Imagine that you’re sitting on a Cretan beach. The sun’s shining and waves are lapping on shore, when suddenly a set of jaws dripping copious amounts of saliva appear above you like some sort of CGI horror masterpiece, wanting to bore a hole in you big enough to crawl through. While this is hopefully not something you need to worry about, it is in fact a concern for the Albinaria land snails that inhabit the Greek islands. Who are the boorish culprits? No other than small beetle larvae of the genus Drilus (shown above), a land snail predator.
In a study recently published in PLOS ONE, researchers aimed to gain a better understanding of the predator-prey interactions between Drilus beetle larvae and Albinaria land snails. They predicted that land snail species with a greater number of ribs on their shell were better protected from invasion; if correct, this would mean the type of predation may affect shell evolution in this species.
The authors surveyed over 1,000 groups of land snail shell samples from a museum and mapped, by region, the frequency of land snail deaths by beetle larvae. Then, using DNA sequencing, they found that while some species of beetle larvae only prey on Albinaria, others take a more generalist approach and feed on a variety of land snail species.
The authors also found that beetle larvae can kill without ever actually having to bore a hole in the snail’s shell. In fact, of the ~170 Albinaria shells the authors collected that showed evidence of a beetle larvae attack, 60 shells had no holes. The researchers suggest that despite the potential challenges of entering through the main opening, such as encountering the clausilium—essentially a front door that the snail can shut (as drawn above)—boring into the shell is still a more rigorous task.
The scientists’ also directly observed the beetle larvae preying on the land snails, which reinforced that it was not necessary to bore a hole for entry; however, they found that the beetle larvae almost always exited by boring. While there does not seem to be an obvious explanation for why this variation in entry/exit method exists, each choice has its own advantages and disadvantages. The observation period further revealed that the beetle larvae took its time leaving the shell, often living inside it for 22-32 days after each kill before molting and moving on.
Though we still do not have a clear understanding of how these interactions directly impact shell evolution, the authors hope this research provides a basis for future work to build upon. Regardless, I think it’s safe to say that this ‘boring’ research yielded some rather informing results.
Citation: Baalbergen E, Helwerda R, Schelfhorst R, Castillo Cajas RF, van Moorsel CHM, et al. (2014) Predator-Prey Interactions between Shell-Boring Beetle Larvae and Rock-Dwelling Land Snails. PLoS ONE 9(6): e100366. doi:10.1371/journal.pone.0100366
Images: All images are from the article.