Energetic constraints on mating performance in the sand goby

I tested the effect of food addition on reproductive success in male sand gobies, Pomatoschistus minutus, by comparing food-supplemented males with unfed, control males. The sand goby is a small marine fish with paternal egg care. The males were breeding in artificial nest sites in otherwise natural conditions in the field. I quantified energy reserves by extracting nonpolar lipids. The food supplement improved the fat reserves of the fed males as compared to unfed males. Fed males spent more time at the nest, whereas unfed males spent a much smaller proportion of their time at the nest. As a consequence, fed males mated sooner than unfed males and tended to get more eggs. In the unfed group, mating speed was correlated to body length so that bigger males mated sooner. The results suggest that the reproductive success of breeding sand goby males is constrained by the availability of energy but that this constraint is most severe for small males and less severe for bigger males. Energy availability through its effect on condition will affect the investment in reproductive effort.