Costs and benefits of parental effort in a brood-guarding fish (Ambloplites rupestris, Centrarchidae)

Abstract

The hypothesis that parental effort can enhance offspring survival but at a cost to the parent(s) in terms of reduced residual reproductive value was tested in male rock bass (Ambloplites rupestris), a temperate fresh water fish with uniparental male care. Relative change in wet mass incurred by male rock bass while caring for and defending the brood was used as an index of parental effort. Results of a field experiment in which brood size was manipulated in nests guarded by males of three different size classes showed that: (1) brood size has a significant linear effect on parental mass loss, with males allocating a greater proportion of their initial mass when guarding larger broods, and a negative effect on per capita offspring survival, with offspring survival dropping with increasing brood size; (2) parental body size has a significant nonlinear effect on mass loss, with medium-sized males allocating relatively more body mass to brood care than either large or small males, and a positive effect on per capita offspring survival, with offspring survival increasing with parental body size; and (3) loss of parental body mass had an enhancing effect on offspring survival only in large-sized males, but the effect was not independent of parental body size or brood size. The impact of parental mass loss on residual reproductive value was quantified by assessing its effect on subsequent parental survival. Change in body mass was quantified for an entire reproductive season in 191 brood-guarding males. The probability of recapturing a parental male the subsequent breeding season significantly dropped with an increase in the proportion of initial mass lost the previous season.