VISUAL ORIENTATION TO GASTROPOD SHELLS BY CHEMICALLY STIMULATED HERMIT-CRABS, CLIBANARIUS-VITTATUS (BOSC)

Visually directed movements of the hermit crab Clibanarius vittatus (Bosc) toward 6 species of gastropod shells were studied in a circular arena with a white wall. The study tested the hypothesis that crabs visually discriminate between different species of shells. Only Investigating Crabs, those exhibiting chemically induced shell-investigation behavior, were tested. All trials were in the presence of chemical cues generated by freezing and thawing flesh from the gastropods Busycon carcia or Polinices duplicatus. Directional orientation orientation was absent when crabs were presented with the white background alone. Each shell was tested in different positions (e.g., anterior, posterior, upside-down, lateral). Crabs were attracted to shells in 9 of the 18 test conditions, with strongest attraction to Polinices duplicatus (posterior position) and Busycon contrarium (lateral position). Since attraction was not related to shell height, width, or surface area, it was concluded that crabs can discriminate between shells and were most attracted to shells that attain larger sizes. In a second experimental series, shells of B. contrarium or P. duplicatus were presented simultaneously in different positions. Crabs could distinguish between both species in different positions. When these 2 shell species were presented simultaneously, crabs were significantly attracted to P. duplicatus in the presence of the odor of either B. carica or P. duplicatus. Thus, these results support the hypothesis and further indicate that attraction to a shell involves a complex interaction of proprioreceptive input from the host shell, chemical cues indicating the availability of a new shell, and visual recognition of a particular shell species.