Abstract
BackgroundCo-dispersal of sperm-dependent hybrids and their sexual relatives is expected to result in consistent spatial patterns between assemblages of hybrids and genetic structure of parental species. However, local hybridization events may blur this signal as assemblages could be organized under different connectivity constraints. This study aims at testing the hypothesis of local hybridization events by comparing the assemblage of hybrid fish Chrosomus eos-neogaeus to the genetic diversity of one of its parental species, Chrosomus eos.ResultsAn extensive survey performed on a total of 132 sites located in two regions of Southern Quebec (West-Qc and East-Qc) revealed a distinct organization of hybrid lineages. One of the six hybrid lineages detected in West-Qc is widespread throughout this region resulting in a low α-diversity (1.38) and β-diversity (4.35). On the other hand, 36 hybrid lineages were detected in East-Qc and displayed narrow geographic distributions leading to a high α-diversity (2.30) and β-diversity (15.68). In addition, the C. eos multilocus haplotype of several of these hybrids is assigned to their respective sympatric C. eos population. Finally, contrasting with hybrids, the paternal species C. eos displayed a higher ρST in West-Qc (0.2300) than in East-Qc (0.0734).ConclusionThe unusually high diversity of hybrid lineages in East-Qc as well as the spatial organization and the close genetic relationship with C. eos sympatric populations support the hypothesis that multiple hybridization events occurred in situ. These findings coupled to the near absence of the maternal species Chrosomus neogeaus suggest that the decline of this species could be the trigger event at the origin of the high rates of spontaneous hybridization in this region.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0754-5) contains supplementary material, which is available to authorized users.
Highlights
Co-dispersal of sperm-dependent hybrids and their sexual relatives is expected to result in consistent spatial patterns between assemblages of hybrids and genetic structure of parental species
In spite of the sperm dependence of hybrids, there is a lack of correspondence between the spatial organization of hybrid lineages and the genetic diversity of paternal species C eos, this is especially clear in East-Qc
In situ hybridization events appear to be rare in most sperm-dependent unisexual hybrids and our results provide the first strong evidence of locally produced hybrid lineages during the Holocene in the Chrosomus eos-neogaeus system
Summary
Co-dispersal of sperm-dependent hybrids and their sexual relatives is expected to result in consistent spatial patterns between assemblages of hybrids and genetic structure of parental species. If contemporary evolutionary forces and current landscape elements contribute to the spatial organization of genetic diversity [1,2,3,4,5,6], historical factors such as geological events, glacial cycles and post-glacial dispersal are known to play a major role in shaping current species distributions [7,8,9,10] Because all these factors act independently on species populations, two unrelated species are not expected to display a similar genetic structure except if they have been influenced by the action of important geological processes (e.g. vicariance [11,12,13]) or are linked by strong ecological associations (e.g. host–parasite [14,15,16,17]). Sperm-dependent unisexual organisms are closely tied to parental species for their persistence and are restricted to the geographic range of their sexual host [32]
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