The Effects of the Sex Chromosomes on the Inheritance of Species Specific Traits of the Shape of the Copulatory Organ in Drosophila virilis and Drosophila lummei

Abstract Background. It is well known that the shape of the male copulatory system is strongly associated with mating behavior in Drosophila. The shape of the male genitalia is also known as the most rapidly evolving structure among all morphological characters. However, only a part of the male copulating system, namely epandrium, has actually been used as the only model to study the genetic basis of species-specific differences in the shape of the copulatory system in D. simulans and D. mauritiana. Almost nothing is known about the effects of both sex chromosomes on the shape of the male mating organ. Results. Seven factors were isolated that describe variation of different parts of the male mating organ. The shape of the male mating organ depends on the combination of the sex chromosome status, the autosome status, and the male parent identity as an epigenetic factor. The effect of the male parent identity is possibly mediated through the epigenetic marking of chromosomes in interspecific hybrids during gametogenesis and a subsequent effect of the resulting signatures on the ontogeny of offspring. Epistatic interactions of the sex chromosomes and autosomes and epigenetic effects of the male parent origin from interspecific crosses influence the expression of species-specific traits in the shape of the male copulatory system. Conclusions. Epistatic interactions of the sex chromosomes and autosomes and epigenetic effects of the male parent origin from interspecific crosses influence the expression of species-specific traits in the shape of the male copulatory system. It can be assumed that sexual selection for specific genes associated with male traits implemented in the courtship ritual prevents the well-known effect of demasculinization of the X chromosome.