Meeting Abstract

87.1  Wednesday, Jan. 7  Copulation kinematics in Poecilia, a genus of livebearing fish SCHULTZ, Eric T.*; BLOB, Richard W.; PTACEK, Margaret B.; University of Connecticut; Clemson University; Clemson University eric.schultz@uconn.edu

Copulatory organs evolve rapidly in response to diverse selective pressures affecting survival and mating success. In livebearer fishes (subfamily Poeciliinae), intromission of sperm is accomplished with the gonopodium, a modified anal fin. Gonopodium length evolves in concert with mating behavior, but this association varies at different taxonomic levels. In the mollies (genus Poecilia), unlike at the family level, the gonopodium is 10% longer in species that copulate following courtship than in species that copulate without courtship. Furthermore, gonopodium length varies hypoallometrically in every species; the gonopodium is one-third of the body length in small males but only one-fifth of the body length in large males. In an effort to clarify the functional consequences of these morphological patterns, we are quantifying both intra- and interspecific variability in copulatory kinematics. Using high speed digital videography at 500 frames per second, we have recorded the copulation attempts of five species of mollies, including a range of male sizes within each species. We focused on the speed with which the gonopodium is moved in a circumduction, from resting to the angle of intromission. Circumduction speed is predicted to vary with the size of the gonopodium, its musculoskeletal base, and with mating behavior. Circumductions are expected to occur at slower speeds in species with courtship, and in smaller individuals with relatively longer gonopodia. Our tests of these hypotheses contribute to reconstructing the evolutionary history of copulatory organ form in a functional context.