Facultative drilling behavior of Nucella species (Muricidae) upon the thatched barnacle (Semibalanus cariosus) from field and experimental observations: consequences for the fossil record of predation

ARCHUBY, FERNANDO M; LEIGHTON, LINDSEY R.

Mendoza

Congreso; 4th International Paleontological Congress; 2014

CCT CONICET Mendoza y otros

RESUMEN ENVIADO. EL CONGRESO SE CELEBRARÁ ENTRE FINES DE SEPTIEMBRE Y COMIENZOS DE OCTUBRE. Gastropod drilling predation leaves identifiable traces that permit the study of this biotic interaction in the fossil record. Study of these drilling patterns have mainly focused on prey bearing one (gastropods) and two (bivalves, brachiopods) valves, but not on the multiple-plated shells of barnacles. In addition, it is generally accepted that a shell with a complete hole indicates successful predation while incomplete traces are the result of a failed attack. However, it has been shown that some gastropod species can kill without drilling or leaving incomplete holes. To address these issues, we examined the predator-prey relationship between Nucella spp. (predator) and the thatched barnacle Semibalanus cariosus (prey) using both field sampling of dead shells and experiments. A total of 720 dead shells of S. cariosus with complete walls were collected from multiple localities on San Juan Island, Washington State, USA, and examined for drill holes. In addition, three size classes of S. cariosus and Nucella lamellosa were combined in nine treatments and set in water tables with continuous marine water flow to permit direct observation of drilling patterns and barnacle mortality. Drill holes were described in terms of: plate of occurrence, vertical position on plates and with respect to contact between plates. 9% of the dead shells have drill holes on their wall plates. 53 out of 54 barnacles killed during the experiments were not drilled or the holes they bear are incomplete or failed. Nucella species exhibit site selection for drilling in favor of the ventral plates that cover the soft tissues of the barnacles, and of positions below the articulation of aperture plates. Aperture plates are never drilled. Drill holes are rarely complete or functional which indicates that Nucella rarely eat S. cariosus through the holes, and are thus capable of killing and consuming the barnacles without necessarily drilling. This raises the possibility that Nucella species narcotize the barnacle prey by applying a salivary toxin and eat the soft tissues through the aperture. Such a toxin has previously been described for Nucella haemostoma. Thus, the record of predation traces in this particular predator-prey system differs markedly from other systems: most of the prey is killed without drilling and the majority of the incomplete drill holes are probably not examples of predator failure, suggesting that complete/incomplete drilling frequencies observed on fossil barnacles may not be indicative of predator success.