University of Hull, Department of Biological Sciences, Hull, UK.
BMC Biol. 2010 Mar 30;8:25. doi: 10.1186/1741-7007-8-25.
Sexual selection theory predicts that females, being the limiting sex, invest less in courtship signals than males. However, when chemical signals are involved it is often the female that initiates mating by producing stimuli that inform about sex and/or receptivity. This apparent contradiction has been discussed in the literature as 'the female pheromone fallacy'. Because the release of chemical stimuli may not have evolved to elicit the male's courtship response, whether these female stimuli represent signals remains an open question. Using techniques to visualise and block release of urine, we studied the role of urine signals during fighting and mating interactions of crayfish (Pacifastacus leniusculus). Test individuals were blindfolded to exclude visual disturbance from dye release and artificial urine introduction.
Staged female-male pairings during the reproductive season often resulted in male mating attempts. Blocking female urine release in such pairings prevented any male courtship behaviour. Artificial introduction of female urine re-established male mating attempts. Urine visualisation showed that female urine release coincides with aggressive behaviours but not with female submissive behaviour in reproductive interactions as well as in intersexual and intrasexual fights. In reproductive interactions, females predominately released urine during precopulatory aggression; males subsequently released significantly less urine during mating than in fights.
Urine-blocking experiments demonstrate that female urine contains sex-specific components that elicit male mating behaviour. The coincidence of chemical signalling and aggressive behaviour in both females and males suggests that urine release has evolved as an aggressive signal in both sexes of crayfish. By limiting urine release to aggressive behaviours in reproductive interactions females challenge their potential mating partners at the same time as they trigger a sexual response. These double messages should favour stronger males that are able to overcome the resistance of the female. We conclude that the difference between the sexes in disclosing urine-borne information reflects their conflicting interests in reproduction. Males discontinue aggressive urine signalling in order to increase their chances of mating. Females resume urine signalling in connection with aggressive behaviour, potentially repelling low quality or sexually inactive males while favouring reproduction with high quality males.
性选择理论预测，雌性作为限制性别，在求偶信号上的投入比雄性少。然而，当涉及到化学信号时，通常是雌性通过产生关于性和/或接受性的刺激来启动交配。这种明显的矛盾在文献中被讨论为“雌性信息素谬误”。由于化学刺激的释放可能不是为了引起雄性的求偶反应，这些雌性刺激是否代表信号仍然是一个悬而未决的问题。使用可视化和阻断尿液释放的技术，我们研究了尿液信号在螯虾（Pacifastacus leniusculus）的战斗和交配互动中的作用。测试个体被蒙住眼睛，以排除染料释放和人工尿液引入造成的视觉干扰。
在繁殖季节进行的有预谋的雌雄配对通常会导致雄性求偶行为。在这种配对中阻断雌性尿液释放会阻止任何雄性求偶行为。人工引入雌性尿液重新建立了雄性求偶行为。尿液可视化显示，雌性尿液释放与攻击性行为同时发生，但与繁殖互动以及两性间和同性间战斗中的雌性顺从行为无关。在繁殖互动中，雌性在交配前的攻击行为中主要释放尿液；而雄性在交配时释放的尿液明显少于战斗时。
尿液阻断实验表明，雌性尿液中含有特定于性别的成分，可引发雄性交配行为。化学信号与雌雄两性的攻击性行为同时发生，表明尿液释放已在螯虾的两性中进化为一种攻击性信号。雌性通过将尿液释放限制在繁殖互动中的攻击行为中，同时挑战它们潜在的交配伴侣，同时触发性反应。这些双重信息应该有利于能够克服雌性抵抗的更强壮的雄性。我们的结论是，雌雄两性在揭示尿液信息方面的差异反映了它们在繁殖方面的利益冲突。雄性为了增加交配机会而停止攻击性尿液信号。雌性在与攻击性行为有关的情况下恢复尿液信号，可能会排斥低质量或性不活跃的雄性，同时有利于与高质量雄性的繁殖。
