Abstract The shared genome prevents independent responses to sex differences in selection. Each sex does not evolve in response to its own sex-specific selection but is influenced by selection on the other sex via the shared genome. We used experimental evolution in Drosophila melanogaster to create separate pools of Chromosome 3s for males (male-limited “ML” chromosomes) and females (female-limited “FL” chromosomes), thereby separating the gene pool, for 15 generations. Viewing each sex as a separate environment, this separation of the genome allows sex-specific adaptation to each sex environment. We performed a reciprocal transplant between the sexes to quantify the strength of local adaptation to each sex. We found each chromosome type was more beneficial in the sex it had been selected for (i.e., local adaptation to sex). Because it has been postulated that sex-differences in selection may depend on how well adapted a population is to the abiotic environment, we performed experimental evolution at two thermal regimes (3 replicate populations each): one benign temperature to which the populations were well-adapted and one novel temperature. Female-specific adaptation was stronger at the benign temperature whereas male-specific adaptation was stronger in the novel temperature. Within chromosome pools, male and female fitness were more positively correlated in the novel compared to the benign conditions. Though males carrying ML chromosomes were typically more fit than males carrying FL chromosomes, they were also more harmful to their female mating partners.
Abstract In the context of global change, such as climate change, resurrection ecology—where ancestors and descendants are phenotyped in a common environment—has recently emerged as a powerful method for characterizing evolution. This approach has been applied across diverse organisms, provided they possess a dormant stage in their life cycle. While limitations have been raised (e.g., the impact of propagule storage on phenotypes), methodological solutions have also been developed. Here, we identify metapopulation dynamics and within-population selection as a potential drivers of evolutionary change in resurrection ecology studies. Using a simple population genetic model, we show how allele frequencies can change with population age. Second, we propose a method to disentangle the evolutionary effects of metapopulation dynamics from those driven by external factors such as climate change. The method is based on the analysis of a set of populations at the initial sampling time and a new, independent set of populations after a given period, moving beyond from the classical “ancestor-descendant” paired approach.
Abstract Mito-nuclear discordance can obscure the interpretation of evolutionary history, particularly in fragmented systems where multiple processes can generate similar phylogenetic patterns. We investigated pronounced discordance between mitochondrial and nuclear genomes in two parapatric montane skinks, Sphenomorphus taiwanensis and S. luelaiorum, from Taiwan’s sky islands. Using mitochondrial sequences and genome-wide ddRAD-seq SNPs, we evaluated incomplete lineage sorting, introgression, and ghost introgression as alternative explanations, while assessing sex-biased dispersal, selection, and demographic history. Model-based analyses supported historical introgression between extant lineages but provided little evidence for ghost introgression. An expanded coalescent analysis favored bidirectional over unidirectional introgression. Genomic indices showed no consistent sex-biased dispersal, whereas mitochondrial selection signals were restricted to particular lineages. Coalescent estimates and forward simulations indicated that small effective population sizes could increase the probability of mitochondrial capture. We interpret the discordance as the outcome of ancestral bidirectional introgression followed by genetic drift in isolated montane populations, with selection potentially facilitating fixation under high-altitude conditions. These findings illustrate how gene flow and demographic processes in fragmented landscapes can generate persistent mito-nuclear discordance, underscoring the importance of integrating genomic and ecological evidence when interpreting mitochondrial phylogenies.
Abstract Threshold traits are widespread forms of dimorphism in which an underlying continuous liability produces discrete phenotypes once a threshold is crossed. The threshold trait model predicts that phenotypic variation will be observed only when the distribution of liability spans the threshold, and may otherwise remain latent, complicating predictions of how genetic and environmental variation shape responses to selection. We tested this prediction in the wing-polymorphic cricket Gryllus lineaticeps, in which wing length is a heritable, plastic threshold trait with an endocrine basis. We confirmed the final juvenile instar as the sensitive period for wing-morph determination and validated general esterase activity as a predictor of adult wing morph. We manipulated genetic variation in liability through directional selection on wing morph and then measured plasticity in wing morph and esterase activity. Selected populations, predicted to have extreme liability distributions not spanning the threshold, were non-plastic for wing-morph frequency despite maintaining plasticity in esterase activity. Thus, physiological plasticity persisted but became cryptic at the morphological level. These results support predictions of the threshold trait model and demonstrate that shifts in the liability distribution can mask environmental sensitivity, providing a framework for understanding the dynamic evolution and role of phenotypic plasticity in threshold traits.
Abstract Light environments dictate how effective the colours that species adopt are for signalling or certain physiological functions, such as UV protection. Beltrán et al. (2026) show that light environments may, however, play only a marginal role in shaping variation in colour for hummingbird plumage, while sex and phylogeny are primary drivers of variation. These findings raise several questions about how hummingbirds overcome the demands of their light environment on their plumage colour and how colour evolves.
