Primate Traits Research Articles

Effect of binocular visual cue availability on fruit and insect grasping performance in two cheirogaleids: Implications for primate origins hypotheses

Forward-facing eyes with parallel optic axes, which provide a wide field of binocular vision and precise depth perception, are among the diagnostic features of crown primates; however, the adaptive significance of this feature remains contentious. Two of the most prominent primate-origins hypotheses propose that either foraging for fruit or nocturnal predation on insects created selective pressures that led to the evolution of diagnostic primate traits, including a wide binocular field. To determine whether either of these hypotheses provides a viable explanation for the evolution of primates' derived eye orientation, the importance of binocular depth cues for the two tasks invoked by these hypotheses was evaluated experimentally in Microcebus murinus and Cheirogaleus medius, cheirogaleids' considered reasonable living analogs of the earliest euprimates. Performance in grasping insects and fruit was evaluated when the animals made use of their full binocular visual field and when their binocular visual field was restricted using a helmet-mounted blinder. Restriction of the binocular field had no effect on fruit grasping performance; however, restriction of the binocular field resulted in a significant deficit in insect predation performance. Differences in behavioral variables also suggest that insect predation is a more visually demanding task than fruit foraging. These results support the role of insect predation, but not fruit foraging, in contributing to the selective pressures that led to the evolution of parallel optic axes and a wide binocular field in crown primates.

Differential modularity of the mammalian Engrailed 1 enhancer network directs sweat gland development.

Enhancers are context-specific regulators of expression that drive biological complexity and variation through the redeployment of conserved genes. An example of this is the enhancer-mediated control of Engrailed 1 (EN1), a pleiotropic gene whose expression is required for the formation of mammalian eccrine sweat glands. We previously identified the En1 candidate enhancer (ECE) 18 cis-regulatory element that has been highly and repeatedly derived on the human lineage to potentiate ectodermal EN1 and induce our species' uniquely high eccrine gland density. Intriguingly, ECE18 quantitative activity is negligible outside of primates and ECE18 is not required for En1 regulation and eccrine gland formation in mice, raising the possibility that distinct enhancers have evolved to modulate the same trait. Here we report the identification of the ECE20 enhancer and show it has conserved functionality in mouse and human developing skin ectoderm. Unlike ECE18, knock-out of ECE20 in mice reduces ectodermal En1 and eccrine gland number. Notably, we find ECE20, but not ECE18, is also required for En1 expression in the embryonic mouse brain, demonstrating that ECE20 is a pleiotropic En1 enhancer. Finally, that ECE18 deletion does not potentiate the eccrine phenotype of ECE20 knock-out mice supports the secondary incorporation of ECE18 into the regulation of this trait in primates. Our findings reveal that the mammalian En1 regulatory machinery diversified to incorporate both shared and lineage-restricted enhancers to regulate the same phenotype, and also have implications for understanding the forces that shape the robustness and evolvability of developmental traits.

Current advances in primate genomics: novel approaches for understanding evolution and disease.

Primate genomics holds the key to understanding fundamental aspects of human evolution and disease. However, genetic diversity and functional genomics data sets are currently available for only a few of the more than 500 extant primate species. Concerted efforts are under way to characterize primate genomes, genetic polymorphism and divergence, and functional landscapes across the primate phylogeny. The resulting data sets will enable the connection of genotypes to phenotypes and provide new insight into aspects of the genetics of primate traits, including human diseases. In this Review, we describe the existing genome assemblies as well as genetic variation and functional genomic data sets. We highlight some of the challenges with sample acquisition. Finally,we explore how technological advances in single-cell functional genomics and induced pluripotent stem cell-derived organoids will facilitate our understanding of the molecular foundations of primate biology.

Transposable Elements Continuously Remodel the Regulatory Landscape, Transcriptome, and Function of Decidual Stromal Cells.

Gene expression evolution underlies the origin, divergence, and conservation of biological characters including cell-types, tissues, and organ systems. Previously we showed that large-scale gene expression changes in decidual stromal cells (DSCs) contributed to the origins of pregnancy in eutherians and the divergence of pregnancy traits in primates and that transposable elements likely contributed to these gene expression changes. Here we show that two large waves of TEs remodeled the transcriptome and regulatory landscape of DSCs, including a major wave in primates. Genes nearby TE-derived regulatory elements are among the most progesterone responsive in the genome and play essential roles in orchestrating progesterone responsiveness and the core function of decidual cells by donating progesterone receptor binding sites to the genome. We tested the regulatory abilities of 89 TE consensus sequences and found that nearly all of them acted as repressors in mammalian cells, but treatment with a histone deacetylase inhibitor unmasked latent enhancer functions. These data indicate that TEs have played an important role in the development, evolution, and function of primate DSCs and suggest a two-step model in which latent enhancer functions of TEs are unmasked after they lose primary repressor functions.

