Abstract
BackgroundWhen genetic structure is identified using mitochondrial DNA (mtDNA), but no structure is identified using biparentally-inherited nuclear DNA, the discordance is often attributed to differences in dispersal potential between the sexes.ResultsWe sampled the intertidal rocky shore mussel Perna perna in a South African bay and along the nearby open coast, and sequenced maternally-inherited mtDNA (there is no evidence for paternally-inherited mtDNA in this species) and a biparentally-inherited marker. By treating males and females as different populations, we identified significant genetic structure on the basis of mtDNA data in the females only.ConclusionsThis is the first study to report sex-specific differences in genetic structure based on matrilineally-inherited mtDNA in a passively dispersing species that lacks social structure or sexual dimorphism. The observed pattern most likely stems from females being more vulnerable to selection in habitats from which they did not originate, which also manifests itself in a male-biased sex ratio. Our results have three important implications for the interpretation of population genetic data. First, even when mtDNA is inherited exclusively in the female line, it also contains information about males. For that reason, using it to identify sex-specific differences in genetic structure by contrasting it with biparentally-inherited markers is problematic. Second, the fact that sex-specific differences were found in a passively dispersing species in which sex-biased dispersal is unlikely highlights the fact that significant genetic structure is not necessarily a function of low dispersal potential or physical barriers. Third, even though mtDNA is typically used to study historical demographic processes, it also contains information about contemporary processes. Higher survival rates of males in non-native habitats can erase the genetic structure present in their mothers within a single generation.
Highlights
When genetic structure is identified using mitochondrial DNA, but no structure is identified using biparentally-inherited nuclear DNA, the discordance is often attributed to differences in dispersal potential between the sexes
Sex-specific differences in genetic structure were found in the marine mussel Mytilus edulis [10], despite the fact that it has microscopic larvae with extremely limited swimming abilities and presumably passive dispersal
We did not find differentiation between the COI sequences of males and females when treating these as distinct populations (ΦST = −0.003; p = 0.550; 95% confidence interval: -0.005 – 0.000). These results indicate that no M-mitochondrial DNA (mtDNA) amplified in the males
Summary
When genetic structure is identified using mitochondrial DNA (mtDNA), but no structure is identified using biparentally-inherited nuclear DNA, the discordance is often attributed to differences in dispersal potential between the sexes. Numerous studies have used maternally-inherited mitochondrial DNA (mtDNA) in conjunction with biparentally-inherited nuclear DNA markers [1,2,3,4,5,6,7], and discrepancies between results from the two types of markers have been interpreted as the result of sex-specific differences in dispersal. Sex-specific differences in genetic structure were found in the marine mussel Mytilus edulis [10], despite the fact that it has microscopic larvae with extremely limited swimming abilities and presumably passive dispersal. The family Mytilidae includes 33 genera [11] and in five of these, including Mytilus [12,13], doubly uniparental inheritance (DUI [14]) has been identified Males have both a male (MmtDNA) and a female (F-mtDNA) mitochondrial genome, whereas females only have a female genome. Levels of trans-Atlantic gene flow differ for the two genomes of
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