Genetic structure, UV-vision, wing coloration and size coincide with colour polymorphism in Fabriciana adippe butterflies.

Colour polymorphisms have long served as model systems in evolutionary studies and continue to inform about processes involved in the origin and dynamics of biodiversity. Modern sequencing tools allow for evaluating whether phenotypic differences between morphs reflect genetic differentiation rather than developmental plasticity, and for investigating whether polymorphisms represent intermediate stages of diversification towards speciation. We investigated phenotypic and genetic differentiation between two colour morphs of the butterfly Fabriciana adippe using a combination of ddRAD-sequencing and comparisons of body size, colour patterns and optical properties of bright wing spots. The silvery-spotted adippe form had larger and darker wings and reflected UV light, while the yellow cleodoxa form displayed more green scales and reflected very little UV, showcasing that they constitute distinct and alternative integrated phenotypes. Genomic analyses revealed genetic structuring according to source population, and to colour morph, suggesting that the phenotypic differentiation reflects evolutionary modifications. We report 17 outlier loci associated with colour morph, including ultraviolet-sensitive visual pigment (UVRh1), which is associated with intraspecific communication and mate choice in butterflies. Together with the demonstration that the wings of the adippe (but essentially not the cleodoxa) morph reflect UV light, that UV reflectance is higher in females than males and that morphs differ in wing size, this suggests that these colour morphs might represent genetically integrated phenotypes, possibly adapted to different microhabitats. We propose that non-random mating might contribute to the differentiation and maintenance of the polymorphism.

Linking large-scale genetic structure of three Argynnini butterfly species to geography and environment.

Understanding which factors and processes are associated with genetic differentiation within and among species remains a major goal in evolutionary biology. To explore differences and similarities in genetic structure and its association with geographical and climatic factors in sympatric sister species, we conducted a large-scale (>32° latitude and >36° longitude) comparative phylogeographical study on three Argynnini butterfly species (Speyeria aglaja, Fabriciana adippe and F. niobe) that have similar life histories, but differ in ecological generalism and dispersal abilities. Analyses of nuclear (ddRAD-sequencing derived SNP markers) and mitochondrial (COI sequences) data revealed differences between species in genetic structure and how genetic differentiation was associated with climatic factors (temperature, solar radiation, precipitation, wind speed). Geographical proximity accounted for much of the variation in nuclear and mitochondrial structure and evolutionary relationships in F. adippe and F. niobe, but only explained the pattern observed in the nuclear data in S. aglaja, for which mitonuclear discordance was documented. In all species, Iberian and Balkan individuals formed genetic clusters, suggesting isolation in glacial refugia and limited postglacial expansion. Solar radiation and precipitation were associated with the genetic structure on a regional scale in all species, but the specific combinations of environmental and geographical factors linked to variation within species were unique, pointing to species-specific responses to common environments. Our findings show that the species share similar colonization histories, and that the same ecological factors, such as niche breadth and dispersal capacity, covary with genetic differentiation within these species to some extent, thereby highlighting the importance of comparative phylogeographical studies in sympatric sister species.

Size, connectivity and edge effects of stream habitats explain spatio-temporal variation in brown trout (Salmo trutta) density.

Ecological theory postulates that the size and isolation of habitat patches impact the colonization/extinction dynamics that determine community species richness and population persistence. Given the key role of lotic habitats for life-history completion in rheophilic fish, evaluating how the distribution of swift-flowing habitats affects the abundance and dynamics of subpopulations is essential. Using extensive electrofishing data, we show that merging island biogeography with meta-population theory, where lotic habitats are considered as islands in a lentic matrix, can explain spatio-temporal variation in occurrence and density of brown trout (Salmo trutta). Subpopulations in larger and less isolated lotic habitat patches had higher average densities and smaller between-year density fluctuations. Larger lotic habitat patches also had a lower predicted risk of excessive zero-catches, indicative of lower extinction risk. Trout density further increased with distance from the edge of adjacent lentic habitats with predator (Esox lucius) presence, suggesting that edge- and matrix-related mortality contributes to the observed patterns. These results can inform the prioritization of sites for habitat restoration, dam removal and reintroduction by highlighting the role of suitable habitat size and connectivity in population abundance and stability for riverine fish populations.