Hybridization Reveals the Evolving Genomic Architecture of Speciation

Abstract

SUMMARYThe rate at which genomes diverge during speciation is unknown, as are the physical dynamics of the process. Here, we compare full genome sequences of 32 butterflies, representing five species from a hybridizing Heliconius butterfly community, to examine genome-wide patterns of introgression and infer how divergence evolves during the speciation process. Our analyses reveal that initial divergence is restricted to a small fraction of the genome, largely clustered around known wing-patterning genes. Over time, divergence evolves rapidly, due primarily to the origin of new divergent regions. Furthermore, divergent genomic regions display signatures of both selection and adaptive introgression, demonstrating the link between microevolutionary processes acting within species and the origin of species across macroevolutionary timescales. Our results provide a uniquely comprehensive portrait of the evolving species boundary due to the role that hybridization plays in reducing the background accumulation of divergence at neutral sites.

Multilocus Species Trees Show the Recent Adaptive Radiation of the Mimetic Heliconius Butterflies

“…Heliconiini have been at the center of the debate about species concepts and designation criteria, providing empirical evidence for the permeability of species barriers Nadeau et al 2013;Kronforst et al 2013;Martin et al 2013). Species delimitation with the PTP based on relative branch lengths in the ML tree produced very surprising, although poorly supported results, strongly at odds with biological knowledge of Heliconiini.…”

No evidence for maintenance of a sympatricHeliconiusspecies barrier by chromosomal inversions

“…Modeling suggests that the species diverged around 1.5 million years ago, with hybridization rare or absent for one million years, followed by a period of more abundant gene flow in the last half a million years (Kronforst et al. 2013; Martin et al. 2015b), suggesting that the species originated in parapatry, but have been broadly sympatric and hybridizing during their recent history.…”

Quantified reproductive isolation in Heliconius butterflies: Implications for introgression and hybrid speciation

“…Heliconius butterflies have likewise become a model system for studying patterns of speciation in the putative presence of ongoing gene flow (Dasmahapatra et al., 2012; Kronforst et al., 2006, 2013; Nadeau et al., 2013). Most Heliconius species are Müllerian mimics of one another, as well as other unpalatable taxa, displaying shared, aposematic wing patterns that are maintained by positive numerically dependent selection.…”