A STABLE ISOTOPIC ASSESSMENT OF CANNIBALISM IN THE NATICID NEVERITA DELESSERTIANA

Cannibalism, the consumption of prey belonging the same genus or species as the predator, plays an important role in structuring communities. Predatory drillholes in the shells of marine animals made by drilling gastropods (family Naticidae) provide a unique window to study cannibalism in the geologic past. While naticid drillholes present in shells of Neverita delessertiana and N. duplicata throughout time show evidence of cannibalism, questions remain regarding the frequency and relative importance of cannibalism in the naticid diet. A study of the naticid Natica tigrina indicated that cannibalism was more likely to occur when preferred food sources were scarce and when the variation in gastropod size was greatest (Chattopadhyay et al., 2014). However, work on Neverita duplicata from the middle Miocene suggests that cannibalism comprised a substantial portion of the species’ diet and that prey size scaled with predator size (Kelley, 1991). Here we evaluate the prevalence of cannibalism by performing N and C stable isotopic trophic analysis on the soft tissues N. delessertiana (formerly N. duplicata) of various sizes (shell width: 21.4 to 55.0 mm) from Alligator Harbor, Florida, home of the largest recorded Neverita. C and N isotopic signatures consistent with cannibalism were present in one (n=30) small-bodied individual (shell width =24.4 mm). Possible explanations for the rarity of cannibalistic isotopic signatures given the prevalence of cannibalism traces in the shell record include: 1)The analyzed individuals were not large enough for conspecifics to comprise a substantial part of their diet. This seems unlikely given the small body size of the single cannibal recovered. 2) The frequency of cannibalism may vary seasonally, with tissue turnover rates preventing cannibalistic isotope signatures from being observed during the season sampled (winter). 3) Cannibalism amongst N. delessertiana may be rare, but the time averaged accumulation of cannibalized Neverita shells inflates the apparent frequency of the behavior. Future research to test these theories could include dating of cannibalized shells to quantify time averaging, analyzing isotopic compositions of large N. delessertiana (shell width greater than >50 mm), or Alligator Harbor populations during other seasons.