title: Multiple origins of sex chromosome fusions correlated with chiasma localization in Habronattus jumping spiders (Araneae: Salticidae).
abstract: 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 X1 X2 0 sex chromosomes in males, 10 have X1 X2 Y, 15 have X1 X2 X3 Y, 2 have X0, and one has both X1 X2 0 and X1 X2 X3 Y. Chromosome numbers and behavior suggest neo-Ys formed by an autosome-X fusion to make X1 X2 Y, with a second fusion to an autosome to make X1 X2 X3 Y. 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.
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia, V6T 1Z4. wmaddisn@mail.ubc.ca
authors.forename: Wayne P
authors.initials: WP
authors.lastname: Maddison
authors.forename: Geneviève
authors.initials: G
authors.lastname: Leduc-Robert
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002875:Chromosomes; D005260:Female; D008297:Male; D008540:Meiosis; D013112:Spiders / Q000145:classification* / Q000166:cytology / Q000235:genetics*; D014960:X Chromosome; D014998:Y Chromosome
keywords: Chromosome evolution; intralocus sexual conflict; neo-Y; phylogenetic correlation; segregation constraints; sexual antagonism