HARPER, F.M.*; HART, M.W.; Dalhousie Univ, Halifax, NS; Dalhousie Univ, Halifax, NS: In vitrohybridization of the seastars Asterias forbesiand A. rubens

Zones of secondary contact for sibling species provide natural environments to study speciation and mechanisms of pre- and post-zygotic reproductive isolation. The Gulf of Maine extending into the Bay of Fundy is a secondary contact zone for two species of seastar, Asterias forbesiand A. rubens, which initally differentiated into separate North American and European species respectively following a vicariance event. As part of a larger study of introgression and hybridization in these species, we conducted a series of cross-fertilization experiments to examine interspecific gamete compatibility by analyzing the effects of sperm concentration, egg concentration, and sperm age on intra- and interspecific fertilization success. Early development rates were also determined to assess acrosome recognition times. No differences were found between hybrid and non-hybrid crosses and heterogametic fertilization success was high. Although larval mortality was high for all crosses, larvae from each type of cross successfully metamorphosed. After one year of culturing juveniles in the laboratory, hybrid and non-hybrid animals attained an average size R = 39.1 mm (± 4.1), but were not yet sexually mature. Fertility in F1 backcrosses is not yet known. Ready hybridization of these two sibling species in the laboratory indicates gamete incompatibility is not a mechanism in maintaining their reproductive isolation.