Strong reproductive barriers in a narrow hybrid zone of West-Mediterranean green toads (Bufo viridis subgroup) with Plio-Pleistocene divergence.
Strong reproductive barriers in a narrow hybrid zone of West-Mediterranean green toads (Bufo viridis subgroup) with Plio-Pleistocene divergence.
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DOI：
10.1186/1471-2148-10-232
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发表时间：
2010-07-29
影响因子：
3.4
通讯作者：
Stöck M
中科院分区：
文献类型：
--
作者：
Colliard C;Sicilia A;Turrisi GF;Arculeo M;Perrin N;Stöck M
进化生物学的一个关键问题涉及异域物种形成过程中生殖隔离积累的模式和速率。人们对最近分化的无尾动物物种的次生接触知之甚少。在这里，我们进行了多位点实地研究，以调查两个绿蟾蜍谱系之间的接触区，估计分歧时间为 2.7 My，并报告初步实验杂交的结果。西西里特有的蟾蜍和原产于意大利大陆的巴利阿里蟾蜍在埃特纳火山以东形成了一个狭窄的混合区。尽管双向 mtDNA 渗入超过 ca。 40公里的南北线，没有发现F1杂种，核基因组几乎没有混合。接触区两侧的种群均表现出较低的遗传多样性和非常强的分化（FST = 0.52）。初步实验杂交表明，F1 杂种的适应性略有下降，回交后代（F1 x 亲本，很少达到变态）的杂种严重崩溃，F2（F1 x F1）完全且早期死亡。接触区的遗传模式是通过漂移和选择塑造的。接触带的地理和历史导致局部有效规模减小，巴利阿里杆菌种群正处于最近扩张的前浪（更新世晚期）。针对杂种的选择可能是由内在基因组原因（回交和F2杂种中的共适应基因组的破坏）引起的，可能通过局部适应而得到加强（两个类群的范围大致与半干旱和干旱气候的边界一致）。 F1 在田间的缺失可能是由于交配前的隔离机制造成的。我们的结果表明，这些谱系在大约 2.7 My 的分化后已经进化出几乎完全的生殖隔离，这与实验室实验的证据形成鲜明对比，实验室实验表明一些无尾目物种在 > 20 My 的分化后仍可能产生可存活的 F1 后代。
One key question in evolutionary biology deals with the mode and rate at which reproductive isolation accumulates during allopatric speciation. Little is known about secondary contacts of recently diverged anuran species. Here we conduct a multi-locus field study to investigate a contact zone between two lineages of green toads with an estimated divergence time of 2.7 My, and report results from preliminary experimental crosses. The Sicilian endemic Bufo siculus and the Italian mainland-origin B. balearicus form a narrow hybrid zone east of Mt. Etna. Despite bidirectional mtDNA introgression over a ca. 40 km North-South cline, no F1 hybrids could be found, and nuclear genomes display almost no admixture. Populations from each side of the contact zone showed depressed genetic diversity and very strong differentiation (FST = 0.52). Preliminary experimental crosses point to a slightly reduced fitness in F1 hybrids, a strong hybrid breakdown in backcrossed offspring (F1 x parental, with very few reaching metamorphosis) and a complete and early mortality in F2 (F1 x F1). Genetic patterns at the contact zone are molded by drift and selection. Local effective sizes are reduced by the geography and history of the contact zone, B. balearicus populations being at the front wave of a recent expansion (late Pleistocene). Selection against hybrids likely results from intrinsic genomic causes (disruption of coadapted sets of genes in backcrosses and F2-hybrids), possibly reinforced by local adaptation (the ranges of the two taxa roughly coincide with the borders of semiarid and arid climates). The absence of F1 in the field might be due to premating isolation mechanisms. Our results, show that these lineages have evolved almost complete reproductive isolation after some 2.7 My of divergence, contrasting sharply with evidence from laboratory experiments that some anuran species may still produce viable F1 offspring after > 20 My of divergence.
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影响因子：
6.5
作者：
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通讯作者：
BLAIR, WF
影响因子：
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Excoffier, Laurent
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作者：
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