Genomic introgression from a distant congener in the Levant fritillary butterfly, Melitaea acentria

Abstract

Introgressive hybridization is more common in nature than previously thought, and its role and creative power in evolution is hotly discussed but not completely understood. Introgression occurs more frequently in sympatry between recently diverged taxa, or when the speciation process has not yet been completed. However, there are relatively few documented cases of hybridization that erodes reproductive barriers between distantly related species. Here, we use whole genome and mitochondrial data to examine how introgression from a distant congener affects pattern of genetic differentiation in the Levant fritillary butterfly Melitaea acentria. We show that this local taxon has evolved as a peripatric geographic isolate of the widespread Melitaea persea, and that there has been significant unidirectional gene flow from the sympatric, nonclosely related Melitaea didyma to M. acentria. We found direct evidence of ongoing sporadic hybridization between M. didyma and M. acentria, which are separated by at least 5 million years of independent evolution. Elevated differentiation and lower level of introgression on the sex Z chromosome compared to autosomes suggest that the Z chromosome has accumulated loci acting as intrinsic postzygotic barriers. Our results show that introgression from M. didyma has been an additional source of nucleotide diversity in the M. acentria population, providing material for drift and selection.

Linked selection, differential introgression and recombination rate variation promote heterogeneous divergence in a pair of yellow croakers

“…Above all, differential gene flow is a major factor promoting genomic islands of interspecific divergence in the second phase of divergence under secondary contact scenario. The reduced introgression in low‐recombining regions is probably related to the effects of linked selection, divergent sorting of ancient polymorphisms, genetic drift, accumulation of different mutations and selection against introgressed alleles from the alternated species due to for example, genetic incompatibilities (Jahner et al, 2021 ; Martin & Jiggins, 2017 ; Pazhenkova & Lukhtanov, 2021 ).…”

Chromosomal conservatism vs chromosomal megaevolution: enigma of karyotypic evolution in Lepidoptera

“…Sex chromosomes evolve faster than autosomes (Charlesworth et al, 2018; Mongue et al, 2022), and, at the same time, in case of interspecific hybridization, are less prone to introgression than autosomes (Martin et al, 2013; Pazhenkova & Lukhtanov, 2021). Both phenomena explain the exceptional role of sex chromosomes in speciation.…”

Discerning structure versus speciation in phylogeographic analysis of Seepage Salamanders (Desmognathus aeneus) using demography, environment, geography, and phenotype

“…While substantial differences may exist between germ‐line mutation and long‐term substitution rates, this issue has not been evaluated in‐depth and recent studies have used values of 6e‐9–1e‐8 for amphibians and reptiles (see Burbrink, Bernstein, et al., 2022; Gehara et al., 2017 and references therein). Similarly, recent authors using GADMA employed rates of ~1–4e‐9 for analyses of butterflies, crustaceans, molluscs, and rodents (Agwamba & Nachman, 2023; Amador et al., 2022; Pazhenkova & Lukhtanov, 2021; Peluso et al., 2023). To account for this range of variation, we ran additional analyses with mutation rates of 2e‐9 and 1e‐8 to provide a range of parameter estimates under plausible empirical variation in substitution dynamics.…”