JOHNSON, S.L.*; YUND, P.O.; Darling Marine Center, University of Maine; Darling Marine Center, University of Maine: Sperm longevity and fertilization in the colonial ascidian, Botryllus schlosseri.

Sperm longevity in free-spawning marine invertebrates that broadcast their eggs is typically assumed to be irrelevant to field fertilization processes. If gametes are quickly diluted after release, contact between eggs and sperm may become unlikely long before gamete viability limits fertilization. By contrast to broadcasters, many free-spawning brooders that retain eggs for internal fertilization may use filter-feeding mechanisms to concentrate dilute sperm from the water throughout a prolonged period of egg viability. If so, variation in sperm longevity may significantly affect field fertilization levels. Consequently, we explored the effects of temperature, mixing, and sperm behavior on sperm longevity in the colonial ascidian, Botryllus schlosseri. Our data indicate that B. schlosseri sperm live considerably longer than sperm of many other marine invertebrate taxa and are able to fertilize at extremely low sperm concentrations, but that sperm longevity and behavior may differ across the range of temperatures commonly encountered in nature. These results also have implications for our understanding of sperm metabolism and function in B. schlosseri. Viability of sperm on the time scale that we report suggests that sperm must remain inactive for much of their life span.