COMPUTER-SIMULATION SUGGESTS THAT THE SPATIAL-DISTRIBUTION OF MALES INFLUENCES FEMALE VISITING BEHAVIOR IN THE RIVER BULLHEAD

It is known from previous laboratory studies that female choice in the river bullhead, Cottus gobio, is mainly influenced by the size of the male, and that the presence of eggs in the nest also plays a role. Ho wever, the process by which females visit and choose among prospective mates is still poorly understood We examined eight possible tactics o f female choice through computer simulation, and me compared their fit to the reproductive patterns observed in two natural populations. Nei ther of the tactics proposed for other species, nor combinations of th em, mere able to predict accurately the field data, although one of th em (fixed threshold) provided a fairly good fitting. Conversely, a new model (cluster sampling), which takes into account the spatial distri bution of males, produced for both populations a set of predictions on the male mating success not significantly different from the data rec orded in the field. Under this model, females sample more males when m ales are clumped, thus reducing substantially on the average, the rati o between the distance travelled before spawning and the number of sam pled males. When models incorporated the preference ibr already mated males, good fitting was obtained if females preferred nests containing eggs not older than 36 h, a finding that agrees with field results.