Biology subjects

Brien, M. N.

Publications and source records attributed to Brien, M. N..

4 recordsLinked to original sources

bioRxiv2026

Independent major-effect loci and limited trait associations characterise warning colour variation across sexes and life stages in the wood tiger moth (Arctia plantaginis)

Variation in warning colouration is common, despite strong positive frequency-dependent selection favouring the most common morph, and may arise from spatially or temporally variable selection or associations with other traits. We investigated the maintenance of warning colour variation in the wood tiger moth, Arctia plantaginis, which shows sexual dimorphism in colouration: two distinct male morphs controlled by a single locus, and continuous variation in female hindwing colour and larval warning signal size. Using whole-genome sequencing of 657 individuals from a laboratory stock derived from a wild polymorphic population, we examined the genetic basis of multiple life-history traits, chemical defence, pheromones, and male activity. We specifically tested for associations with male colour and aimed to identify the genetic basis of female and larval colour variation. We detected separate major-effect loci for female colour and larval signal size, which were different from the male colour locus. Hindwing melanism was the only trait associated with male colour, mapping to a nearby major-effect locus and showing a link to reduced activity at higher temperatures. Female colour was phenotypically correlated with pheromone amount. However, apart from melanism, none of the other traits measured showed an association with any of the loci controlling warning colours and we found no evidence that male colour is part of a supergene or complex co-adapted phenotype. Instead, our results indicate largely independent genetic architectures for warning colours suggesting that variable selection rather than genetic associations may contribute to the maintenance of colour polymorphisms in this species.

evolutionary biology↗

bioRxiv2022

Colour polymorphism associated with a gene duplication in male wood tiger moths

Colour is often used as an aposematic warning signal, with predator learning expected to lead to a single colour pattern within a population. However, there are many puzzling cases where aposematic signals are also polymorphic. The wood tiger moth, Arctia plantaginis, displays bright hindwing colours associated with unpalatability, and males have discrete colour morphs which vary in frequency between localities. In Finland, both white and yellow morphs can be found, and these colour morphs also differ in behavioural and life-history traits. Here, we show that male colour is linked to an extra copy of a yellow family gene that is only present in the white morphs. This white-specific duplication, which we name valkea, is highly upregulated during wing development, and CRISPR knockouts validate the role of valkea in producing white wing colour. We also characterise the pigments responsible for yellow, white and black colouration, showing that yellow is partly produced by pheomelanins, while black is dopamine-derived eumelanin. Our results add to a growing number of studies on the genetic architecture of complex and seemingly paradoxical polymorphisms, and the role of gene duplications and structural variation in adaptive evolution.

evolutionary biology↗

bioRxiv2021

The genetic basis of structural colour variation in mimetic Heliconius butterflies

Structural colours, produced by the reflection of light from ultrastructures, have evolved multiple times in butterflies. Unlike pigmentary colours and patterns, little is known about the genetic basis of these colours. Reflective structures on wing-scale ridges are responsible for iridescent structural colour in many butterflies, including the Mullerian mimics Heliconius erato and Heliconius melpomene. Here we quantify aspects of scale ultrastructure variation and colour in crosses between iridescent and non-iridescent subspecies of both of these species and perform quantitative trait locus (QTL) mapping. We show that iridescent structural colour has a complex genetic basis in both species, with offspring from crosses having wide variation in blue colour (both hue and brightness) and scale structure measurements. We detect two different genomic regions in each species that explain modest amounts of this variation, with a sex-linked QTL in H. erato but not H. melpomene. We also find differences between species in the relationships between structure and colour, overall suggesting that these species have followed different evolutionary trajectories in their evolution of structural colour. We then identify genes within the QTL intervals that are differentially expressed between subspecies and/or wing regions, revealing likely candidates for genes controlling structural colour formation.

evolutionary biology↗

bioRxiv2020

Limited genetic parallels underlie convergent evolution of quantitative pattern variation in mimetic butterflies

Mimetic systems allow us to address the question of whether the same genes control similar phenotypes in different species. Although widespread parallels have been found for major effect loci, much less is known about genes that control quantitative trait variation. In this study, we identify and compare the loci that control subtle changes in the size and shape of forewing pattern elements in two Heliconius butterfly co-mimics. We use quantitative trait locus (QTL) analysis with a multivariate phenotyping approach to map the variation in red pattern elements across the whole forewing surface of Heliconius erato and Heliconius melpomene. These results are compared to a QTL analysis of univariate trait changes, and show that our resolution for identifying small effect loci is improved with the multivariate approach. QTL likely corresponding to the known patterning gene optix were found in both species but otherwise, a remarkably low level of genetic parallelism was found. This lack of similarity indicates that the genetic basis of convergent traits may not be as predictable as assumed from studies that focus solely on Mendelian traits.

evolutionary biology↗