primates, the Colobinae. All data were transformed into phylogenetically independent contrasts and were analyzed using bivariate regressions, multiple regression, and a maximum likelihood approach using Akaike's Information Criterion to assess model performance. Once an outlier was removed from the data set, species that devote a smaller proportion of their diet to mature leaf consumption appear to be at a greater risk of extinction. Also, as female body mass increases, so does extinction risk. In contrast, as maximum latitude and the number of habitat types increase, extinction risk appears to decrease. These findings emphasize the importance of examining detailed dietary variation for predicting extinction risk at a relatively fine taxonomic scale and, consequently, may help improve conservation management.