The role of prolactin in the regulation of brood care in the cooperatively breeding fish Neolamprologus pulcher

Abstract

The hormone prolactin (PRL) is important for the regulation of parental care in many species of mammals, birds and fish, and for alloparental care (care directed at nondescendant young) in some mammals and birds. Its significance in alloparental brood care of cooperatively breeding fish has not yet been assessed. Here, we test the role of PRL in brood care behavior of the cooperatively breeding cichlid Neolamprologus pulcher. The expression of PRL mRNA was determined in the pituitary glands of breeders of both sexes, helpers that showed brood care behavior and nonbreeding fish as controls. In addition, PRL levels were experimentally manipulated in male breeders and helpers by intraperitoneal injections of ovine PRL, and the behavior of these test fish was recorded toward standardized clutches. Adult females had higher levels of PRL mRNA than adult males, which was true both for breeders and nonbreeders. Contrary to expectation, there was no positive correlation between PRL and brood care behavior in any category of test fish, and the experimental application of PRL did not change brood care propensity. Interestingly, brood-caring adult females had significantly lower levels of PRL mRNA than adult female nonbreeders, whereas there was no difference between helpers and similar-sized nonbreeding group members. PRL mRNA levels increased with body mass in juveniles, but decreased with body mass in adults. In conclusion, we found no evidence that elevated levels of PRL are directly involved in the regulation of brood care behavior in this species.

Comparative gene expression profiles for highly similar aggressive phenotypes in male and female cichlid fishes (Julidochromis)

“…Therefore, the male bias in expression may be consistent with the observation that in fish prolactin is particularly important for paternal rather than maternal care (Schradin and Anzenberger, 1999). The bias in prolactin expression in our present study of monogamous species is inconsistent with findings from a related cooperative breeding cichlid species (Bender et al, 2008).…”

Hormonal control of brood care and social status in a cichlid fish with brood care helpers

“…In an accompanying study we found no evidence for a positive effect of prolactin on parental or alloparental care in N. pulcher [36]. Furthermore, several studies showed similar androgen levels in male breeders and male helpers of N. pulcher [5,37], which probably relates to the fact that in this species male helpers may participate in reproduction [38,39].…”

The role of prolactin in fish reproduction

“…In this species, PRL does not appear to be important for nest maintenance, and females providing brood care have lower PRL mRNA levels than non-brooding females [8]. As this study used both observational and manipulative experiments and a highly sensitive quantitative real-time PCR (qPCR) assay (see Section 5.3), its counterintuitive results appear to be robust, and may be explained by the fact that N. pulcher is a cooperatively brooding species with a complex social hierarchy.…”

“…This approach was taken by Bender et al [8] in their study of parental behaviour in the daffodil cichlid (described in Section 4.3.4). This two-pronged tactic provides an increased degree of sensitivity to identify subtle variation in endocrine function and adds greater confidence to experimental results.…”