Recent climatic warming may be leading to discordant shifts in wing morphology in a butterfly hybrid zone

Background/Question/Methods

In response to a changing climate many species are predicted to undergo shifts in their geographic range and many such cases have already been documented.  However, species traits may also change in response to climate change via evolution and plasticity, but studies demonstrating changes in species traits to climate change remain lacking.  Here we looked at the hybrid zone of two butterfly species to ask whether recent (within the last thirty years) warming has affected the wing morphology of these species and examine the concordance of these responses.  Using historic (collected from 1983-1985) and contemporary (collected in 2007, 2010-11), eight wing traits from the butterflies Papilio glaucus and Papilio canadensis from across a latitudinal transect in Wisconsin were measured using ImageJ. Morphology data were analyzed in R using a general linear model where each wing trait was regressed across latitude with time (historic vs new) as a covariate. Additionally, DNA was also collected for the genotyping of 16 microsatellite markers to look at genetic structure across the hybrid zone, in both historic and contemporary time periods; genetic structure was analyzed using STRUCTURE. 

Results/Conclusions

Based on 16 microsatellite markers we found very little genetic structure between species, suggesting that gene flow is relatively high across the hybrid zone.  Surprisingly, while a number of morphological (wing) traits significantly varied with latitude as previously observed, only one wing trait was found to have significantly changed over the last thirty years.  Interestingly, the trait that appears to have undergone the greatest change is putatively involved in thermoregulation (black band on the anal hindwing).  These results provide further evidence that species’ traits may already be undergoing changes in response to recent climate warming. Moreover, the finding that some wing traits have changed while others have remained static suggests that species’ traits may be responding discordantly to climate change.  Whether the observed change in wing traits is due to an evolutionary or plastic response remains unknown.