Forever young - a strategy for niche differentiation?Submitted by editor on 13 February 2018.Get the paper!
On the right: paedomorphic alpine newt, a phenotype that retains gills at the adult stage (Photo by Mathieu Denoël). On the left: Fig. 2 of the article illustrating the isotopic niche of alpine newts, with paedomorphic females foraging more on planktonic organisms than the other phenotypes. Paedomorphs: thick red lines, metamorphs: thin blue lines. Females: solid lines, males: dashed lines.
Facultative paedomorphosis in newts and salamanders is a heterochronic polymorphism in which one phenotype (the paedomorph) retains gills and a fully aquatic life at the adult stage whereas the other phenotype (the metamorph) fully metamorphoses, allowing for a terrestrial life-stage. Paedomorphosis and metamorphosis have been primarily seen as results of trade-offs between the advantages of using aquatic versus terrestrial habitats in newts and salamanders. However, because facultative paedomorphosis affects trophic structures and feeding mechanism, one hypothesis is that it may be maintained as a trophic polyphenism, with the advantage to lessen intraspecific competition during the shared aquatic life-stage. In this study, we used integrative tools (stomach contents and stable isotope analysis) to test this hypothesis in the alpine newt Ichthyosaura alpestris alpestris
The study site, an alpine lake where paedomorphic and metamorphic alpine newts coexist. Photo by Mathieu Denoël.
Our results revealed differences between phenotypes corresponding to a trophic polyphenism along the littoral-pelagic axis and an extension of the niche of paedomorphs to otherwise underused resources (i.e. pelagic resources), with both tactics providing similar gains. Additionally, stable isotope analysis revealed that the trophic polyphenism was less marked in males than in females during the reproductive period, which may be linked to reproductive activities. We thoroughly discuss the implications of such sex-specific trophic differences in the long-term maintenance of facultative paedomorphosis and the importance of considering sex differences to understand the evolution of trophic polyphenisms. Altogether, we provide evidence that facultative paedomorphosis promotes resource partitioning between morphs during the aquatic life-stage and that this may be an important factor to understand the long-term maintenance of this dimorphism in heterogeneous environments, such as alpine lakes.
The authors through Benjamin Lejeune