Strong reproductive barriers in a narrow hybrid zone of West-Mediterranean green toads (Bufo viridissubgroup) with Plio-Pleistocene divergence

BMC Evolutionary Biology

Research Article

Nicolas Perrin¹  Matthias Stöck¹  Caroline Colliard¹  Marco Arculeo²  Alessandra Sicilia²  Giuseppe Fabrizio Turrisi³ 

[1] Department of Ecology and Evolution, Biophore, University of Lausanne, CH-1015, Lausanne, Switzerland;Dipartimento di Biologia Animale, University of Palermo, Via Archirafi, 18, 90123, Palermo, Italy;University of Catania, CUTGANA, Section of Nature Reserve Management, via Terzora 8, 95027, San Gregorio di Catania, Catania, Italy;

关键词: Contact Zone;    Reproductive Isolation;    Hybrid Zone;    Green Toad;    Hybrid Breakdown;   

DOI  :  10.1186/1471-2148-10-232

 received in 2010-04-07, accepted in 2010-07-29,  发布年份 2010

来源: Springer

【 摘 要 】

BackgroundOne 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.ResultsThe 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).ConclusionGenetic 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.

【 授权许可】

Unknown   
© Colliard et al; licensee BioMed Central Ltd. 2010. This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.