Parental care and neuropeptide dynamics in a cichlid fish Neolamprologus caudopunctatus

Parental care behaviour in response to perceived paternity is not mediated by 11-ketotestosterone in bluegill sunfish

Parental care is critical for the survival of many young animals, but parental care can be costly to the individual providing care. To balance this cost, parents can allocate their care to offspring based on their value, which can be dependent on the offspring's relatedness to the parent. Bluegill (Lepomis macrochirus) is a fish characterized by uniparental male care and high levels of cuckoldry. While parental males of this species have been shown to adaptively adjust their care in response to paternity, the mechanisms for this adjustment are not well understood. Androgens are steroid hormones that are associated with parental care behaviours in many species including bluegill. Here, we test the hypothesis that circulating androgen concentrations mediate the adjustment in care provided by bluegill parental males by manipulating perceived paternity and then measuring circulating 11-ketotestosterone concentration and parental care behaviour. We show that males with higher perceived paternity provide higher levels of nurturing and nest defense behaviour, but contrary to expectations, we found that these males had lower concentrations of 11-ketotestosterone. Furthermore, we found positive correlations between individual circulating plasma 11-ketotestosterone concentrations and nurturing behaviour, but not with the aggressive behaviours that differed between paternity treatments. While bluegill make behavioural changes in response to perceived paternity, these changes do not appear to be modulated by 11-ketotestosterone.

What is a pair bond?

Pair bonding is a psychological construct that we attempt to operationalize via behavioral and physiological measurements. Yet, pair bonding has been both defined differently in various taxonomic groups as well as used loosely to describe not just a psychological and affective phenomenon, but also a social structure or mating system (either social monogamy or just pair living). In this review, we ask the questions: What has been the historical definition of a pair bond? Has this definition differed across taxonomic groups? What behavioral evidence do we see of pair bonding in these groups? Does this observed evidence alter the definition of pair bonding? Does the observed neurobiology underlying these behaviors affect this definition as well? And finally, what are the upcoming directions in which the study of pair bonding needs to head?

Galanin and prolactin expression in relation to parental care in two sympatric cichlid species from Lake Tanganyika

Our understanding of the hormonal mechanisms underlying parental care mainly stems from research on species with uniparental care. Far less is known about the physiological changes underlying motherhood and fatherhood in biparental caring species. Here, using two biparental caring cichlid species (Neolamprologus caudopunctatus and Neolamprologus pulcher), we explored the relative gene-expression levels of two genes implicated in the control of parental care, galanin (gal) and prolactin (prl). We investigated whole brain gene expression levels in both, male and female caring parents, as well as in non-caring individuals of both species. Caring males had higher prl and gal mRNA levels compared to caring females in both fish species. Expression of gal was highest when young were mobile and the need for parental defense was greatest and gal was lowest during the more stationary egg tending phase in N. caudopunctatus. The onset of parenthood was associated with lower expression of prl and higher expression of gal in N. pulcher, but this pattern was not observed in N. caudopunctatus. Our study demonstrates that gal gene expression is correlated with changes in parental care in two biparental cichlid species and extends both knowledge and taxonomic coverage of the possible neurogenetic mechanisms underlying parental care.

Arg-Vasotocin Directly Activates Isotocin Receptors and Induces COX2 Expression in Ovoviviparous Guppies

Oxytocin (OT) is a crucial regulator of reproductive behaviors, including parturition in mammals. Arg-vasopressin (AVP) is a nonapeptide homologous to Arg-vasotocin (AVT) in teleosts that has comparable affinity for the OT receptor. In the present study, ovoviviparous guppies (Poecilia reticulata) were used to study the effect of AVT on delivery mediated by the activation of prostaglandin (PG) biosynthesis via isotocin (IT) receptors (ITRs). One copy each of it and avt and two copies of itrs were identified in guppies. The results of the affinity assay showed that various concentrations of AVT and IT (10^-6, 10^-7, and 10^-8 mol/L) significantly activated itr1 (P < 0.05). In vitro experiments revealed significant upregulation (P < 0.05) of cyclooxygenase 2 (cox2), which is the rate-limiting enzyme involved in PG biosynthesis, and itr1 by AVT and IT. Furthermore, dual in situ hybridization detected positive signals for itr1 and cox2 at the same site, implying that ITR1 may regulate cox2 gene expression. Measurement of prostaglandin F_2a (PGF_2a) concentrations showed that AVT induced PGF_2a synthesis (P < 0.05) and that the effect of IT was not significant. Finally, intraperitoneal administration of PGF_2a significantly induced premature parturition of guppies. This study is the first to identify and characterize AVT and ITRs in guppies. The findings suggest that AVT promotes PG biosynthesis via ITR and that PGF_2a induces delivery behavior in ovoviviparous guppies.

Female reproductive state is associated with changes in distinct arginine vasotocin cell types in the preoptic area of Astatotilapia burtoni

Nonapeptides play a crucial role in mediating reproduction, aggression, and parental care across taxa. In fishes, arginine vasotocin (AVT) expression is related to social and/or reproductive status in most male fishes studied to date, and is linked to territorial defense, paternal care, and courtship. Despite a plethora of studies examining AVT in male fishes, relatively little is known about how AVT expression varies with female reproductive state or its role in female social behaviors. We used multiple methods for examining the AVT system in female African cichlid fish Astatotilapia burtoni, including immunohistochemistry for AVT, in situ hybridization for avt-mRNA, and quantitative PCR. Ovulated and mouthbrooding females had similar numbers of parvocellular, magnocellular, and gigantocellular AVT cells in the preoptic area. However, ovulated females had larger magnocellular and gigantocellular cells compared to mouthbrooding females, and gigantocellular AVT cell size correlated with the number of days brooding, such that late-stage brooding females had larger AVT cells than mid-stage brooding females. In addition, we found that ventral hypothalamic cells were more prominent in females compared to males, and were larger in mouthbrooding compared to ovulated females, suggesting a role in maternal care. Together, these data indicate that AVT neurons change across the reproductive cycle in female fishes, similar to that seen in males. These data on females complement studies in male A. burtoni, providing a comprehensive picture of the regulation and potential function of different AVT cell types in reproduction and social behaviors in both sexes.