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.
Abstract Hybridization is increasingly recognized as an important evolutionary process that can reshape genomes and generate novel lineages. One striking outcome is the origin of obligately parthenogenetic populations, often through interspecific hybridization. Here, we use genome-wide data and coalescent models to reconstruct the evolutionary history of Liolaemus parthenos, the only known parthenogenetic pleurodont lizard. We sampled the darwinii complex (L. darwinii, L. grosseorum, L. laurenti, and L. parthenos) and L. josei from the donosobarrosi group, selected as a candidate paternal lineage based on phylogenetic and biogeographic evidence. Mitochondrial data place L. parthenos within northern L. darwinii, consistent with a maternal origin, whereas nuclear genomic summaries position it between L. darwinii and L. josei. Bayesian model comparison supports a hybrid speciation model involving northern L. darwinii and L. josei, rejecting alternative parental combinations and models without introgression. Triangle plots further support a stabilized hybrid lineage. Climatic niche analyses reveal strong divergence from northern L. darwinii but substantial overlap with L. josei, partially supporting geographical parthenogenesis. More broadly, our study demonstrates the utility of model-based genomic approaches for resolving hybrid origins in non-model systems and expands the comparative framework for understanding the emergence and persistence of asexual vertebrate lineages.
Abstract Egg size represents a primary form of parental investment, but whether it is causally related to offspring fitness is difficult to establish. We mated Japanese quail (Coturnix japonica) from replicated selection lines for high and low maternal investment in egg size to partners from the same and alternate selection line. We combined this with detailed pedigree information to partition variation in the size and hatching success of their eggs into their underlying genetic and non-genetic components, and estimated the correlation between these traits at all levels. Variation in egg size was primarily explained by additive genetic variation among mothers (h2 = 65%) and variation in hatching success also had an additive genetic component among mothers (h2 = 16%), with little evidence for additive effects of the father on both traits. Importantly, the correlations between egg size and hatching success were positive and similar at the genetic level among mothers and the non-genetic level within mothers. Furthermore, in one of the two replicates, the eggs from females selected for high maternal investment in egg size had higher hatching success. We interpret these results as being most parsimoniously explained by a positive causal effect of egg size on hatching success.
