Morphological variation of genetically confirmedAlouatta Pigra×A. palliatahybrids from a natural hybrid zone in Tabasco, Mexico

Abstract

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.

Phenotypic traits of primate hybrids: Recognizing admixture in the fossil record

“…For example, the hybrids of howler monkey species (Alouatta palliata x A. pigra) differ in size from parental groups, with males being particularly large relative to both parental species. 47 Large size has also been documented in subspecific crosses of saddle-back tamarins (S. fuscicollis illigeri x S. f. lagonotus and S. f. illigeri x S. f. leucogenys) relative to midparental expectations for several observed cranial and postcranial dimensions, 25,48 although, the amount and significance of this deviation varies depending on the subspecies pairs hybridizing. Overall, what has been observed in the pelage of living primate hybrids and in other metric trait variation fits fairly well with both theoretical predictions of what hybrid morphology should look like and evidence from studies of hybridization in other organisms.…”

Applications of Genomic Methods to Studies of Wild Primate Populations

“…Debate regarding the importance of the role of hybridization in primate evolution continues (Zinner et al 2011), and is receiving renewed interest given the finding that a number of genes have introgressed from Neanderthals into modern humans (Green et al 2010). So far, researchers have been able to detect hybrid primate individuals using relatively few diagnostic microsatellite loci (Cortés-Ortiz et al 2007;Tung et al 2008;Kelaita and Cortés-Ortiz 2013). Yet, initial identification of these loci and subsequent testing is time consuming and cumbersome.…”

“…Whole genome data could potentially address the role of the number of loci and the size of their effects, dominance, epistasis, or chromosomal rearrangements in causing outbreeding depression. Hybridization has been shown to produce highly variable morphological characteristics in nonhuman primates (Ackermann et al 2010;Kelaita and Cortés-Ortiz 2013) and it remains unclear what genetic interactions are the cause of this variability. Genomic approaches could also produce more accurate estimates of each hybrid's proportion of admixture (Allendorf et al 2010;Steiner et al 2013).…”

“…This chapter will build on this existing body of knowledge by providing a brief background on genomic methods but will focus on other tools and applications of relevance to field primatologists that center on detecting variation in wild populations. Population genetics methods can inform studies of primate conservation (Chaves et al 2011), hybridization (Kelaita and Cortés-Ortiz 2013), behavior and social organization (Di Fiore 2003), and demographic history (Lawler 2011). DNA can now be obtained through noninvansive sampling methods, which are preferred by many primatologists knowing the potential harm that could result during capture.…”

La genética como herramienta para el estudio y conservación del género Alouatta en México

“…En esta región se observaron tropas con individuos de A. palliata y A. pigra (basado en caracteres morfológicos), así como de individuos con características de ambas especies. La existencia de hibridación entre las dos especies fue después confirmada con evidencia genética y comparaciones morfológicas (Cortés-Ortiz et al 2007;Kelaita & Cortés-Ortiz 2013).…”