McKay Alexa Fritzsche, Ezenwa Vanessa O, Altizer Sonia
Physiol Biochem Zool. 2016 Sep-Oct;89(5):389-401. doi: 10.1086/687989. Epub 2016 Jul 25.
Organisms have a finite pool of resources to allocate toward multiple competing needs, such as development, reproduction, and enemy defense. Abundant resources can support investment in multiple traits simultaneously, but limited resources might promote trade-offs between fitness-related traits and immune defenses. We asked how food restriction at both larval and adult life stages of the monarch butterfly (Danaus plexippus) affected measures of immunity, fitness, and immune-fitness interactions. We experimentally infected a subset of monarchs with a specialist protozoan parasite to determine whether parasitism further affected these relationships and whether food restriction influenced the outcome of infection. Larval food restriction reduced monarch fitness measures both within the same life stage (e.g., pupal mass) as well as later in life (e.g., adult lifespan); adult food restriction further reduced adult lifespan. Larval food restriction lowered both hemocyte concentration and phenoloxidase activity at the larval stage, and the effects of larval food restriction on phenoloxidase activity persisted when immunity was sampled at the adult stage. Adult food restriction reduced only adult phenoloxidase activity but not hemocyte concentration. Parasite spore load decreased with one measure of larval immunity, but food restriction did not increase the probability of parasite infection. Across monarchs, we found a negative relationship between larval hemocyte concentration and pupal mass, and a trade-off between adult hemocyte concentration and adult life span was evident in parasitized female monarchs. Adult life span increased with phenoloxidase activity in some subsets of monarchs. Our results emphasize that food restriction can alter fitness and immunity across multiple life stages. Understanding the consequences of resource limitation for immune defense is therefore important for predicting how increasing constraints on wildlife resources will affect fitness and resistance to natural enemies.
生物体拥有有限的资源库，需要分配用于多种相互竞争的需求，如发育、繁殖和抵御天敌。丰富的资源可以同时支持对多种性状的投入，但有限的资源可能会促使与适应性相关的性状和免疫防御之间进行权衡。我们研究了帝王蝶（黑脉金斑蝶）幼虫和成虫阶段的食物限制如何影响免疫、适应性以及免疫与适应性相互作用的指标。我们通过实验用一种专性原生动物寄生虫感染了一部分帝王蝶，以确定寄生是否会进一步影响这些关系，以及食物限制是否会影响感染结果。幼虫期的食物限制降低了帝王蝶在同一生命阶段（如蛹重）以及后期生命阶段（如成虫寿命）的适应性指标；成虫期的食物限制进一步缩短了成虫寿命。幼虫期的食物限制降低了幼虫阶段的血细胞浓度和酚氧化酶活性，当在成虫阶段检测免疫指标时，幼虫期食物限制对酚氧化酶活性的影响仍然存在。成虫期的食物限制仅降低了成虫的酚氧化酶活性，而没有降低血细胞浓度。寄生虫孢子负荷随着幼虫免疫的一项指标而降低，但食物限制并没有增加寄生虫感染的概率。在所有帝王蝶中，我们发现幼虫血细胞浓度与蛹重之间呈负相关，并且在被寄生的雌性帝王蝶中，成虫血细胞浓度与成虫寿命之间的权衡很明显。在某些帝王蝶亚组中，成虫寿命随着酚氧化酶活性的增加而延长。我们的结果强调，食物限制可以在多个生命阶段改变适应性和免疫力。因此，了解资源限制对免疫防御的影响对于预测对野生动物资源日益增加的限制将如何影响适应性和对天敌的抵抗力至关重要。
