This has been a fun week for my lab. My second Master’s student, Patrick Terry, successfully defended his thesis on Tuesday. Patrick came to the lab from Ohio University, where he had worked on some turtle projects and developed a strong interest in all things Testudines. Here at EMU, Patrick has been an incredibly independent and self-motivated student, and basically took on developing (and funding!) his own project. His thesis addresses a long-standing question among Michigan herpetologists: is the red-eared slider native or introduced in the state? The mystery arises from the fact that we’re at the edge of the native range. There are some other herps with similarly odd, disjunct populations in the state that are suspected to result from glacial refugia or postglacial recolonization. There is also some (somewhat contentious) fossil evidence indicating that the turtles may have been present in the state long ago. In short, it’s a question that genetic evidence might help shed some light on.
Patrick did a lot of sampling on his own, and worked with collaborators in other states to collect tissue samples for genetic analysis. In the end, he had sufficient sample size from three populations in Michigan, two in Indiana, and one in Ohio.
This was a nice set for comparison, because the Indiana sites were within the native range of the turtle (purple in the map above), as it is currently understood. The Ohio population is well outside the range and considered introduced.
The pictures above show Patrick after flipping his kayak to catch a turtle (L), and taking a tissue sample for genetic analysis (R). The joys of fieldwork! 🙂
Patrick conducted a whole suite of analyses to look at how his populations compared to one another, and they all had the same answer: one of his Michigan sites is very different from the rest of the sites, which are all quite similar to one another. The picture below is a visualization from the program Geneland.
This is basically a “heat map” showing how likely it is that various sampled sites cluster together. You can see that most sites are quite similar (all the red-orangy-ness). But there is one, TL, which is “white-hot-different.” All of the results reflected this same pattern. Among the sites Patrick sampled, it looks like that one is a likely introduction (and probably from a fairly distant source population). The other Michigan sites are more ambiguous. They may be naturally occurring, or they may be introduced from more regional (genetically similar) source populations.
Patrick is preparing a manuscript for submission, so keep an eye out for the full report soon! In the meantime, congrats to Patrick on the terrific work and the shiny new degree!