Genetic effects of recent habitat fragmentation in the Thousand-Island Lake region of southeast China on the distylous herb Hedyotis chrysotricha (Rubiaceae).

摘要

Premise of the Study: Known-age artificial-lake islands provide ideal model systems to elucidate the genetic and evolutionary consequences of anthropogenic habitat fragmentation on very recent time scales. Here, we studied a distylous herb, Hedyotis chrysotricha (Rubiaceae), in the artificially created Thousand-Island Lake (TIL) region of southeast China to explore the genetic consequences of islanding for this species. Methods: Seven microsatellite loci were used to genotype 384 individuals of H. chrysotricha from 18 populations to estimate genetic diversity, population structure, and demographic parameters. Key Results: Island populations had significantly lower mean genetic diversity than those from the western/eastern mainland (e.g., H_E=0.381 vs. 0.461) and also displayed higher mean subdivision (F_ST=0.12 vs. 0.042/0.051). BayesAss analyses indicated moderate levels of migration rates among most populations, whereas Bottleneck did not provide strong evidence for such effects. In consequence, 2MOD strongly favored a gene flow-drift model over a pure drift model in the study area, but concomitantly revealed a relatively greater influence of drift in the island populations as evidenced by their significantly higher probabilities of allelic coancestry (F=0.184 vs. 0.085). Conclusions: The observed genetic patterns in H. chrysotricha indicate that recent anthropogenic habitat fragmentation in the TIL region can lead to significant loss of genetic diversity in isolated fragments (islands) due to ongoing drift. By contrast, patterns of random mating, gene flow, and population connectivity have not greatly been modified yet, possibly owing to the species' fruit (seed) dispersal capabilities providing resilience in the face of habitat fragmentation.