Earthwatch high school student fellowship winners contribute to research on the proximate causes of cleaning symbioses

Cleaning interactions between coral reef fish, the curious behavior of picking tiny parasites and dead tissue off of other fish, are considered a textbook example of symbiosis benefiting both parties. A recent field study in the Caribbean, assisted by fellows in Earthwatch Institute's Student Challenge Awards Program (SCAP), shows evidence of a direct link between cleaning behavior and the level of ectoparasite load under natural conditions.

The findings were reported in the journal Animal Behaviour, in an article titled "In situ evidence for ectoparasites as a proximate cause of cleaning interactions in reef fish," based on research in Puerto Rico and St. John. The authors found that parasite loads of longfin damselfish (Stegastes diencaeus) peaked in the morning, correlating with the time of day that these fish were "cleaned" most by cleaning gobies (Elacatinus spp.)

"It was very significant to establish in the field that peaks in gnathiid ectoparasite loads correspond with peaks in interactions with cleaners," said lead author Dr. Paul Sikkel (Murray State University, Kentucky). "Before this, the only direct evidence of the proximate causes of cleaning interactions has come from lab studies." Sikkel's coauthors are Drs. Karen Cheney and Isabelle Cote of the University of East Anglia.

The authors found that the number of gnathiids (tiny larval crustaceans that latch onto fish and feed on their tissues) found on damselfish sampled, in turn, correlated with the timing of the ectoparasites' emergence from the coral reef each morning. Although lab studies had shown the correlation between gnathiid load and cleaning interactions, this was the first direct evidence of that link in a field study.

"Cleaning symbioses are one of the classic examples of mutualism. Yet, we know little about the mechanisms that bring the mutualists together," said Sikkel. In addition to "proximate" causes, immediate stimuli such as the gnathiids in this study, scientists still debate the "ultimate" benefits that resulted in the evolution of cleaning behavior. "This study brings us closer to that understanding."

Sikkel and his wife, Dr. Claire Fuller (Murray State University), are principal investigators for Earthwatch's Student Challenge Award's Program (SCAP), and SCAP fellows were instrumental in the collection of data in St. John leading to this study. SCAP offers high school students with limited experience in the sciences an opportunity to expand their appreciation for science and conservation by working directly with leading scientists. While Sikkel works on parasites of fish, Fuller explores parasites of termites at the same location, offering SCAP fellows both terrestrial and aquatic experience with host-parasite interactions.

Earthwatch Institute is an international nonprofit organization which supports scientific field research worldwide by offering members of the public unique opportunities to work alongside leading field scientists and researchers. The Institute's mission is to engage people worldwide in scientific field research and education to promote the understanding and action necessary for a sustainable environment.

For more information, see "In situ evidence for ectoparasites as a proximate cause of cleaning interactions in reef fish." Paul C. Sikkel, Karen L. Cheney, and Isabelle M. Cote.
Animal Behaviour 2004 68: 241-247.

Information about the Student Challenge Awards Program