Bone growth plasticity among populations of Salamandra salamandra: Interactions between internal and external factors

Salamandra salamandra is a highly polytypic species characterized in the Ib erian Peninsula by major differences in reproductive strategies, coloration patterns and morphological features. The aim of this paper is to focus on some aspects of this large phenotypic variability, especially the origin of differences in body size observed among populations. Skeletochronological methods were used to assess age and rates of bone grow th in individuals from 14 populations throughout the Iberian Peninsula. Sig nificant variation in the growth curves as well as in the relative growth r ates were found among the populations sampled. Two bone growth patterns are recognizable. The population from Ronda (south ern Spain) exhibits a basically linear growth rate through the first eight or more years of life instead of just four years as in the other population s. Such a linear growth rate means that for a given age (older than four ye ars) the individual body size of salamanders from Ronda is higher than in o ther populations. All of the other populations show nonlinear growth curves . Bone growth rate is influenced by different factors (internal versus extern al) depending on the populations. The phenotypic variability encountered am ong the populations of salamanders from the Iberian Peninsula is, at least in part, caused by environmental conditions that influence the duration of the activity period of the salamanders and consequently the annual increase of growth. Nevertheless, the populations From northern Spain, characterize d by some degree of viviparity (Lindus) or predominantly viviparous (Oviedo ), show a significantly lower bone growth rate per month (mBGR) than the ot her populations. This lower mBGR, in addition to environmental factors, is responsible for the small body size observed in these populations.