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

Abstract

Understanding the processes underlying spatial patterns of genetic diversity and structure of natural populations is a central topic in evolutionary biogeography. In this study, we combine data on ancient and contemporary landscape composition to get a comprehensive view of the factors shaping genetic variation across the populations of the scrub‐legume grasshopper (Chorthippus binotatus binotatus) from the biogeographically complex region of southeast Iberia. First, we examined geographical patterns of genetic structure and employed an approximate Bayesian computation (ABC) approach to compare different plausible scenarios of population divergence. Second, we used a landscape genetic framework to test for the effects of (1) Late Miocene paleogeography, (2) Pleistocene climate fluctuations, and (3) contemporary topographic complexity on the spatial patterns of population genetic differentiation. Genetic structure and ABC analyses supported the presence of three genetic clusters and a sequential west‐to‐east splitting model that predated the last glacial maximum (LGM, c. 21 Kya). Landscape genetic analyses revealed that population genetic differentiation was primarily shaped by contemporary topographic complexity, but was not explained by any paleogeographic scenario or resistance distances based on climate suitability in the present or during the LGM. Overall, this study emphasizes the need of integrating information on ancient and contemporary landscape composition to get a comprehensive view of their relative importance to explain spatial patterns of genetic variation in organisms inhabiting regions with complex biogeographical histories.

Integrating genomic and phenotypic data to evaluate alternative phylogenetic and species delimitation hypotheses in a recent evolutionary radiation of grasshoppers

“…Phylogenomic analyses also indicated that the recently described French subspecies ( C. b. armoricanus ) and the Iberian one ( C. b. binotatus ) constitute two well‐supported lineages (Defaut, ; Figure ). Recent phylogeographic studies on this species have shown that it exhibits a strong population genetic structure at mtDNA and nuclear microsatellite markers (Noguerales, Cordero, & Ortego, , ), a pattern in line with the relatively deep lineage divergence found in the present study (Figure ). The large distribution range of C. binotatus together with its montane character and narrow feeding requirements could have promoted long‐term population isolation in different regions and, ultimately, the formation of cryptic lineages (Defaut, , ; Noguerales et al., , ).…”

Inferring the demographic history of an oligophagous grasshopper: Effects of climatic niche stability and host-plant distribution

“…Pre-evaluation of results based on Principal Components Analyses (PCA) as implemented in DIYABC showed that the cloud of simulated SS were not enough close to our observed SS for any competing scenario. Following the approach by Fontaine et al 2013(see also Andersen et al, 2017;Noguerales et al, 2017), we solved this issue by discarding those microsatellites markers with the highest frequency of null alleles, estimated using the Expectation Maximization (EM) algorithm implemented in the program FREENA (Chapuis and Estoup, 2007). Accordingly, we retained a subset of seven microsatellite markers for all ABC analyses (Noguerales et al, 2017).…”

“…Following the approach by Fontaine et al 2013(see also Andersen et al, 2017;Noguerales et al, 2017), we solved this issue by discarding those microsatellites markers with the highest frequency of null alleles, estimated using the Expectation Maximization (EM) algorithm implemented in the program FREENA (Chapuis and Estoup, 2007). Accordingly, we retained a subset of seven microsatellite markers for all ABC analyses (Noguerales et al, 2017). Information from previous studies (Noguerales et al, 2017) and a pre-evaluation of scenarios and prior distributions were employed to adjust the priors of effective population sizes (N e ) and timing of divergence (t) to their most appropriate values (see Table S4), assuming a uniform prior probability distribution for them.…”

“…Accordingly, we retained a subset of seven microsatellite markers for all ABC analyses (Noguerales et al, 2017). Information from previous studies (Noguerales et al, 2017) and a pre-evaluation of scenarios and prior distributions were employed to adjust the priors of effective population sizes (N e ) and timing of divergence (t) to their most appropriate values (see Table S4), assuming a uniform prior probability distribution for them. This procedure was also performed to evaluate different magnitudes of reduction in effective population sizes (10, 25, 50, 75, 90 %) in population groups for which we hypothesized to have experienced a demographic bottleneck.…”

“…This taxon is distributed throughout France, Spain and Portugal (Defaut, 2011) and occupies primarily montane habitats between 900 and 2500 m.a.s.l., often forming highly isolated populations separated by unsuitable low elevation areas (Noguerales et al, 2017). The scrub-legume grasshopper can be also exceptionally found at low elevations (even at sea level) near to the Atlantic coast, where it forms small populations in highly isolated patches of suitable habitat (Picaud et al, 2003;Pratz and Cloupeau, 2010).…”