Morphological And Molecular Evidence Revealed The Introgression And Formation Mechanism Of Three Relative Species Of Huaxi Crab

Understanding the formation and maintenance of biodiversity is one focus of evolutionary biology.When differentiation of intrinsic barriers does not fully develop,reproductive isolation between species derived from rapid radiation remains incomplete and can lead to introgressive hybridization in related species.Sinopotamon yangtsekiense,S.honanense and S.shensiense are three related,parapatric species within endemic Chinese mainland Sinopotamon.This group has diversified because of recent rapid radiation events and provides a good model for exploring introgressive hybridization between related species and the formation and maintenance of freshwater crab diversity.Here,we combined population morphological analysis and intensive molecular evidence to explore(1)introgressive hybridization between three parapatric Sinopotamon pairs,(2)formation mechanisms and(3)the effect of introgressive hybridization on species diversity in the evolution of inland freshwater crabs.Sinopotamon are typical internally fertilizing freshwater crabs and the male gonopod 1(G1)is necessary for reproductive isolation between species.Morphological analysis shows that three allied Sinopotamon species have obvious differentiation in G1,but the characteristics of the carapace,abdomen,cheliped and pereiopod are similar and even overlap.Population molecular data acquisition united mitochondrial and nuclear microsatellite DNA molecular markers.Mitochondrial analysis revealed that the three species have shared haplotypes and the distribution of populations with shared haplotypes is aggregated rather than randomly distributed,suggesting that three species pairs have undergone mitochondrial introgressive hybridization.Introgressive hybridization analysis based on microsatellite data showed that admixture individuals exist in three species pairs,and deviation occurs when S.yangtsekiense and S.shensiense exhibit asymmetric introgression hybridization.Population mitochondrial(matrilineal)and microsatellite DNA(parents)indicates that introgressive hybridization has occurred.Even when allied species G1 morphological separation is obvious,its differentiation is not sufficient to achieve complete reproductive isolation and results in extensive hybridization in parapatric or sympatric populations.These data also imply that the three species have experienced recent rapid radiation.Population dynamics analysis shows that populations of these species expanded rapidly historically,increasing the chance of species contact and further promoting introgressive hybridization.Introgressive hybridization populations are distributed within the scope of the narrow parapatric or sympatric area,and limited hybridization ultimately failed to cause a decline in these species.Inversely,morphology analysis indicates that the difference in G1 morphology among S.yangtsekiense shanxianense,S.yangtsekiense tongbaiense and S.shensiense is small,but morphological differentiation among S.yangtsekiense shanxianense,S.yangtsekiense tongbaiense and S.yangtsekiense yangtsekiense is large.Microsatellite data analysis showed that extensive genetic information in S.shensiense introgressed to S.yangtsekiense shanxianense and S.yangtsekiense tongbaiense,suggesting that introgressive hybridization promoted morphological differentiation among these subspecies.Mitochondrial DNA markers evaluating genetic diversity in these three species shows that introgressive hybridization benefits Sinopotamon species genetic diversity and abundant genetic diversity in this group is significant to the maintenance of species diversity.