A review of experimental, natural, and anthropogenic hybridization in callithrix marmosets

Abstract

Natural and anthropogenic hybridization both occur in primates, but the effects of these distinct processes on primate evolution and population dynamics can be difficult to disentangle from one another. With most primate species being endangered, conservation prioritizes natural over anthropogenic hybrids. However, anthropogenic hybridization can generate genetic diversity and novelty, and fully understanding hybridization is important for primate conservation and evolutionary biology. The neotropical genus Callithrix, an emerging hybridization model, provides a good opportunity to study natural and anthropogenic hybridization separately, and here I review Callithrix hybridization work from the 1970s to the 2010s. Natural hybridization in these species occurs under secondary contact at their distribution borders. In contrast, C. jacchus and C. penicillata, species native to northern, northeastern, and central-eastern Brazil, have been widely introduced in southeastern Brazil. Such introductions have resulted in artificial sympatry and hybridization between exotic C. jacchus and C. penicillata with themselves or with native Callithrix species. Hybridization between native C. aurita and exotic Callithrix results in mixed pure species and hybrid groups, whereas hybridization between pairings of C. jacchus, C. penicillata, and C. geoffroyi results in populations of advanced hybrids. These findings indicate differences in reproductive isolation, and as such, distinct genomic and evolutionary consequences of these hybridization events. Genomic and genetic work is still rare for wild Callithrix populations, and most hybridization studies have been qualitative or descriptive. I point future priorities for Callithrix hybridization research toward hybrid fitness, reproduction, and health as well as investigation of genetic introgression among hybrids and nonhybrids.