At the proximate level, hormones are known to play a critical role in influencing the life history of mammals, including humans. The pituitary gland is directly responsible for producing several ...hormones, including those related to growth and reproduction. Although we have a basic understanding of how hormones affect life history characteristics, we still have little knowledge of this relationship in an evolutionary context. We used data from 129 mammal species representing 14 orders to investigate the relationship between pituitary gland size and life history variation. Because pituitary gland size should be related to hormone production and action, we predicted that species with relatively large pituitaries should be associated with fast life histories, especially increased foetal and post‐natal growth rates. Phylogenetic analyses revealed that total pituitary size and the size of the anterior lobe of the pituitary significantly predicted a life history axis that was correlated with several traits including body mass, and foetal and post‐natal growth rates. Additional models directly examining the association between relative pituitary size and growth rates produced concordant results. We also found that relative pituitary size variation across mammals was best explained by an Ornstein–Uhlenbeck model of evolution, suggesting an important role of stabilizing selection. Our results support the idea that the size of the pituitary is linked to life history variation through evolutionary time. This pattern is likely due to mediating hormone levels but additional work is needed. We suggest that future investigations incorporating endocrine gland size may be critical for understanding life history evolution.
Countershading is often thought to be an adaptation for increasing crypsis, yet few quantitative studies have examined this assumption. A recent study showed that large primates display weaker ...countershading compared with small species, possibly due to a reduced predation risk. In addition to body mass, other factors likely affect countershading intensity. We predicted that if countershading is related to crypsis, then countershading intensity should be negatively related to the frequency of being in a vertical postural position because dorsoventral countershading is most effective when an animal adopts a horizontal position. In addition, countershading intensity may be positively related to group size if individuals are more conspicuous living in large groups or negatively related to group size if countershading further enhances a cryptic life style. We used color-corrected digital photographs of museum skins to quantify the luminance values of the ventral and dorsal surfaces of 113 primate species. We analyzed these data in a multiple regression using phylogenetically independent contrasts. While accounting for body mass, we found a significant negative relationship between the degree of countershading and the frequency of being in a vertical postural position. In contrast, we did not find a strong effect of group size on countershading. Our results suggest that countershading is weak or absent in species of any size that often adopt vertical postural positions because a crypsis benefit is only gained when being horizontal. Finally, the increased conspicuousness of species in large groups does not have a major effect on countershading intensity.
Vertebrates possess different types of retinal specializations that vary in number, size, shape, and position in the retina. This diversity in retinal configuration has been revealed through ...topographic maps, which show variations in neuron density across the retina. Although topographic maps of about 300 vertebrates are available, there is no method for characterizing retinal traits quantitatively. Our goal is to present a novel method to standardize information on the position of the retinal specializations and changes in retinal ganglion cell (RGC) density across the retina from published topographic maps. We measured the position of the retinal specialization using two Cartesian coordinates and the gradient in cell density by sampling ganglion cell density values along four axes (nasal, temporal, ventral, and dorsal). Using this information, along with the peak and lowest RGC densities, we conducted discriminant function analyses (DFAs) to establish if this method is sensitive to distinguish three common types of retinal specializations (fovea, area, and visual streak). The discrimination ability of the model was higher when considering terrestrial (78%-80% correct classification) and aquatic (77%-86% correct classification) species separately than together. Our method can be used in the future to test specific hypotheses on the differences in retinal morphology between retinal specializations and the association between retinal morphology and behavioral and ecological traits using comparative methods controlling for phylogenetic effects.
Allomaternal care is a rare, though phylogenetically widespread, mammalian infant care strategy. Among primates, the effects of allomaternal care are marked; its presence correlates with faster ...infant growth, younger age at weaning, and shorter interbirth intervals. Recent comparative research has found that such fertility benefits are absent in other mammals and are thus unique to primates. In large part because data describing lemur allomaternal care were lacking, the reproductive advantages of allomaternal care have never been demonstrated in Malagasy strepsirrhines. Using newly available data and rigorous phylogenetic methods, we extend this hypothesis to strepsirrhines and test whether allomaternal care in lemurs confers similar maternal reproductive benefits. Contrary to expectations, the presence of allomaternal care did not significantly impact lemur reproductive output; we did not find relationships between allomaternal care and either fetal or postnatal growth rates or interbirth intervals. Rather, infant parking and nesting, strategies employed primarily by litter-bearing species, were positively associated with faster fetal and postnatal infant growth, while nesting was negatively associated with interbirth interval. Thus, although each form of haplorrhine allomaternal care is also observed in Malagasy primates, the effects that these behaviors have on female reproductive output more closely resemble nonprimate mammals. We suggest that Malagasy strepsirrhines may not equally benefit from allomaternal care compared to haplorrhines because reproductive rates are less flexible and allomaternal care may instead increase infant survival in Madagascar's harsh and unpredictable environment. Our study has significant implications for understanding the evolution of infant care and developmental trajectories in mammals.
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.
