Fish Ecology and Conservation Physiology Laboratory, Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6.
Horm Behav. 2012 Jun;62(1):67-76. doi: 10.1016/j.yhbeh.2012.05.001. Epub 2012 May 8.
Life-history theory predicts that stress responses should be muted to maximize reproductive fitness. Yet, the relationship between stress and reproduction for semelparous salmon is unusual because successfully spawning individuals have elevated plasma cortisol levels. To tease apart the effects of high baseline cortisol levels and stress-induced elevation of cortisol titers, we determined how varying degrees of cortisol elevation (i.e., acute and chronic) affected behavior, reproductive physiology, and reproductive success of adult female pink salmon (Oncorhynchus gorbuscha) relative to different states of ovulation (i.e., ripe and unripe). Exhaustive exercise and air exposure were applied as acute stressors to manipulate plasma cortisol in salmon either confined to a behavioral arena or free-swimming in a spawning channel. Cortisol (eliciting a cortisol elevation to levels similar to those in post-spawn female salmon) and metyrapone (a corticosteroid synthesis inhibitor) implants were also used to chemically manipulate plasma cortisol. Cortisol implants elevated plasma cortisol, and impaired reproductive success; cortisol-treated fish released fewer eggs and died sooner than fish in other treatment groups. In contrast, acute stressors elevated plasma cortisol and the metyrapone implant suppressed plasma cortisol, but neither treatment significantly altered reproductive success, behavior, or physiology. Our results suggest that acute stressors do not influence behavior or reproductive outcome when experienced upon arrival at spawning grounds. Thus, certain critical aspects of salmonid reproduction can become refractory to various stressful conditions on spawning grounds. However, there is a limit to the ability of these fish to tolerate elevated cortisol levels as revealed by experimental elevation of cortisol.
生活史理论预测，为了最大限度地提高繁殖适应性，应激反应应该受到抑制。然而，对于单次产卵的鲑鱼来说，应激和繁殖之间的关系是不寻常的，因为成功产卵的个体血浆皮质醇水平升高。为了区分高基础皮质醇水平和应激诱导的皮质醇浓度升高的影响，我们确定了不同程度的皮质醇升高（即急性和慢性）如何影响成年粉鲑（Oncorhynchus gorbuscha）的行为、生殖生理和生殖成功率，相对于不同的排卵状态（即成熟和未成熟）。我们采用了 exhaustive exercise 和 air exposure 作为急性应激源，来操纵被限制在行为场或在产卵通道中自由游动的鲑鱼的血浆皮质醇。皮质醇（引发类似于产卵后雌鲑鱼的皮质醇升高）和 metyrapone（一种皮质类固醇合成抑制剂）植入物也被用于化学操纵血浆皮质醇。皮质醇植入物升高了血浆皮质醇，并损害了生殖成功率；皮质醇处理的鱼比其他处理组的鱼释放的卵子更少，死亡更早。相比之下，急性应激源升高了血浆皮质醇，而 metyrapone 植入物抑制了血浆皮质醇，但这两种处理都没有显著改变生殖成功率、行为或生理。我们的研究结果表明，急性应激源在到达产卵场时不会影响行为或生殖结果。因此，某些鲑鱼繁殖的关键方面可能对产卵场的各种应激条件产生抗性。然而，正如通过实验性升高皮质醇所揭示的那样，这些鱼耐受升高的皮质醇水平的能力是有限的。
