Harrison Xavier A, York Jennifer E, Young Andrew J
Zoological Society of London, Regent's Park, London, NW1 4RY, UK; Centre for Ecology & Conservation, University of Exeter, Cornwall Campus, Penryn, TR10 9FE, UK.
Mol Ecol. 2014 Dec;23(23):5740-55. doi: 10.1111/mec.12978. Epub 2014 Nov 15.
Sex-biased dispersal is pervasive and has diverse evolutionary implications, but the fundamental drivers of dispersal sex biases remain unresolved. This is due in part to limited diversity within taxonomic groups in the direction of dispersal sex biases, which leaves hypothesis testing critically dependent upon identifying rare reversals of taxonomic norms. Here, we use a combination of observational and genetic data to demonstrate a rare reversal of the avian sex bias in dispersal in the cooperatively breeding white-browed sparrow weaver (Plocepasser mahali). Direct observations revealed that (i) natal philopatry was rare, with both sexes typically dispersing locally to breed, and (ii), unusually for birds, males bred at significantly greater distances from their natal group than females. Population genetic analyses confirmed these patterns, as (i) corrected Assignment index (AIc), FST tests and isolation-by-distance metrics were all indicative of longer dispersal distances among males than females, and (ii) spatial autocorrelation analysis indicated stronger within-group genetic structure among females than males. Examining the spatial scale of extra-group mating highlighted that the resulting 'sperm dispersal' could have acted in concert with individual dispersal to generate these genetic patterns, but gamete dispersal alone cannot account entirely for the sex differences in genetic structure observed. That leading hypotheses for the evolution of dispersal sex biases cannot readily account for these sex-reversed patterns of dispersal in white-browed sparrow weavers highlights the continued need for attention to alternative explanations for this enigmatic phenomenon. We highlight the potential importance of sex differences in the distances over which dispersal opportunities can be detected.
性别偏向的扩散现象普遍存在且具有多样的进化意义，但扩散性别偏向的根本驱动因素仍未得到解决。部分原因在于分类群内部在扩散性别偏向方向上的多样性有限，这使得假设检验严重依赖于识别分类标准的罕见逆转。在此，我们结合观察数据和遗传数据，证明了在合作繁殖的白眉麻雀织雀（Plocepasser mahali）中鸟类扩散性别偏向出现了罕见的逆转。直接观察表明：（i）出生地留居现象罕见，两性通常在本地扩散以进行繁殖；（ii）与鸟类通常情况不同的是，雄性在离其出生群体显著更远的距离处繁殖。群体遗传分析证实了这些模式，因为：（i）校正后的分配指数（AIc）、FST检验和距离隔离指标均表明雄性的扩散距离比雌性更长；（ii）空间自相关分析表明雌性群体内的遗传结构比雄性更强。对群体外交配空间尺度的研究突出表明，由此产生的“精子扩散”可能与个体扩散共同作用产生了这些遗传模式，但仅配子扩散不能完全解释所观察到的遗传结构中的性别差异。扩散性别偏向进化的主要假设难以轻易解释白眉麻雀织雀中这些性别逆转的扩散模式，这凸显了持续关注这一神秘现象其他解释的必要性。我们强调了在可检测到扩散机会的距离上性别差异的潜在重要性。
