32 Paleontology (Posters) I - Morphology and Biotic Interactions

Sunday, 31 October 2010
8:00 AM - 6:00 PM
Hall D

WHO SAYS THAT SIZE IS NOT IMPORTANT? PREY AND PREDATOR BODY SIZE AND STEREOTYPY IN NATICID DRILL-HOLE LOCATION

Paper number: 32-3
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

Selectivity of naticid predators with respect to drill hole location is well known, but the relationship between prey and predator size and drilling behavior is not as well documented. In this study we integrate results from laboratory experiments with material collected at local beaches to examine the affects of prey and predator body size on the location and type of drilling behavior. We focus on three locally abundant species of venerid bivalve, Iliochione subrugosa, Lirophora obliterata, and Protothaca asperrima. Experiments involved testing for selectivity by Natica unifasciata on multiple prey species, along with controlled generation of drilled valves from combinations of predator and prey with varying body size. Additional shells were obtained from bulk sampled high-tide drift on beaches along the eastern Pacific coastline of Panama. We also compare the stereotypy of drill hole location in these taxa to morphologically similar species Panchione mactropsis and Lirophora falconensis from the Late Miocene Gatun Formation of Panama.

The spatial distribution of drill holes was determined using landmark analysis, and shell length and hole diameter were used as proxies of shell size and predator size, respectively. We found that, independent of sampling site, larger shells (Lirophora >12 mm, Iliochione and Protothaca >20 mm) of all three species were attacked more often on the antero-ventral margin, whereas smaller specimens were drilled most commonly close to the umbo. The anterior and posterior shell margins that correspond with the position of the adductors muscles present the lowest drilling intensity. This spatial distribution is most strongly expressed in the thick-shelled Iliochione. Thinner Protothaca were most commonly drilled in a very tightly clustered area around the umbo, while drilling was scattered across the smaller and more heavily ribbed Lirophora. These results highlight the plasticity in feeding behavior of naticids when encountering prey of varying body size and morphology.