Demographic consequences of dispersal‐related trait shift in two recently diverged taxa of montane grasshoppers*

Abstract

Although the pervasiveness of intraspecific wing‐size polymorphism and transitions to flightlessness have long captivated biologists, the demographic outcomes of shifts in dispersal ability are not yet well understood and have been seldom studied at early stages of diversification. Here, we use genomic data to infer the consequences of dispersal‐related trait variation in the taxonomically controversial short‐winged (Chorthippus corsicus corsicus) and long‐winged (Chorthippus corsicus pascuorum) Corsican grasshoppers. Our analyses revealed lack of contemporary hybridization between sympatric long‐ and short‐winged forms and phylogenomic reconstructions supported their taxonomic distinctiveness, rejecting the hypothesis of intraspecific wing polymorphism. Statistical evaluation of alternative models of speciation strongly supported a scenario of Pleistocene divergence (<1.5 Ma) with ancestral gene flow. According to neutral expectations from differences in dispersal capacity, historical effective migration rates from the long‐ to the short‐winged taxon were threefold higher than in the opposite direction. Although populations of the two taxa present a marked genetic structure and have experienced parallel demographic histories, our coalescent‐based analyses suggest that reduced dispersal has fueled diversification in the short‐winged C. c. corsicus. Collectively, our study illustrates how dispersal reduction can speed up geographical diversification and increase the opportunity for allopatric speciation in topographically complex landscapes.

Digest: Dispersal reduction drives rapid diversification in alpine grasshoppers

“…Ortego et al. (2021) thus illustrate the links between dispersal traits and both microevolutionary and macroevolutionary processes (Figure 1; see also Harvey et al. 2019).…”

“…In summary, Ortego et al. (2021) clearly demonstrated that shifts in dispersal‐associated traits can directly influence geographic structuring and intraspecific diversification in a topographically complex habitat. Increased rate of intraspecific diversification in the short‐winged lineages may ultimately lead to higher rates of speciation and interspecific diversification.…”

“…These results may suggest a strong selection against full-winged individuals across the distribution of the short-winged lineage, though further investigation is required to uncover the selective pressures driving flight loss in these environments. Ortego et al (2021) also identified significantly deeper divergences among populations of the short-winged lineage compared to populations of the long-winged lineage, with almost no contemporary migration detected among the short-winged populations. Their results reflect the differences in dispersal ability of the lineages, with less dispersive organisms often showing marked genetic structure, reduced gene flow, and increased diversification rates (Harvey et al 2019).…”

“…Ortego et al. (2021) also identified significantly deeper divergences among populations of the short‐winged lineage compared to populations of the long‐winged lineage, with almost no contemporary migration detected among the short‐winged populations. Their results reflect the differences in dispersal ability of the lineages, with less dispersive organisms often showing marked genetic structure, reduced gene flow, and increased diversification rates (Harvey et al.…”

“…In this issue, Ortego et al. (2021) used genomic data to test the evolutionary impacts of wing size reduction on two sister lineages of alpine grasshoppers from Corsica, a mountainous Mediterranean island. Chorthippus corsicus corsicus and C. c. pascuorum have similar ecological preferences but distinct wing size phenotypes: C. c. corsicus is short‐winged, while C. c. pascuorum is long‐winged.…”