Behavioural mechanisms of reproductive isolation between two hybridizing dung fly species

Geographic patterns of postzygotic isolation between two closely related widespread dung fly species (Sepsis cynipseaandSepsis neocynipsea; Diptera: Sepsidae)

“…Contrary to the precopulatory behavioural traits investigated by Giesen et al. (), we here obtained only little evidence for reinforcement by natural selection in sympatric areas of the two species in the Swiss Alps (in egg production). Instead, generally strong reproductive barriers between the two species in para‐ and allopatric situations were evident, with similar barriers between the isolated continental populations of the same species ( S. neocynipsea ).…”

“…Strongest reproductive isolation is typically expected in sympatric species pairs following reinforcement and/or some sort of purging of genetic incompatibilities due to natural selection (Coyne & Orr, ; Turelli & Moyle, ; Via, , ). Contrary to a number of precopulatory behavioural traits (Giesen et al., ), we obtained only weak evidence for such reinforcement in sympatric areas (the Swiss Alps) for the (postcopulatory) fecundity traits assessed here (egg production only). It thus appears that precopulatory behavioural traits, which are inherently plastic and can potentially evolve fast, are of overriding importance in preventing hybridisation in nature in this and other systems (Eberhard, ; Puniamoorthy, ; Puniamoorthy et al., ; Beysard, Krebs‐Wheaton, & Heckel, ; Schmidt & Pfennig, ).…”

“…We here provided a thoroughly replicated, hierarchically subdivided case study of reproductive barriers in a pair of very closely related sepsid flies, by comparing three lineages (i.e., species and continental populations) at a continuum of stages in the speciation process (European sympatry, European parapatry, and cross‐continental allopatry). The sister species Sepsis cynipsea and S. neocynipsea differ in their behaviour and morphology (Giesen et al., ; Pont & Meier, ), with minor genetic differentiation evident at the mitochondrial COI and Cytb gene sequences (Su et al., ). North American and European S. neocynipsea , by contrast, are traditionally regarded as the same species based on great similarities in morphology and behaviour, although sexual size dimorphism is reversed on the two continents (Rohner et al., ) and microsatellite nuclear markers indicate substantial continental differences in population genetic structure ( F ST = 0.16; see Introduction).…”

“…More detailed descriptions of the maintenance of the flies in our laboratory and their behaviour can be found in Giesen et al. ().…”

Exaggerated male forelegs are not more differentiated than wing morphology in two widespread sister species of black scavenger flies

“…The sister species S. cynipsea (Linnaeus, 1758) and S. neocynipsea (Melander & Spuler, 1917) exhibit only little differentiation at the mitochondrial barcoding genes Cytochrome c oxidase I ( COI ) and Cytochrome b ( CyB ) (Su, Kutty, & Meier, ), but are differentiated in behavior, distribution, and ecology (Giesen et al, ; Pont & Meier, ; Puniamoorthy et al, ; Rohner et al, ). Sepsis cynipsea is the most abundant sepsid in north‐central Europe, where it occurs in sympatry with the rare S. neocynipsea in some mountainous regions such as the Swiss Alps (Rohner & Bächli, ; Rohner et al, ).…”