Traditional explanations for the evolution of high orbital convergence and stereoscopic vision in primates have focused on how stereopsis might have aided early primates in foraging or locomoting in ...an arboreal environment. It has recently been suggested that predation risk by constricting snakes was the selective force that favored the evolution of orbital convergence in early primates, and that later exposure to venomous snakes favored further degrees of convergence in anthropoid primates. Our study tests this snake detection hypothesis (SDH) by examining whether orbital convergence among extant primates is indeed associated with the shared evolutionary history with snakes or the risk that snakes pose for a given species. We predicted that orbital convergence would be higher in species that: 1) have a longer history of sympatry with venomous snakes, 2) are likely to encounter snakes more frequently, 3) are less able to detect or deter snakes due to group size effects, and 4) are more likely to be preyed upon by snakes. Results based on phylogenetically independent contrasts do not support the SDH. Orbital convergence shows no relationship to the shared history with venomous snakes, likelihood of encountering snakes, or group size. Moreover, those species less likely to be targeted as prey by snakes show significantly higher values of orbital convergence. Although an improved ability to detect camouflaged snakes, along with other cryptic stimuli, is likely a consequence of increased orbital convergence, this was unlikely to have been the primary selective force favoring the evolution of stereoscopic vision in primates.
Body mass plays an important role in shaping an individual's behavior, especially with respect to dietary behavior. Larger animals tend to consume higher quantities of low quality foods. In contrast, ...smaller individuals, with relatively higher metabolic rates require a high quality diet. Therefore, species that exhibit high amounts of sexual dimorphism in body mass should also display high levels of male-female dietary differentiation. This study investigated the relationship between body mass dimorphism and dietary sex differences for 38 primate species. We conducted multiple regressions using female body mass and body mass dimorphism as independent variables. We found that body mass dimorphism was significantly negatively correlated with male-female differences in fauna consumption using species values as well as phylogenetically independent contrasts. In addition, body mass dimorphism was positively related to male-female differences in percent time feeding using phylogenetically independent contrasts. Body mass dimorphism was not significantly related to male-female differences in the percent of fruit and leaves in the diet. The results suggest that, as body mass dimorphism increases, there is some degree of dietary niche separation between the sexes of primates. These results will be discussed in the context of existing studies of intersexual niche separation.
PNU-286607 is the first member of a promising, novel class of antibacterial agents that act by inhibiting bacterial DNA gyrase, a target of clinical significance. Importantly, PNU-286607 displays ...little cross-resistance with marketed antibacterial agents and is active against methicillin-resistant staphylococcus aureus (MRSA) and fluoroquinoline-resistant bacterial strains. Despite the apparent stereochemical complexity of this unique spirocyclic barbituric acid compound, the racemic core is accessible by a two-step route employing a relatively obscure rearrangement of vinyl anilines, known in the literature as the “tert-amino effect.” After a full investigation of the stereochemical course of the racemic reaction, starting with the meso cis-dimethylmorpholine, a practical asymmetric variant of this process was developed.
Aim: In 1833, C. L. Gloger observed that bird populations living in warm and wet habitats were darker than those found in dry, cool areas. However, this hypothesis has seldom been evaluated, ...particularly for mammals. Here, we test Gloger's rule using a dataset consisting of more than 100 primate species representing all major primate clades. Location: Africa, Madagascar, Asia and the Neotropics. Methods: We used museum skins, digital photography, and colour correction software to quantify the brightness of the dorsal and ventral pelage surface of each species. We utilized the mean actual evapotranspiration (AET) within the geographic range of each species as a proxy for habitat conditions and accounted for additional variables that may influence coloration. To analyse the data, we used a generalized linear model that simultaneously accounts for the effects of phylogenetic and spatial autocorrelation. Results: We found that increasing levels of AET were significantly related to increasing pelage darkness on the dorsal surface of species, while accounting for other effects. Main conclusions: Our finding provides further support for the applicability of Gloger's rule to mammals, and is the first broad-scale evaluation for primates. The mechanism driving Gloger's rule is not easy to discern, but may include increased background matching for species living in relatively light or dark habitats, increased resistance to keratin-degrading micro-organisms in hair with large amounts of eumelanin, and/or thermoregulation.
Understanding trait evolution is essential for explaining modern biological diversity, and this is particularly exemplified by studies of coloration. Recent studies have applied evolutionary models ...to understand animal coloration, yet we have limited knowledge of how this trait evolves in mammals in a comparative context. Here we use phylogenetic methods to examine how different traits are associated with the evolutionary diversity of primate hair color. We hypothesize that hair color evolves independently across body regions, and that variation in biological and ecological traits influence patterns of hair color evolution. To test this, we quantify the phylogenetic signal of coloration for each body region, then compare the fit of three evolutionary models and a null, non-phylogenetic model to explain color variation across 94 primate species. We then test how trait optima and rate of color evolution covary with biological traits, clade membership, and habitat. Phylogenetic signal varies across regions, with head and forelimb coloration exhibiting the highest values. Head and forelimb coloration is best explained by an Ornstein-Uhlenbeck model, which could suggest stabilizing selection, whereas a null model best fits other body regions. Rates of hair color evolution and optimal color values vary across species with different visual systems, activity patterns, habitat types, and clade memberships. These results suggest that selective pressures are acting independently across body regions and across different primate taxa. Our results emphasize the importance of investigating patterns of trait evolution across regions of the body, as well as incorporating relevant biological and ecological traits into evolutionary models.
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