The role of environment and core‐margin effects on range‐wide phenotypic variation in a montane grasshopper

Abstract

The integration of genetic information with ecological and phenotypic data constitutes an effective approach to gain insight into the mechanisms determining interpopulation variability and the evolutionary processes underlying local adaptation and incipient speciation. Here, we use the Pyrenean Morales grasshopper (Chorthippus saulcyi moralesi) as study system to (i) analyse the relative role of genetic drift and selection in range-wide patterns of phenotypic differentiation and (ii) identify the potential selective agents (environment, elevation) responsible for variation. We also test the hypothesis that (iii) the development of dispersal-related traits is associated with different parameters related to population persistence/turnover, including habitat suitability stability over the last 120 000 years, distance to the species distribution core and population genetic variability. Our results indicate that selection shaped phenotypic differentiation across all the studied morphological traits (body size, forewing length and shape). Subsequent analyses revealed that among-population differentiation in forewing length was significantly explained by a temperature gradient, suggesting an adaptive response to thermoregulation or flight performance under contrasting temperature regimes. We found support for our hypothesis predicting a positive association between the distance to the species distribution core and the development of dispersal-related morphology, which suggests an increased dispersal capability in populations located at range edges that, in turn, exhibit lower levels of genetic variability. Overall, our results indicate that range-wide patterns of phenotypic variation are partially explained by adaptation in response to local environmental conditions and differences in habitat persistence between core and peripheral populations.

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

“…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, 2016). 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.…”

“…Our geometric morphometric analyses showed that the subtle phenotypic differences found among populations were not explained by genetic differentiation, geographical distances or environmental dissimilarity. Overall, this suggests that the weak phenotypic differences found among populations are not a consequence of genetic drift or environmental‐driven selection (Keller, Alexander, Holderegger, & Edwards, ; Leinonen, Cano, Makinen, & Merila, ; Leinonen, O'Hara, Cano, & Merila, ) and might be explained by ecological and evolutionary aspects not considered in this study such as sexual selection, predation risk, microhabitat structure or adaptations to different feeding resources (e.g., Ingley, Billman, Belk, & Johnson, ; Laiolo, Illera, & Obeso, ; Noguerales, García‐Navas, Cordero, & Ortego, ).…”

“…MMRR analyses for phenotypic differentiation (P ST ) showed that no trait was significantly correlated in any sex with geographical dis- Table 4). 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, 2016) 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, 2016).…”

Contrasting patterns of neutral and functional genetic diversity in stable and disturbed environments

“…Depending on the questions and hypothesis under investigation, contrasting environments can consist of habitats that represent different environmental conditions, disturbance regimes (as in the present study), populations inhabiting large (source) as opposed to small (sink) habitat patches, populations in ephemeral or temporal as opposed to permanent habitat patches, or populations at the core of the distribution range as opposed to populations in marginal areas that represent invasion fronts of expanding species (Johansson et al, 2016;Noguerales et al, 2016;Quintela et al, 2014;Shine, Brown, & Phillips, 2011;Sunde, Tamario, Tibblin, Larsson, & Forsman, 2018). To broaden utility, environments could be characterized not as binary states but along continuous gradients, such as age of habitat or time since disturbance event (Forsman, Karlsson et al, 2011).…”

“…Adaptive or functional genetic diversity is influenced by the same suite of processes discussed above for neutral diversity. In addition, functional diversity is affected by differential fitness among individuals within populations (Endler, ; Holderegger, Kamm, & Gugerli, ) and by divergent selection in populations that inhabit different environments, potentially leading to local adaptations and differentiation (Dudaniec, Yong, Lancaster, Svensson, & Hansson, ; Johansson, Quintela, & Laurila, ; Lenormand, ; Noguerales, García‐Navas, Cordero, & Ortego, ; Quintela, Johansson, Kristjansson, Barreiro, & Laurila, ; Zhi‐Xiang, Fang, & Guo‐Fang, ). Unlike neutral diversity, functional genetic and phenotypic variability can in turn have a positive impact on the fitness of populations, by increasing evolvability, dampening fluctuations, increasing production of dispersers (emigrants), improving establishment success, and reducing extinction (Forsman, ; Forsman, Ahnesjö, Caesar, & Karlsson, ; Forsman & Wennersten, ; Forsman, Wennersten, Karlsson, & Caesar, ; Hughes, Inouye, Johnson, Underwood, & Vellend, ; Mills et al., ; Reed & Frankham, ; Rius & Darling, ; Vergeer, Sonderen, & Ouborg, ; Wennersten & Forsman, ; Whitlock, ; Willi, Van Buskirk, & Hoffmann, ).…”