"Our research aimed to understand how two related organisms that interbreed (hybridize) have responded and will respond to climate change. Many studies have observed the movement of entire species in response to changing climate, but the movement of a entire species is just one possible reaction to climate change. In order to better understand the complexities of how organisms adapt to a changing environment, we must also look within species to see how traits and genes within a species’ range are moving and adjusting to climatic change. These traits and genes determine how an organism will be affected by climate change: where helpful genes are lacking, populations can decline; and where new genes arrive, evolutionary rescue can occur. Regions (or “zones”) of hybridization between related species are ideal places to study the movement of traits within and among species because, theoretically, genes can move across geography independent of the species that contain them. Our NSF-funded research focused on this lesser-studied aspect of climate change science: the movement of genes within and across species under climate change and changes in the flow of genetic information that results.
We examined the following questions: 1) Have traits (genes) moved across geography in two species of butterfly, Papilio glaucus and P. canadensis, in response to recent climatic change? 2) How do the parental forms of the two species and their hybrids perform under simulated climate and climate change? Papilio glaucus and P. canadensis are ideal candidates for answering these questions because they have been studied previously and they hybridize over a wide area in the upper Midwest US.
To answer the first question, we compared specimens of butterflies that were collected in the 1980s and again after 2007 from a wide area in Illinois and Wisconsin that spans the zone of hybridization. We measured these specimens for wing traits and genetic markers that are thought to be related to climate and for traits and markers that are likely not climate-related (control). We found that some traits appear to have moved northward in the last 30 years, while others are not. The ones that have shifted northward appear to be related to temperature and are associated with warming that has occurred most strongly in the southern portion of the hybrid zone. This result suggests that climate change can shape the geographic distribution of traits within species, but not alter others. In other words, climate change is altering the association of traits in these butterflies and the genetic composition of them.
To answer the second question, we performed an experiment with pure forms of each butterfly species and hybrid crosses that we created in the lab. We then exposed experimental animals to a range of climatic conditions that span the hybrid zone. For the northerly species and its hybrids, this experiment simulated a warming event. We found significant differences in the timing of life events in the two species and in the different types of hybrids, and these differences were affected by climate treatment. To make future projections with this information, we built a model that predicts the number of generations that will occur across Wisconsin under alternative climate scenarios. The number of generations per year affects the amount and direction of gene movement between the species and can be used to infer future changes in the northward flow of traits and genes.
Seven undergraduate students participated in this research project, one funded by the NSF on a supplement to this grant and six from other sources. One graduate student is earning a PhD with this project, and three full- or part-time research staff advanced their technical skills and career path with employment on this project. Work on this grant also enabled public presentations and outreach by the PI and the graduate student about climate change and its ecological consequences, and the project compiled a large and highly unique database of thousands of specimens from the hybrid zone. This resource will be made accessible to future researchers. Protocols and equipment from this project also informed research and conservation planning for other Lepidoptera, including one federally-listed endangered species. Most importantly, this work advances our understanding of how climate change can alter living systems, a crucial goal given the amount of warming that is projected to occur in the coming decades and centuries."