Prey selection by the tropical marine snail Thais melones : a study of the effects of interindividual variation and foraging experience on growth and gonad development

Graduation date: 1986I studied the feeding behavior of marked individuals of the\ud carnivorous marine snail Thais melones in a rocky shore habitat of\ud Pacific Panama. The population of snails consume a variety of\ud invertebrate species such as bivalves, limpets, and polychaetes.\ud Individuals exhibited a range of diet breadth, with some\ud specialized, but others generalized. Some individuals foraging\ud over the same patch of habitat chose strikingly different diets.\ud Interindividual variability in diet was not due solely to foraging\ud by individuals in a homogeneous patch of a few prey species nor was\ud it likely to be determined by relative abundance of prey in the\ud environment. Shell growth was influenced by the consistency within\ud an individual diet rather than by the identification of the prey\ud consumed. Significantly more shell growth occured in those\ud individuals that ate fewer prey species or ate relatively more of\ud one species than other species represented in the diet. There was\ud no significant relationship between type of prey species and\ud growth.\ud A six-month laboratory feeding experiment showed that shell\ud growth but not gonad development was affected significantly by\ud previous experience with particular prey, and by species\ud composition of the diet. Snails grouped by previous experience\ud (diet chosen during 1 month in laboratory experiments) were fed\ud single species and restricted mixed diets. Different combinations\ud of diet and experience had both positive and negative influences on\ud shell growth, depending on the specific combinations of the\ud original and restricted diets. After feeding for 5 months on a\ud restricted diet of a certain prey species, individuals presented\ud with a choice of the 3 prey species usually chose prey\ud corresponding to the species of their restricted diet.\ud Monthly gonad samples of 20 adult snails indicate that male\ud gonad indices remained almost constant over a year whereas females\ud peaked from June through October. Fertile individuals of both\ud sexes were found throughout the year.\ud Thais melones females deposit their flattened, lens-shaped egg\ud capsules inside clean, recently dead bivalve or barnacle shells.\ud Egg capsules were deposited throughout the year with larvae\ud hatching from capsules as swimming planktonic veligers