DISCRIMINATION OF CHEMICAL SIGNALS FROM GASTROPODS BY HERMIT CRABS by Deirdre C. Gonsalves A Thesis Submitted to the Faculty of The College of Science in Partial Fulfillment of the Requirements for the Degree of Master of Science Florida Atlantic University Boca Raton, Florida August 1996 Discrimination of Chemical Signals from Gastropods by Hermit Crabs by Deirdre C. Gonsalves This thesis was prepared under the direction of the candidate's thesis advisor, Dr. William R. Brooks, Department of Biological Sciences, and has been approved by the members of her supervisory committee. It was submitted to the faculty of The College of Science and was accepted in partial fulfillment of the requirements for the degree of Master of Science. SUPERVISORY COMMITTEE: dAJLrtuiL Thesis Advisor -1//A~ ~ ~~4p~ s and Research Date 11 Acknowledgements I would like to thank Dr. Randy Brooks for his guidance, assistance and faith in me as a graduate student and researcher. He is truly a role model for all aspiring scientists. Thanks to my committee members, Dr. Sheldon Dobkin and Dr. Alex Marsh for their significant contributions to the manuscript. I would also like to thank Drs. Dan Rittschof and Mike Salmon for their creative comments and ideas. I owe an enormous debt of gratitude to Patty Baechler for her assistance in crab collection and maintenance and George Jones at Gumbo Limbo Marine Lab for his help in maintaining hermit crab tanks. Special thanks to the love of my life, Craig Campbell Jackson who now knows more about hermit crabs than most psychologists care to know. Lastly, thanks to my aunt, E. Yvonne Irving who supported me in all my endeavors and instilled in me the importance of education and laughter. This work was supported by a grant from the National Science Foundation to Dr. William R. Brooks. ill ABSTRACT Author: Deirdre C. Gonsalves Title: Discrimination of Chemical Signals from Gastropods by Hermit Crabs Institution: Florida Atlantic University Thesis Advisor: Dr. William R. Brooks Degree: Master of Science Year: 1996 Some species of hermit crabs can locate chemically predation sites where snails are consumed and subsequently obtain their shells. This study addressed four questions: 1) Is chemotaxis to snail odors prevalent among hermit crabs? 2) Do members of hermit crab lineages respond similarly to common snail odors? 3) Do hermit crabs respond more acutely to snails whose shells they most frequently occupy? and 4) Does phylogeny of snails influence responses by hermit crabs? Two sets of congeners (C/ibanarius vittatus/ C. tricolor and Dardanus venosus/ D. fucosus) in the family Diogenidae, and three congeners (Pagurus pollicaris, P. longicarpus, and P. annulipes) in the family Paguridae were tested. Fifteen species of snails from 11 families served as test odors. Hermit crab response was measured by the fondling display, where one hermit crab investigates the shell of a neighboring crab. The diogenids discriminated odors more readily than did the pagurids. Correlations between responses and shells most frequently occupied existed for C. vittatus and D. venosus. Clibanarius tricolor was the only crab to respond to confamilial test odors. IV \ Table of Contents Acknowledgements ................... ............ .... .. ...... .... ..... ... ... ..... ..... ... .... ... ...... .. ...... ............. iii Abstract ............................................ .... ....... ....... .. ... .... .................................... ... ...... ... .... iv List of Tables .. ... ................ ..... .... ... .. .... .. .... ... .. ... ... ............................. ........... ... .... ... .. ... .... vi List of Figures ............... ... .... ........... ......................................... .... .... ......... .. ........ ... ......... vii lntroduction .. .... ................................................................. ............... ......... ... .. .... ... ........... 1 Materials and Methods ............... ... .. ...... .. ..... ....... .. ....... ...... ... .... .. ... ....... ...... .. .. ..... ... .. ....... 4 Hermit crab and snail species .... .. .. .. .. .. ..... ... .... ... ... .... ... .. .. ................ .. .... ..... ... ..... .4 Crab maintenance ....................................... ... ... ..... .. .. .... .. ...... ..... ..... .................... 5 Extract preparation and experimental apparatus ... ... ... ... ... .................................... 8 Experimental procedure .................. .. ....... .... ..... .... ... ... ... ........................ ... .... ........ 8 Results ........... ......... ...... .. ..... ................... ... ...... .... .. .......... ......................... ..... .... ...... ...... 10 Diogenids .... .. ........................ .. .... .. .... .. ....... .. .......... ... .. .. ................. ...... .... .......... 10 Pagurids ... ............ .. .. ........... ............ ..... ............ ... .... ... ... .... ................................. 11 Discussion ........ ............................................... ... .... .... ..... .. .. .... ... ... .... .. ... .. ... .. ..... ........... 26 Prevalence of Responses .... .. .. .... ..... .... ..... .... ..... .... ............................... ...... ....... 26 Patterns of Responses within Hermit Crab Lineages .. ......... ... ...... .... .................. 28 Shell Occupancy Patterns and Responses ..... ......... ... .......... ... ... .. .. ... .... .. ........ ... 29 Snail Phylogeny and Responses ... ...... ... .......... ... ... ..... .. .... ....................... .. ......... 30 Conclusions ....... ............ ........ ... ...................................... .... .. .. ... .. ... .. ... .. ............. 31 References ..... ... ..... .. .... ... ...... ..... .... ............ ... .. ... .. ..... ..... ... ... ... .... .... .............................. 32 v List of Tables Table 1. Odors presented to hermit crabs during bioassays to test for shell­ investigative or fondling behavior Most odors were extracts from snail species, but shrimp extract was also used as a control odor (to distinguish fondling from feeding response). Phylogeny of the snails is given. The column labeled "KEY" indicates the symbol for identification of test odors given on result figures .. .. ............. .... .. .... ... .... ....6 Table 2. Shell occupancy patterns for the seven hermit crab test species collected in study area. Bold type indicates snail species that served as sources of test odors in this study .... .. .. ...... ...... .. .... ..... .. .. .......... 7 V1 List of Figures Figure 1. Percentage fondling of Clibanarius vittatus in response to snail odors. Rank shows most commonly occupied shells by C. vittatus. "*" indi­ cates significant difference between pairwise control and treatment trials for a given snail odor. N=133 for each coupled control/treatment sequence .. ... .... ..... ... .. ... ............................................. .......... .. .... ... ........ .. 12 Figure 2. Percentage fondling of Clibanarius tricolor in response to snail odors. Rank shows most commonly occupied shells by C. tricolor. "*" indi­ cates significant difference between pairwise control and treatment trials for a given snail odor. N=147 for each coupled control/treatment sequence ..... ..... ..... ............. ......... ........ .... ..... ..... ........... ........ .. .. .... ... ...... 14 Figure 3. Percentage fondling of Dardanus venosus in response to snail odors. Rank shows most commonly occupied shells by D. venosus. "*" indi­ cates significant difference between pairwise control and treatment trials for a given snail odor. N= 131 for each coupled control/treatment sequence .. ..... .. .. ... ..... .... ........ ... .. .......... .... ... ... ... ... .. ... ... .. .. ... .. ... .... .. .. .. ... 16 Figure 4. Percentage fondling of Dardanus fucosus in response to snail odors. Rank shows most commonly occupied shells by D. fucosus. "*" indi­ cates significant difference between pairwise control and treatment trials for a given snail odor. N=28 for each coupled control/treatment sequence .... .............. ... .... .... ..... .... .. .................. .. ... .. ... ..... ..... ................. 18 Figure 5. Percentage fondling of Pagurus pol/icaris in response to snail odors. Rank shows most commonly occupied shells by P. pollicaris. "*" indi­ cates significant difference between pairwise control and treatment Vl1 trials for a given snail odor. N=37 for each coupled control/treatment sequence ................... .. .... .......... .. ......... ... .. .. .... ........ ..... .. ... .. ...... ... ..........20 Figure 6. Percentage fondling of Pagurus Jongicarpus in response to snail odors. Rank shows most commonly occupied shells by P. Jongicarpus. "*" indi­ cates significant difference between pairwise control and treatment trials for a given snail odor. N=101 for each coupled control/treatment sequence .................................. ......... .... ....... .. .. ............ .... .. .. .. ...... ...... .... 22 Figure 7. Percentage fondling of Pagurus annulipes in response to snail odors. Rank shows most commonly occupied shells by P. annu/ipes. "*" indi­ cates significant difference between pairwise control and treatment trials for a given snail odor. N=138 for each coupled control/treatment sequence .... ........ ........ ... .. ............................ .. ...... ... ...... .. ..... ... .. .... ..... ..... 24 VU1 INTRODUCTION The shells from dead gastropods are important habitat resources for