Bender Nicole, Heg Dik, Hamilton Ian M, Bachar Zina, Taborsky Michael, Oliveira Rui F
Institute of Zoology, University of Bern, Wohlenstrasse 50a, Hinterkappelen CH-3032, Switzerland.
Horm Behav. 2006 Aug;50(2):173-82. doi: 10.1016/j.yhbeh.2006.02.009. Epub 2006 Apr 19.
We 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.
在一个全因子重复测量实验设计中，我们测试了坦噶尼喀湖合作繁殖的丽鱼科鱼类美丽新亮丽鲷的从属雄性帮手，与生活在有大型繁殖雄性的群体中的类似帮手雄性相比，当它们与小型繁殖雄性生活在同一群体中时，应激激素皮质醇的排泄水平是否升高，以及11-酮睾酮和睾酮水平是否降低。我们还测量了有和没有帮手雄性的繁殖雄性的相同激素。先前的研究表明，该物种群体中大型雄性帮手和雄性繁殖者之间的体型差异会影响行为和生长决策。与我们的预期相反，未检测到帮手雄性和繁殖雄性之间的体型差异对帮手激素水平有影响。此外，帮手雄性的激素排泄水平与没有帮手的体型匹配的繁殖雄性以及小型繁殖雄性相似。在实验过程中，产卵对繁殖雄性和帮手的激素水平没有影响。有趣的是，无论繁殖雄性的大小如何，所有三种激素水平在对繁殖者表现出较高顺从行为水平的帮手中都显著较低。低皮质醇水平表明，帮手雄性可以通过顺从安抚繁殖雄性来成功减轻压力。此外，表现出高度顺从行为的帮手雄性的雄激素水平低于不太顺从的帮手，这表明顺从的帮手的繁殖潜力较低。我们提出，在这个物种中，帮手的顺从可能被用作向繁殖雄性表明对繁殖兴趣降低的一种诚实信号。
