These large, carnivorous, non-native cousins of the ubiquitous house mouse (Mus musculus) are about to get scrubbed off of Gough Island in the south Atlantic as part of measures to protect the seabirds that breed there. But before they go, we get the opportunity to study the evolution and ecology of one of the most well studied vertebrates in the lab, only this time - mother nature has done the experiment for us!
If you try and read up on the mice of Gough Island (e.g. google “Gough” and “mouse”), you’ll hear about the damage they are doing to the island’s nesting sea birds – some of which are of great concern as they are not known to nest anywhere other than this one island.
The mice of Gough Island have a different story. They were accidentally introduced by ships in the 19th century, and have since become larger in size than the typical house mouse, weighing in at a whopping 35g (normal mice are nearly half that size)! If you’re curious as to how they have reached this size, consider their life on Gough Island. There are no large predators, and their diet includes a hearty (though seasonal) food source: seabird chicks! And we aren’t just talking about hapless, naked, sparrow-sized birds here - some of them (such as albatross) are as large as a turkey!
Interestingly, this is a classic example of what some call the "island rule" for the evolution of body size: small animals seem to evolve to be larger than their mainland counterparts, and large animals tend to be smaller. This from the sizable body of knowledge arising from studies of the evolution of body size (which, for example, might occur in response to resource limitation, sexual selection via competition for mating opportunities, predation, and even predation by humans).
Super-sized or not, in order to protect the island's breeding seabirds from this jumbo sized pest, the UK has awarded The Royal Society for the Protection of Birds (a conservation organization) funding to eradicate them from the island, and most of the world seems to be quite pleased about it.
In our effort to save the seabird colonies (which I fully support, I’ll have you know) we may be destroying a fantastic opportunity to learn something from what scientists call a natural experiment - a situation that arises in nature but can reveal to us the kind of information we might hope to get from specifically designed scientific experiment. In this case, the evolution of a wild population that has been adapting to a new environment over the better part of a century or more.
So why is this particular population so noteworthy? I’m glad you asked! First, there been very significant phenotypic changes in this population (suggesting there are likely to be interesting genetic or other evolutionary changes in the population that are worth studying) - fortunately, people are already hard at work studying these hefty little rodents. Second, we know about some of the major aspects of the ecology and natural history of this population - an important first step to understanding the role their environment has played in shaping the evolutionary trajectory of the population.
If that doesn't seem promising enough, the house mouse is probably the most well studied vertebrate on earth! Taking the tools and insights gleaned from studying from studying mice in the laboratory and combining them with studies of wild populations seems like a promising approach to advance our understanding of evolution in wild populations.
So, as we embark on ridding this island of its pesky rodent problem, I do feel a little bummed to see a monkey wrench thrown into the system. What would those mice look like in another century? As much as I would love to know, however, the price of loosing even one of the sea bird species that nest there would be far to great a cost!
If the links above have left you wanting more, check out the Payseur Laboratory website for some of the work on understanding more about the mice of Gough Island, and the Global Invasive Species Database which includes video of mice attacking an Albatross chick.