Risk perception and terrestriality in primates: A quasi‐experiment through habituation of chacma baboons (Papio ursinus) in Gorongosa National Park, Mozambique

ObjectivesHabituation is a common pre‐requisite for studying noncaptive primates. Details and quantitative reporting on this process are often overlooked but are useful for measuring human impact on animal behavior, especially when comparing studies across time or sites. During habituation, perceived risk of a stimulus—human observers—is assumed to decline with repeated exposure to that stimulus. We use habituation as a quasi‐experiment to study the landscape of fear, exploring relationships between actual risk, perceived risk, mediating environmental variables, and behavioral correlates.Materials and MethodsWe recorded vocalizations and observer‐directed vigilance as indicators of perceived risk during habituation of two troops of chacma baboons (Papio ursinus) in Gorongosa National Park, Mozambique. Here, we model changes in these variables as a function of habituation time, troop, time of day, and habitat features. We also model the relationship between each of the anti‐predator behaviors and ground‐use, exploring whether they predict greater terrestriality in the baboons.ResultsIn both troops, vocalization rates and observer‐directed vigilance declined with cumulative exposure to observers, but were heightened later in the day and in denser habitat types. We found that terrestrial activity was negatively related to levels of both vocalizations and observer‐directed vigilance.DiscussionThis study provides a quantitative assessment of the impact of human observation on primate behavior and highlights environmental variables that influence anti‐predator behaviors, perhaps indicating heightened perception of risk. The relationship between perceived risk and terrestriality is significant for understanding the evolution of this rare trait in primates.

Evolutionary insights into primate skeletal gene regulation using a comparative cell culture model.

The evolution of complex skeletal traits in primates was likely influenced by both genetic and environmental factors. Because skeletal tissues are notoriously challenging to study using functional genomic approaches, they remain poorly characterized even in humans, let alone across multiple species. The challenges involved in obtaining functional genomic data from the skeleton, combined with the difficulty of obtaining such tissues from nonhuman apes, motivated us to consider an alternative in vitro system with which to comparatively study gene regulation in skeletal cell types. Specifically, we differentiated six human (Homo sapiens) and six chimpanzee (Pan troglodytes) induced pluripotent stem cell lines (iPSCs) into mesenchymal stem cells (MSCs) and subsequently into osteogenic cells (bone cells). We validated differentiation using standard methods and collected single-cell RNA sequencing data from over 100,000 cells across multiple samples and replicates at each stage of differentiation. While most genes that we examined display conserved patterns of expression across species, hundreds of genes are differentially expressed (DE) between humans and chimpanzees within and across stages of osteogenic differentiation. Some of these interspecific DE genes show functional enrichments relevant in skeletal tissue trait development. Moreover, topic modeling indicates that interspecific gene programs become more pronounced as cells mature. Overall, we propose that this in vitro model can be used to identify interspecific regulatory differences that may have contributed to skeletal trait differences between species.

Odontochronologies in male and female mandrills (Mandrillus sphinx) and the development of dental sexual dimorphism.

We examine how dental sexual dimorphism develops in mandrills, an extremely sexually dimorphic primate. We aimed to (a) establish the chronology of dental development (odontochronology) in male and female mandrills, (b) understand interindividual and intersex variation in odontochronologies, and (c) determine how dental sexual dimorphism is achieved. We prepared histological ground sections from the permanent teeth of four female and four male mandrills from the semi-free ranging colony at the Centre International de Recherches Médicales, Franceville, Gabon. We used the microscopic growth increments in the sections to create odontochronologies. We compared ages at crown initiation, crown formation times (CFT) and crown extension rates (CER) between individuals and sexes to assess interindividual and intersex variation. All mandrill teeth are sexually dimorphic in size. Dental sexual dimorphism in mandrills is achieved via sex differences in the duration of growth (bimaturism) and in growth rates. We also found interindividual and intersex variation in the ages at initiation and completion of crown formation. Our results show that the rate of ameloblast differentiation varies between individuals and that selection for both the age at tooth initiation and CER has occurred independently in males and females to ensure that the teeth develop at appropriate times relative to the growth of the sexually dimorphic jaws. They also show that canine dimorphism is achieved through differences in both CER and CFT, unlike extant great apes or Cantius. Given at least three mechanisms for achieving canine dimorphism, we need more information to trace the evolution of this trait in primates.

