Early Filial Cannibalism in Fish Revisited: Endocrinological Constraint, Costs of Parental Care, and Mating Possibility.

AbstractOffspring desertion by parents generally occurs at an early stage of parental care, which is thought to minimize the costs of parental care prior to desertion. This study investigated the effects of endocrinological constraints on early total filial cannibalism by male Rhabdoblennius nitidus in the field, a paternal brooding blennid fish with androgen-dependent brood cycling. In brood reduction experiments, cannibal males showed low levels of plasma 11-ketotestosterone (11-KT) relative to noncannibals and also similar levels of 11-KT to males in the parental care phase. Since 11-KT regulates male courtship intensity, males with decreased courtship activity would exhibit total filial cannibalism. However, there is a possibility that a transient increase in 11-KT levels at the early stage of parental care delays total filial cannibalism. In contrast, total filial cannibalism could occur before a decline to the lowest 11-KT levels, at which point males might still be able to exhibit courtships, possibly to reduce the costs of parental care. To understand how much and when caregiving males exhibit mating and parental care behaviors, it is important to consider not only the presence of endocrinological constraints but also its intensity and flexibility.

Effect of the administration of prolactin-releasing peptide2 on feeding activity in the intertidal blenny Rhabdoblennius nitidus (Günther, 1861).

Prolactin-releasing peptide2 (PrRP2) was administered intraperitoneally to male intertidal blenny Rhabdoblennius nitidus, a species with male uniparental care of eggs, to investigate the effect on their feeding activity. A significant inhibitory effect on appetite was observed in the breeding season, but not in the nonbreeding season. These results suggest that PrRP2 and PrRP2 receptors are more active during the breeding season. The presence of a mechanism to inhibit feeding activity while parents take care of their offspring may be important for the success of parental care.