EXAMINING THE INFLUENCE OF SEASONALITY ON DRILLING FREQUENCY OF NEVERITA DUPLICATA THROUGH FIELD AND LABORATORY EXPERIMENTS: IMPLICATIONS FOR PATTERNS OF DRILLING PREDATION IN THE FOSSIL RECORD

Drilling predation provides much of the support for escalation in the fossil record. Although paleontologists are careful to constrain paleoenvironments when assessing drilling through time, fluctuations in seasonality within these habitats are often not considered. Similarly, geographic differences in drilling are usually not examined in the context of seasonality despite changes in the presence and duration of seasons with latitude. This work explores seasonal variation in drilling predation using modern naticids. Because other factors related to seasonality may affect frequency of drilling in nature, experiments were conducted in both a field and controlled laboratory setting.

Laboratory experiments consisted of 12 tanks occupied by a single Neverita duplicata each (all initially ~30mm). Six Mercenaria mercenaria (~20mm) per tank were offered as prey at the start of each season; any consumed clams were replaced with new individuals every 3 days for 45 days. Temperatures fluctuated mostly between 27–30°C (summer), 16–20°C (fall), 8–12°C (winter), and 21–25°C (spring). Total number of clams drilled was not uniform across seasons (p < 0.0001): summer (~41%), fall (~30%), winter (~11%), and spring (~25%).

The field approach incorporated planting 20 clams in 25 plots (0.5 m²) at the UNCW research lease near the Intracoastal Waterway. Five plots were caged to investigate recovery and background mortality. Mercenaria mercenaria between ~16mm and ~18mm were marked, planted, and recovered after 4 weeks. Total seasonal recovery of non-caged plots ranged ~80%–98% (summer data not yet recorded). Of clams recovered, number of clams drilled was not uniform across seasons (p < 0.0001): fall (~25%), winter (~6%), and spring (~10%).

These results indicate that drilling is greatly impacted by seasonality and is not solely linked to temperature. Thus, seasonal effects should be considered not only in spatial analyses of drilling, but upon evaluating temporal patterns as well. For example, changes in drilling across an extinction could be due to altered seasonality influencing behavior of naticids (not necessarily a loss of predators or prey). Future work shall integrate literature data and seasonal differences quantified here for predictive modeling of drilling in time-averaged deposits with varied seasonal regimes.