Abstract
Gene flow strongly influences the regional genetic structuring of plant populations. Seed and pollen dispersal patterns can respond differently to the increased isolation resulting from habitat fragmentation, with unpredictable consequences for gene flow and population structuring. In a recently fragmented landscape we compared the pre- and post-fragmentation genetic structure of populations of a tree species where pollen and seed dispersal respond differentially to forest fragmentation generated by flooding. Castanopsis sclerophylla is wind-pollinated, with seeds that are dispersed by gravity and rodents. Using microsatellites, we found no significant difference in genetic diversity between pre- and post-fragmentation cohorts. Significant genetic structure was observed in pre-fragmentation cohorts, due to an unknown genetic barrier that had isolated one small population. Among post-fragmentation cohorts this genetic barrier had disappeared and genetic structure was significantly weakened. The strengths of genetic structuring were at a similar level in both cohorts, suggesting that overall gene flow of C. sclerophylla has been unchanged by fragmentation at the regional scale. Fragmentation has blocked seed dispersal among habitats, but this appears to have been compensated for by enhanced pollen dispersal, as indicated by the disappearance of a genetic barrier, probably as a result of increased wind speeds and easier pollen movement over water. Extensive pollen flow can counteract some negative effects of fragmentation and assist the long-term persistence of small remnant populations.
Highlights
The spatial distribution of genetic variation can provide perspectives into current and past population dynamics, and is of great significance for biological conservation (Escudero et al 2003; Lowe et al 2005; Storfer et al 2007)
Changes in spatial genetic structure of pre- and post-fragmentation cohorts of C. sclerophylla were detected among small populations, with reduced SGS in the post-fragmentation cohort, no difference was detected in large populations
Further analyses indicated that the postfragmentation reduction in SGS resulted from the removal of a pre-fragmentation genetic barrier that existed around one small island (GM)
Summary
The spatial distribution of genetic variation can provide perspectives into current and past population dynamics, and is of great significance for biological conservation (Escudero et al 2003; Lowe et al 2005; Storfer et al 2007). The existence of spatial genetic structure (SGS) decreases effective population size, affecting population genetic diversity and even progeny fitness in the long term (Kalisz et al 2001; Fenster et al 2003; Wang et al 2009). Both theoretical and empirical studies have shown that gene flow plays a critical role in determining the extent of relatedness among adjacent individuals and levels of local random genetic drift, and that gene flow is the predominant determinant of SGS in the absence of selection.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
