Browsing by Author "Carneiro, L. A."
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- 11-ketotestosterone inhibits the alternative mating tactic in sneaker males of the peacock blenny, Salaria pavoPublication . Oliveira, R. F.; Carneiro, L. A.; Gonçalves, D.; Canario, Adelino; Grober, M. S.In the peacock blenny, Salaria pavo, a species with courtship sex-role reversal, smaller, younger males mimic the courtship behavior and the nuptial coloration of females in order to get access to nests during spawning and to parasitize egg fertilization from nest-holder males. Later in their life, sneakers transform both morphologically and behaviorally into nest-holder males. In the present paper we investigate the activational role of 11-ketotestosterone (KT), the most potent androgen in most teleost species, to promote the switch between tactics in sneaker males of S. pavo. Sneakers were implanted either with KT or with control (i.e. castor oil) silastic implants. A week after implantation they were subjected to a set of behavioral tests and morphometric measurements. KT treatment promoted the differentiation of secondary sex characters, such as the anal glands, and inhibited the expression of female courtship behavior. KT-treated sneakers also showed a trend toward less frequent display of female nuptial coloration. There was no effect of KT treatment on the expression of typical nest-holder male behavior. Finally, there was no effect of KT treatment on the number or soma size of arginine vasotocin neurons in the preoptic area, which are often associated with the expression of vertebrate sexual behavior. Thus, KT seems to play a key role in mating tactic switching by inhibiting the expression of female courtship behavior and by promoting the development of male displaying traits (e.g. anal glands). The lack of a KT effect on behavior typical of nest-holding males and vasotocinergic preoptic neurons suggests that a longer time frame or other endocrine/social signals are needed for the initiation of these traits in males that are switching tactics.
- Behavioural endocrinology: no hormonal response in tied fightsPublication . Oliveira, R. F.; Carneiro, L. A.; Canario, Adelino V. M.Fish androgens may start to surge only when there seems to be a good chance of winning a contest. Duel action: a cichlid attacks its reflection. Androgens are the principal sex steroids controlling reproduction and aggression in male fish1, but their production can also be affected by social interactions2, 3. Here we show that androgen concentrations are not significantly increased in cichlid fish (Oreochromis mossambicus) that are fighting their own image in a mirror, despite their aggressive behaviour towards the virtual intruder. Our results indicate that the hormonal response normally triggered in male contests is not induced under these circumstances by the act of fighting itself, and that it may therefore depend on some indicator of relative fighting ability that cannot be delivered by a mirror-image challenger.
- Effects of 11-ketotestosterone on genital papilla morphology in the sex changing fish Lythrypnus dalliPublication . Carisle, S. L.; Marxer-Miller, S. K.; Canario, Adelino V. M.; Oliveira, R. F.; Carneiro, L. A.; Grober, M. S.Five days after implantation with 11-ketotestosterone (KT) female Lythrypnus dalli exhibited elevated urinary KT levels and male-like genital papilla morphology. Papilla length increased, width decreased, and length : width ratio increased. Control fish exhibited increases in papilla length, and length : width ratio on day 3, but not on day 5. Changes in the total area of the papilla were not statistically significant. It is suggested that KT mediates genital papilla morphology rapidly and thus may be a useful indicator of circulating KT in L. dalli.
