Causes and consequences of voluntary anorexia during the parental care period of wild male smallmouth bass ( Micropterus dolomieu)

Abstract

By definition, parental care behaviors increase offspring survival, and individual fitness, at some cost to the parent. In smallmouth bass ( Micropterus dolomieu), parental males provide sole care for the developing brood that includes an increase in activity during brood defense and decreased foraging resulting in a decline in endogenous energy reserves. No mechanisms have been proposed for cessation of voluntary foraging, though regulation of appetite hormones such as ghrelin have been documented to affect feeding behavior in other fishes. We documented baseline fluctuations in plasma ghrelin concentrations across parental care. Plasma ghrelin concentrations were lowest during the early stages of parental care before increasing as the brood developed to independence. Additionally, we performed an intervention experiment whereby plasma ghrelin levels were artificially increased through an injection of rodent ghrelin at the onset of parental care. Despite measuring a significant increase in plasma ghrelin approximately 1 week after injection, we noted no differences in plasma-borne indicators of recent foraging activity indicating that voluntary anorexia is possibly reinforced by receptor insensitivity to appetite hormones. Finally, we assessed the ultimate consequences of foraging during parental care by feeding fish to satiation and measuring post-prandial changes in swimming performance and aggression. Fish fed to satiation showed significant decreases in burst swimming ability and aggressiveness towards potential brood predators. Voluntary anorexia during smallmouth bass parental care is an adaptive behavior that avoids potentially deleterious declines in swimming performance and aggression apparently through a modulation of production and reception of appetite hormones including ghrelin.