Browsing by Author "Bachar, Zina"
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- Hormonal control of brood care and social status in a cichlid fish with brood care helpersPublication . Bender, Nicole; Bachar, Zina; Oliveira, Rui Filipe; Canário, Adelino V. M.; Taborsky, MichaelWe 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.
- The relationship between social status, behaviour, growth and steroids in male helpers and breeders of a cooperatively breeding cichlidPublication . Bender, Nicole; Heg, Dik; Hamilton, Ian M.; Bachar, Zina; Taborsky, Michael; Oliveira, Rui FilipeWe tested whether subordinate helper males of the Lake Tanganyika cooperatively breeding cichlid Neolamprologus pulcher show elevated excretion levels of the stress hormone cortisol and reduced levels of 11-ketotestosterone and testosterone when living in groups with a small breeder male, compared to similar helper males living in groups with a large breeder male, in a full-factorial repeated measures experimental design. We also measured the same hormones in breeder males with and without helper males. Previous research showed that the size difference between large male helpers and male breeders in groups of this species influences behaviour and growth decisions. Contrary to our expectation, no effect of the size-difference between helper males and breeder males on helper hormone levels was detected. Furthermore, helper males had similar hormone excretion levels to those of size-matched breeder males without helpers, and to small breeder males. There was no influence of egg laying on breeder male and helper hormone levels during the experiment. Interestingly, all three hormone levels were significantly lower in helpers showing elevated levels of submissive behaviour towards the breeders, independently of the size of the breeder males. The low cortisol levels suggest that helper males can successfully reduce stress by appeasing breeder males through submission. Furthermore, helper males showing a high level of submissive behaviour had lower levels of androgens than less submissive helpers, suggesting a lower reproductive potential in submissive helpers. We propose that helper submission may be used as an honest signal of reduced interest in reproduction towards the breeder male in this species.