Latitudinal and altitudinal variation of life history traits in natterjack toads (Bufo calamita)genetic adaptation vs. phenotypic plasticity

Résumé

The aim of the present study is to analyse the latitudinal and altitudinal variations of life history traits (thermal behaviour, migratory range, age structure and size variation) in natterjack toads (Bufo calamita) and its relationship with genetic variability. This species is an excellent model organism because of its wide distribution that ranges from 36° to 58° of latitude and from sea level up to 2540 m (Sinsch, 2008). Life history traits of B. calamita seem to depend on the contraction of the annual activity period along latitudinal and altitudinal gradient. The substrate type determines the shelter used by toads for hibernation that affects the size variation and the migratory ranges. Females respond more sensitively than males to environmental changes. Whereas the pattern of size variation suggests a covariance of females' size and potential reproductive lifespan (PRLS) to optimize the lifetime fecundity rather in a latitudinal cline, lifetime fecundity decreases at the upper altitudinal ranges because PRLS is similar to the lowland population but females are smaller. This reduction in lifetime fecundity can explain the inability of natterjack toads to colonize elevations exceeding 2500 m and probably to expand geographical range further north. As there is little evidence for genetic isolation by distance or altitude, the variation of life history traits in natterjack toads seems to be mainly or entirely related to phenotypic plasticity. The high gene flow between populations suggest genetic cohesion of metapopulations systems as predicted the migratory capacity of dispersing natterjacks estimated in this study.