Browsing by Author "Taborsky, M."
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- Androgen levels of reproductive competitors in a co-operatively breeding cichlidPublication . Oliveira, R. F.; Hirschenhauser, K.; Canario, Adelino V. M.; Taborsky, M.Androgen levels of family groups of Neolamprologus pulcher were assessed using non-invasive methods. There were no significant differences in the excretion rates neither of testosterone nor of 11-ketotestosterone between territorial and helper males.
- Hormonal control of brood care and social status in a cichlid fish with brood care helpersPublication . Bender, N.; Heg-Bachar, Z.; Oliveira, R. F.; Canario, Adelino V. M.; Taborsky, M.We studied the role of steroid hormones for parental and alloparental brood care and social status in a cooperatively breeding fish. We measured excretion levels of testosterone and 11-ketotestosterone in males, estradiol-17β in females and cortisol in both sexes at different stages of the breeding cycle, and compared these values to data measured in non-reproductive fish. Brood care behaviour does not seem to relate to steroid hormone excretion levels in this species. Steroid hormones varied with social status, however. Non-territorial male aggregation members, for example, showed high testosterone and low 11-ketotestosterone excretion levels, suggesting that they might pursue a “stand-by strategy” for breeding to react quickly if an occasion for breeding arises. Cortisol excretion levels are high in juvenile helpers compared to same-size aggregation members, suggesting higher stress levels in subordinate members of reproductive groups. This is the first study assessing if steroid hormone control mechanisms are involved in brood care and social roles in a cooperatively breeding fish.
- 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.
- A test of the ‘challenge hypothesis’ in cichlid fish: simulated partner and territory intruder experimentsPublication . Hirschenhauser, K.; Taborsky, M.; Oliveira, T.; Canario, Adelino V. M.; Oliveira, R. F.In male birds, the responsiveness of androgens to sexual and territorial behaviour is predicted to vary with mating system and the degree of paternal investment (‘challenge hypothesis’, CH; Wingfield et al. 1990, American Naturalist, 136, 829–846). The CH predicts a higher and longer lasting ‘breeding baseline’ androgen level in males of polygynous species with no or only short-term paternal investment than in males of monogamous species with a high degree of paternal investment. Since the applicability of the CH to nonavian vertebrates has been unclear, we experimentally tested its predictions in several cichlid fish (Neolamprologus pulcher, Lamprologus callipterus, Tropheus moorii, Pseudosimochromis curvifrons and Oreochromis mossambicus) using a simulated territorial intruder protocol. Androgens (11-ketotestosterone: 11-KT; testosterone: T) were measured from fish-holding water. In all species sampled, the 11-KT patterns confirmed the predictions of the CH originating from the avian literature, but T patterns did not. Males of all species sampled were highly responsive to territorial intrusions; however, the magnitude and duration of this response, that is, the rapid return to baseline 11-KT levels, could not clearly be explained by the degree of paternal care. 11-KT responses to interactions with ovulating females were observed in maternal mouthbrooders but not in biparental species (e.g. Lamprologini). At the interspecific level, androgen responsiveness was greater among males of monogamous species, as predicted, but also in species with more intense pair bonding (e.g. Tropheus moorii). Thus, this study confirms the predictions of the CH in cichlid fish at both the intraspecific and the interspecific levels.
- The role of prolactin in the regulation of brood care in the cooperatively breeding fish Neolamprologus pulcherPublication . Bender, N.; Taborsky, M.; Power, DeborahThe hormone prolactin (PRL) is important for the regulation of parental care in many species of mammals, birds and fish, and for alloparental care (care directed at nondescendant young) in some mammals and birds. Its significance in alloparental brood care of cooperatively breeding fish has not yet been assessed. Here, we test the role of PRL in brood care behavior of the cooperatively breeding cichlid Neolamprologus pulcher. The expression of PRL mRNA was determined in the pituitary glands of breeders of both sexes, helpers that showed brood care behavior and nonbreeding fish as controls. In addition, PRL levels were experimentally manipulated in male breeders and helpers by intraperitoneal injections of ovine PRL, and the behavior of these test fish was recorded toward standardized clutches. Adult females had higher levels of PRL mRNA than adult males, which was true both for breeders and nonbreeders. Contrary to expectation, there was no positive correlation between PRL and brood care behavior in any category of test fish, and the experimental application of PRL did not change brood care propensity. Interestingly, brood-caring adult females had significantly lower levels of PRL mRNA than adult female nonbreeders, whereas there was no difference between helpers and similar-sized nonbreeding group members. PRL mRNA levels increased with body mass in juveniles, but decreased with body mass in adults. In conclusion, we found no evidence that elevated levels of PRL are directly involved in the regulation of brood care behavior in this species.