Meeting Abstract

63.5  Jan. 7  The effect of fertilization distance on the relationship between sperm production and male reproductive success in a colonial marine invertebrate JOHNSON, S.L.*; YUND, P.O.; University of Maine; University of New England sherij@maine.edu

The shape of the function that describes the relationship between resources allocated to sperm production and resulting male fertilization success (the male gain curve) plays a central role in models of sex allocation in hermaphrodites. A variety of ecological factors are expected to affect the shape of this function. In some free-spawning taxa, high levels of sperm production may be the result of selective pressures to maximize male fertilization success in competitive situations. When male gain curves saturate at fairly low sperm production levels in the absence of competitors, higher levels of sperm production may only be adaptive in competitive situations. Alternatively, high levels of sperm production might instead be adaptive if they enhance the ability of a male to fertilize distant eggs. Thus, even if the male gain curve saturates for fertilization of nearby eggs, it may remain linear through higher allocation levels if distant fertilizations are considered. We have explored the effect of distance on male gain curves in the colonial ascidian, Botryllus schlosseri. The performance of focal males was assayed at 10, 60 and 160 cm. Microsatellite markers were utilized for paternity assignment in experimental populations. Fertilization decreased with distance from focal males and microsatellite data confirmed short-distance gain curves previously reported from allozyme data. Results suggest that high levels of sperm production may enhance male fitness, both in competitive situations, and with fertilization distance. These results highlight the need to consider distance effects when evaluating gain curves in free-spawners.