THE COST OF DRILLING IN THE COLD: CLIMATE CHANGE AND CANNIBALISM IN NATICID GASTROPODS FROM THE LA MESETA FORMATION AT SEYMOUR ISLAND, ANTARCTICA

The frequency of shell-drilling predation by living naticid gastropods is influenced by temperature. Reduction of metabolic rates due to cooling temperatures results in reduced activity patterns such as e.g., encounter rates with prey species or foraging due to different metabolic needs. Cold temperatures also increase the physical demands on the drilling predator during capture and handling of the prey and slow down the chemical reaction used to dissolve the shell during drilling.

We examined the record of cannibalistic drilling by the Eocene naticid Polinices subtenius from the La Meseta Formation of Seymour Island, Antarctica to assess the impact of a cooling climate on this mode of predation. As the climate cooled through the Eocene, cannibalistic drilling frequencies remained stable at around 5%, but an important behavioral aspect of cannibalism changed. Although the size structure of the Polinices population remained stable through time, the drilled individuals were on average over 30% smaller than they were before cooling began.

The observed pattern may be related to the propensity of naticids to select prey to maximize energy returns. The preferred prey size at a given temperature reflects a combination of prey-handling efficiency and feeding efficiency. P. subtenius may have adapted or acclimated to cooling temperatures by shifting to smaller, thinner prey, which would have been easier to drill in a colder environment.