PHENOTYPIC VARIATION IN METAMORPHOSIS IN 5 ANURAN SPECIES ALONG A GRADIENT OF STREAM INFLUENCE

The respective influences of adaptation and of phylogenetic relations was investigated by comparing size and age at metamorphosis in five an uran species (Discoglossidae: Bombina variegata; Bufonidae: Bufo bufo, B. calamita; and Ranidae: Rana dalmatina, R. temporaria). All these s pecies inhabit the alluvial floodplain of the Middle Rhone River. With in the floodplain, these species differ by the time during which water is present in their breeding habitats Phenotypic plasticity was estim ated by rearing tadpoles of each species under two different temperatu res. Phylogenetic relations explained a larger part of the variation i n plasticity among species than did habitat use. Bombina variegata dif fered from the other species in the unvariance of size at metamorphosi s as temperature varied In the other species, a longer larval period w as related to a larger size at metamorphosis at the lower temperature and a shorter larval period was related to a smaller size at metamorph osis at the higher temperature However, bivariate reaction norms showe d trajectories that proved to be related to the taxonomic status of th e family. We conclude therefore that adaptation to the instability of the aquatic habitat may be attributed more to the adult stage than to the larval stage Other variables than those operating during the larva l stage must be investigated to understand the distribution of amphibi an communities in the floodplain. Such comparative studies ran play an important role in developing and testing hypotheses about adaptative plasticity and habitat variability.