Owen Greenwood: Trapping skinks in paradise

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To start us off, we’re taking a trip to the Atlantic islands of Bermuda where Manchester Metropolitan and Chester Zoo PhD student Owen Greenwood spent the summer working with Bermuda skinks, all thanks to his 2023 Heredity Fieldwork Grant funded by the Genetics Society.

Bermuda skinks are tiny lizards, found only on Bermuda. Once abundant across the islands, they’re now critically endangered

Owen: The skinks used to live pretty much across the islands entirely, so it used to be covered in cedars, which would have fairly minimal undergrowth. So the thinking is that the skinks were quite happy moving around in that area. Humans colonised Bermuda in the early 1600s. Unfortunately, with humans, rats were also introduced basically as soon as we landed and rats predate the skinks as well, and so that's one pressure.

Owen: Humans building things is another pressure, so that wipes out a lot of their habitat, so there no longer is cedar forest. The predominant land cover is, unfortunately, mostly grass and housing nowadays, and now there are cats on the islands as well, which also predate them. So they're under a lot of population pressure.

Owen: So we think there's around 5, 000 left, but that's like the upper end of the estimate. 

Sally: So tell me what you were doing on your fieldwork project. Presumably you got to go to Bermuda and you had to catch a bunch of skinks? 

Itty-Bitty Lizard

A very young Bermuda skink

Owen: Yes, I was in Bermuda from June to August in 2023. Thanks to the Heredity Field Grant, I was able to take a field assistant with me.

Owen: We were staying on one island called Nonsuch Island, which is an area that they're trying to conserve as much of the native species as possible because, as you can imagine, the same with all islands, invasive species are a real problem over there. So we were staying on Nonsuch and we were setting pitfall traps, big jars that we were baiting to attract the skinks into.

Owen: We'd do this from around eight in the morning and bait them for five to six hours. We'd check the traps at least hourly. Basically, as you might guess, Bermuda gets quite hot, and so, with them being in the traps, we didn't want to leave them for any longer, because otherwise they might get heat stress.

Sally: Because these are the kind of pitfall traps where you're trying to catch them alive, not the kind of pitfall traps where you've put some poison or beer for those that might have tried to catch slugs in their garden before. 

Owen: Oh yeah, exactly, we definitely want to keep them alive because it would somewhat defeat the point to collect the genetics of ones that are no longer in the population.

Skink & Swab

Performing a buccal swab on a Bermuda skink

Owen: But yeah, once we caught them in the trap, we would take them out, we would take a mouth swab to scrape off cheek cells or buccal cells, which we then brought back with us to the UK to extract DNA from, which is what's going to allow us to do the genetics work. 

Owen: So what we do is we set the traps in the morning. And then each of us would be responsible for checking a certain section of the traps and then bringing them back to our sort of processing station where we do the swabbing and taking biometric measurements and checking to see if they're tagged already, and if not putting PIT tags on them, which is basically like a barcode reader so you can scan the skink.

Owen: And if it's been tagged, it comes up with a number to tell you which individual it is, so you know when you swabbed it before, what its measurements were, and so on. And the idea is, if we recapture them, we can tell we've recaptured them, so it gives us a much more accurate idea of how big their population sizes are.

Sally: How many did you collect in total? Few hundred? Few dozen? 

Owen: So we caught 140 total, of which there were around 120 that were unique. 

Sally: And you've got cheek swabs from all of them, presumably to collect their DNA. What are you gonna do with that DNA? 

Owen: So yeah, we took swabs from all of them. There was one we didn't because we caught a hatchling and the entire skink was probably the same size as the head of the swab. Definitely the cutest skink I saw out there. 

Owen: With the buccal swabs we've got a few aims. Broadly speaking, we want to do population genetics, so we want to get an idea of how healthy the skink populations are. So, generally speaking, the more heterozygous a species is, the more genetically healthy it is.

Owen: And what we want to do is see whether: 

Owen: a) the populations are genetically healthy, because a lot of them are fairly small, and all of them are very isolated from each other. So there's not a huge amount of gene flow. In fact, I'd probably go as far as to say there's, for all intents and purposes, none between the vast majority of sites.

Owen: And b), we want to see whether the level of heterozygosity correlates with actual fitness of the individuals to see whether body mass index differs between populations in the same way that heterozygosity does. So that's one of the questions we're trying to answer. We also want to look at just the population structure of the Bermuda skink.

Owen: We surveyed ten different locations. And Bermuda's made up of two or three big islands and then a lot of smaller islands, and so many of the persisting skink populations are found on the smaller islands where people aren't living. 

Owen: What we want to do is see just how much genetic variability there is in the species as a whole, but also to see whether either reintroduction or relocation would be a potential option for the conservation of the species. So Chester Zoo have been carrying out a captive breeding programme for the skinks for just over a decade and they've been very successful, they've bred a lot of skinks. 

Owen: But the population of individuals that they used to start the breeding programme in the first place all came from one particular island. So what we want to do in the interest of conservation is see whether that island is genetically similar enough to the other sites that we could use individuals from this population to support the existing populations elsewhere. 

Sally: So now it sounds like you're going into kind of the hardcore genetics part of your PhD.

Sally: You've done all the fun experimental work in the field and now you're heading back to the lab. You started off from an ecology and conservation point of view. Is this kind of what you expected a career in genetics to be like? 

Owen: Honestly, I never expected to get as much field work as I did through genetics.

Owen: Because most of my exposure to it has either been through the medical lab I worked in, or when I was at University of Exeter, there were some amazing genetic researchers there. A lot of them work on invertebrates though, and so they breed them up in the labs and then do all their work in the lab.

Owen: So I kind of always envisaged it just in the lab, throughout. The fact I had the opportunity to go out into the field for three months has been fantastic. And for me, anyway, it's helped me to sort of ground what I'm now going to be doing in the lab into the real world. Having been to Bermuda and experienced it all, it's given me a much better appreciation of what we might actually be able to do with the output of it.

Images courtesy of Owen Greenwood