Pelage Variation and Morphometrics of Closely RelatedCallithrixMarmoset Species and Their Hybrids

Abstract

Background: Hybrids are expected to show greater phenotypic variation than their parental species, yet how hybrid phenotype expression varies with genetic distances in closely-related parental species remains surprisingly understudied. Here we study pelage and morphometric trait variation in anthropogenic hybrids between four species of BrazilianCallithrixmarmosets, a relatively recent primate radiation. Marmoset species are distinguishable by pelage phenotype and level of morphological specialization for eating tree exudates. Here, we (1) describe qualitative phenotypic pelage differences between parental species and hybrids; (2) test whether significant quantitative differences exist between parental and hybrid morphometric phenotypes; and (3) determine which hybrid morphometic traits show heterosis, dysgenesis, trangression, or intermediacy relative to the parental trait. For morphometric traits, we investigated both cranial and post-cranial traits, particularly as most hybrid morphological studies focus on the former instead of the latter. Finally, we estimate mitogenomic distances between marmoset species from previously published data. Results: Hybrid facial and overall body pelage variation reflected coloration and patterns seen in parental species. In morphometric traits,C. jacchusandC. penicillatawere the most similar to each other, whileC. auritawas the most distinct, andC. geoffroyitrait measures fell between these other species. Most traits inC. jacchusxC. penicillatahybrids showed either heterosis or were intermediate relative to the parental trait values. We observed heterosis and dygenesis in traits ofC. penicillataxC. geoffroyihybrids. Trangressive segregation was observed in hybrids ofC. auritaand the other species. These hybrids were alsoC. aurita-like for a number of traits. Genetic distance was closest betweenC. jacchusandC. penicillataand farthest betweenC. auritaand the other species. Conclusion: We attributed significant phenotypic differences between marmoset species to differences in morphological exudivory specialization in these species. Our results suggest that intermediate hybrid traits relative to the parental trait values are more likely in crosses between species with relatively lesser genetic distance. More extreme phenotypic variation is more likely in parental species with greater genetic distance, with transgressive traits appearing in hybrids of the most genetically distant parental species. We further suggest that that less developmental disturbances can be expected in hybrids of more recently diverged parental species.