Could a tiny snail living along the rocky Western coastline not only provide scientists with clues about the history of a coastal ecosystem but also hint at how it may respond to a rapidly changing climate? For Emily Longman, a post-doctoral associate in the UVM Department of Biology, the answer to that question is a resounding yes. 

Longman and her team have been studying the evolutionary story written into the DNA and shells of a species of coastal dogwhelk, a species of snail found along the West Coast of the United States from central California all the way up to Alaska. Their research paper, “Geographic Divergence in Population Genomics and Shell Morphology Reveal History of Glacial Refugia in a Coastal Dogwhelk,” for which Longman serves as both lead and corresponding author, was just published in the journal Proceedings of the Royal Society B.

This research allows an unprecedented view into the evolutionary history of coastal systems, as it is the first population genomics study of a low-dispersal marine species. We sat down with Longman to talk about her findings.

College of Arts and Sciences: What big question were you trying to answer with this study?

Emily Longman: The big question we were trying to answer was, can the DNA of a common coastal snail ultimately reveal the hidden evolutionary history of an ecosystem that spans thousands of kilometers of coastline? Additionally, we were trying to understand what that history tells about how these ecosystems might ultimately respond to future environmental changes.

CAS: What makes the coastal dogwhelk snail so important for understanding coastal ecosystems?

EL: Many marine species ultimately disperse early in life as larvae, drifting along in the ocean currents over great distances, getting mixed up with all kinds of different larvae. But this snail is different. It lives on rocky shores, laying capsules that attach firmly to the rocky surfaces. Once the juvenile snails develop and hatch, they crawl away as baby snails. As a result, the offspring ultimately live on the same rocky shores as their parents. Due to this form of reproduction, populations of this snail can be quite isolated from other nearby populations along the same coastline. These deep divergences are ultimately written into their DNA, so the genetics of these snails hold long-lasting information about the evolutionary history of coastal ecosystems.

CAS: Can you explain what “genomic diversity” means and why it’s important to understand?

EL: DNA is like an instruction manual for life, and genomic diversity is the natural variation in DNA that's present in different individuals and populations. This variation ultimately reflects a mix of many different processes, including the evolutionary history of a species, changes in population size, and how populations have been influenced by previous conditions via natural selection. So, understanding how genomic diversity naturally varies is important for understanding whether species have enough raw genetic material to adapt to future environmental changes.

CAS: What do your findings tell us about how coastal species evolve over long periods of time?

EL: Our results indicate that climatic changes that happened a long time ago have had long-lasting impacts on the current genetic patterns of the species. During the last Glacial Maximum, which happened thousands of years ago, the distribution of many coastal species contracted and shifted toward the equator. Later, when it got warmer and conditions improved, these species’ ranges expanded once more toward the poles. We were able to not only determine that the genetic makeup of snails in southern populations looks really different from the genetic makeup of the snail populations in the north, but also that at least one tiny northern population must have persisted through these cycles of glaciation. 

CAS: What was the most exciting thing you discovered?

EL: Snail shells have long been studied as a way of understanding evolutionary patterns in marine systems, since historical events like glaciation can have long-lasting impacts on the shape of snail shells. Beyond looking at the genetic data, we were also interested in seeing if there were changes in snail shell shape along the coastline and whether those patterns matched the places where we saw strong genetic differences. We ultimately found that the shell data and the genetic data told really similar stories about the evolutionary history of the coastal populations, which further supported our findings. Another major goal was to link those trait variations to underlying genetics. We assembled the first genomic resources for this species, and by doing that, we were able to look at the underlying genetics and identify specific regions of the genome that are associated with the shell shape variation that is naturally occurring along the coastlin For example, the southern snails are rounder and less pointy than their northern relatives.

CAS: How might the historical patterns you uncovered help us understand how species may respond to future climate change?

EL: Understanding how species have previously responded to other kinds of natural environmental conditions, like glaciation, can help us improve our predictions for how species will ultimately react to future changes in climate. So, these insights are becoming increasingly important, particularly because of the speed and scope of the climate changes that are happening now. 

CAS: What’s the main takeaway for a general reader?

EL: I think the big takeaway would be that coastal ecosystems still bear the imprints of historical events like glaciation that happened a really long time ago while simultaneously also being shaped by accelerating rates of climate change and other stressors. So, studying the DNA and shells of snails can be a unique window into the history of these dynamic coastal environments.