Can age and growth patterns explain the geographical variation in the body size of two toad species?

Abstract

Determining both the age structure and growth pattern allows to establish the causal factors, environmental and/or genetic, that eventually may be responsible for the observed pattern of divergence. We examined the variation in age structure and growth pattern across populations of two toad species, Pelobates cultripes and Epidalea calamita that exhibit a geographic variation in body size in southern Spain.For both species, populations differed in mean age but age structure did not correlate with body size variation across populations. Although the population with the youngest females found for E. calamita was the smallest in body size, the oldest males for both species were found in a small body size population. The growth pattern fi t well to a von Bertalanffy growth model and interdemic divergence were found for both the asymptotic body size (S m ) and the growth coeffi cients (k). As expected, Large-Bodied populations of both species attained higher S m but, Small-Bodied population had higher, although non signifi cantly different, k growth coeffi cients. Also, the Small-Bodied population attained sexual maturity sooner but had also high longevity. The observed pattern may refl ect both environmental variations in resources availability affecting body size observed across populations, but also different growth and maturity pathways that may respond to contrasting selective pressures.

Modeling Sexual Differences of Body Size Variation in Ground Beetles in Geographical Gradients: A Case Study of Pterostichus melanarius (Illiger, 1798) (Coleoptera, Carabidae)

“…Clinal variation may indicate such local adaptation, as geographical clines are strongly related to environmental gradients, which may pose differential challenges to survival and reproduction. In addition, animals may also exhibit striking body size variation at smaller spatial scale for nearby locations with similar climate characteristics but with variation in microhabitat conditions, such as the nature of the substrate, which may impose nutritional and/or hydric constraints [63].…”