Strong genetic differentiation but not local adaptation toward the range limit of a coastal dune plant

Abstract

All species have limited geographic distributions; but the ecological and evolutionary mechanisms causing range limits are largely unknown. That many species' geographic range limits are coincident with niche limits suggests limited evolutionary potential of marginal populations to adapt to conditions experienced beyond the range. We provide a test of range limit theory by combining population genetic analysis of microsatellite polymorphisms with a transplant experiment within, at the edge of, and 60 km beyond the northern range of a coastal dune plant. Contrary to expectations, lifetime fitness increased toward the range limit with highest fitness achieved by most populations at and beyond the range edge. Genetic differentiation among populations was strong, with very low, nondirectional gene flow suggesting range limitation via constraints to dispersal. In contrast, however, local adaptation was negligible, and a distance-dependent decline in fitness only occurred for those populations furthest from home when planted beyond the range limit. These results challenge a commonly held assumption that stable range limits match niche limits, but also raise questions about the unique value of peripheral populations in expanding species' geographical ranges.

Consequences of multiple mating‐system shifts for population and range‐wide genetic structure in a coastal dune plant

“…Statistically controlling for geographic distance, population size and range‐wide genetic subdivision, we detected no difference in pairwise G′ ST between population clusters that differed in mating system. Instead pairwise differentiation among populations within instruct clusters was consistently strong (mean G′ ST = 0.59), even among outcrossing LF‐SI populations (0.53), suggesting very little gene flow among populations of C. cheiranthifolia (see also Samis et al., ). We also did not find stronger isolation by distance (IBD) among LF than SF populations.…”

Quantitative genetic methods depending on the nature of the phenotypic trait

“…The approach was implemented in the aster R package. Since then, aster models have been used in various studies on adaptation, especially on plants . Recently, aster models have been extended to include random effects using a modified version of the PQL approach .…”

Local adaptation primes cold‐edge populations for range expansion but not warming‐induced range shifts

“…; Samis et al . ). Moreover, many beyond‐the‐edge transplant experiments omit the early life history stages most related to offspring quality (Donohue ), and most do not replicate in time (multiple generations of fitness) or space (multiple edge and beyond‐range sites), increasing idiosyncratic year or site effects (Hargreaves et al .…”