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HOST SELECTION, CHEMICAL DETECTION, AND PROTECTION OF THE SYMBIOTIC PINNOTHERID CRABS DISSODACTYLUS CRINITICHELIS AND CLYPEASTEROPHILUS RUGATUS ASSOCIATED WITH ECHINODERMS By Misty N. Reeves A Thesis Submitted to the Faculty of the Charles E. Schmidt College of Science in Partial Fulfillment of the Requirements for the Degree of Master of Science Florida Atlantic University Boca Raton, Florida August 2000 HOST SELECTION, CHEMICAL DETECTION, AND PROTECTION OF THE SYMBIOTIC PINNOTHERID CRABS DJSSODACTYLUS CRJNJTJCHELJS AND CLYPEASTEROPHJLUS RUGATUS ASSOCIATED WITH ECHINODERMS By Misty N. Reeves This thesis was prepared under the direction of the candidate's thesis advisor, Dr. W. Randy 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. Thesis Advisor Dr. W. Randy Brooks Ch~artment of Biologic 7 6 ~I) Date ll ACKNOWLEDGEMENTS I would like to thank Dr. W. Randy Brooks for his patience and assistance throughout this project as my major professor. I am also grateful to Dr. A Marsh for his kind and generous support and to Dr. J. Baldwin for accepting my invitation into the project. I am grateful to my thesis committee for the time and energy they have put into serving on my committee and reviewing my manuscript. I would also like to thankS. Tuxbury, S. Perez, and C. Miller for their assistance in field collections and advice. Additional thanks goes to Dr. D. Felder of the University ofLouisiana-Lafayette and the Smithsonian laboratory in Fort Pierce, Florida for help in identification of the tiny crabs involved in this study. I would like to express my deepest gratitude to my parents, Lee Kruse and Beverly Hite; my brother, Nolan; my father-in-law & mother-in-law, Mr. and Mrs. Don Reeves; and my husband Patrick for his love, unconditional support, and his way of fmding the best in things. Ill ABSTRACT Author: Misty N. Reeves Title: Host Selection, Chemical Detection, and Protection of the Symbiotic Pinnotherid Crabs Dissodactylus crinitichelis and Clypeasterophilus rugatus Associated with Echinoderms Institution: Florida Atlantic University Thesis Advisor: Dr. W. Randy Brooks Degree: Master of Science Year: 2000 Host selection by Dissodactylus crinitichelis and Clypeasterophi/us rugatus for different echinoderms was investigated. Initial preference (within 24 h of collection) and preference after "conditioning" with an alternate host were compared. D. crinitichelis initially preferred its field host, the sand dollar Encope michelini, but after conditioning switched its host preference to a non-field host, the sea biscuit Clypeaster rosaceus. This switch in host preference after conditioning occurred despite consumption of numerous crabs (86 out of 167) by C. rosaceus. Clypeasterophilus rugatus initially preferred its field host, the sea biscuit Clypeaster rosaceus, but showed little change in host preference after conditioning. These results indicate significant behavioral differences in these closely related crabs in their association with echinoderms. Chemical detection by the crabs was investigated, and no significant use of chemical cues by adults or juveniles of either species was found, even though chemical responses have been observed in other closely related pinnotherid crabs. Using the checkered pufferfish, Sphoeroides testudineus, as a predator, the possibility that crabs may receive protection by living with echinoderms was also examined. Crabs with echinoderms survived significantly longer than crabs without echinoderms, which is the first direct evidence that these crabs are protected by associating with echinoderms. IV TABLE OF CONTENTS . fF. .. L1St 0 1gures ........ ..................................................................... VII Introduction ................................................................................. 1 Materials and Methods ..................................................................... 5 Collection and Maintenance of Specimens ........................................ 5 Habitat Description & Field Associations ................................... ....... 5 Crab Identification ..................................................................... 6 Host Preference Trials ................................................................ 6 Initial Preference Tests ................................................................ 6 Post-Conditioning Preference Tests ................................................. 7 Chemical Detection Trials ............................................................ 8 Predation Trials ........................................................................ 9 Substitute Host .. ........................................................................ 9 Results ...................................................................................... 10 General Observations .............................................................. .. 10 Host Preference Trials .............................................................. 10 Initial Preference Tests ............................................................... 10 Crab Size Influence ................................................................. 11 Post-conditioning Preferences ....................................................... 11 Crab Attrition .......................................................................... 12 Chemical Detection Trials ........................................................... 12 v Predation Trials ....................................................................... 12 Substitute Host ........................................................................ 12 Behavior of Crabs and Fish in Predation Trials .................................. 13 Discussion .................................................................................. 14 Host Preferences ...................................................................... 14 Chemical Detection .................................................................. 17 Protection ............................................................................. 18 Appendix 1 ................................................................................ 20 Clypeasterophilus ruga/us on a ruler .................. ..... .. ... ........ .......... 20 Clypeasterophilus rugatus on the sea biscuit Clypeaster rosaceus ... ......... 20 Appendix 2 ................................................................. .... ... ........ 21 Dissodactylus crinilichelis next to a nickel.. ...................................... 21 Dissodactylus crinilichelis on the sand dollar Encope michelini ............... 21 Bibliography ................. .. ................... .. ...................................... 22 VI LIST OF FIGURES Figure 1. Four-chambered choice apparatus used in chemical detection tests ............ 24 Figure 2. Trough apparatus used in chemical detection tests ............................ ... 25 Figure 3. Results of initial preference tests made within 24 h of collection ............... 26 Figure 4. Results of initial host preference versus crab size ..... ....... .. .............. .. ... 28 Figure 5. Results of post-conditioning preference tests, comparing initial host preferences with subsequent preferences after "conditioning" (fmal preference) ......... 29 Figure 6. Predation results showing survival times for D. crinitichelis with a pufferfish predator Sphoeroides testudineus ............................................................... 30 Figure 7. Predation results showing survival times for C. rugatus with a pufferfish predator Sphoeroides testudineus ....... ...................................................... 31 VII INTRODUCTION Many examples of symbiosis exist in the sea where smaller symbionts or epibionts seek out larger hosts, presumably because suitable refuge is limited and competition for space high. Such associations allow for the study of behavioral interactions among species and innovations by the symbionts to facilitate the initiation and maintenance of the association. A common marine example involves pinnotherid crabs of the genera Dissodactylus and Clypeasterophilus living with various types of echinoderms. A specific example involves Dissodactylus mellitae, which lives on the sand dollar Mel/ita quinquiesperforata (in Beaufort, North Carolina) clinging to spines via modified chelae and pereiopods (Telford, 1982; Bell, 1987). Because of their small size and inconspicuous nature, it is unlikely the crabs provide benefit such as protection to the echinoderms. In fact, they are generally regarded as commensals or parasites (Telford, 1982). How the crabs benefit from the symbiosis has been a topic of investigation. Some reports indicate that D. mellitae eats spines and tube feet (Telford, 1982; Bell, 1987), as these structures have been found in gut analyses (Telford, 1982). However, it is unclear whether the tissues consumed were live or necrotic; thus, the relative harm to the echinoderm is unknown. The crabs also frequent the oral surface of the sand dollar (Bell, 1987). While near the mouth or ambulacral grooves, food collected by M quinquiesperforata may also be available to the crabs. Although echinoderms are unlikely to be effectively defended by these tiny crabs, protection to the crab is a possible benefit of the association. The crab's cryptic coloration and positioning on the