The importance of sperm competition risk and nest appearance for male behavior and female choice in the sand goby, Pomatoschistus minutus

To test if an increased sperm competition risk affects male behavior and mating decisions of both sexes, we performed two experiments using the sand goby, Pomatoschistus minutus, a nest-building fish with exclusive paternal care. In our first experiment, a nest-holding male, with a confined female, was sequentially exposed to a vial with a sneaker male or an empty vial. While male courtship, nest building, displacement fanning, and time outside the nest were unaffected, individual males showed a higher mucus preparation effort inside the nest in the presence of a sneaker male than when alone. We found such mucus to contain sperm, thus clearly suggesting an importance in sperm competition. In our second experiment, a female was free to spawn with two different males, one of which was exposed to a confined sneaker male. Male mating success was not affected by the presence of a sneaker male. However, the volume of sand the male had put on his nest was positively associated with female spawning decision, while nest-opening width was not. In a partial correlation of five traits thought to attract females (nest-opening width, sand volume, male courtship display, displacement fanning, and male size), males that fanned well were found to also build large nests or display intensely, but not both. This indicates that rather than being jacks-of-all-trades, individual males focus on a subset of traits for attracting females. Copyright 2005.