Data_from_Chromosome Variation as a Strategy for Speciation

The red brocket deer, Mazama americana, has at least six distinct karyotypes in different regions of South America that may suggest the existence of various species that are today all referred to as M. americana. As a relatively recent clade from an evolutionary perspective, the red brockets have gone through intense diversification. This study sought to prove the existence of post-zygotic reproductive isolation in animals that have been born from distinct chromosome lineages. In order to do so, inter-cytotype and intra-cytotype crosses were performed, which resulted in both F1 hybrid offspring (n=5) and pure offspring (n=3) in captivity. F1 females were analyzed in terms of their karyotypes, ovarian histology, estrous cycles and production of embryos in vitro. Pure females had parameters that were similar to those that have been previously reported for M. americana, though the parameters for hybrid females were different. Two hybrids were found to be sterile. The other hybrids presented with characteristics of subfertility. The results prove the existence of well-established reproductive isolation among the most distant karyotype lines and shows the need to define all karyotype variants and their geographical ranges in order to define the number of species of red brocket.