Possible effect of a sex chromosome on reproductive performance in Columbidae

In comparison with the reproductive performance of matings within Streptopelia risoria, the species hybrid males, from matings to S. risoria of males of S. chinensis or S. senegalensis, displayed increased infertility, but not an increase of embryo mortality. Previous findings of a high percentage of sperm abnormalities provide a basis that explains in part the infertility of the species hybrid males. The infertility and embryo mortality of both kinds of species hybrid females, the heterogametic sex, was much higher than in the S. risoria X S. risoria matings. The reproductive performance of the backcross females of the first, second and third backcross generations, having either species hybrid or backcross hybrid males as parents, could be divided into two classes, differing significantly either in percentage of infertility or embryo mortality, or in both categories. The backcross females producing the lower reproductive performance presumably carried the X chromosome of the wild parental species. Limited date obtained following a mating between a S. senegalensis female and a S. chinensis male showed a very low percentage of infertility of eggs from two species hybrid females and a backcross female (1/4-S. chinensis), indicating that the adverse effect of changes affecting infertility, presumably on the X-chromosome of these two wild species, towards S. risoria, had occurred in parallel during their evolution. The genetic changes affecting embryo mortality, and particularly the death of the squabs before becoming adults, are located on somatic chromosomes.