Genetic structure of lake and stream populations in a Pyrenean amphibian ( Calotriton asper ) reveals evolutionary significant units associated with paedomorphosis

Abstract

Differences in environmental conditions such as those between lakes and streams can produce phenotypic variation and ultimately promote evolutionary diversification. Some species of newts and salamanders can occupy these habitats and express alternative phenotypes: metamorphs that lose gills at metamorphosis and paedomorphs that retain them at the adult stage. Whereas this process is facultative in some species, it is obligatory in others, thus suggesting that isolation and environmental pressures may have canalized developmental pathways. In this study, we focused our research on the Pyrenean brook newt, Calotriton asper, which is present in both lakes and streams, but whose fully aquatic paedomorphic individuals are only present in lakes. We aimed to determine the genetic structure and differentiation of two paedomorphic populations, including their surrounding stream and lake metamorphic populations, to test whether populations of paedomorphs can constitute evolutionary significant units. Although gene flow was identified between lakes and nearby stream populations, there was a low percentage of dispersers, and the paedomorphic populations were genetically differentiated from the populations of metamorphs. It is likely that the studied lakes have offered peculiar conditions that have allowed the development of a paedomorphic phenotype. These populations and phenotypes therefore constitute good models to understand local adaptations. As each of these populations of paedomorphs can be considered evolutionary significant units that cannot be replaced by other nearby populations in case of a population crash, conservation actions should be focused directly on them.

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

“…Moreover, as there are no remaining populations of paedomorphs near the studied populations, colonizers would come only from populations of metamorphs (see also Oromi et al. ). In fact, fish were extirpated in one of the mountain lakes (Ridsko Jezero), but paedomorphs did not recover as only metamorphic newts were found during the last surveys.…”

“…However, selection against paedomorphosis can alter its expression (Semlitsch and Wilbur 1989), which might decrease the likelihood of the resilience of paedomorphic populations after a long period of time of counter selection, as is probably the case in Montenegro. Moreover, as there are no remaining populations of paedomorphs near the studied populations, colonizers would come only from populations of metamorphs (see also Oromi et al 2019). In fact, fish were extirpated in one of the mountain lakes (Ridsko Jezero), but paedomorphs did not recover as only metamorphic newts were found during the last surveys.…”

Quantifying rarity of intraspecific diversity at multiple spatial scales by combining fine-grain citizen-based data across national boundaries

“…Regardless of the origin of intraspecific variation (e.g. genetic polymorphisms or polyphenisms), genotypes or phenotypes can have peculiar distribution patterns as a result of their adaptation to specific environments and their evolutionary history (Bush and Adams, 2007;Emel and Bonett, 2011;Thomasen et al, 2011;McLean and Stuart-Fox, 2014;Bonett et al, 2018;Oromi et al, 2018;Foster et al, 2021). This means that some variants may have an inherently smaller distribution range and be rarer than the species to which they belong, such as shown for facultatively paedomorphic newts Denoël, 2007), viviparous fire salamanders (Lourenço et al, 2019) and ovoviparous common lizards (Horreo et al, 2018).…”

Demographic Traits Variation in a Pyrenean Newt (Calotriton asper) among Lacustrine and Stream Populations

“…These life history traits can vary due to many factors such as climatic conditions, trophic resources, predator vs. prey interactions, or interspecific competition [5]. Besides that, these different environmental conditions, such as between lakes and streams, cause variability and promote ecological diversification [6]. The expression of a trait is determined by genetic factors, environmental influences, and interactions between genotype and environment [7].…”