Animals adapt to their environments through several processes that act on different time scales, from rapid changes within an individual to longer-term evolution across entire populations. This project investigates the mechanisms behind adaptation to temperature in a widespread invasive species, the European green crab. Green crab populations across Europe, where the species is native, will be studied for the limits of their temperature tolerance, and to determine the genes and pathways involved in this tolerance. These results will be compared with data already collected in the invasive range to determine whether populations from different environments and histories respond to temperature differently, and to examine whether they use the same genes in the same ways to deal with temperature.
Invasive species have to adapt to novel environments quickly, and offer a wonderful opportunity to examine the pace and mechanisms of rapid adaptation. The way that animals adapt in nature over short time scales is not well-understood, but is particularly important in predicting and planning for their response to rapid environmental shifts. Understanding how green crabs adapt to novel temperatures will be useful in understanding how many species will react to climate change. In addition, this project will foster collaboration with European researchers, and will provide opportunities for public outreach in the field.
An Empire of Crabs I'm in the basement of a 17th-century Portuguese fort, surrounded by massive, rough-hewn stone walls built to repel an assault from marauding Spaniards. I'm not too concerned about attack from sea today, though. The fort now houses a marine biology laboratory, and my focus is on getting a handful of small green crabs to hold still long enough for me to hook them up to tiny heart monitors. It's fitting that I'm studying these particular crabs in the heart of Portugal, one of the world's most expansive colonial empires. Green crabs are expansive colonizers, too, hitching rides across the seas and putting down roots all over the globe. It's this kind of behavior, along with a voracious and undiscriminating appetite, that have earned the species a spot on the World's 100 Worst Invasive Species list. What makes green crabs so successful? My five years of thesis research have been driven by that single, simple question. They thrive in Portugal, and in Norway, and on every continent except Antarctica. I want to know how they do it. Have sun-drenched Portuguese crabs adapted to deal with the heat better than crabs in chilly Norway? This is where the tiny heart monitors come in. I use them to look at how green crabs living in very different environments deal with extreme temperature. In that fortress of science, I found that Portuguese crabs' hearts can handle temperatures of nearly 100ºF. Farther north, under a near-midnight sun, I found that Norwegian crabs hit their limits around 94ºF. But even the Norwegian crabs are impressive by comparison to their non-invasive neighbors: most other crabs and lobsters can barely manage 90ºF, at best. These are the first pieces of the puzzle. All greens crabs can handle a very wide range of temperatures. On top of that, specific populations have adapted over time, fine-tuning to match their local environments. Back in the lab, I've turned to cutting-edge genetics to dig deep into the causes of these differences. Using this technology, I can examine many thousands of genes at the same time, reconstructing the tiny genetic changes that have built up between green crab populations as their empire expands. Many of these changes are random and unremarkable, but a handful stand out – they show strikingly different patterns between populations, a tell-tale sign of selection. Even more telling, many of these patterns seem to vary with temperature. In warmer sites, like Portugal and New Jersey, one version of a gene is common, while in chilly Norway and Newfoundland, a different version dominates the population. These genetic differences may be the reason why Portuguese crabs are more resilient to high heat than their northern neighbors. A few degrees of difference between populations may not seem like much, but to a lot of species, it could mean the difference between survival and extinction. Global temperatures are rising quickly. To understand how animals and ecosystems will change in the near and warming future, we need to know the details of how adaptation works. This research suggests that small genetic changes could lead to big differences in how populations of the same species are able to cope with temperature change. The expansion of the empire of crabs provides a template for successful adaptation, and can help us dig deeper into how animals will cope with changing environments.
