In C. elegans, fertilization occurs only within the spermathecae, specialized regions of the hermaphrodite gonad in which newly ovulated oocytes interact with stored sperm. Thus, a key determinant of male reproductive success is the ability of sperm cells to be present within the spermathecae at the time of ovulation. We have found that the divergent kinase COMP-1 functions in sperm to promote their residence within the spermathecae. Surprisingly, we detect only subtle defects in the directional migration of mutant sperm. Instead, comp-1 sperm accumulate just outside the spermathecae, and largely fail to gain entry until self sperm are depleted. Both sperm usage and localization defects in comp-1 mutants are limited to competitive contexts, raising the question of how sperm signal to other sperm to influence their function. Our data suggest that rather than interacting directly, sperm resident within the sperm storage organ may signal through the female gonad. Bidirectional communication between sperm and the female gonad is known to be used to recruit sperm to migrate toward oocytes and to couple ovulation to the presence of sperm. We find that a subset of these signaling pathways also influence sperm competition, and that wild-type and comp-1 sperm respond differentially to perturbations of the signaling environment. For example, wild-type sperm, unlike those of comp-1, show defects within older hermaphrodites that have depleted their sperm. While oocyte-derived prostaglandins promote migration of wild-type sperm, prostaglandins appear to inhibit comp-1 mutant sperm. Mutants for spe-9 generate sperm that localize correctly but fail to fertilize oocytes; when spe-9 sperm is present in the spermathecae, comp-1 sperm migration is rescued, but wild-type sperm migration is perturbed. Thus, it seems that sperm signal their presence using a mechanism distinct from release of MSP, but potentially involving spe-9. In addition to analyzing known signaling pathways, we are testing whether different substrates for migration, such as fertilized eggs vs. unfertilized oocytes, are differentially permissive for sperm migration or affect the outcome of competition.