Fruit Selectivity in Anthropoid Primates: Size Matters

Certain features of both extant and fossil anthropoid primates have been interpreted as adaptations to ripe fruit foraging and feeding particularly spatulate incisors and trichromatic color vision. Here, we approach the question of anthropoid fruit foraging adaptations in light of the sensory and mechanical properties of anthropoid-consumed fruits in Kibale National Park, Uganda. We quantify the color, odor, size, and puncture resistance of fruits in Kibale that are consumed by anthropoid primates (N = 44) and compare these with the same traits of fruits that are not consumed by anthropoid primates (N = 24). Contrary to extant hypotheses, color and odor of anthropoid-consumed fruits do not differ from non-anthropoid–consumed fruits. However, we find that anthropoids in this system consume fruits that are significantly larger than non-anthropoid–consumed fruits, and with the exception of elephants that consume very large fruits, are the only dispersers of fruits with a surface area <4032 mm2, and a maximum diameter of 52 mm. While our findings do not support most extant hypotheses for the evolution of derived anthropoid primate traits as adaptations to ripe fruit foraging, we find some evidence to support the hypothesis that spatulate incisors may be an adaptation to foraging on large fruits, which tend to be harder.

Effect of Site Attributes and Matrix Composition on Neotropical Primate Species Richness and Functional Traits: A Comparison Among Regions

Fragmentation threatens biodiversity and forest-dwelling animals can be especially vulnerable. Neotropical primates inhabit forests and play ecological roles in maintaining forest biodiversity. Currently, many primate communities are restricted to forest fragments. We (1) evaluated the influence of environmental, matrix, and site attributes on species richness and functional traits of primates in the Neotropics; and (2) evaluated the effect of the sub-region on the relationships between primates and environmental, matrix, and site attributes. We conducted literature searches to find published data on primate communities in forest fragments throughout the Neotropics. Each fragment was assigned to 1 of 11 sub-regions: Mesoamerica, Tumbes-Chocó-Magdalena, Caribbean, Orinoco, Amazon, Atlantic Forest, Cerrado, Chaco, Andes, Caatinga, and Pampa. Based on actual and expected species occurrences, we calculated the proportion of primate species retained in the fragments, the mass retained, and dietary items retained considering reproductive and vegetative plant parts and prey. We used linear mixed models to correlate primate variables with environmental, matrix, and site attributes. Fragment area was more important for primate retention than environmental, matrix, and site attributes, with primate retention being higher in larger fragments. Fragment size was positively correlated with all primate variables, except for retention of prey consumption, whose retention decreased as water bodies and density of buildings in the matrix increased. Fragments within protected areas retained larger species than unprotected fragments. The proportion of extant mass retained and vegetative plant parts in the diet were highest in Mesoamerica and lowest in the Atlantic Forest. Conservation planning of Neotropical primates should consider both the differences among sub-regions, forest restoration to increase fragment size, and the creation of new protected areas, even in fragmented landscapes.

Confronting data sparsity to identify potential sources of Zika virus spillover infection among primates

The recent Zika virus (ZIKV) epidemic in the Americas ranks among the largest outbreaks in modern times. Like other mosquito-borne flaviviruses, ZIKV circulates in sylvatic cycles among primates that can serve as reservoirs of spillover infection to humans. Identifying sylvatic reservoirs is critical to mitigating spillover risk, but relevant surveillance and biological data remain limited for this and most other zoonoses. We confronted this data sparsity by combining a machine learning method, Bayesian multi-label learning, with a multiple imputation method on primate traits. The resulting models distinguished flavivirus-positive primates with 82% accuracy and suggest that species posing the greatest spillover risk are also among the best adapted to human habitations. Given pervasive data sparsity describing animal hosts, and the virtual guarantee of data sparsity in scenarios involving novel or emerging zoonoses, we show that computational methods can be useful in extracting actionable inference from available data to support improved epidemiological response and prevention.

