Population Genetic Structure And Gene Flow Of Curculio Bimaculatus In Fragmented Habitats

The ecological effects and mechanisms of habitat fragmentation are important ecological issues under the background of human disturbance and global climate change.Fragment size and isolation are known to affect the population genetic structure,which is usually related to the trophic status of the species.Some species are disadvantaged on small or isolated habitats,so both community structure and interactions of species with their biotic or abiotic environment could change.For example,an increasing biotic interaction may promote pollination and seed predation of plants.The disruption of interactions may also lead to extinction.Based on the the typical fragmented habitat of Thousand-Island Lake in Zhejiang province,the genetic structure and its maintenance mechanism of Curculio bimaculatus were analyzed from the aspects of host plant type and degree of fragmentation by using the molecular markers of mitochondrial COI and 9 pairs of microsatellite markers.The main results are as follows:(1)Clustering results showed that the genetic structure of the population from different host plants were similar,indicating the host did not cause the differentiation of C.bimaculatus.(2)On the scale of patches,habitat fragmentation directly reduced the effective population size though this is not resulting from increasing the inbreeding of small populations.On landscape scale,the size of contemporary effective population is obviously lower than that of historical effective population.(3)Habitat fragmentation had no significant effect on genetic differentiation of C.bimaculatus,and no geographic isolation pattern was found.Gene-flow analysis found that mean number of effective migrants reaching each population from all other populations in the contemporary population was significantly lower than that in the historical population(V=120,p<0.001),but the migration rate among each two populations in contemporary populations was significantly higher than that in the historical population(V=22155,p<0.001).(4)The overall gene flow obtained from the mitochondrial data 10.5 was smaller than that calculated by microsatellite 124.7;Under two different migration schemes of female dispersal before mating and female dispersal after mating,the radio of male to female migration rates(r=m_m/m_f)are both biger than 1(r1=4.87,r2=3.87),suggesting there may be a male-biased dispersal in C.bimaculatus.The population of C.bimaculatus showed hardly preference among different host plants and no obvious genetic differentiation among different islands because of the strong gene flow dominated by male.The results are helpful to understand the diffusion adaptation mechanism of C.bimaculatus to fragmented habitats,and provide a basis for further understanding the impact of habitat fragmentation on plant-insect relationships.