Proximate mechanisms determining latitudinal size variability in natterjack toads
SINSCH, U.; MARANGONI, F.; OROMI, N.; LESKOVAR, C.; SANUY, D.; TEJEDO, M.
JOURNAL OF ZOOLOGY (1987)
Zoological Society of London
Lugar: London, UK; Año: 2010 vol. 281 p. 272 - 281
In Amphibia, presence and direction of intra- and interspecific latitudinal body size (=Bergmann) clines are controversially debated. To analyse the proximate causes of intraspecific body size variation in the toad Bufo calamita which roughly follows a converse Bergmann cline, we chose five populations in Spain and Germany representing a variation of adult size from 39 mm to 95 mm snout-vent length, a latitudinal gradient from 37° to 50°, and an altitudinal gradient from sea level to 420 m. Skeletochronological age estimation revealed that populations differed considerably with respect to age distribution and lifetime growth pattern. Toads from southern populations matured earlier and reproduced earlier than those from northern ones, but had a reduced potential reproductive lifespan. Differences of age-adjusted adult size were based on the size achieved during the first terrestrial activity period of life, i.e. between metamorphosis and first hibernation or aestivation. Environmental attributes determining first-year snout-vent length were the duration of the aboveground activity period, temperature during the activity period, and the type of shelter sites and hibernacula available in the habitat. Interactions of these proximate causes accounted for adult size variation and explained the presence of a small-sized population in southern Spain which did not fit to the clinal pattern predicted by the ecogeographical rules. In contrast, our case study suggests that body size variation among B. calamita populations may be the evolutionary byproduct of optimized lifetime fecundity