Comparative evidence for the independent evolution of hair and sweat gland traits in primates

Humans differ in many respects from other primates, but perhaps no derived human feature is more striking than our naked skin. Long purported to be adaptive, humans' unique external appearance is characterized by changes in both the patterning of hair follicles and eccrine sweat glands, producing decreased hair cover and increased sweat gland density. Despite the conspicuousness of these features and their potential evolutionary importance, there is a lack of clarity regarding how they evolved within the primate lineage. We thus collected and quantified the density of hair follicles and eccrine sweat glands from five regions of the skin in three species of primates: macaque, chimpanzee and human. Although human hair cover is greatly attenuated relative to that of our close relatives, we find that humans have a chimpanzee-like hair density that is significantly lower than that of macaques. In contrast, eccrine gland density is on average 10-fold higher in humans compared to chimpanzees and macaques, whose density is strikingly similar. Our findings suggest that a decrease in hair density in the ancestors of humans and apes was followed by an increase in eccrine gland density and a reduction in fur cover in humans. This work answers long-standing questions about the traits that make human skin unique and substantiates a model in which the evolution of expanded eccrine gland density was exclusive to the human lineage.

The efficacy, biodistribution and safety of an inhibinDNAvaccine delivered by attenuatedSalmonella choleraesuis

Summary DNA vaccines, the third‐generation vaccines, were extensively studied. The attenuated Salmonella choleraesuis (S. choleraesuis) was widely focused as a carrier to deliver DNA vaccines in the chromosome–plasmid balanced‐lethal system. The efficacy of inhibin DNA vaccine delivered by attenuated S. choleraesuis was proved in mice and cows in our previous studies. In this study, the efficacy of inhibin DNA vaccine was confirmed in rhesus monkeys. To further study the biodistribution and safety, the mice were immunized under laboratory conditions. The results of the rhesus monkeys showed the plasma IgA and IgG titres against inhibin were elevated, and the oestradiol (E2) and progesterone (P4) levels were increased with immunizing inhibin DNA vaccine. The biodistribution and safety assessment displayed the body weight, pathological change and haematology indexes where there is no significant difference between vaccinated mice and control. And the genomics analysis showed there was no integration of the inhibin gene into the mouse genome 2 months after immunization. This study indicated the inhibin DNA vaccine delivered by attenuated S. choleraesuis was safe. And this vaccine was a potential means to improve their reproductive traits in primates and other animals.

The role of leaf toughness on foraging efficiency in Angola black and white colobus monkeys (Colobus angolensis palliatus).

Examining the relationships among foraging behavior, food mechanical properties, and masticatory morphology is a bourgeoning research topic among behavioral ecologists and functional morphologists. The purpose of this study was to assess the degree to which leaf toughness influences foraging efficiency with regard to ingestion rate, masticatory investment, and masticatory rate. Diet and feeding data were collected on adults from three groups of Colobus angolensis palliatus in the Diani Forest, Kenya, from July 2014 to December 2015. Ingestion rates were estimated by counting the number of items consumed during feeding bouts and multiplying this value by the mean mass of a particular food item. The number of mastications was also counted during 3-5 minute focal periods. Mechanical toughness of commonly eaten young leaves (n = 27 species) and mature leaves (n = 13 species) was recorded using a toughness tester equipped with a razor blade. Ingestion rates (g/min) negatively correlated with leaf toughness (r(2) = 0.73; p < 0.01) while masticatory investment (chews/g) positively correlated with leaf toughness (r(2) = 0.72; p < 0.01). Chewing rate (chews/min) was remarkably consistent regardless of leaf species and toughness values (r(2) = 0.09; p = 0.07). Our findings highlight the degree to which toughness values can vary among leaves and how this variation can dramatically influence ingestion rates and chewing efficiency in black and white colobus monkeys. Studies that link food mechanical properties with oral processing behaviors will ultimately provide important context for understanding craniofacial and dentognathic traits in primates.

Noncoding origins of anthropoid traits and a new null model of transposon functionalization.

