Habitat fragmentation caused by human activity poses a serious threat to biodiversity worldwide, with severe negative impacts on species genetic diversity. In recent years, many attentions have been paid to the genetic effects of anthropogenic habitat fragmentation on plants and animals, mainly focusing on terrestrial habitat islands created by agricultural development, deforestation and so on. However, the habitat islands have confused history, fuzzy boundary, and varied matrix which can cause confusion of results. Conversely, known-age land-bridge islands in artificial lakes are more ideal model systems to elucidate the ecological, genetic and evolutionary consequences of habitat fragmentation. The Thousand Island Lake (TIL) in East China (Chunan County, Zhejiang Province) is a large reservoir, which was formed in 1959 by the damming of the Xinanjiang River for constructing a hydroelectric power station. So far, the fragmented islands are formed around 50 years. Based on this superiority, we studied a dispersal-limited species of soil arthropod Pachycondyla luteipes at TIL to explore the genetic consequences of recent habitat fragmentation of this species.
Sequence-related amplified polymorphism (SRAP) molecular markers were used to study the genetic diversity on population levels. Five SRAP primer combinations were used to measure 42 individuals of P. luteipes from 14 islands to estimate the genetic diversity and structure. The result showed that 5 SRAP primer combinations amplified 71 bands with 63 (88.73%) polymorphic. The percentage of polymorphic bands (PPB) at the population level ranged from 35.21% to 91.55%, with an average of 58.25%, and the largest JSE island owned the highest percentage of polymorphic bands. The Nei's gene diversity index (H) ranged from 0.2662 to 0.4905, with an average of 0.4753. The islands attributes such as area and elevation, had no significant correlation with PPB and H, but the isolation degree among different islands had significant correlation with them. The analysis of AMOVA showed that the main variance between populations was 65.03%, and 34.97% within populations. The genetic differentiation coefficient (G_st) among populations ranged from 0.0777 to 0.9328, with an average of 0.4419. Gene flow (N_m) among populations, based on the genetic differentiation coefficient, ranged from 0.0360 to 5.9350, with an average of 1.0451. The N_m and G_st value implied that the gene flow was at a low level and genetic differentiation was high. The dendrogram obtained by UPGMA cluster analysis showed that populations with nearest distance were clustered firstly. In addition, Mantel test (r=0.7757, P < 0.01) suggested that there was significant association between genetic distance and geographic distance.
These results indicate that the P. luteipes populations in the TIL had gene drift mainly due to the isolation between islands. However, the gene flow is still high between some adjacent islands, because these islands could connect each other when the water level is enough low. In this context, the corridor may play an important role in affecting the genetic diversity in this fragmented landscape. We suggest that beside the island attributes, other factors such as the physical and chemical properties of soils should also be considered into the future studies.