Night Monkey Hybrids Exhibit De Novo Genomic and Karyotypic Alterations: The First Such Case in Primates

Using molecular chromosomal analyses, we discovered night monkey hybrids produced in captivity from matings between a female Aotus azarae boliviensis (2n = 50) and a male Aotus lemurinus griseimembra (2n = 53). The parents produced seven offspring in total, including one male and six females-a pattern consistent with Haldane's rule. Chromosomal studies were conducted on four of the hybrid offspring. Two of them showed relatively "simple" mixture karyotypes, including different chromosome numbers (2n = 51, 52), which were formed because of a heteromorphic autosome pair in the father (n = 26, 27). The other two hybrid monkeys exhibited de novo genomic and karyotypic alterations. Detailed analysis of the alterations revealed that one individual carried a mixture karyotype of the two parental species and an X chromosome trisomy (53, XXX). The second individual displayed trisomy of chromosome 18 (52, XX, +18) and a reciprocal translocation between autosomes 21 and 23 (52, XX, +18, t(21;23)). Interestingly, the second monkey exhibited mosaicism among blood cells (mos52, XX, +18[87]/52, XX, +18, t(21;23)[85]), but only a single karyotype (52, XX, +18) in skin fibroblast cells. The X- and 18-trisomies were derived from a doubling of the mother's chromosomes in early embryonic cell division, and the reciprocal translocation likely developed in the bone marrow of the offspring, considering that it was observed only in blood cells. Such occurrence of trisomies in hybrid individuals is a unique finding in placental mammals.