Habitat Partitioning in Facultatively Paedomorphic Populations of Palmate Newts Triturus helveticus

Abstract

The life cycle of newts of the genus Triturus is characterized by an aquatic larval stage, followed by a succession of transitions between the aquatic and terrestrial habitats. Water remains essential because it is the place for reproduction (1). However, in some populations, the terrestrial component is eliminated. The larvae acquire sexual maturity before metamorphosis, and then retain their gills and gill slits. This alternative path of development is paedomorphosis. In most cases, only a part of the population follows the paedomorphic ontogenetic pathway, while the other part normally metamorphoses (facultative paedomorphosis) (2). Habitat is an essential key in the persistence of facultative paedomorphosis in natural populations of newts and salamanders. Laboratory experiments have shown that more larvae become paedomorphic in permanent waters than in temporary waters (3). In drying ponds, larvae and paedomorphs are constrained either to die or to metamorphose into the terrestrial morph. However, when other aquatic habitats are in proximity, they can survive by migrating without losing their larval attributes (4). Heterogeneous habitats composed of permanent and temporary habitats are usually differently used by the two morphs. Both paedomorphs and metamorphs breed in permanent ponds, but only the metamorphs are able to use drying ponds to forage on transient energetic resources (5). Heterogeneity acts also within a single aquatic habitat on the scale of microhabitats that differ by components such as water depth. Strong space partitioning has been observed in deep lakes, in which paedomorphs were abundant in the water column and metamorphs in benthic areas and at the water surface (2, 6). In more homogeneous ponds, although some partitioning existed, the two morphs largely used all available microhabitats (7). Because all these results were obtained in a single species (the Alpine newt Triturus alpestris), comparative studies on other model species are needed. Paedomorphosis was observed not only in the Alpine newt, but also in the palmate newt Triturus helveticus (8). Most populations of T. helveticus are located in southern France and inhabit environments different from that of paedomorphic Alpine newts (8, 9). In this area, all the aquatic habitats of T. helveticus are manmade ponds surrounded by arid lands (limestone plateau). The aim of this study was to find out whether paedomorphic and metamorphic palmate newts use their aquatic habitat differently.