Hematology and blood biochemistry in a declining population of mantled howler monkeys (Alouatta palliata palliata) at La Pacifica, Costa Rica.

BACKGROUND: Alouatta palliata palliata are an ecologically flexible howler monkey subspecies that has recently been relisted as Endangered. Populations are declining through much of the subspecies' range, including at our study site at La Pacifica, Costa Rica. Our objectives were to screen blood hematology and biochemistry samples collected from this wild population to elucidate their baseline health. METHODS: We collected blood samples from 38 adult individuals from across the study site and analyzed 13 hematology and 14 biochemistry parameters. RESULTS: Most hematology and blood biochemistry parameter values were similar between males and females. However, mean hemoglobin was significantly lower, and mean white blood cell count was significantly higher in females; and mean calcium and mean creatinine were significantly lower in females compared to males. CONCLUSIONS: Overall, the La Pacifica population appeared healthy based on the blood parameters analyzed from sampled individuals. Our results were also largely consistent with published data available from other populations of A. p. palliata, and with reference values for captive Alouatta caraya.

Insights into hominin phenotypic and dietary evolution from ancient DNA sequence data.

Nuclear genome sequence data from Neandertals, Denisovans, and archaic anatomically modern humans can be used to complement our understanding of hominin evolutionary biology and ecology through i) direct inference of archaic hominin phenotypes, ii) indirect inference of those phenotypes by identifying the effects of previously-introgressed alleles still present among modern humans, or iii) determining the evolutionary timing of relevant hominin-specific genetic changes. Here we review and reanalyze published Neandertal and Denisovan genome sequence data to illustrate an example of the third approach. Specifically, we infer the timing of five human gene presence/absence changes that may be related to particular hominin-specific dietary changes and discuss these results in the context of our broader reconstructions of hominin evolutionary ecology. We show that pseudogenizing (gene loss) mutations in the TAS2R62 and TAS2R64 bitter taste receptor genes and the MYH16 masticatory myosin gene occurred after the hominin-chimpanzee divergence but before the divergence of the human and Neandertal/Denisovan lineages. The absence of a functional MYH16 protein may explain our relatively reduced jaw muscles; this gene loss may have followed the adoption of cooking behavior. In contrast, salivary amylase gene (AMY1) duplications were not observed in the Neandertal and Denisovan genomes, suggesting a relatively recent origin for the AMY1 copy number gains that are observed in modern humans. Thus, if earlier hominins were consuming large quantities of starch-rich underground storage organs, as previously hypothesized, then they were likely doing so without the digestive benefits of increased salivary amylase production. Our most surprising result was the observation of a heterozygous mutation in the first codon of the TAS2R38 bitter taste receptor gene in the Neandertal individual, which likely would have resulted in a non-functional protein and inter-individual PTC (phenylthiocarbamide) taste sensitivity variation, as also observed in both humans and chimpanzees.

Morphological variation of genetically confirmed Alouatta Pigra × A. palliata hybrids from a natural hybrid zone in Tabasco, Mexico.

While hybridization has been reported for a large number of primate taxa, there is a general lack of data on hybrid morphology for wild individuals with known genetic ancestry. A confirmed hybrid zone for the closely related Neotropical primates Alouatta palliata and A. pigra has provided a unique opportunity to study primate hybrid morphological variation. Here we used molecular evidence based on mitochondrial, Y-chromosome, and autosomal data to assess hybrid ancestry. We conducted univariate and multivariate statistical comparisons of morphometric data collected from individuals both outside and within the hybrid zone in Tabasco, Mexico. Our results show that of all the hybrids detected (N = 128), only 12% of them were approximately genetically intermediate, and none of them were first generation hybrids. Univariate pairwise comparisons among parental individuals, multigenerational backcrossed hybrids, and intermediate hybrids showed that overall, multigenerational backcrossed hybrids resemble the parental species with which they share most of their alleles. Conversely, intermediates were highly variable. Similarly, principal component analysis depicts an overlap between the parental species and their backcrosses when considering overall morphological differences. Finally, discriminant function analysis of the morphological variables was overall unreliable for classifying individuals into their assigned genotypic classes. Taken together, our results suggest that primate natural hybridization studies should incorporate molecular methods for determining ancestry, because morphology may not always be a reliable indicator of hybrid status. Hybrid zones could comprise a large number of multigenerational backcrossed hybrids that are indistinguishable from the parental species. The implications for studying hybridization in the primate fossil record are discussed.

Impact of intrasexual selection on sexual dimorphism and testes size in the Mexican howler monkeys Alouatta palliata and A. pigra.

One of the goals of physical anthropology and primatology is to understand how primate social systems influence the evolution of sexually selected traits. Howler monkeys provide a good model for studying sexual selection due to differences in social systems between related species. Here, we examine data from the sister howler monkey species Alouatta palliata and A. pigra inhabiting southeastern Mexico and northern Guatemala. We use a resampling approach to analyze differences in sexual dimorphism of body and canine size. In addition, we compare testes size as a way of gauging the intensity of sperm competition in both species. Morphometric data were collected from wild-caught individuals, including body mass and length, and dental data were obtained from casts from wild individuals and from museum specimens. Although A. pigra individuals are larger than their A. palliata counterparts, we find that both species exhibit similar levels of sexual dimorphism for all of the variables considered. Testicular volume results indicate that A. palliata male testes are on average twice as large as those of A. pigra males, suggesting more intense sperm competition in the former species. Our study shows that A. pigra is not highly sexually dimorphic as was once thought, and testes size differences suggest the need for a clearer understanding of howler monkey social systems.