CAREER: Colonizing Land Via the Estuarine Route: Ontogeny of Osmoregulation and Settlement Behaviors in Three Brackish Water Fiddler Crabs

University South Carolina Research Foundation, Columbia SC

Investigators

Abstract

CAREER: Colonizing land via the estuarine route: ontogeny of osmoregulation and settlement behaviors in three brackish water fiddler crabs Renae J. Brodie University of South Carolina The colonization of land is one of the most significant evolutionary events in the history of animal life. While vertebrates are conspicuous members of terrestrial faunas, the most prolific and diverse land animals are actually invertebrates that have evolved from marine ancestors. One of the first challenges faced by colonizing marine invertebrates is the need to modify larval stages so they recruit near adult terrestrial habitats. Larval settlement behaviors must change and larvae must evolve the capability to tolerate physiological stresses that they encounter on land. In completely terrestrial animals, these early life stages develop on land within protective egg membranes or inside the adult parent. This study will examine changes in larval behavior and physiology in Uca minax, a freshwater fiddler crab that is at an intermediate stage of land invasion. To examine these changes, U. minax will be compared to two less terrestrial relatives, Uca pugilator and Uca pugnax. All three species undergo larval development in coastal marine waters. Using molecular genetic techniques, these fiddler crab species will be tracked from when they leave open coastal waters and enter South Carolina's north inlet estuary, until they join adult populations as juveniles. This will resolve the mystery of whether young crabs settle directly into adult habitats, move in gradually as they develop and grow, or settle randomly throughout the estuary, dying out in areas that are not suitable for them. Once patterns of settlement are established, larval responses to adult odor cues in different salinity environments will be investigated in the lab. A different suite of behavioral responses by U. minax compared to the other two species may help to explain how it invades adult freshwater and terrestrial habitats. To determine if young U. minax are physiologically adapted to survive low-salinity conditions, survivorship of larval and juvenile U. minax in a series of salinities (ocean-strength to freshwater) will be compared to that of U. pugilator, U. pugnax and U. uruguayensis, a distantly-related species from Brazil. Osmoregulatory ability (ability to control internal salt concentrations) at these salinities will also be assessed. In this way, it will be possible to explore the evolution of osmoregulatory changes in development that accompany the invasion of land in fiddler crabs. In addition to yielding evolutionary insights, this study will have ecological and educational impacts. Fiddler crabs are dominant players in southeastern estuaries, where they are important prey for birds and fishes, and modify landscape topography and species composition in areas where they burrow and feed. A more detailed understanding of the dispersal patterns, behavior and physiology of young fiddler crabs will facilitate the monitoring of estuaries. The educational benefits of this work will come from a strong effort to increase the level of participation of people of color in biological research. To this end, graduate and undergraduate students of color will be recruited from the University of South Carolina and nearby Historically Black Colleges and Universities to assist in the proposed research. Also, undergraduate and graduate students will turn aspects of the scientific work into hands-on activities for K-12 students that will be developed for a Web site about marine and terrestrial invertebrates with the assistance of local elementary-school children.