摘要
Sex-determination mechanisms evolve rapidly and vary between species.Occasionally,polymorphic systems are found,like in the housefly.Studying the dynamics and stability of such systems can provide a better understanding of the evolution of sex-determination systems.In the housefly,dominant male-determining loci(M)can lie not only on the Y chromosome(M^(Y)),but also on autosomes(M^(A))or the X chromosome(M^(X)).M enforces male development by inhibiting the female-determining gene transformer(tra).A mutant tra allele,tra^(D),is insensitive to M and is a dominant female determiner.M^(Y) prevails at high latitudes and polymorphic M loci together with tra^(D) at low latitudes.To get more insight into the stability and frequencies of these sex determiners with mutually exclusive dominance,we investigated 5 regional Spanish populations.We found strong variation among populations.Two populations with hemizygous M^(III) were found,2 contained homozygous M^(X) with additional hemizygous MI and M^(II) in 1 population.One population contained homozygous and hemizygous M^(X) with additionally hemizygous M^(II).All females in populations with homozygous M,had tra^(D),whereas no tra^(D) was found in populations without homozygous M.Our results indicate locally stable systems may either harbor a single hemizygous M and no tra^(D),corresponding to a male heterogametic system,or homozygous and/or multiple M and heterozygous tra^(D),reminiscent of a female heterogametic system.They support that M loci can accumulate in the presence of a dominant female determiner.Limited migration between populations may contribute to the stability of these systems.
基金
supported by China Scholarship Council(CSC)Scholarship no.201706300123
supported by CSC Scholarship no.201606330077.
