Study On The Effects Of Habitat Fragmentation On The Genetic Diversity Of Natural Chinensis Populations

Habitat fragmentation(HF)is one of main factors decreased biodiversity.Most studies focused on the effects of HF on species diversity and ecosystem diversity but not on genetic diversity.Actinidia plants are important wild genetic resources.Actinidia chinensis var.chinensis is a species with high economic value.We sampled natural A.chinensis populations in the Thousand-Island Lake(TIL),the Zhoushan Archipelago(ZSA)and national distributed boundary points in China.Employing micro satellite markers and ploidy detection experiments,we studied the effects of short-term and long-term HF on the genetic diversity of A.chinensis populations.We investigated the main mechanisms influencing genetic effects of HF,with island biogeography theory(IBT).Our results provided scientific basis for conserving important genetic resources under threat from HF.Main results are shown as follow:(1)Short-term HF did not affect the genetic diversity and genetic differentiation of A.chinensis populations in TIL.The genetic diversity of A.chinensis populations between TIL islands and their neighbor mainland(Ne=6.536 vs 7.206,P value=0.080;He=0.790 vs 0.813,P value=0.209)was not significantly different.Low genetic differentiation was revealed among TIL populations(FST=0.003-0.135).No evidence was found for recent bottlenecks in TIL populations except of the YJI population with small population size and small island area.(2)The population size of A.chinensis populations in TIL islands was positively correlated with island features,including island area and length.It is consistent with the IBT.However,there was no significant correlation between the genetic diversity of A.chinensis populations and island features.(3)Long-term HF significantly affect the genetic diversity and genetic differentiation of A.chinensis populations in ZSA.Genetic diversity indices of the A.chinensis population in ZSA were significantly lower than other inland A.chinensis populations(Ne=5.289 vs.7.920,P value<0.001;He=0.783 vs 0.848,P value=0.001).Genetic differentiation caused by oceanic isolation in ZSA was higher than short-term isolation in TIL(FST=0.023 vs.0.015).Recent bottleneck events were found in the ZSA island population.(4)Geographic isolation decreased the genetic differentiation of the inland A.chinensis populations.Isolation-by-distance effect(R2=0.383,P value=0.033)and recent bottleneck events were detected in these inland populations.(5)We discussed likely mechanisms in explaining the genetic effects of HF on A.chinensis.In the TIL region,for example,the fruits of A.chinensis dispersed through water in the TIL lake,which weakened the effect of lake isolation in decreasing gene flow among populations.However,in the ZSA and other inland populations,there was lack of mechanisms in weakening the decrease of gene flow among populations.(6)Our results indicate a time-delayed effect of HF on the genetic diversity of A.chinensis populations.The time-delayed effect is likely to lead to an occurrence of extinction debt.Therefore,it is important to reinforce conservation on the genetic diversity of wild genetic resources and their habitats,and to focus on time-delayed effect and possible extinction debt from HF.