The intricate relationship between sexually antagonistic selection and the evolution of sex chromosome fusions.
Sex chromosomes are among the most evolutionarily labile features in some groups of animals. One of the mechanisms causing structural changes of sex chromosomes is fusion with an autosome. A recent study showed that the establishment rates of Y chromosome-autosome fusions are much higher than those of other fusions (i.e., X-autosome, W-autosome, and Z-autosome fusions) in fishes and reptiles. Although sexually antagonistic selection may be one of the most important driving forces of sex chromosome-autosome fusions, a previous theoretical analysis showed that sexually antagonistic selection alone cannot explain the excess of Y-autosome fusions in these taxa. This previous analysis, however, is based on the assumption that sexually antagonistic selection is symmetric, sexually antagonistic alleles are maintained only by selection-drift balance (i.e., no supply of mutation), and only one type of fusion arises within a population. Here, we removed these assumptions and made an individual-based model to simulate the establishment of sex chromosome-autosome fusions. Our simulations showed that the highest establishment rate of Y-autosome fusion can be achieved when the fusion captures a rare male-beneficial allele, if the recurrent mutation rates are high enough to maintain the polymorphism of alleles with asymmetric, sexually antagonistic effects. Our results demonstrate that sexually antagonistic selection can influence the dynamics of sex chromosome structural changes, but the type of fusion that becomes the most common depends on fusion rates, recurrent mutation rates, and selection regimes. Because the evolutionary fate of sex chromosome-autosome fusions is highly parameter-sensitive, further attempts to empirically measure these parameters in natural populations are essential for a better understanding of the roles of sexually antagonistic selection in sex chromosome evolution.
Division of Evolutionary Genetics, National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411-8540, Japan. Electronic address: tomotakamatsumoto2@gmail.com.
Tomotaka
T
Matsumoto
Division of Ecological Genetics, National Institute of Genetics, Yata 1111, Mishima, Shizuoka 411-8540, Japan.
Jun
J
Kitano
D000818:Animals; D005075:Biological Evolution; D003198:Computer Simulation; D005260:Female; D008297:Male; D059645:Mutation Rate; D011336:Probability; D012727:Sex Characteristics; D012730:Sex Chromosomes / Q000235:genetics*; D013997:Time Factors
Karyotype evolution; Meiotic drive; Sexual antagonism; Sexual conflict