A lot of convergence, a bit of divergence: Environment and interspecific interactions shape body colour patterns in Lissotriton newts

Abstract

Coexistence with related species poses evolutionary challenges to which populations may react in diverse ways. When exposed to similar environments, sympatric populations of two species may adopt similar phenotypic trait values. However, selection may also favour trait divergence as a way to reduce competition for resources or mates. The characteristics of external body parts, such as coloration and external morphology, are involved to varying degrees in intraspecific signalling as well as in the adaptation to the environment and consequently may be diversely affected by interspecific interactions in sympatry. Here, we studied the effect of sympatry on various colour and morphological traits in males and females of two related newt species Lissotriton helveticus and L. vulgaris. Importantly, we did not only estimate how raw trait differences between species respond to sympatry, but also the marginal responses after controlling for environmental variation. We found that dorsal and caudal coloration converged in sympatry, likely reflecting their role in adaptation to local environments, especially concealment from predators. In contrast, aspects of male and female ventral coloration, which harbours sexual signals in both species, diverged in sympatry. This divergence may reduce opportunities for interspecific sexual interactions and the associated loss of energy, suggesting reproductive character displacement (RCD). Our study emphasizes the contrasting patterns of traits involved in different functions and calls for the need to consider this diversity in evolutionary studies.

Inconsistent estimates of hybridization frequency in newts revealed by SNPs and microsatellites

“…2B). The lack of introgression is consistent with the maintenance of a broad sympatric zone and supports the hypothesis that convergence of certain color traits (dorsum, tail) observed in sympatry would primarily be the result of plastic or adaptive responses to environmental variables and not introgression (de Solan et al 2022). This result also echoes the findings of Drillon et al (2019) who found hardly any hybridization and no introgression between Hyla tree frog species that diverged around 20 Mya.…”

“…2B). The lack of introgression is consistent with the maintenance of a broad sympatric zone and supports the hypothesis that convergence of certain color traits (dorsum, tail) observed in sympatry would primarily be the result of plastic or adaptive responses to environmental variables and not introgression (de Solan et al 2022).…”

Convergence in sympatric swallowtail butterflies reveals ecological interactions as a key driver of worldwide trait diversification

“…On the contrary, sympatry did not have any significant effect on the evolution of several traits in haemulid fishes, including their color patterns (43). Interestingly, a study focusing on color pattern variations in sympatric species of newt revealed convergence in dorsal patterns, involved in concealment from predators and divergence in the ventral colors, likely in relation with mate choice (8). In Papilionidae, the dorsal wing color pattern is likely involved in interactions with both predators and mating partners.…”

“…Importantly, the effect of species interactions in the convergence vs. divergence of trait may depend on their level of relatedness. For instance, interspecific competition for territory (3) or mates (8) can promote either phenotypic convergence or divergence between sympatric species depending on their phylogenetic proximity. Closely-related species are indeed more likely to share similar ecological niches and to display similar suite of traits.…”

Sex chromosomes as supergenes of speciation: why amphibians defy the rules?

“…Moreover, reinforcement has been rarely demonstrated in amphibians. The few convincing cases involved character displacement of advertisement calls in Australian tree frogs [132], or coloration in poison frogs [122] and newts [133]. By contrast, several attempts to demonstrate reinforcement were inconclusive.…”