EFFECT OF HUNGER ON DRILLING PREDATION BY NATICID GASTROPODS

Drilling predation is one of the unique scenarios where past biotic interactions could be studied quantitatively and can be used to model the behavioural evolution of involved groups. Although, it is recognized that hunger plays an important role in determining the behavior of terrestrial predatory groups, its specific effect on drilling gastropods is yet unexplored. While major behavioural modifications in predators including change in prey size preference is considered to be an outcome initiated by hunger in certain groups, it is yet to be tested for drilling gastropods.

In order to evaluate the effect of hunger on behavior of drilling gastropods, we run a series of experiments in synthetic saltwater aquarium setup. Using live naticid gastropods, Natica tigrina and their bivalve prey Cardium sp., we evaluated the effect of hunger on the following aspects of predation: 1. Size selectivity, 2. Site selectivity, 3. Success rate. Using three different stages of hunger we evaluated the effect. Hunger is found to play an important role in prey size-selectivity. However, the success rate (measured by the ratio of complete and incomplete drill holes) and site selectivity is not observed to be affected significantly by hunger. Similar effects are seen in various ontogenetic stages of naticid gastropods.

It has been postulated that prey selection by gastropods are correctly modelled by cost-benefit analysis. However, standard cost-benefit analysis does not take hunger into consideration. Our study demonstrates the relative importance of hunger in guiding behavioural traits and should be considered while modelling the biotic interactions. As hunger is often related to nutrient depleted conditions, these modifications in behavior could be used to identify such events in geologic record.