Abstract
BackgroundUnraveling the genetic mechanisms associated with reduced gene flow between genetically differentiated populations is key to understand speciation. Different types of structural variations (SVs) have been found as a source of genetic diversity in a wide range of species. Previous studies provided detailed knowledge on the potential evolutionary role of SVs, especially copy number variations (CNVs), between well diverged species of e.g. primates. However, our understanding of their significance during ongoing speciation processes is limited due to the lack of CNV data from closely related species. The genus Sus (pig and its close relatives) which started to diverge ~4 Mya presents an excellent model for studying the role of CNVs during ongoing speciation.ResultsIn this study, we identified 1408 CNV regions (CNVRs) across the genus Sus. These CNVRs encompass 624 genes and were found to evolve ~2.5 times faster than single nucleotide polymorphisms (SNPs). The majority of these copy number variable genes are olfactory receptors (ORs) known to play a prominent role in food foraging and mate recognition in Sus. Phylogenetic analyses, including novel Bayesian analysis, based on CNVRs that overlap ORs retain the well-accepted topology of the genus Sus whereas CNVRs overlapping genes other than ORs show evidence for random drift and/or admixture.ConclusionWe hypothesize that inter-specific variation in copy number of ORs provided the means for rapid adaptation to different environments during the diversification of the genus Sus in the Pliocene. Furthermore, these regions might have acted as barriers preventing massive gene flow between these species during the multiple hybridization events that took place later in the Pleistocene suggesting a possible prominent role of ORs in the ongoing Sus speciation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1449-9) contains supplementary material, which is available to authorized users.
Highlights
Unraveling the genetic mechanisms associated with reduced gene flow between genetically differentiated populations is key to understand speciation
Since our main goal was the identification of inter-population Copy number variable region (CNVR), the two samples from the same population were combined
We found that the copy number differences (CNDs) between pairs of individuals from different populations were significantly higher than between individuals from the same population (p-value
Summary
Unraveling the genetic mechanisms associated with reduced gene flow between genetically differentiated populations is key to understand speciation. Only a few genes have so far been identified to be involved in speciation, for example Prdm in mouse [15], and Odysseus-site homeobox [16], JYalpha [17] and GA19777 Overdrive [18] in flies. These sparse examples of identified speciation genes do not seem to suggest a common or general universal pathway/process leading to speciation but rather point to the involvement of a variety of different mechanisms in the evolution of pre- and post-zygotic barriers between different species
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