:: Current research project

Role of androgens in the regulation of life-history trade-offs in the Rock-pool blenny, Parablennius parvircornis

Androgen hormones have been shown to initiate many central and peripheral effects that can be considered to play a role in increasing competitive ability. High levels of testosterone are typical for periods of competition and facilitate the expression of agonistic behavioural traits. Peripheral anabolic effects of the hormone are thought to be promoted by a change in resource allocation. In salmons cells of the humoral immune system have receptors for androgens, and these receptors regulate antibody production and apoptosis. This allows for a direct androgen mediated down regulation of immunocompetence, which is thought to be an energetically costly trait. More general, androgens may indirectly produce behavioural and peripheral changes by interacting with other steroids, like cortisol, and peptides, like prolactine. In the last decades, this broad range of action of androgen hormones has greatly stimulated theory about causal mechanisms underlying trade-offs in life history theory.

In males of Blenniidae that express alternative reproductive tactics (ART), the switch between tactics (parasitic and bourgeois) comprises an increase in the levels of the androgen 11-ketotestosterone (11-KT), growth of the secondary sexual characters, sperm traits and changes in behavioural traits. Bourgeois males show high parental investment combined with territorial behaviour, whereas parasitic males do not show parental behaviour. Moreover, males of the Azorean rock pool blenny that differ in ART showed differences in immunocompetence that were negatively correlated with 11-KT. This species therefore provides an excellent model to study life history trade-offs.

The results of these studies will allow a further assessment of proposed trade-offs between androgen dependent trade-offs and parental care and immunocompetence. This will contribute to the knowledge about how differences in behavioural styles of males have evolved.

Funded by: FCT - SFRH/BPD/7143/2001

:: Selected publications

- Ros, A.F.H., Bouton, N., Santos, R.S. and Oliveira, R.F. 2006. Alternative male reproductive tactics and the immunocompetence handicap in the Azorean rock-pool blenny, Parablennius parvicornis. Proceedings of the Royal Society B 273: 901-909.

- Ros A.F.H., Becker, K., Canário, A.V.M. and Oliveira R.F. 2004. Androgen levels and energy metabolism in the Mozambique tilapia, Oreochromis mossambicus. Journal of Fish Biology 65: 895-905.

- Ros A.F.H., Bruintjes, F., Santos, R.S., Canário, A.V.M. and Oliveira, R.F. 2004. The role of androgens in the trade-off between territorial and parental behavior in the Azorean rock-pool blenny, Parablennius parvicornis. Hormones and Behavior 46: 491-497.

- Ros, A.F.H., Canario A.V.M., Couto, E., Zeilstra, I. and Oliveira, R.F. 2003. Endocrine correlates of intra-specific variation in the mating system of the St. Peter's fish (Sarotherodon galilaeus). Hormones and Behavior 44: 365-373.

- Ros A.F.H., Dieleman S.J. and Groothuis T.G.G. 2002. Social stimuli, testosterone, and aggression in gull chicks: support for the challenge hypothesis. Hormones and Behavior 41:334-342.

- Ros A.F.H., Groothuis T.G.G. and Apanius V. 1997. The relation among gonadal steroids, immunocompetence, body mass, and behavior in young black-headed gulls. The American Naturalist 150:201-219.