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

Abstract

Aim Analysing the drivers of intraspecific variation and how reproductive barriers arise is an essential step to infer the mechanisms of biogeographic differentiation. In populations of a specialized alpine species, we explore the role of geography and climate in the divergence of genetic, morphological and acoustic characters, and analyse the functional consequences of variation on mate choice. Taxon Chorthippus cazurroi (Orthoptera: Caelifera, Acrididae, Gomphocerinae). Location The entire distribution of the species (23 populations from six massifs of the Cantabrian Mountains, NW Spain). Methods First, we analysed the extent of intraspecific spatial divergence and the covariation among climatic niche, genetic (mtDNA), acoustic (song structure) and morphological (body size) traits. Then, we analysed the consequences of phenotypic variation by means of a crossing experiment among populations from different elevations. This served to test for differences in sexual selection among body size‐divergent populations and for the relationship between male traits, female preference and reproduction. Results Genetic, morphologic and acoustic divergence increased with geographic distance. Female morphology was also affected by climate variation, while male one tightly covaried with the song differentiation. Females more closely approached males investing more time in song activities, but weakly responded to the rest of acoustic features and morphological variation. They also distanced themselves slightly more from males from different populations, although this behaviour did not lead to clear differences in reproductive parameters. Main conclusions The process of colonization of mountain massifs has led to significant genetic and phenotypic changes in C. cazurroi. Phenotypic divergence does not constitute a strong intrinsic barrier to reproduction and is largely unpaired from female preference, overall suggesting that sexual selection is a minor actor in the process of differentiation as compared, for instance, to drift. This does not exclude that traits associated with individual condition are under strong selection and, therefore, do not vary so extensively. This study dismisses the idea that alpine specialists with narrow distributions lack genetic and phenotypic variability, and highlights the importance of synthesizing biogeographic and experimental approaches to obtain stronger and deeper inferences about the dynamics and mechanisms of biological differentiation.

Gradual Distance Dispersal Shapes the Genetic Structure in an Alpine Grasshopper

“…Our results suggest that after glacial retreat, Chorthippus cazurroi started a process of slow and gradual range expansion along the Cantabrian sky islands using, most likely, narrow alpine corridors to achieve its current distribution (Figure 2). Our findings also show a slight genetic differentiation of new founded populations, probably due to local adaptations and genetic drift [36,39]. Interestingly, our findings suggest a scenario where gene flow could be mostly determined by the proximity of neighbouring populations, which agrees with the pattern of isolation by distance found in this species [39].…”

“…Our findings also show a slight genetic differentiation of new founded populations, probably due to local adaptations and genetic drift [36,39]. Interestingly, our findings suggest a scenario where gene flow could be mostly determined by the proximity of neighbouring populations, which agrees with the pattern of isolation by distance found in this species [39].…”

“…To determine genetic variability of Chorthippus cazurroi , we amplified a 575 bp fragment of the cytochrome oxidase subunit I (COI) using the primers LCO1490 and HCO2198 [38]. Polymerase chain reactions (PCR) were set up in 10 µl total volumes following the procedures and conditions described in previous studies [36,39]. PCR products were checked by electrophoresis on 1.5% agarose gels stained with GelRed TM nucleic acid gel stain (Biotium, Inc., Hayward, CA, USA).…”

“…PCR products were checked by electrophoresis on 1.5% agarose gels stained with GelRed TM nucleic acid gel stain (Biotium, Inc., Hayward, CA, USA). We performed sequencing reactions using the Perkin Elmer BigDye v. 3.1 (Applied Biosystems, Carlsbad, CA, USA) terminator reaction mix in a volume of 10 µL, following the procedures and conditions described in Pato et al [39]. The final product was purified and sequenced on an ABI PRISM ® 3130xl Genetic Analyzer (Thermo Fisher Scientific Inc., Waltham, MA, USA).…”

Ambient temperature correlates with geographic variation in body size of least horseshoe bats

“…Understanding the patterns and causes of phenotypic divergence has been a central theme in ecology and evolutionary biology since Darwin ( Darwin 1859 ; Schlichting and Pigliucci 1998 ; Guo et al. 2016 ; Santana and Cheung 2016 ; Pato et al. 2019 ).…”