Hierarchical genetic structure shaped by topography in a narrow-endemic montane grasshopper

Abstract

BackgroundUnderstanding the underlying processes shaping spatial patterns of genetic structure in free-ranging organisms is a central topic in evolutionary biology. Here, we aim to disentangle the relative importance of neutral (i.e. genetic drift) and local adaptation (i.e. ecological divergence) processes in the evolution of spatial genetic structure of the Morales grasshopper (Chorthippus saulcyi moralesi), a narrow-endemic taxon restricted to the Central Pyrenees. More specifically, we analysed range-wide patterns of genetic structure and tested whether they were shaped by geography (isolation-by-distance, IBD), topographic complexity and present and past habitat suitability models (isolation-by-resistance, IBR), and environmental dissimilarity (isolation-by-environment, IBE).ResultsDifferent clustering analyses revealed a deep genetic structure that was best explained by IBR based on topographic complexity. Our analyses did not reveal a significant role of IBE, a fact that may be due to low environmental variation among populations and/or consequence of other ecological factors not considered in this study are involved in local adaptation processes. IBR scenarios informed by current and past climate distribution models did not show either a significant impact on genetic differentiation after controlling for the effects of topographic complexity, which may indicate that they are not capturing well microhabitat structure in the present or the genetic signal left by dispersal routes defined by habitat corridors in the past.ConclusionsOverall, these results indicate that spatial patterns of genetic variation in our study system are primarily explained by neutral divergence and migration-drift equilibrium due to limited dispersal across abrupt reliefs, whereas environmental variation or spatial heterogeneity in habitat suitability associated with the complex topography of the region had no significant effect on genetic discontinuities after controlling for geography. Our study highlights the importance of considering a comprehensive suite of potential isolating mechanisms and analytical approaches in order to get robust inferences on the processes promoting genetic divergence of natural populations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0663-7) contains supplementary material, which is available to authorized users.

Genomic data reveal deep genetic structure but no support for current taxonomic designation in a grasshopper species complex

“…Accordingly, landscape genetic analyses indicated that genetic differentiation was explained by both the geographical distance among populations and resistance distances defined by topographic roughness (Table ). These results might reflect the low dispersal capability of the studied taxon, males being brachypterous and females micropterous, and are comparable to those obtained by previous studies showing the impact of steep slopes and complex landscapes on structuring genetic variation in montane/alpine grasshoppers (Noguerales, Cordero, et al, ). Genetic structure analyses showed that the split of the different populations at local/regional scales followed a longitudinal cline rather than a segregation of alpine and Mediterranean‐montane populations (e.g., SET and BAT), indicating no support for either ecologically driven divergence or the taxonomic separation between the supposedly Mediterranean O. navasi and the alpine O. antigai .…”

“…Collectively, our analyses rejected the current hypothesis of two species and indicated that populations assigned to O. antigai and O. navasi show a distribution of genetic variation that (a) does not match with their respective taxonomic designation and (b) is incompatible with ecological/environmental speciation. Our results show the presence of two main genetic groups corresponding to an east–west split analogous to that found in many other Pyrenean taxa (Wallis, Waters, Upton, & Craw, ) and a marked genetic differentiation at local spatial scales reflecting limited population connectivity across the abrupt landscapes characterizing the study region (e.g., Noguerales, Cordero, & Ortego, ).…”

Testing the role of ancient and contemporary landscapes on structuring genetic variation in a specialist grasshopper

“…We used a backward procedure to select final models, eliminating nonsignificant variables from an initial full model including all explanatory predictors. We tested the significance of the remaining variables again until no additional term reached significance (Noguerales et al., ; Ortego, Gugger,et al., ).…”

The roles of geography, climate and sexual selection in driving divergence among insect populations on mountaintops

“…In this study, we assess the potential role of geography, environment (specifically climate) and female preference in modelling spatial patterns of genetic and phenotypic (morphological and acoustic) divergence in Chorthippus cazurroi (Bolívar, 1898), an annual alpine grasshopper endemic to the Cantabrian Mountains, north‐western Spain. Previous studies have shown that isolation and habitat determined genetic and phenotypic differentiation in grasshoppers (Hernández‐Teixidor et al., ; Noguerales, Cordero, & Ortego, ; Ortego, Aguirre, & Cordero, ; Sathyan, Engelbrecht, & Couldridge, ). Orthopterans represent also an ideal model to address sexual selection issues (Greenfield, ; Robinson & Hall, ), since female uses male song and morphology both for species recognition and selection between conspecific males (Klappert & Reinhold, ; Saldamando et al., ).…”