Stress and Dominance in a Social Fish

Abstract

Many aspects of reproductive physiology are subject to regulation by social interactions. These include changes in neural and physiological substrates of reproduction. How can social behavior produce such changes? In experiments reported here, we manipulated the social settings of teleost fish and measured the effect (1) on stress response as reflected in cortisol production, (2) on reproductive potential as measured in production of the signaling peptide, gonadotropin-releasing hormone, and (3) on reproductive function measured in gonad size. Our results reveal that the level of the stress hormone cortisol depends critically on both the social and reproductive status of an individual fish and on the stability of its social situation. Moreover, the reproductive capacity of an individual fish depends on these same variables. These results show that social encounters within particular social contexts have a profound effect on the stress levels as well as on reproductive competence. Social behavior may lead to changes in reproductive state through integration of cortisol changes in time. Thus, information available from the stress pathway may provide socially relevant signals to produce neural change.

Social and reproductive physiology and behavior of the Neotropical cichlid fish Cichlasoma dimerus under laboratory conditions

“…In both sexes, nRnT individuals had higher serum cortisol than RT ones. In A. burtoni it was clearly demonstrated that nT males had more plasma cortisol levels than T ones, but this is also highly dependent on community conditions and length of time in these conditions (Fox et al, 1997;. In C. dimerus cortisol may serve as an endogenous signal relating the social environment to the social status of the animal, behavior and internal reproductive state.…”

“…There are strong interactions between behavior, the endocrine and nervous systems that affect the interactions between an animal and its environment, including social interactions. For example, dominance status has been shown to control fertility (Fraley & Fernald, 1982;Abbot et al, 1998;Faulkes & Bennet, 2001), suppressing gonadal maturation in subordinate individuals (Barret et al, 1990), and also influence on neurogenesis (Kozorovitskiy & Gould, 2004), growth rate (Hofmann et al, 1999), and stress (Fox et al, 1997;Abbot et al, 2003). Although social regulation on several physiological processes is a well-established phenomenon, little is known about the mechanisms linking the social environment to physiological changes associated with dominance.…”

“…Although social regulation on several physiological processes is a well-established phenomenon, little is known about the mechanisms linking the social environment to physiological changes associated with dominance. Fox et al (1997) found that the level of the stress hormone cortisol depends critically on both the social and reproductive status of an individual fish and on the stability of its social situation.…”

“…Reversible changes in reproductive competence, adoption of distinct reproductive strategies within one sex, and reversible or permanent changes in gonadal sex are examples of the influence of the behavior on the reproduction (Ross, 1990;Taborsky, 1994). In this context, cichlids (Perciformes: Cichlidae) have been intensively used as experimental models for studies of social control of reproduction, in particular African cichlids, such as the African tilapia Astatotilapia burtoni (Günther, 1894) (= Haplochromis burtoni) and Oreochromis mossambicus (Peters, 1852) (Fox et al, 1997;Ogawa et al, 2006). Behavior of African cichlids is better characterized than the Neotropical cichlids, and most of whose species have not been extensively studied at the behavioral level.…”

Physiological consequences of social descent: studies in Astatotilapia burtoni

“…However, the relationship of cortisol to social status in A. burtoni appears to depend not only on the status of the individual, but also on the social community and maturational state of the animals. For example, when males are housed in T-NT social pairs, GnRH neuronal soma size differences are significantly up-regulated in Ts vs NTs and differences in cortisol are statistically significant in older fish that lived as stable pairs for 2 weeks (Fox et al 1997). Among younger fish and in the first week of such pairings, cortisol levels were significantly more variable and showed only a trend towards higher values in NT males.…”