The main focus of my Master’s was, in a sense, change. With time, everything changes and animals are no exception. We call it evolution and it is what has led us to a world that contains both the remarkable beauty and complexity of the mantis shrimp and the seemingly impossible irrationality of the duckbilled platypus. Evolution is the nigh unstoppable force which pushes all of life forward into countless wondrous and varied forms, forever changing, forever new. This is, in a sense, what I studied in Glasgow, peering between lines of genetic code to see, in some small part, how the world was made.
In a much less dramatic sense, I studied frogs. And not just any frogs mind you, the most average frogs you could possibly imagine, Rana temporaria. Typically called the “common frog,” there really is no over-emphasizing how mundane this creature is. Scattered all across Europe, you can find them from Spain and Italy to Sweden and Russia. You can come across them in lowland bogs or at the tops of mountains, along the edges of forest-flanked lochs or in suburban gardens. In Scotland alone, I found R. temporaria halfway up the mountain Meall an Araich in the Black Mount Region, at the top of Cairn Gorm, a heady 669 meters above sea level (that’s just under 2200 feet for the Americans in the audience), and even right on the University of Glasgow’s campus, behind the Queen Margaret Union (QMU), in a small, unkempt and overgrown garden pond.
Being so incredibly common, you might, logically, expect a fair amount of diversity from R. temporaria. Evolution being “nigh unstoppable” and all that, you could feel pretty safe in predicting that frogs found in the alpine meadows of the Alps will be different from frogs found in the bogs of the Scottish Highlands. You might even, if you were feeling bold, go so far as to say that frogs at one end of the Scottish Highlands might be different from frogs at the other end. In perhaps the most accurate sense, this is really what I did in Glasgow. I looked to answer these questions of difference of frogs in Scotland. It is worth noting here that when I talk about diversity and difference, I am talking about genetic diversity. For those who aren’t biologists, I plan on doing some future posts on the basics of genetics, what genes are and how they change, to make all this a bit clearer.
Before we really get into my work, we need to cover some previous studies. Amphibians are widely regarded to have low dispersal rates (meaning they don’t move far from where they are born) and high site fidelity (meaning they tend to return to places where they have bred). When this is the case, you can see very clear genetic evidence in what we call “population structure.”
Population structure, in a loose kind of definition, describes how individuals interact across a landscape. Do squirrels at one end of a forest go to the other end and make adorable squirrel babies regularly? If so, we can expect that squirrels at one end will be very similar genetically to squirrels at the other end. If not, we expect them to be different. Thus we either have one large population, where individuals all interbreed, or we have two populations, where squirrels at each end of the forest tend to keep to themselves, with West Side squirrels seldom eschewing public decency to run off and elope with some disreputable rapscallion from the East Side. What? Squirrels can’t have scandals now? Please. Squirrels are insufferable gossips. I’m a biologist, trust me.
Anyways, if we have low dispersal and high site fidelity, we see a lot of population structure. A series of studies carried out in Fennoscandia found that R. temporaria populations showed a lot of structuring along an altitudinal gradient. Basically, you have populations being increasingly different as you go North. This would confirm the idea that frogs don’t go far and they tend to breed in the same places year after year. (Scholarly articles from those studies: Laugen et al. 2003a; Laugen et al. 2003b; Palo et al. 2004; there are others but I don’t want any overkill on a blog post here)
Previous work at the University of Glasgow (Muir et al. 2013) found precisely the opposite of the Fennoscandian studies, thickening the plot to a suitable degree. Looking at a cluster of five mountains north of Glasgow, the group found that only one mountain had populations that were genetically distinct. This would point towards higher levels of dispersal, meaning more mobile frogs, and lower levels of site fidelity. There are some technical differences between the Fennoscandian studies the Glasgow study that are worth discussing, but I’ll save that for a future post.
This is where I come in. My project expanded on the previous Scottish work, adding three new sampling locations to widen the range considered. The goal was simply to see whether or not this lack of population structure held up at greater distances. I also looked at variation in the mitochondrial genes cytochrome b and cytochrome oxidase subunit I, but the goals there are a bit more technical and would best be saved for a future post where I can get into more details. For now, we’ll say that looking at these mitochondrial genes helped me to show how Scottish populations had diverged from populations in mainland Europe and to discover which areas they would be most related to.
So what did I find you ask? Well if I told you everything here you wouldn’t have much incentive to come back would you. So I guess the results, and the myriad technical details and biostatistical fun-facts that make them interesting and understandable, will just have to wait until later.