Evolution of Growth Rate: Tradeoffs Between Costs of Growth and Benefits of Increased Size

遗传变异和局部适应可能是造成鱼类和其他生物种群中常见的体细胞生长率差异的原因。幼年生长中遗传变异的存在是一个谜，挑战了生物体应该在生命早期阶段最大限度地摄入和利用能量的信念。如果更高的速率少年生长和更大的规模转化为更大的健身，亚？最高比率只能用与快速增长相关的权衡来解释。最近的证据表明，一个主要的权衡之间存在的能量分配给增长，而不是运动性能和易受捕食者。本计画以大西洋银汉鱼（Menidia menidia）为模式系统，探讨造成此一交换的机制及其生活史意义。在银汉鱼中，生长的遗传能力与不同纬度的生长季节长度成反比（称为“逆梯度变化”）。北方基因型的生长速度是南方基因型的两倍，因为它们消耗更多的食物，并更有效地将食物转化为体细胞组织。但是北方的鱼游泳能力很差，与南方的鱼相比，它们更容易受到捕食者的攻击。在种群中，吃大餐和/或生长更快的青少年也更容易受到捕食者的攻击。这个项目将结合联合收割机模型，实验和实地研究，探讨贸易？在不同的环境中，增长的成本和规模增加的好处之间的平衡。有五个主要目标。首先，1）建立一个生命史模型来评估最优的增长策略时，都增长率？死亡率和繁殖成功率的依赖性和大小依赖性来源影响适合度。该模型将被用来预测最佳增长战略如何在纬度梯度上变化。2)为了参数化模型，将进行实验以确定游泳性能对摄食水平的功能反应，以及3）长？将利用中期围隔生态系统实验来检验模型的预测。4)以证明这些贸易的重要性？在自然条件下，将测试野外银鱼的生长速度（根据耳石估计）与其主要捕食者幼蓝鱼（Pomatomus saltatrix）胃中发现的生长速度之间的关联。5)最后，为了将结果推广到其他物种，将进行实验，以确定贸易的生理基础？生长速度和游泳成绩之间的关系。该项目的结果将大大增加对幼鱼在补充到成年阶段期间采用的战略和战术的理解，并将进一步说明海洋生物适应非生物和生物变化的能力。

Genetic variation and local adaptation may be responsible for many of the differences in somatic growth rate that are common among populations of fishes and other organisms. The existence of genetic variation in juvenile growth is an enigma, challenging the belief that organisms should maximize energy intake and utilization in the early life stages. If higher rates of juvenile growth and larger size translate into greater fitness, sub?maximal rates can only be explained by the existence of tradeoffs associated with rapid growth. Recent evidence suggests that a major tradeoff exists between the amount of energy allocated to growth as opposed to locomotory performance and vulnerability to predators. Using a marine fish, the Atlantic silverside (Menidia menidia) as a model system, this project will explore the mechanisms responsible for this tradeoff and its life history implications. In silversides, the genetic capacity for growth varies inversely with length of the growing season across latitudes (termed "countergradient variation"). Northern genotypes grow at up to twice the rate of southern forms by consuming more food and converting it more efficiently into somatic tissue. But northern fish are poor swimmers and are more vulnerable to predators compared with southern fish. And within populations, juveniles that consume large meals and/or grow more rapidly are also more vulnerable to predators. This project will combine modeling, experimental, and field studies to explore the trade?off between the cost of growth and the benefits of increased size in different environments. There are five major objectives. First, 1) a life history model will be constructed to evaluate the optimal growth strategy when both grow rate?dependent and size-dependent sources of mortality and reproductive success affect fitness. The model will be used to predict how the optimal growth strategy changes across a latitudinal gradient. 2) To parameterize the model, experiments will be conducted to determine the functional response of swimming performance to feeding level, and 3) long?term mesocosm experiments will be used to test the model's predictions. 4) To validate the importance of these trade?offs under natural conditions, tests for an association between growth rate of silversides in the field (as estimated from otoliths) and those found within the stomachs of their major predator, young bluefish (Pomatomus saltatrix), will be conducted. 5) Finally, in order to generalize results to other species, experiments will be conducted to determine the physiological basis of the trade?off between grow rate and swimming performance. The results of this project will greatly increase understanding of the strategies and tactics that larval and juvenile fishes employ during recruitment to the adult stage and will further illustrate the capacity of marine organisms to adapt to abiotic and biotic change.