Facultative paedomorphosis as a mechanism promoting intraspecific niche differentiation

Abstract

Organisms with complex life cycles are characterized by a metamorphosis that allows for a major habitat shift and the exploitation of alternative resources. However, metamorphosis can be bypassed in some species through a process called paedomorphosis, resulting in the retention of larval traits at the adult stage and is considered important at both micro‐ and macroevolutionary scales. In facultatively paedomorphic populations of newts, some individuals retain gills and a fully aquatic life at the adult stage (paedomorphs), while others undergo complete metamorphosis (metamorphs), allowing for a terrestrial life‐stage. Because facultative paedomorphosis affects trophic structures and feeding mechanism of newts, one hypothesis is that it may be maintained as a trophic polymorphism, with the advantage to lessen intraspecific competition during the shared aquatic life‐stage. Here, we tested this hypothesis combining stomach content data with stable isotope techniques, using carbon and nitrogen stable isotopes, in facultatively paedomorphic alpine newts Ichthyosaura alpestris. Both stomach content and stable isotope analyses showed that paedomorphs had smaller trophic niches and were more reliant on pelagic resources, while metamorphs relied more on littoral resources, corresponding to a polyphenism along the littoral–pelagic axis and the extension of the population's trophic niche to otherwise ‘underused’ pelagic resources by paedomorphs. Interestingly, stable isotopes revealed that the trophic polyphenism was less marked in males than in females and potentially linked to sexual activity. Although paedomorphosis and metamorphosis are primarily seen as results of tradeoffs between the advantages of using aquatic versus terrestrial habitats, this study provides evidence that additional forces, such as intraspecific trophic niche differences between morphs and trophic niche expansion, may play an important role in the persistence of this dimorphism in heterogeneous environments. Moreover, the different patterns found in males and females show the importance of considering sex to understand the evolutionary ecology of trophic polymorphisms.

Traditionally managed landscapes do not prevent amphibian decline and the extinction of paedomorphosis

“…, Lejeune et al. ). Unfortunately, the longer persistence of metamorphs proved to be, in most cases, only a transient state, given that in the last years they showed a pattern of decline comparable to the one of paedomorphs in the 2000s.…”

“…Second, it has been suggested that metamorphs in water bodies with fish could come from nearby fishless ones, i.e., through a source-sink dynamic process (Breuil 1985). Third, paedomorphic newts are more pelagic than metamorphs and, therefore, are more easily preyed upon by large predators such as salmonids (Deno€ el et al 2005b, Lejeune et al 2018. Unfortunately, the longer persistence of metamorphs proved to be, in most cases, only a transient state, given that in the last years they showed a pattern of decline comparable to the one of paedomorphs in the 2000s.…”

Same but different: aquatic prey capture in paedomorphic and metamorphic Alpine newts

“…Next to different capabilities for capturing elusive prey, also different prey preferences were found between morphs [11, 15]. Furthermore, it has been shown that paedomorphic and metamorphic Alpine newts from the same population partition their trophic habitats [14, 45]. Depending on size and heterogeneity of habitats, paedomorphs tend to live in the entire water column and deep benthic areas where they mainly capture small elusive prey, such as Daphnia and other small pelagic invertebrates while metamorphs live close to the shoreline and mainly rely on terrestrial arthropods that fell into the water [14].…”

Fins are relevant non-lethal surrogates for muscle to measure stable isotopes in amphibians

“…This is probably partly because non-lethal sampling methods are rarely used (but see e.g. Sepulveda et al, 2012;Gillespie, 2013;Remon et al, 2016, Lejeune et al, 2018. Only one study thoroughly explored the relevance of tail clips (i.e.…”