Asymmetric introgression reveals the genetic architecture of a plumage trait

Abstract

Genome-wide variation in introgression rates across hybrid zones offers a powerful opportunity for studying population differentiation. One poorly understood pattern of introgression is the geographic displacement of a trait implicated in lineage divergence from genome-wide population boundaries. While difficult to interpret, this pattern can facilitate the dissection of trait genetic architecture because traits become uncoupled from their ancestral genomic background. We studied an example of trait displacement generated by the introgression of head plumage coloration from personata to alba subspecies of the white wagtail. A previous study of their hybrid zone in Siberia revealed that the geographic transition in this sexual signal that mediates assortative mating was offset from other traits and genetic markers. Here we show that head plumage is associated with two small genetic regions. Despite having a simple genetic architecture, head plumage inheritance is consistent with partial dominance and epistasis, which could contribute to its asymmetric introgression.

The genetic basis of spatial cognitive variation in a food-caching bird

“…This analysis revealed little ability of predicting an individual's phenotype based on its genotype (r 2 = 0.0027, p = 0.74; Figure S1), likely due to a modest sample size unable to provide predictive power. Partial dominance and epistasis can create a non-linear relationship between genotype and phenotype even in traits with a simple genetic architecture (e.g., Semenov et al 26 ), and such effects are expected to accumulate rapidly with an increasing number of causal variants. It is important to note that BSLMM may overestimate the heritability of phenotypes; 25 combined with our rather small sample size, these results should be interpreted with caution.…”

Evolution of assortative mating following selective introgression of pigmentation genes between two Drosophila species

“…By contrast, when Amlou et al (1997) tried to introgress resistance to a fruit toxin from D. sechellia into D. simulans, their attempt has failed, likely due to the difficulty of measuring toxicity and to the polygenic nature of survival as a phenotype. Indeed, many known cases of cross-species adaptive introgression involve color variation, e.g., coat in wolves (Anderson et al 2009), skin and hair colors in humans (Dannemann and Kelso 2017), wing patterns in mimetic butterflies (Edelman et al 2019), winter-coats in hares (Giska et al 2019), plumage in pigeons (Vickrey et al 2018) and wagtails (Semenov et al 2021), and beaks in Darwin's finches (Enbody et al 2021).…”

Extensive introgression despite Haldane’s rule: insights from grasshopper hybrid zones

“…The observation that the amount of introgression decreases with the geographic distance to the current hybrid zone suggests that introgression is at least partially explained by gene flow after the recent secondary contact. The observation of extensive rates of introgression in spite of strong reproductive barriers has been described in multiple hybridising systems, such as in birds (Poelstra et al, 2014;Semenov et al, 2021), butterflies (Heliconius Genome Consortium, 2012), and mice (Teeter et al, 2007). Future studies of differential patterns of introgression across the genome may help in pinpointing the genes that resist to such prevailing pattern of genome wide introgression (Rafati et al, 2018;Turner & Harr, 2014), and therefore that are involved in barriers to gene flow (Barton & Hewitt, 1989;Harrison & Larson, 2014).…”