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The effects of early and late androgen treatments and induced sex-reversals on the behavior of Sarotherodon mossambicus (Pisces: Cichlidae) Billy, Allen J.

Abstract

The goal of this thesis was to investigate the relationship between early hormone treatments and the development of behaviour in a teleost. Groups of Sarotherodon mossambicus (n = 60 fish/group) were exposed to androgen treatment at different stages of development, and the effects of the treatment on gonadal and behavioural differentiation were assessed. The first experiment examined the effects of androgen treatments on gonadal differentiation. All of the fish in each treatment group were sexed, and group sex ratios were compared to determine which treatment had influenced gonadal development. Three treatments administered at different times during the first 7 weeks of life masculinized groups of fish, indicating that gonadal sex direction could be influenced by androgen over a wide period in development. However, gonadal sensitivity to hormonal influences changed over time as each type of hormone treatment (immersion or oral) most effectively influenced gonadal sex direction during a short period (one to three weeks) in gonadal development. The second experiment evaluated the effect of androgen treatment on the development of male behaviour. Behavioural differences were detected between treatment groups in five measures of territorial defense and aggression: intra-territorial fighting (duration of fighting and frequency of aggressive acts initiated during fights), inter-territorial fighting (duration of fighting and frequency of aggressive acts initiated during fights), and attacking (frequency). Male behaviours were influenced only by androgen treatments initiated during the first 5 weeks of life. Treatments started after week 5 did not affect male behavioural development. The third experiment examined the effects of androgen treatment on the development of female behaviour. Behavioural differences were detected between groups in two measures of male-female courtship interactions: tilts received from males and butts received from males. These results indicate that the development of a female courtship behaviour (nest approaching) was influenced by exposure to androgen treatments. An androgen treatment initiated after the fifth week of life produced the most striking influence on female behavioural development, suggesting that female behavioural development follows male behavioural development. Females exposed to androgen before week 5 were either sex-reversed and possessed typical male behaviour patterns, or appeared to be unaffected by treatment and possessed typical female behaviour patterns. The fourth experiment examined the possibility that female fish were sensitized to subsequent androgen treatment after exposure to an early androgen treatment. Females tested in the third experiment were exposed to a second androgen treatment and their behaviour patterns were retested. Females in one group were very sensitive to a second androgen treatment as they adopted male colouration, male behaviour (tilts given and lateral displays given), and visited male nests more frequently than females in any other group. Females in the other treatment groups were less sensitive, or not sensitive, to the second androgen treatment. These results indicate that the hormone-dependent mechanisms underlying the expression of adult behaviour are sensitized to androgen early in development. The fifth experiment was designed to detect genetic females sex-reversed by an early androgen treatment. Sex-reversed genetic females were detected by breeding presumptive males from the various treatment groups with untreated females and then sexing all of the offspring. Crosses between a genetic male and a genetic female produced roughly equal numbers of male and female offspring while crosses between two genetic females produced nearly all female offspring. Since the behaviour of each male had been tested in the second experiment, it was possible to compare the behaviour of sex-reversed genetic females to the behaviour of untreated genetic males. This comparison indicated that behaviour differences existed between sex-reversed females and control males in four measures: inter-territorial fighting, attacking, digging and tilting to females. However, no behavioural differences were detected between sex-reversed and non sex-reversed fish in the same treatment groups. This finding indicates that early androgen treatments influence the development of male behaviours in a similar manner in sex-reversed and non sex-reversed fish. The final chapters of this thesis discuss the characteristics of gonadal and behavioural development in a teleost in greater depth. Insights into the relationship between androgen and behavioural development in a teleost are compared to what is known about hormonal influences on behavioural development in other vertebrates. This comparison indicates that androgen influences behavioural development in a similar manner in both teleosts and mammals.

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