The Pleistocene species pump past its prime: Evidence from European butterfly sister species

Abstract

Divergence in allopatry provides a simple null model of speciation (Mayr, 1947). Following geographic isolation and given enough time, reproductive isolation is inevitable as incompatibilities will eventually become fixed as a result of genetic drift and/or selection (Bateson, 1909;Dobzhansky, 1937;Muller, 1942). Taxa that evolved partial reproductive isolation in allopatry may come into secondary contact as a result of range shifts and-depending on their degree of reproductive isolation and niche overlap-either form a contact zone or invade each other's range (Barton, 1985;Pigot, 2013). If allopatric divergence dominates speciation, then local alpha diversity for a given clade cannot accrue until secondary sympatry is achieved (Weir & Price, 2011). Thus, the forces that facilitate or hamper secondary sympatry and the timescale over which this occurs have profound consequences both for speciation and for the spatial distribution of species diversity. While modern ranges only provide a snapshot of the dynamic history of range shifts, understanding the

The genome sequence of the scarce swallowtail, Iphiclides podalirius

“…We note that our estimate of 4D site heterozygosity is comparable, but slightly higher, than π 4D estimates previously reported for I. podalirius based on transcriptome assemblies and data from two individuals (0.0052, 0.0057) (Ebdon et al 2021;Mackintosh et al 2019). This difference most likely reflects the fact that transcriptome assemblies are biased towards highly expressed transcripts which experience greater indirect effects of purifying selection (Marek and Tomala 2018).…”

Delimiting Continuity: Comparison of Target Enrichment and ddRAD for Delineating Admixing Parapatric Melitaea Butterflies

“…Parapatric taxa tend to be morphologically and ecologically very similar, and morphologically intermediate individuals may occur (Saino and Villa 1992; Guiller et al 2017; Slender et al 2017). From a temporal perspective, parapatric systems are presumably usually young – although initial differentiation may be much older (Ebdon et al 2021) – and may have undergone either slow merging of populations or increased differentiation, the latter being promoted by disruptive selection and reinforcement (Barton and Hewitt 1985). These complexities also characterize our study system, which we assume is resulting from a postglacial secondary contact of populations differentiated in two refugia during the last glaciation, and possibly in earlier ones (Tahami et al 2021).…”

Extensive introgression at late stages of species formation: Insights from grasshopper hybrid zones

“…Most of the current knowledge on Haldane’s rule stems from experimental crosses between highly divergent species, namely drosophilids (Masly & Presgraves, 2007; Payseur et al, 2018; Presgraves, 2018; Presgraves & Meiklejohn, 2021) that speciated between 4,000,000 and 300,000 years ago (Kliman et al, 2000; Wang & Hey, 1996). With some exceptions (Ebdon et al, 2021; Matute, 2010; Teeter et al, 2007), these species rarely hybridize in nature and laboratorial hybrids are often lethal or inviable (Matute & Cooper, 2021). Thus, incompatibilities manifested in these systems may have arisen after reproductive isolation has been established (Coyne, 2018; Matute, 2010), questioning their role in limiting gene flow between incipient species and hence in facilitating species formation.…”