- Effects of androgens on social behavior and morphology of alternative reproductive males of the Azorean rock-pool blennyPublication . Oliveira, R. F.; Carneiro, L. A.; Canario, Adelino V. M.; Grober, M. S.In the Azorean rock-pool blenny Parablennius sanguinolentus parvicornis two sequential reproductive tactics occur. Larger and older males establish breeding territories, while some of the smaller males become attached to nest-holder territories, acting as satellites on these territories, which they help to defend while trying parasitic fertilizations when females go in the nests to spawn. In the present paper we tested the effects of the androgens 17a-methyltestosterone (MT) and 11-ketotestosterone (KT) in the expression of male secondary sex characters and bourgeois behavior in satellite males. One week after satellites were implanted with Silastic tubes containing MT, KT, or castor oil (control), androgen-treated satellites had developed male secondary sex traits such as longer and wider male-type genital papilla and anal glands that secrete a sex pheromone, both traits being less expressed or absent, respectively, in satellite males. Androgen treatment had no effect on the gonadosomatic index or on the development of the testicular gland. KT treatment had a positive effect on relative liver weight. In terms of behavior, androgen-implanted individuals were less aggressive both in a mirror test and toward females when these were introduced into their tanks. MT-treated individuals spend more time inside the provided nests. Only androgen-implanted satellites managed to have the females entering their nests. When given a chance in a group tank either to try to attract females to their own nest or to act as satellites of an already established nest-holder’s nest, MT-implanted males spent significantly more time in their own nest than near the nest-holder nest. These data suggest that androgens, particularly testosterone testosterone, may be involved in mating tactic switching in this species.
- Social modulation of androgen levels in male teleost fishPublication . Oliveira, R. F.; Hirschenhauser, K.; Carneiro, L. A.; Canario, Adelino V. M.Androgens are classically thought of as the sex steroids controlling male reproduction. However, in recent years evidence has accumulated showing that androgens can also be affected by the interactions between conspecifics, suggesting reciprocal interactions between androgens and behaviour. These results have been interpreted as an adaptation for individuals to adjust their agonistic motivation and to cope with changes in their social environment. Thus, male–male interactions would stimulate the production of androgens, and the levels of androgens would be a function of the stability of its social environment [‘challenge hypothesis’, Gen. Comp. Endocrinol. 56 (1984) 417]. Here the available data on social modulation of androgen levels in male teleosts are reviewed and some predictions of the challenge hypothesis are addressed using teleosts as a study model. We investigate the causal link between social status, territoriality and elevated androgen levels and the available evidence suggests that the social environment indeed modulates the endocrine axis of teleosts. The association between higher androgen levels and social rank emerges mainly in periods of social instability. As reported in the avian literature, in teleosts the trade-off between androgens and parental care is indicated by the fact that during the parental phase breeding males decreased their androgen levels. A comparison of androgen responsiveness between teleost species with different mating and parenting systems also reveals that parenting explains the variation observed in androgen responsiveness to a higher degree than the mating strategy. Finally, the adaptive value of social modulation of androgens and some of its evolutionary consequences are discussed.
- The effect of arginine vasotocin on courtship behaviour in a blenniid fish with alternative reproductive tacticsPublication . Carneiro, L. A.; Oliveira, R. F.; Canario, Adelino V. M.; Grober, M. S.In a sex-role reversed population of the peacock blenny, Salaria pavo, two alternative male types are present: (a) older and larger nest-holder males that defend nests in which females come to spawn, and (b) younger and smaller sneaker males that mimic female-courtship behaviour and nuptial colouration in order to try to sneak fertilizations during spawning episodes. In this study the effects of exogenous administration of arginine vasotocin (AVT, 3 μg/g body weight) on the behaviour of nest-holder males, sneakers and females was tested. AVT induced the expression of female courtship behaviour in sneakers and female nuptial colouration in sneakers and in females, but failed to promote the expression of male courtship behaviour in both male types.
- Watching fights raises fish hormone levels - cichlid fish wrestling for dominance induce an androgen surge in male spectatorsPublication . Oliveira, R. F.; Lopes, M.; Carneiro, L. A.; Canario, Adelino V. M.Social interactions among the animals in a group affect their subsequent behaviour, manifesting as dominance hierarchies or territoriality, for example, and meaning that behaviour is adjusted to social context. These interactions are thought to be modulated by androgens, allowing the agonistic motivation of individuals to adjust to changes in their social environment; androgen production is itself determined by sexual status and by social contacts among conspecifics.