Consequences of reproductive barriers for genealogical discordance in the European corn borer

Abstract

Speciation involves the origin of trait differences that limit or prevent gene exchange and ultimately results in daughter populations that form monophyletic or exclusive genetic groups. However, for recently diverged populations or species between which reproductive isolation is often incomplete, gene genealogies will be discordant, and most regions of the genome will display nonexclusive genealogical patterns. In these situations, genome regions for which one or both species are exclusive groups may mark the footprint of recent selective sweeps. Alternatively, such regions may include or be closely linked to ''speciation genes,'' genes involved in reproductive isolation. Therefore, comparisons of gene genealogies allow inferences about the genetic architectures of both reproductive isolation and adaptation. Contrasting genealogical relationships in sexually isolated pheromone strains of the European corn borer moth (Ostrinia nubilalis) demonstrate the relevance of this approach. Genealogies for five gene regions are discordant, and only one molecular marker, the sex-linked gene Tpi, has evidence for pheromone strain exclusivity. Tpi maps to a position on the sex chromosome that is indistinguishable from a major factor (Pdd) affecting differences in postdiapause development time. The major factor (Resp) determining male behavioral response to pheromone is also sex-linked, but maps 20 -30 cM away. Exclusivity at Tpi may be a consequence of these linkage relationships because evidence from phenotypic variation in natural populations implicates both Pdd and Resp as candidates for genes involved in recent sweeps and͞or reproductive isolation between strains.genealogy ͉ genetic linkage map ͉ introgression ͉ selective sweep ͉ speciation

From Russia with lobe: genetic differentiation in trilobed uncus Ostrinia spp. follows food plant, not hairy legs

“…The first set is sex-linked, as often in lepidopteran incipient species (Prowell, 1998). It includes genes affecting post-diapause development time (Pdd: Glover et al, 1992;Dopman et al, 2005Dopman et al, , 2010, male behavioural response to different female sex pheromones (Resp: Glover et al, 1990;Dopman et al, 2004Dopman et al, , 2005Dopman et al, , 2010, differential success rate in larval development on either host plant (Calcagno et al, 2007) and/or other genes located in the vicinity of Tpi (Bourguet et al, 2000;Martel et al, 2003;Bontemps et al, 2004;Dopman et al, 2004Dopman et al, , 2005. The second set of candidates is autosomal and includes genes responsible for differences in female sex pheromones (Pher: Roelofs et al, 1987;Dopman et al, 2004Dopman et al, , 2010Lassance et al, 2010), an unidentified close-range mechanism ensuring assortative mating in laboratory settings (AssMat: Pélozuelo et al, 2007) and/or other genes located in the vicinity of Mpi (Bourguet et al, 2000;Martel et al, 2003;Bontemps et al, 2004).…”

A recombination suppressor contributes to ecological speciation in OSTRINIA moths

“…Markers consisted of Tpi at 9 Mb, Per at 13 Mb and Ldh at 17.4 Mb (International Silkworm Genome Consortium, 2008). We adopted methods developed elsewhere for Tpi and Ldh (Dopman et al, 2005), whereas initial Per sequence for the ECB was obtained using degenerate PCR.…”

“…Consequently, a major research theme has emerged that aims to characterize genome-wide patterns of differentiation between diverging populations, races and species. Pockets of divergence or 'genomic islands of speciation,' as well as larger 'continents,' have been uncovered and could reflect the effect of genes contributing to reproductive isolation ('barrier loci') (Dopman et al, 2005;Turner et al, 2005;Feder, Egan et al, 2012). However, connecting these fundamental genetic signatures with their biological cause remains elusive (Noor and Bennett, 2009;Dopman, 2011;Nachman and Payseur, 2012;Cruickshank and Hahn, 2014).…”

“…Current and historical gene exchange between ECB strains is likely, as indicated by hybridization in Europe and North America (Dopman et al, 2010;Coates et al, 2013), geographic variation in strength of reproductive isolation (ranging from 0.91 to 0.99; Dopman et al, 2010) and molecular evidence for an isolationwith-migration model of divergence (2 Nm~10; Malausa et al, 2007). Whereas most loci show extensive shared polymorphism (for example, F ST o0.05), a possible island of speciation along an~1-cM swath of the Z chromosome consists of four genes (Tpi and three olfactory receptors, ORs) and reveals ECB strains as nearly reciprocally monophyletic (for example, F ST 40.7; Dopman et al, 2005;Dopman, 2011;Lassance et al, 2011). Evolutionary divergence can be explained by several tightly linked barrier loci on the sex chromosome or by a regional selective sweep at these or other loci.…”

“…Strains are recently diverged (~100 000 ya; Malausa et al, 2007) and are textbook examples of speciation (Coyne and Orr, 2004), in which one species is splitting into two through the evolution of many forms of reproductive isolation (Dopman et al, 2010). The sex (Z) chromosome harbors several known genetic factors for adaptation and/or barrier traits, including those underlying behavioral isolation (Roelofs et al, 1987;Dopman et al, 2004) and temporal isolation (Glover et al, 1992;Dopman et al, 2005). Current and historical gene exchange between ECB strains is likely, as indicated by hybridization in Europe and North America (Dopman et al, 2010;Coates et al, 2013), geographic variation in strength of reproductive isolation (ranging from 0.91 to 0.99; Dopman et al, 2010) and molecular evidence for an isolationwith-migration model of divergence (2 Nm~10; Malausa et al, 2007).…”