Department of Ecology, Evolution, and Natural Resources, Rutgers University, 14 College Farm Road, New Brunswick, NJ 08901, USA.
Integr Comp Biol. 2009 Oct;49(4):393-407. doi: 10.1093/icb/icp060. Epub 2009 Jul 13.
We used the "morphology-performance-fitness" paradigm (Arnold, 1983) as our framework to investigate endocrine control of performance and fitness in Sceloporus undulatus (Eastern Fence Lizard). Focusing on males, we used the "natural experiments" of seasonal, sexual, and developmental variation in growth and in exercise endurance to identify testosterone and corticosterone as potential modulators of performance and related traits of interest. We followed with experimental manipulations of testosterone to investigate functional relationships, both in the laboratory and in the field. Further, we used focal observations and demographic studies, coupled with genetic determination of paternity, to test associations between performance and fitness, measured as reproductive success. We found that in males, endurance and plasma concentrations of testosterone and corticosterone are at their peaks in the spring breeding season, when lizards are most actively engaged in patrolling home ranges and in reproductive behavior. At that time, plasma concentrations of testosterone are correlated with body size; plasma concentrations of corticosterone and parameters of home range, including area and the number of overlapped females, are correlated with home-range overlap between males and females. During prereproductive development, males (but not females) experience a maturational increase in plasma testosterone. At about the same time, they become more active, expand their home ranges, and grow less quickly than do females, suggesting a trade-off in the allocation of energy, mediated by testosterone. Experimentally, testosterone has positive effects on fitness by stimulating endurance and reproductive activity and increasing home-range area, but it exacts costs in fitness by increasing ectoparasitism, decreasing growth, and decreasing survivorship. We found evidence of selection on body size, endurance, and home-range size (and thus access to potential mates). Despite having positive effects on performance traits, plasma concentrations of testosterone were not correlated with number of offspring sired by males. However, we found a strong correlation between the level of plasma corticosterone and the number of offspring sired. We also found evidence of size-assortative mating, indicating that for males, both the number and the size (and thus, fecundity) of their mates increase with body size. Our studies exemplify the power of natural history combined with experimental endocrine manipulations to identify hormonal regulators of performance and linkages to fitness. Furthermore, our results illustrate ecological and evolutionary significance of individual variation in endocrine traits.
我们使用“形态-表现-适应度”范式(Arnold,1983)作为研究框架,研究了塞氏蜥蜴(Eastern Fence Lizard)内分泌对表现和适应度的控制。我们专注于雄性蜥蜴,利用生长和运动耐力的季节性、性和发育变化的“自然实验”,确定睾酮和皮质酮是表现和相关特征的潜在调节剂。然后,我们通过实验性地操纵睾酮来研究功能关系,包括在实验室和野外。此外,我们还利用焦点观察和人口研究,结合遗传确定亲代关系,测试表现和适应度之间的关联,适应度以繁殖成功率来衡量。我们发现,在雄性蜥蜴中,耐力和睾酮及皮质酮的血浆浓度在春季繁殖季节达到峰值,此时蜥蜴最积极地巡逻领地并进行繁殖行为。此时,血浆睾酮浓度与体型相关;血浆皮质酮浓度和领地范围的参数,包括面积和重叠雌性的数量,与雄性和雌性之间的领地重叠相关。在生殖前发育期间,雄性蜥蜴(而非雌性)经历了血浆睾酮的成熟增加。大约在同一时间,它们比雌性更加活跃,扩大了领地范围,生长速度也比雌性慢,这表明能量的分配存在权衡,这是由睾酮介导的。实验中,睾酮通过刺激耐力和生殖活动以及增加领地面积,对适应度有积极影响,但通过增加外寄生虫、降低生长和降低存活率,对适应度产生了代价。我们发现了体型、耐力和领地大小(以及潜在配偶的获得)的选择证据。尽管睾酮对表现特征有积极影响,但血浆睾酮浓度与雄性产生的后代数量无关。然而,我们发现血浆皮质酮水平与产生的后代数量之间存在很强的相关性。我们还发现了体型相关交配的证据,表明对于雄性来说,其伴侣的数量和体型(因此,生育能力)随着体型的增加而增加。我们的研究例证了自然历史与实验性内分泌操纵相结合的力量,可用于确定表现的激素调节剂,并将其与适应度联系起来。此外,我们的研究结果说明了内分泌特征的个体变异在生态和进化方面的重要性。