Exploring the evolution and function of sensory structures in turtles using a phylogenetic comparative approach

Background/Question/Methods

Sensory systems play a key role in interactions between organisms and their environment, and the diverse sensory morphologies that underlie these systems are typically under strong selection to facilitate resource acquisition, reproductive success, and survival. Barbels are examples of such sensory morphologies, diverse integumentary appendages that extend from the head and/or neck, and documented in a variety of different vertebrates, including fish, amphibians, and reptiles. The study of these structures is strongly biased toward fish, with little research investigating the ecological drivers of their evolution in other vertebrates. Barbels are present in four turtle families, but study of their function and evolution has been scarce. The prevailing hypothesis for their utility is that they serve a mechanosensory function in bottom-feeding, carnivorous species; however, evidence supporting this hypothesis is largely anecdotal. In this study, we employ phylogenetic methods to test the hypothesis that barbels are mechanosensory structures that aid in the capture of bottom-dwelling prey. More broadly, we probe the association between feeding ecology and barbel evolution.

Results/Conclusions

Our findings reveal a strong association between bottom-feeding and bottom-dwelling behaviour in turtles and the presence of barbels, but provide little evidence that barbels have evolved in response to shifts in feeding mode or habitat. Rather, barbel evolution is conservative, and the gain and loss of barbels may have precipitated later changes in the feeding ecology of turtles.