Multiple Origins Of Sex Chromosome Fusions Correlated With Chiasma Localization In Habronattus Jumping Spiders (Araneae: Salticidae)

摘要

Entelegyne spiders rarely show fusions yielding neo-Y chromosomes, which M. J. D. White attributed to a constraint in spiders, namely their proximal chiasma localization acting to upset meiotic segregation in males with fusions. Of the 75 taxa of Habronattus and outgroups studied, 47 have X_1X_20 sex chromosomes in males, 10 have X_1X_2Y, 15 have X_1X_2X_3Y, 2 have X0, and one has both X_1X_20 and X_1X_2X_3Y. Chromosome numbers and behavior suggest neo-Ys formed by an autosome-X fusion to make X_1X_2Y, with a second fusion to an autosome to make X_1X_2X_3Y. Phylogeny shows at least 8-15 gains (or possibly some losses) of neo-Y (i.e., X-autosome fusions), a remarkable number for such a small clade. In contrast to the many X-autosome fusions, at most one autosome-autosome fusion is indicated. Origins of neo-Y are correlated significantly with distal localization of chiasmata, supporting White's hypothesis that evolution of neo-Y systems is facilitated by looser pairing (distal chiasmata) at meiosis. However, an alternative (or contributing) explanation for the correlation is that X-autosome fusions were selected to permit isolation of male-favored alleles to the neo-Y chromosome, aided by distal chiasmata limiting recombination. This intralocus sexual conflict hypothesis could explain both the many X-autosome fusions, and the stunning complexity of male Habronattus courtship displays.