Abstract
The impact of environmental change on population structure is not well understood. This study aimed to examine the effect of a climate change event on gene flow over space and time in two populations of Brassica rapa that evolved more synchronous flowering times over 5 years of drought in southern California. Using plants grown from seeds collected before and after the drought, we estimated genetic parameters within and between populations and across generations. We expected that with greater temporal opportunity to cross-pollinate, due to reduced phenological isolation, these populations would exhibit an increase in gene flow following the drought. We found low but significant FST, but no change in FST or Nm across the drought, in contrast to predictions. Bayesian analysis of these data indicates minor differentiation between the two populations but no noticeable change in structure before and after the shift in flowering times. However, we found high and significant levels of FIS, indicating that inbreeding likely occurred in these populations despite self-incompatibility in B. rapa. In this system, we did not find an impact of climate change on gene flow or population structuring. The contribution of gene flow to adaptive evolution may vary by system, however, and is thus an important parameter to consider in further studies of natural responses to environmental change.
Highlights
Climate change is a major environmental concern and one of the greatest threats to biodiversity (Williams et al 2008; Bellard et al 2012)
The current study focuses on the impacts of the change in flowering times on the genetics of these natural populations
Between two and nine alleles were found per locus [see Supporting Information] and between zero and eight private alleles (PA) were found in each population (Table 1)
Summary
Climate change is a major environmental concern and one of the greatest threats to biodiversity (Williams et al 2008; Bellard et al 2012). Several recent studies have illustrated the potential for rapid evolution in response to changes in species’ surroundings (Huey et al 2000; Stockwell et al 2003; Franks et al 2007) Adaptive responses in both plants and animals frequently involve the evolution of phenological traits (Fitter and Fitter 2002; Penuelas et al 2002; Menzel et al 2006; Hoffmann et al 2010), which often depend on seasonal cues, such as temperature and/or precipitation conditions (Franks et al 2007; Jarrad et al 2008). In populations that are differentially affected by changes in environmental conditions, phenology (i.e. timing of reproduction) may become more or less synchronized, impacting the opportunity for reproduction across populations
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