Male body size and paternal behaviour in smallmouth bass, Micropterus dolomieui (Pisces: Centrarchidae)

Male smallmouth bass defend nest sites and progeny after spawning. Females may consequently discriminate between potential mates with respect to characters that indicate paternal quality. Survivorship of offspring was previously found to be positively related to the site tenacity of a male following a disturbance at the nest. In this study, a comparison of the behaviour of 462 males over four spawning seasons indicated that both body size and the developmental stage of offspring in nests influenced male guarding behaviour. Large males were more site-tenacious than small males following a human disturbance at the nest, but the strength of the association differed between spawning seasons. Males that were guarding eggs at the time of intrusion were more tenacious than males that were guarding larvae, suggesting the higher ventilation requirements of eggs may motivate males to assume higher risks of injury. Male tenacity depended neither on the date of the spawning season on which male behaviour was evaluated, male age, nor the number of offspring defended after accounting for male body size and the developmental stage of offspring. Male body size could thus provide female M. dolomieui with an a priori indicator of the paternal quality of potential mates. Comparisons of male mortality indicated that the cost of reproduction did not depend on body size and that large parental males suffered a higher reproduction-independent mortality than small parental males. Size-dependent mortality could consequently favour a relatively higher investment into current progeny by large males. Large males should also be capable of a higher absolute investment into current offspring than small males because of size-dependent metabolism and reduced feeding during the period of parental care. Higher absolute investment by large males may explain the apparent female mate preference for large male M. dolomieui and the tendency for females to prefer large males as mates in other fishes with paternal care.