Browsing by Author "Ros, A. F. H."
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- Androgen levels and energy metabolism in Oreochromis mossambicusPublication . Ros, A. F. H.; Becker, K.; Canario, Adelino V. M.; Oliveira, R. F.Two studies were conducted to test the relationship between androgens and routine metabolism in the Mozambique tilapia Oreochromis mossambicus. In the first study, endogenous levels of plasma levels of androgens and oxygen consumption rate were measured. In accordance with expectations routine metabolism corrected for metabolic body mass, was positively correlated with the behaviourally active metabolite of testosterone, 11-ketotestosterone, but not with testosterone itself.
- Androgens and Mating Systems in Fish: Intra- and Inter-specific AnalysisPublication . Oliveira, R. F.; Ros, A. F. H.; Hirschenhauser, K.; Canario, Adelino V. M.One of the predictions of the ‘challenge hypothesis’ (Wingfield et al., 1990) is that androgen patterns during the breeding season should vary among species according to the parenting and mating system. Here we assess this prediction of the challenge hypothesis both at the intra- and at the inter-specific level. To test the hypothesis at the inter-specific level, a literature survey on published androgen pat- terns from teleost fish with different mating systems was carried out. The results confirm the predicted effect of mating system on andro- gen levels. To test the hypothesis at an intra-specific level, a species with flexible reproductive strategies (i.e. monogamy vs. polygyny), the Saint Peter’s fish was studied. Polygynous males had higher 11- ketotestosterone levels. However, males implanted with methyl-tes- tosterone did not became polygynous and the variation of the ten- dency to desert their pair mates was better explained by the repro- ductive state of the female partner. This result stresses the point that the effects of behaviour on hormones cannot be considered without respect to the social context.
- Endocrine correlates of intra-specific variation in the mating system of the St. Peter's fish (Sarotherodon galilaeus)Publication . Ros, A. F. H.; Canario, Adelino V. M.; Couto, Elsa; Zeilstra, IIja; Oliveira, R. F.The Challenge Hypothesis postulates that androgen levels are a function of the social environment in which the individual is living. Thus, it is predicted that in polygynous males that engage in social interactions, androgen levels should be higher than in monogamous animals that engage in parental care. In this study, we tested this hypothesis at the intra-specific level using a teleost species, Sarotherodon galilaeus, which exhibits a wide variation in its mating system. Experimental groups of individually marked fish were formed in large ponds with different operational sex-ratios (OSR) to study the effects of partner availability on blood plasma levels of sex steroids [11-ketotestosterone (11-KT), testosterone (T), and 17,20B-dihydroxy-4-pregnen-3-one (17,20B-P)] and gonadosomatic index (GSI). Polygyny mostly occurred in the female biased OSR groups. 17,20B-P and gonadosomatic index did not differ among OSR groups. However, 11-KT was high in male biased OSR and positively correlated with aggressive challenges, thereby supporting the central postulate of the Challenge Hypothesis. The results of T were the inverse of those of 11-KT, probably because 11-KT is metabolized from T. 11-KT levels of polygynous males did not differ neither from those of monogamous males, nor from those of males that participated in parental care. These results do not support the expected relationships between polygyny, parental care, and androgen levels. The differences from expectations for 11-KT may be related to the fact that in S. galilaeus, the mating and the parenting phase are not clearly separated and thus, males may still fight and court while they are brooding.
- Social context may affect urinary excretion of 11-ketotestosterone in African cichlidsPublication . Hirschenhauser, K.; Canario, Adelino V. M.; Ros, A. F. H.; Taborsky, M.; Oliveira, R. F.We previously investigated the androgen responsiveness of males to simulated partner and territory intrusions in five African cichlid species (Neolamprologus pulcher, Lamprologus callipterus, Tropheus moorii, Pseudosimochromis curvifrons, Oreochromis mossambicus; Hirschenhauser et al., 2004). Here we re-analysed data on 11 ketotestosterone (11-KT) levels in holding water to compare the free (presumably from the gills) and conjugated (presumably from urine and faeces) 11-KT fractions. We sampled (i) pre-test baseline control levels from individual males in social isolation and (ii) response levels released after social interactions, either with an ovulating female or a male territory intruder. In four out of five species, conjugated metabolites contributed to the observed total 11-KT responses in water during social context, which was particularly apparent in peak responsive individuals exposed to male intruders. Thus, in water from males sampled in isolation immunoreactive 11-KT seemed to derive both from gills and urine, whereas the urinary 11-KT component apparently increased in the social context, particularly when a male was challenged by a same-sex intruder. These results suggest that (i) the social context may affect urine release patterns of males and (ii) 11-KT data acquired by using fish-holding water may not simply reflect the passive transmission of steroid hormones via the gills.
- The role of androgens in the trade-off between territorial and parental behavior in the Azorean rock-pool blenny, Parablennius parvicornisPublication . Ros, A. F. H.; Bruintjes, R.; Santos, Ricardo Serrão; Canario, Adelino V. M.; Oliveira, R. F.Androgen hormones have been shown to facilitate competitive ability in courtship and territorial behavior, while suppressing paternal behavior. The rock-pool blenny, Parablennius parvicornis, provides an excellent model to study the proximate regulation of such a trade-off between territorial and parental behavior, because nest-holder males of this species display these behaviors simultaneously. A field study was carried out in which territorial nest holder males were either treated with long-lasting implants filled with 11-ketotestosterone (11-KT) or with control implants. Males treated with 11-KT showed a higher frequency of aggressive behavior, were more responsive to aggressive challenges, and were more persistent in aggressive behavior than control males. In addition, territories were larger in males treated with 11-KT than in controls. We found evidence for incompatibility between defense of a large territory and high levels of parental behavior. However, contrary to expectation, 11-KT did not suppress parental behavior. We suggest that trade-offs between territorial and parental behavior may not be regulated by androgen hormones but may result from a time constraint in the individual’s activity budget.