HC resource01 - Hermit Crab Shell Selection Based on...

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Hermit Crab Shell Selection Based on Coloration Alison N. Rellinger, Lauren T. Chaloux, Trina M. Fisher, and Amanda J. Burns St Mary’s College of Maryland at Historic St Mary’s City Maryland May 2004 Hermit crabs are fully dependant on gastropod shells for survival and they often exhibit fierce competition for a limited resource of shells. Larger, less damaged shells have been shown to be more desirable by crab populations (Bertness, 1981a, 1981b; Childress, 1972; Hazlett, 1981; Lively 1988). This study was intended to determine whether the color of the shell also has an impact on shell preference by the hermit crab Coenobita clypeatus , a large terrestrial hermit crab. It was hypothesized that the hermits would choose lighter colors such as white, red and green over darker colors such as black and a mostly black multi-colored shell because the lighter shells would retain less thermal energy. Results were statistically insignificant, but produced interesting trends that suggested support for the hypothesis. Future experimentation with more trials would probably produce statistically significant results. Introduction Hermit crabs are crustaceans that are found in a wide variety of habitats. They range from fully marine crabs to crabs that are actually fully terrestrial, except for spawning (Museum Victoria,1996). All hermit crabs are fully dependent on the shells of deceased gastropods for protection from predation, and terrestrial hermits depend on the shells for prevention of desiccation (Childress,1972). The size of the shell is often a limitation for the growth of the crab, so hermit crabs must be somewhat selective with their shell choices if they are to survive (Lively, 1988). Crabs also select the shells based on quality; those shells that are not fully intact are less desirable (Bertness, 1981a) The need for acceptable shells is high and the availability of such shells is quite limited, creating fierce competition for desirable shells (Bertness, 1981a). In fact, most species of hermit crabs have evolved some sort of highly ritualized “shell fight” that determines which crabs are dominant and will therefore inhabit the better shells (Lancaster, 1994). Gastropod shells come in very diverse forms, and crabs have been shown to have preference for shells of certain sizes, weights and even shapes (Bertness, 1981a, 1981b; Childress, 1972; Hazlett,1981; Lively, 1988). Interestingly, however, few studies have even mentioned the fact that the shells of these gastropods vary widely in coloration and markings. Even fewer studies have mentioned the possibility of a correlation between these markings and hermit crab preference; however, Hazlett makes note of an indirect correlation between visual displays and shell availability (1981). Hermit crabs have compound eyes that are located on the end of stalks and that appear to be quite accurate at detecting movement, even at distances up to 30 meters away (Museum Victoria,1996). Hermit crabs can distinguish at least some variation in color, but light levels at dusk and dawn may not be high enough for perfect color vision (Marshall,2004). For this
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This note was uploaded on 02/27/2010 for the course PHYSICS 215 taught by Professor Lawn during the Spring '10 term at Academy of Art University.

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HC resource01 - Hermit Crab Shell Selection Based on...

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