Aboagye-Antwi Fred, Alhafez Nahla, Weedall Gareth D, Brothwood Jessica, Kandola Sharanjit, Paton Doug, Fofana Abrahamane, Olohan Lisa, Betancourth Mauro Pazmiño, Ekechukwu Nkiru E, Baeshen Rowida, Traorè Sékou F, Diabate Abdoulaye, Tripet Frédéric
Centre for Applied Entomology and Parasitology, School of Life Sciences, Keele University, Staffordshire, United Kingdom; Department of Animal Biology and Conservation Science, Faculty of Sciences, University of Ghana, Legon, Ghana.
Centre for Applied Entomology and Parasitology, School of Life Sciences, Keele University, Staffordshire, United Kingdom.
PLoS Genet. 2015 Apr 16;11(4):e1005141. doi: 10.1371/journal.pgen.1005141. eCollection 2015 Apr.
Although many theoretical models of sympatric speciation propose that genes responsible for assortative mating amongst incipient species should be associated with genomic regions protected from recombination, there are few data to support this theory. The malaria mosquito, Anopheles gambiae, is known for its sympatric cryptic species maintained by pre-mating reproductive isolation and its putative genomic islands of speciation, and is therefore an ideal model system for studying the genomic signature associated with incipient sympatric speciation. Here we selectively introgressed the island of divergence located in the pericentric region of the X chromosome of An. gambiae s.s. into its sister taxon An. coluzzii through 5 generations of backcrossing followed by two generations of crosses within the introgressed strains that resulted in An. coluzzii-like recombinant strains fixed for the M and S marker in the X chromosome island. The mating preference of recombinant strains was then tested by giving virgin recombinant individuals a choice of mates with X-islands matching and non-matching their own island type. We show through genetic analyses of transferred sperm that recombinant females consistently mated with matching island-type males thereby associating assortative mating genes with the X-island of divergence. Furthermore, full-genome sequencing confirmed that protein-coding differences between recombinant strains were limited to the experimentally swapped pericentromeric region. Finally, targeted-genome comparisons showed that a number of these unique differences were conserved in sympatric field populations, thereby revealing candidate speciation genes. The functional demonstration of a close association between speciation genes and the X-island of differentiation lends unprecedented support to island-of-speciation models of sympatric speciation facilitated by pericentric recombination suppression.
尽管许多同域物种形成的理论模型提出，负责初始物种间选型交配的基因应与受重组保护的基因组区域相关联，但支持这一理论的数据却很少。冈比亚按蚊这种疟蚊，以其通过交配前生殖隔离维持的同域隐性物种及其假定的物种形成基因组岛而闻名，因此是研究与初始同域物种形成相关的基因组特征的理想模型系统。在此，我们通过5代回交，将位于冈比亚按蚊指名亚种X染色体着丝粒周围区域的分化岛，导入其姐妹分类群科氏按蚊，随后在导入菌株内进行两代杂交，从而得到在X染色体岛中固定了M和S标记的类似科氏按蚊的重组菌株。然后，通过让未交配过的重组个体选择与X染色体岛类型匹配和不匹配的配偶，来测试重组菌株的交配偏好。我们通过对转移精子的遗传分析表明，重组雌蚊始终与匹配岛型的雄蚊交配，从而将选型交配基因与分化的X染色体岛联系起来。此外，全基因组测序证实，重组菌株之间的蛋白质编码差异仅限于实验性交换的着丝粒周围区域。最后，靶向基因组比较表明，这些独特差异中的许多在同域野外种群中是保守的，从而揭示了候选物种形成基因。物种形成基因与分化的X染色体岛之间紧密关联的功能证明，为着丝粒重组抑制促进的同域物种形成的物种形成岛模型提供了前所未有的支持。
