Male size determines reproductive output in a paternal mouthbrooding fish

Size can have strong effects on reproductive success in both males and females, and in many species large individuals are preferred as mates. To estimate the potential benefits from mate choice for size in both sexes, I studied the effects of the size of each sex on the reproductive output of pairs of Banggai cardinalfish, Pterapogon kauderni, a sexually monomorphic obligate paternal mouthbrooder. When pairs were allowed to form freely, a size-assortative mating pattern was observed and larger pairs had a higher reproductive output as determined by total clutch weight and egg size. To separate the potential benefits from mate choice for size for each sex, I subsequently used these pairs to form reversed size-assortative pairs, that is, the largest male paired to the smallest female and vice versa. I found a positive correlation between male size and clutch size: relatively heavier clutches were found in pairs where females were given a larger male. This suggests that the size of the male influences clutch weight. For egg size, however, the size of both sexes seemed important. The study reveals the benefits of mutual mate choice on size in this species: larger females provide larger eggs and larger males can brood heavier clutches. Furthermore, these results suggest that females differentially allocate resources into the eggs according to the size of the mate.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .