Colour polymorphism influences species' range and extinction risk

Continuous variation in the shell colour of the snail Cepaea nemoralis is associated with the colour locus of the supergene

While the shell of the land snail Cepaea nemoralis is typically classed as yellow, pink, or brown, the reality is that colour variation is continuously distributed. To further understand the origin of the continuous variation, we used crosses of C. nemoralis to compare quantitative measures of the colour with the inferred genotype of the underlying supergene locus. We also used a recently developed linkage map to find quantitative trait loci that may influence colour. The results show that the colour locus of the supergene-at around 31.385 cM on linkage group 11-is involved in determining the quantitative chromatic differences that are perceptible to human vision. We also found some evidence that variation within colour classes may be due to allelic variation at or around the supergene. There are likely other unlinked loci involved in determining colour within classes, but confirmation will require greater statistical power. Although not investigated here, environmental factors, including diet, may also impact upon variation within colour types.

Genetic basis and expression of ventral colour in polymorphic common lizards

Colour is an important visual cue that can correlate with sex, behaviour, life history or ecological strategies, and has evolved divergently and convergently across animal lineages. Its genetic basis in non-model organisms is rarely known, but such information is vital for determining the drivers and mechanisms of colour evolution. Leveraging genetic admixture in a rare contact zone between oviparous and viviparous common lizards (Zootoca vivipara), we show that females (N = 558) of the two otherwise morphologically indistinguishable reproductive modes differ in their ventral colouration (from pale to vibrant yellow) and intensity of melanic patterning. We find no association between female colouration and reproductive investment, and no evidence for selection on colour. Using a combination of genetic mapping and transcriptomic evidence, we identified two candidate genes associated with ventral colour differentiation, DGAT2 and PMEL. These are genes known to be involved in carotenoid metabolism and melanin synthesis respectively. Ventral melanic spots were associated with two genomic regions, including a SNP close to protein tyrosine phosphatase (PTP) genes. Using genome re-sequencing data, our results show that fixed coding mutations in the candidate genes cannot account for differences in colouration. Taken together, our findings show that the evolution of ventral colouration and its associations across common lizard lineages is variable. A potential genetic mechanism explaining the flexibility of ventral colouration may be that colouration in common lizards, but also across squamates, is predominantly driven by regulatory genetic variation.

Shell color polymorphism in marine gastropods

Marine gastropods are characterized by an incredible variation in shell color. In this review, we aim to introduce researchers to previous studies of shell color polymorphism in this group of animals, trying to provide an overview of the topic and highlighting some potential avenues for future research. For this, we tackle the different aspects of shell color polymorphism in marine gastropods: its biochemical and genetic basis, its patterns of spatial and temporal distribution, as well as its potential evolutionary causes. In particular, we put special emphasis on the evolutionary studies that have been conducted so far to reveal the evolutionary mechanisms responsible for the maintenance of shell color polymorphism in this group of animals, as it constitutes the least addressed aspect in existing literature reviews. Several general conclusions can be drawn from our review: First, natural selection is commonly involved in the maintenance of gastropod color polymorphism; second, although the contribution of neutral forces (gene flow-genetic drift equilibrium) to shell color polymorphism maintenance do not seem to be particularly important, it has rarely been studied systematically; third, a relationship between shell color polymorphism and mode of larval development (related to dispersal capability) may exist. As for future studies, we suggest that a combination of both classical laboratory crossing experiments and -Omics approaches may yield interesting results on the molecular basis of color polymorphism. We believe that understanding the various causes of shell color polymorphism in marine gastropods is of great importance not only to understand how biodiversity works, but also for protecting such biodiversity, as knowledge of its evolutionary causes may help implement conservation measures in those species or ecosystems that are threatened.

A molecularphylogeny offorktail damselflies(genus Ischnura)revealsa dynamic macroevolutionary history of female colour polymorphisms

Colour polymorphisms are popular study systems among biologists interested in evolutionary dynamics, genomics, sexual selection and sexual conflict. In many damselfly groups, such as in the globally distributed genus Ischnura (forktails), sex-limited female colour polymorphisms occur in multiple species. Female-polymorphic species contain two or three female morphs, one of which phenotypically matches the male (androchrome or male mimic) and the other(s) which are phenotypically distinct from the male (heterochrome). These female colour polymorphisms are thought to be maintained by frequency-dependent sexual conflict, but their macroevolutionary histories are unknown, due to the lack of a robust molecular phylogeny. Here, we present the first time-calibrated phylogeny of Ischnura, using a multispecies coalescent approach (StarBEAST2) and incorporating both molecular and fossil data for 41 extant species (55% of the genus). We estimate the age of Ischnura to be between 13.8 and 23.4 millions of years, i.e. Miocene. We infer the ancestral state of this genus as female monomorphism with heterochrome females, with multiple gains and losses of female polymorphisms, evidence of trans-species female polymorphisms and a significant positive relationship between female polymorphism incidence and current geographic range size. Our study provides a robust phylogenetic framework for future research on the dynamic macroevolutionary history of this clade with its extraordinary diversity of sex-limited female polymorphisms.

Colour polymorphism influences species' range and extinction risk

Polymorphisms in a population are expected to increase the growth rate and the stability of the population, leading to the expansion of geographical distribution and mitigation of extinction risk of a species. However, the generality of such ecological consequences of colour polymorphism remains uncertain. Here, via a comparative approach, we assessed whether colour polymorphisms influence climatic niche breadth and extinction risk in some groups of damselflies, butterflies and vertebrates. The climatic niche breadth was greater, and extinction risk was lower in polymorphic species than in monomorphic species in all taxa analysed. The results suggest that colour polymorphism facilitates range expansion and species persistence.