Environmental conditions and individual strategies in early life may have a profound effect on fitness. A critical moment in the life of an organism occurs when an individual reaches independence and stops receiving benefits from its relatives. Understanding the consequences of individual strategies at the time of independence requires quantification of their fitness effects. We explored this period in the Red Grouse (Lagopus lagopus scoticus). In this system, testosterone and parasite (Trichostrongylus tenuis) levels are known to influence survival and reproduction, the two key components of individual fitness. We experimentally and simultaneously manipulated testosterone and parasites at three levels (high, intermediate, and control levels for both factors) in 195 young males in five populations using a factorial experimental design. We explored the effects of our treatments on fitness by monitoring reproduction and survival throughout the life of all males and estimating lambda(ind), a rate-sensitive index of fitness. Parasite challenges increased the number of worms with a time lag, as previously found. However, we did not find significant effects of parasite manipulations on fitness, possibly because parasite abundance did not increase to harmful levels. Our hormone manipulation was successful at increasing testosterone at three different levels. Such increases in hormone levels decreased overall fitness. This was caused by reduced offspring production in the first breeding attempt rather than by any effect of the treatment on bird survival. Our results highlight that investing in high testosterone levels at independence, a strategy that might enhance short-term recruitment probability in territorial species such as Red Grouse, has a fitness cost, and can influence the resolution of the trade-off between reproduction and survival later in life.

译文

早期生活中的环境条件和个人策略可能会对健身产生深远影响。当一个人达到独立并停止从其亲属那里获得利益时,就会发生生物体生命中的关键时刻。了解独立时个人策略的后果需要量化其适应效果。我们在红色松鸡 (Lagopus lagopus scoticus) 中探索了这一时期。在这个系统中,已知睾丸激素和寄生虫 (Trichostrongylus tenuis) 的水平会影响生存和繁殖,这是个体健康的两个关键组成部分。我们使用析因实验设计,对五个种群中的195名年轻男性进行了三个水平 (两个因素的高,中和对照水平) 的实验和同时操纵睾丸激素和寄生虫。我们通过监测所有男性的整个生命中的繁殖和存活并估算lambda(ind) (一种对健康的速率敏感指数),探索了我们的治疗方法对健康的影响。如前所述,寄生虫的挑战会随着时间的滞后而增加蠕虫的数量。但是,我们没有发现寄生虫操纵对健身的显着影响,可能是因为寄生虫的丰度并未增加到有害水平。我们的激素操作成功地提高了三种不同水平的睾丸激素。激素水平的增加降低了总体适应性。这是由于第一次繁殖尝试中后代产量减少所致,而不是由于治疗对鸟类存活的任何影响。我们的结果强调,在独立时投资于高睾丸激素水平,这一策略可能会提高红色松鸡等领土物种的短期招募概率,具有健身成本,并且可能会影响生殖与生存之间权衡的解决方案在以后的生活中。

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