Abstract
Most transplant experiments across species geographic range boundaries indicate that adaptation to stressful environments outside the range is often constrained. However, the mechanisms of these constraints remain poorly understood. We used extended generation crosses from diverged high and low elevation populations. In experiments across low elevation range boundaries, there was selection on the parental lines for abiotic stress‐tolerance and resistance to herbivores. However, in support of a defense‐tolerance trade‐off, extended generation crosses showed nonindependent segregation of these traits in the laboratory across a drought‐stress gradient and in the field across the low elevation range boundary. Genotypic variation in a marker from a region of the genome containing a candidate gene (MYC2) was associated with change in the genetic trade‐off. Thus, using crosses and forward genetics, we found experimental genetic and molecular evidence for a pleiotropic trade‐off that could constrain the evolution of range expansion.
Highlights
Multiple natural phenomenon such as extinction, conserved phy‐ logenetic niche evolution, and limits on geographical and habitat range indicates that constraints are important in the process of bi‐ ological evolution in the wild
This tolerance can be attributed to the abiotic stress as the growth rates were taken from plants that had not yet been attacked by herbivores. This dif‐ ference between populations in abiotic stress‐tolerance outside the low elevation range boundary was predicted based on differences in performance in the drought‐stress growth chamber experiment (Table 1)
Seed dispersal potential and soil germination experiments indicate that barriers to dispersal or establishment cannot explain local range boundaries of B. stricta (Siemens et al, 2012)
Summary
Multiple natural phenomenon such as extinction, conserved phy‐ logenetic niche evolution, and limits on geographical and habitat range indicates that constraints are important in the process of bi‐ ological evolution in the wild. The area across the low elevation range boundary was a more stressful environment to plants of both populations, demon‐ strated by lower survivorship and higher Betacyanin color scores, plants from the high elevation Big Horn population had higher tol‐ erance to the abiotic stress measured as growth rates outside the range relative to inside the range (Range‐by‐population interaction: F1,114 = 7.630, F = 0.007, Figure 2b and Table S6). This tolerance can be attributed to the abiotic stress as the growth rates were taken from plants that had not yet been attacked by herbivores This dif‐ ference between populations in abiotic stress‐tolerance outside the low elevation range boundary was predicted based on differences in performance (i.e., root:shoot mass ratio) in the drought‐stress growth chamber experiment (Table 1).
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