Little is known about novel genetic elements that drove the emergence of anthropoid primates. We exploited the sequencing of the marmoset genome to identify 23,849 anthropoid-specific constrained (ASC) regions and confirmed their robust functional signatures. Of the ASC base pairs, 99.7% were noncoding, suggesting that novel anthropoid functional elements were overwhelmingly cis-regulatory. ASCs were highly enriched in loci associated with fetal brain development, motor coordination, neurotransmission, and vision, thus providing a large set of candidate elements for exploring the molecular basis of hallmark primate traits. We validated ASC192 as a primate-specific enhancer in proliferative zones of the developing brain. Unexpectedly, transposable elements (TEs) contributed to >56% of ASCs, and almost all TE families showed functional potential similar to that of nonrepetitive DNA. Three L1PA repeat-derived ASCs displayed coherent eye-enhancer function, thus demonstrating that the “gene-battery” model of TE functionalization applies to enhancers in vivo. Our study provides fundamental insights into genome evolution and the origins of anthropoid phenotypes and supports an elegantly simple new null model of TE exaptation.

Unlike fellows – a review of primate–non‐primate associations

Throughout many regions of the tropics, non-primate animals - mainly birds and mammals - have been observed to follow primate groups and to exploit dropped food and flushed prey. The anecdotal nature of most of the numerous reports on these primate-non-primate associations (PNPAs) may obscure the biological significance of such associations. We review the existing literature and test predictions concerning the influence of primate traits (body size, activity patterns, dietary strategies, habitat, group size) on the occurrence of PNPAs. Furthermore, we examine the influence of non-primates' dietary strategies on the occurrence of PNPAs, and the distribution of benefits and costs. We detected a strong signal in the geographic distribution of PNPAs, with a larger number of such associations in the Neotropics compared to Africa and Asia. Madagascar lacks PNPAs altogether. Primate body size, activity patterns, habitat and dietary strategies as well as non-primate dietary strategies affect the occurrence of PNPAs, while primate group size did not play a role. Benefits are asymmetrically distributed and mainly accrue to non-primates. They consist of foraging benefits through the consumption of dropped leaves and fruits and flushed prey, and anti-predation benefits through eavesdropping on primate alarm calls and vigilance. Where quantitative information is available, it has been shown that benefits for non-primates can be substantial. The majority of PNPAs can thus be categorized as cases of commensalism, while mutualism is very rare. Our review provides evidence that the ecological function of primates extends beyond their manifold interactions with plants, but may remain underestimated.

Establishing 'quality of life' parameters using behavioural guidelines for humane euthanasia of captive non-human primates.

Chronic pain and distress are universally accepted conditions that may adversely affect an animal's quality of life (QOL) and lead to the humane euthanasia of an animal. At most research institutions and zoological parks in the USA, a veterinarian, who has physically examined the animal and reviewed the clinical records, ultimately decides when an animal has reached a humane endpoint. To aid in the difficult process of interpreting pain and distress, we have developed specific behavioural guidelines, in addition to standard clinical information, to help define unique characteristics and traits of primates to assess and promote discussion of an individual primate's QOL, and thereby, to assist in the decision-making process regarding euthanasia. These guidelines advocate the creation of a QOL team when the animal is diagnosed with a life-threatening or debilitating chronic condition, or at the time the animal is entered into a terminal study. The team compiles a list of characteristics unique to that individual animal by utilising a questionnaire and a behavioural ethogram. This list enables the team to quantitatively assess any deviations from the established normal behavioural repertoire of that individual. Concurrently, the QOL team determines the number of behavioural deviations that are needed to trigger an immediate discussion of the necessity for humane euthanasia of the animal. The team remains intact once created, and revisits the animal's condition as frequently as deemed necessary. This process improves animal welfare by continuing the quest to optimally define QOL for captive primates, and potentially for all captive animals.

