Data from: Multiple origins of sex chromosome fusions correlated with chiasma localization in Habronattus jumping spiders (Araneae: Salticidae)

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 X1X20 sex chromosomes in males, 10 have X1X2Y, 15 have X1X2X3Y, 2 have X0, and one has both X1X20 and X1X2X3Y. Chromosome numbers and behavior suggest neo-Ys formed by an autosome-X fusion to make X1X2Y, with a second fusion to an autosome to make X1X2X3Y. 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.恩特勒吉内蜘蛛（Entelegyne spiders）极少出现可产生新Y染色体（neo-Y chromosomes）的融合事件，M. J. D. 怀特将此归因于蜘蛛类群存在的一项演化约束：即其近端交叉定位（proximal chiasma localization）会干扰携带融合染色体的雄性个体的减数分裂分离过程。在本次研究涉及的75个雅蛛属（Habronattus）类群及外类群（outgroups）中，47个类群的雄性具有X₁X₂O型性染色体，10个为X₁X₂Y型，15个为X₁X₂X₃Y型，2个为X₀型，另有1个类群同时存在X₁X₂O与X₁X₂X₃Y两种性染色体构型。染色体数目与行为特征表明，新Y染色体的形成路径为先通过常染色体-X染色体融合（autosome-X fusion）产生X₁X₂Y型系统，再经第二次与常染色体的融合形成X₁X₂X₃Y型系统。系统发育（phylogeny）分析显示，新Y染色体（即X-常染色体融合事件）至少经历了8至15次起源（或存在部分丢失事件），对于如此小型的演化支而言，这一数量颇为惊人。与大量X-常染色体融合事件形成对比的是，本次研究仅支持至多1次常染色体-常染色体融合事件。新Y染色体的起源与交叉的远端定位（distal localization of chiasmata）存在显著相关性，这验证了怀特的假说：减数分裂中更松散的配对（远端交叉）会促进新Y染色体系统的演化。不过，该相关性也存在另一种（或作为补充）解释：X-常染色体融合事件被正向选择以利于将雄性偏好等位基因隔离至新Y染色体上，而远端交叉可通过限制重组过程辅助这一过程。这一基因座内性冲突（intralocus sexual conflict）假说既可以解释为何存在大量X-常染色体融合事件，也能阐明雅蛛属雄性求偶展示的惊人复杂性。