"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."
