Pool desiccation and developmental thresholds in the common frog, Rana temporaria

摘要

The developmental threshold is the minimum size or condition that a developing organism must havereached in order for a life-history transition to occur. Although developmental thresholds have beenobserved for many organisms, inter-population variation among natural populations has not beenexamined. Since isolated populations can be subjected to strong divergent selection, population divergencein developmental thresholds can be predicted if environmental conditions favour fast or slowdevelopmental time in different populations. Amphibian metamorphosis is a well-studied life-historytransition, and using a common garden approach we compared the development time and thedevelopmental threshold of metamorphosis in four island populations of the common frog Ranatemporaria: two populations originating from islands with only temporary breeding pools and two fromislands with permanent pools. As predicted, tadpoles from time-constrained temporary pools had agenetically shorter development time than those from permanent pools. Furthermore, the variation indevelopment time among females from temporary pools was low, consistent with the action of selection onrapid development in this environment. However, there were no clear differences in the developmentalthresholds between the populations, indicating that the main response to life in a temporary pool is toshorten the development time.