AGAR Workshop 2014: A Firsthand Experience

AGAR Workshop 2014: A Firsthand Experience Darice Westphal The third annual Application of Genomics to Anthropological Research workshop, sponsored by the American Association of Anthropological Genetics (AAAG) was held January 9–10, 2014. The workshop, focusing on laboratory, genetic, and epigenetic techniques in primate research, was co-hosted by the Southwest National Primate Research Center at Texas Biomedical Research Institute. Below, Darice Westphal, AAAG student travel prize winner, reports on the workshop and how it will benefit her research. Click for larger view View full resolution Figure 1. Attendees at the 2014 AGAR Workshop on Primate Genomics. I am a PhD student in physical anthropology at The Graduate Center, City University of New York (CUNY) and The New York Consortium in Evolutionary Primatology (NYCEP) in the proposal stage of my dissertation work. I am interested in understanding the contribution of ecological gradients and landscape barriers to the distribution of adaptive traits in primates. Specifically my proposal will use a combination of morphological and ecological variables to model the effect of hypothesized barriers on genetic variability at a local level. To aid in the development of my dissertation work, I attended the third Application of Genomics to Anthropological Research (AGAR) workshop. This two-day workshop, sponsored by the Education Committee of the American Association of Anthropological Genetics (AAAG) at the Texas Biomedical Research Institute on January 9th and 10th, combined lectures and tutorials to address application of genomic techniques in wild and captive populations of nonhuman primates. [End Page 807] Several of the talks at the AGAR workshop had direct implications for my project. Dr. George (PJ) Perry’s talk on non-invasive sampling focusing on fecal-derived DNA provided perspective on inherent difficulties of working with degraded, low-quality DNA. Dr. Christopher Schmitt’s talk on obesity phenotypes in vervet monkeys offered insight on field collection techniques and solutions to sample preservation and shipment. Dr. Ellen Quillen’s tutorial on empirical kinship calculations using SOLAR provided ideas on how to deal with unknown relationships in field collected samples. Besides the specified talks, many of the researchers in attendance were working on similar primate genomics projects. Talking with many of the participants allowed me to gauge the appropriateness of specific analytical programs and make connections for future troubleshooting. The focused topic of the workshop and the many social activities greatly facilitated the ability to make connections and generate discussion. With my experience at the AGAR workshop I was able to make connections to aid in the continued development of my dissertation and apply what I learned immediately to laboratory protocols and analysis of the resulting data. [End Page 808] Copyright © 2014 Wayne State University Press

The phylogenetic construction of sociocultural phenomena

In this paper I argue that many sociocultural phenomena are best explained by the comparative (phylogenetic) method, which consists of using information on other species, notably our closest relatives, the nonhuman primates, as a means to understand the evolutionary history and biological underpinnings of human traits. The social phenomena considered here embody theunitary social configuration of humankind, the set of traits common to all human societies. Those traits could not be explained by sociocultural anthropology, or the other social sciences, because even though they have a highly variable cultural content, they are not cultural creations but rather the products of human nature, or natural categories. I argue that some of those traits resulted from the cognitive enhancement of specific primate traits in the course of human evolution and others evolved as by-products of the coalescence of several primate traits, and I illustrate each process with a number of examples. I also show that even though many of those traits are crossculturally universal, they need not be: culture may modulate the expression of primate legacies and produce various sociocultural patterns from the same set of universal biological underpinnings, or biological constants. Finally, I discuss the importance for the social sciences of integrating biological constants in their models and theories even when they seek to explain culturaldifferences.

Space-use scaling and home range overlap in primates.

Space use is an important aspect of animal ecology, yet our understanding is limited by a lack of synthesis between interspecific and intraspecific studies. We present analyses of a dataset of 286 estimates of home range overlap from 100 primate species, with comparable samples for other space-use traits. To the best of our knowledge, this represents the first multispecies study using overlap data estimated directly from field observations. We find that space-use traits in primates are only weakly related to body mass, reflecting their largely arboreal habits. Our results confirm a theory that home range overlap explains the differences in allometric scaling between population density and home range size. We then test a suite of hypotheses to explain home range overlap, both among and within species. We find that overlap is highest for larger-bodied species living in large home ranges at high population densities, where annual rainfall is low, and is higher for arboreal than terrestrial species. Most of these results are consistent with the economics of resource defence, although the predictions of one specific theory of home range overlap are not supported. We conclude that home range overlap is somewhat predictable, but the theoretical basis of animal space use remains patchy.

Evidence that gestation duration and lactation duration are coupled traits in primates

Gestation duration and lactation duration are usually treated as independently evolving traits in primates, but the metabolic theory of ecology (MTE) suggests both durations should be determined by metabolic rate. We used phylogenetic generalized least-squares linear regression to test these different perspectives. We found that the allometries of the durations are divergent from each other and different from the scaling exponent predicted by the MTE (0.25). Gestation duration increases much more slowly (0.06 < m < 0.12), and lactation duration much more quickly (0.36 < m < 0.52) with body mass than the MTE predicts. By contrast, we found that the combined duration of gestation and lactation is consistent with the MTE's predictions (0.22 < m < 0.35). These results suggest that gestation duration and lactation duration might best be viewed as distinct but coupled adaptations. When transferring energy to their offspring, primate mothers must meet metabolically dictated physiological requirements while optimizing the timing of the switch from gestation to lactation in relation to some as-yet-unidentified body-size-related factor.