Lurig, M. D. | bioRxiv Science

bioRxiv2025

Nutritional effects on the expression of cryptic pigmentation in freshwater isopods

Cryptic pigmentation is a key phenotypic adaptation that helps many invertebrates evade visual predators. However, little is known about whether and how the expression of pigmentation phenotypes that match the habitat background is influenced by the availability of nutritional resources. Here we investigated whether variation in both the background and the nutritive composition of benthic substrates affect the expressed pigmentation of freshwater isopods (Asellus hilgendorfii). We collected isopods and their predominant substrate from 17 locations across Hokkaido, northern Japan, and quantified substrate background and nutritional composition (total protein, 18 amino acids, and C:N and C:P ratios). We found that variation in isopod pigmentation was better explained by the substrates nutritive composition than by its background darkness. Specifically, isopods were more pigmented when substrates had intermediate C:P ratios, lower C:N ratios, and a higher proportion of tryptophan - an essential amino acid involved in the isopods pigmentation pathway. These results are consistent with previous experiments showing that isopods reared under diets with higher protein concentrations developed more pigmentation, advancing our understanding about the environmental sources of phenotypic variation in natural populations. By demonstrating that nutritional constraints may shape the expression of key phenotypic adaptations in natural populations, our study opens new directions for exploring how organisms navigate adaptive landscapes; particularly in those organisms that rely on pigmentation for signaling and camouflage. Finally, we demonstrate how macronutrients, amino acids, and elemental ratios can serve as biotracers in ecological studies of adaptation, offering new opportunities to examine how stoichiometric traits influence phenotypic plasticity and adaptive capacity, especially in detritivorous taxa.

ecology↗

bioRxiv2024

Morph-specific selection pressures drive phenotypic divergence in a color polymorphic bird

There is a long tradition of using heritable color polymorphisms in natural populations to study selection, gene flow, and other evolutionary processes. However, we still have only limited knowledge on how continuous color variation within genetically discrete morphs affects selective dynamics, which narrows our understanding of how color polymorphisms persist. Our comprehensive analysis of 43 years of plumage color scores from a bi-morphic Finnish population of tawny owls (Strix aluco) reveals that intra-morph variation is substantial, but also unexpectedly dynamic. We show that both morphs recently diverged in their plumage coloration: while the brown morph is on a steady trajectory toward more intense plumage pigmentation, the gray morph has recently shifted toward lighter plumage, following a series of extreme winters. Evidence suggests that this divergence is driven by the brown morphs higher reproductive success and greater plasticity in response to seasonality, while the gray morph, with its more genetically determined plumage color and limited standing variation, has a reduced capacity to respond to selection and track new phenotypic optima. Our study confirms the presence of substantial and dynamic phenotypic variation within genetically discrete color morphs, and demonstrates its relevance for the evolutionary potential of populations to respond to environmental change.

evolutionary biology↗