Résumé
In ectotherms, variation in life-history traits among populations is
common and suggests local adaptation. However, geographic variation itself
is not a proof for local adaptation, since genetic drift and gene flow may
also shape patterns of quantitative variation. We studied local and
regional variation in means and phenotypic plasticity of larval life
history traits in the common frog Rana temporaria using six populations
from central Sweden, breeding in either open canopy or partially closed
canopy ponds. To separate local adaptation from genetic drift we compared
differentiation in quantitative genetic traits (QST) obtained from a
common garden experiment with differentiation in presumably neutral
microsatellite markers (FST). We found that R. temporaria populations
differ in means and plasticities of life-history traits in different
temperatures at local, and in Fst at regional scale. Comparisons of
differentiation in quantitative traits and in molecular markers suggested
that natural selection was responsible for the divergence in growth and
development rates as well as in temperature-induced plasticity, indicating
local adaptation. However, at low temperature the role of genetic drift
could not be separated from selection. Phenotypes were correlated with
forest canopy closure but not with geographical or genetic distance. These
results indicate that local adaptation can evolve in the presence of
ongoing gene flow among populations, and that natural selection is strong
in this system.