Vol.:(0123456789) 1 3 Primates https://doi.org/10.1007/s10329-019-00750-z ORIGINAL ARTICLE Genetic differentiation and diversity of the Bolivian endemic titi monkeys, Plecturocebus modestus and Plecturocebus olallae Julia Barreta Pinto 1  · Jesús Martinez 2  · Yahaira Bernal 1  · Rolando Sánchez 1  · Robert Wallace 2 Received: 4 December 2018 / Accepted: 20 August 2019 © Japan Monkey Centre and Springer Japan KK, part of Springer Nature 2019 Abstract The genetic variability of New World primates is still poorly documented. We present the first genetic study on two threat- ened endemic titi monkey species in northern Bolivia (Plecturocebus modestus and Plecturocebus olallae) using six micro- satellite markers to investigate genetic structure and variability of 54 individuals from two wild populations. A low level of genetic diversity was found (34 alleles in the total sampled population). Locus 1118 presented the greatest number of alleles. The mean number of alleles per locus in the total population was 5.6 and the average heterozygosity was 0.38 (range 0.12–0.88). The F IS value for the total population using all microsatellite loci shows a statistically significant heterozygote deficit. The inbreeding coefficients (F IS ) were positive and significantly different from zero (0.064 for P. olallae and 0.213 for P. modestus). The genetic differentiation between populations (F ST ) was moderate with a pair-wise F ST estimate of 0.14. Population structure analyses assigned the two populations to two differentiated clusters (K = 2). These results suggest that these two species with very close distributional ranges arose from a single population, and that they remain in a process of genetic differentiation and speciation. This study further underlines the urgent need for conservation actions for both endemic primate species. Keywords Olalla brothers monkey · Beni titi monkey · Microsatellites · Genetic diversity · Conservation Introduction The study of genetic variation and population structure is critical to better understand how species evolve, adapt and co-exist, as well as to propose rational conservation and management strategies (Eguiarte 1990). Molecular markers provide an estimate of genetic diversity, with multiple alleles being useful in detecting heterozygosity and polymorphism levels in natural populations, determining inter- and intra- population relations, characterizing genetic population structure, and analyzing genetic distances for evolutionary studies (Avise 2000). As such, genetic studies are increas- ingly relevant to taxonomy, biodiversity conservation and environmental monitoring programs to ensure adequate management of species and populations (Groom 2006). The Olalla brothers’ titi monkey (Plecturocebus olallae) and the Beni titi monkey (Plecturocebus modestus) are two endemic primate species in Bolivia, which were described by Lönnberg (1939). Although their type localities are less than 65 km apart (Fig. 1), the respective specimens were consistently considered as belonging to two different spe- cies in a series of taxonomic assessments for the entire Cal- licebinae group (Hershkovitz 1990; Kobayashi 1995; Van Roosmalen et al. 2002; Wallace et al. 2013). Studies on the distribution of both species have confirmed the pres- ence of two similar, but phenotypically distinct forms that correspond to the original descriptions with distributional ranges quite close to each other (Fig. 1; Felton et al. 2006; Martinez and Wallace 2007, 2013; Martínez and Wallace 2010; Martinez et al., 2013). The two Bolivian titi monkey species were considered Endangered by the IUCN (Veiga et al. 2008a, b), however in the most recent assessment P. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10329-019-00750-z) contains supplementary material, which is available to authorized users. * Julia Barreta Pinto jbarretapinto@yahoo.com 1 Instituto de Biología Molecular y Biotecnología, Universidad Mayor de San Andrés, UMSA, Cota Cota Calle 27 s/n, La Paz, Bolivia 2 Wildlife Conservation Society (WCS), Greater Madidi-Tambopata Landscape Conservation Program, Casilla 3-35181, San Miguel, La Paz, Bolivia