The double-edged sword of Eriophorum vaginatum ecotypes: Locally adapted, but overspecialized?

Background/Question/Methods

Plants are often genetically specialized as ecotypes attuned to local environmental conditions.  When conditions change, the optimal environment may be physically displaced from the local population, unless dispersal or in situ evolution keep pace, resulting in a phenomenon called adaptational lag.  Using a 30 year old reciprocal transplant study across a 475 km latitudinal gradient, we tested the adaptational lag hypothesis by measuring both short-term (tiller population growth rates) and long-term (17 year survival) fitness components of Eriophorum vaginatum ecotypes in Alaska, where climate change may have already displaced the optimum.  We analyzed the transplant study as a climate transfer experiment in which site differences were quantified by the shift in thaw degree days represented by each particular transplant.  

Results/Conclusions

The climate optimum for plant performance was displaced ca. 140 km north of home sites, although plants were not generally declining in size at home sites.  Indeed, performance was only 2.6% and 2.1% less at home sites than at the optimum, suggesting that so far, adaptational lag has not resulted in maladaptation to the home site.  The parabolic shape of the transfer response function suggests that this decline could increase rapidly, however, with further climate change in the Arctic.  Indeed, there is evidence of range collapse with poor performance of all populations at the southernmost site.  While adaptational lag may be appearing first in the Arctic, where climate change has been rapid, this phenomenon is expected to be widespread globally for long-lived, ecotypically specialized plants, with disruptive consequences for communities and ecosystems.