This is the first study analyzing genetic diversity in captive individuals of the endangered black lion tamarin, Leontopithecus chrysopygus, and also comparing genetic diversity parameters between wild populations and captive groups using the same set of molecular markers. We evaluated genetic diversity and differentiation for the Brazilian and European captive groups and a wild population through 15 polymorphic microsatellite markers. The genetic diversity levels were similar among Brazilian captive, European captive and wild animals from the National Forest of Capão Bonito. Expected heterozygosity showed values ranging from 0.403 to 0.462, and significant differences were not observed among the populations. Different allele frequencies were observed among the groups, which showed the presence of distinct private alleles. The PCoA analysis evidenced three main clusters suggesting that the captive Brazilian and European groups are markedly differentiated both from one another and from the wild population of Capão Bonito. Likewise, the most likely number of genetic clusters (K) revealed by Structure was three. Such a structure is probably the result of the strength of drift and non-random reproduction in these small and isolated groups. Despite this differentiation, all groups still have similar genetic diversity levels, comparable to other callitrichids. The data obtained herein are important to increasing knowledge of the genetics of tamarins and supporting breeding programs to prevent loss of genetic diversity and inbreeding depression.

& patrícia Domingues de freitas 1 ✉Breeding strategies based on molecular markers have been adopted by ex-situ conservation programs to assess alternative parameters for the genetic diversity estimates. in this work we evaluated molecular and studbook data for captive populations of black-lion-tamarin (BLt), an endangered primate endemic to Brazil's Atlantic forest. pedigree analyses were performed using BLT studbook information collected from 1973 to 2018. We analyzed the whole captive population since its foundation; the current captive population (ccp); and all extant BLts in the Brazilian captive population (Bcp), separately. Microsatellite analyses were implemented on the Bcp individuals from the eighth generation (BCP-F8) only to avoid generation overlap. The expected heterozygosity for BCP-F8, using molecular, data was 0.45, and the initial expected heterozygosity was 0.69. Kinship parameters showed high genetic relationships in both pedigree and molecular analyses. the genealogybased endogamy evidenced a high inbreeding coefficient, while the molecular analyses suggested a non-inbreeding signature. the Mate Suitability index showed detrimental values for the majority of potential pairs in the ccp. nevertheless, some individuals evidenced high individual heterozygosity and allele representation, demonstrating good potential to be used as breeders. thus, we propose the use of molecular data as a complementary parameter to evaluate mating-pairs and to aid management decision-making.Captive breeding programs have been recognized as a powerful alternative for rescuing endangered species and for biological conservation 1,2 . Often based on pedigree analyses, ex-situ management plans aim to maintain demographically stable populations, retaining genetic diversity, limiting inbreeding, and avoiding adaptation to captivity 1,3-6 . However, this is not an easy task, and consequently captive groups tend to present lower levels of genetic diversity and higher inbreeding rates than expected 2,7 , challenging the success of these captive breeding programs. On the other hand, wild endangered species often present small and fragmented populations subjected to bottleneck effects and absence of gene flow, and low genetic diversity levels are commonly also observed in nature 8,9 . This is the case for the black-lion-tamarin (BLT), Leontopithecus chrysopygus (Callitrichidae, Platyrrhini), an endangered primate inhabiting exclusively the Atlantic Forest of São Paulo state in Southeast Brazil 8,10 .The population size of L. chrysopygus in nature is small 11 , currently estimated at a total of a thousand individuals living in a few small forest fragments 12 . This species was assumed to be extinct about 65 years, when a small population was rediscovered in the Morro do Diabo State Park (SP, Brazil) 13 . At that time, a population census estimated that only about 200 animals existed in nature. In 1973, the first seven wild individuals of two contiguous subgroups of BLT were brought into captivity, at the Biological Bank of Tijuca...