Abstract
Species responses to environmental change are likely to depend on existing genetic and phenotypic variation, as well as evolutionary potential. A key challenge is to determine whether gene flow might facilitate or impede genomic divergence among populations responding to environmental change, and if emergent phenotypic variation is dependent on gene flow rates. A general expectation is that patterns of genetic differentiation in a set of codistributed species reflect differences in dispersal ability. In less dispersive species, we predict greater genetic divergence and reduced gene flow. This could lead to covariation in life‐history traits due to local adaptation, although plasticity or drift could mirror these patterns. We compare genome‐wide patterns of genetic structure in four phenotypically variable grasshopper species along a steep elevation gradient near Boulder, Colorado, and test the hypothesis that genomic differentiation is greater in short‐winged grasshopper species, and statistically associated with variation in growth, reproductive, and physiological traits along this gradient. In addition, we estimate rates of gene flow under competing demographic models, as well as potential gene flow through surveys of phenological overlap among populations within a species. All species exhibit genetic structure along the elevation gradient and limited gene flow. The most pronounced genetic divergence appears in short‐winged (less dispersive) species, which also exhibit less phenological overlap among populations. A high‐elevation population of the most widespread species, Melanoplus sanguinipes, appears to be a sink population derived from low elevation populations. While dispersal ability has a clear connection to the genetic structure in different species, genetic distance does not predict growth, reproductive, or physiological trait variation in any species, requiring further investigation to clearly link phenotypic divergence to local adaptation.
Highlights
There is increasing recognition that species' responses to environmental change depend on their potential for plastic and adaptive responses (Hoffmann & Sgrö, 2011), and yet the evolutionary potential of populations remains difficult to determine due to the complex genetic architecture and quantitative nature of key life-history and physiological traits (Lande, 1982)
Understanding how gene flow facilitates or impedes genomic divergence among populations, and whether emergent phenotypic variation in life-history and physiological traits is limited by gene flow rates, remains an important challenge for predicting how populations respond to environmental change
Considering the overlap among methods, we focus on the sNMF results with K = 4 for M. boulderensis, M. sanguinipes, and A. clava tus, and K = 3 for C. pellucida (Figure 4, but see Figures S4 and S5 for all K values for each species under each model)
Summary
There is increasing recognition that species' responses to environmental change depend on their potential for plastic and adaptive responses (Hoffmann & Sgrö, 2011), and yet the evolutionary potential of populations remains difficult to determine due to the complex genetic architecture and quantitative nature of key life-history and physiological traits (Lande, 1982). We test the hypothesis that clinal differences in growth and reproduction “(life-history traits)” and physiological traits of four ecologically divergent grasshopper species (Buckley & Nufio, 2014; Buckley, Nufio, & Kingsolver, 2014; Levy & Nufio, 2015) are associated with genetic differentiation and reduced demographic estimates of gene flow (local adaptation). Our hypothesis is that the short-winged species will exhibit genetic differentiation, limited phenological overlap, and gene flow, and have a strong association between genetic divergence and phenotypic differentiation along the elevational cline. Long-winged species might exhibit limited genetic differentiation, a source-sink pattern of gene flow, high phenological overlap, and have no association of genetic divergence with phenotypic differentiation
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