Genetic Covariances Among Life History Traits: The Effect of Novel Environments

生态和遗传理论预测，生殖输出和寿命等生活史特征之间应该进行权衡。 导致更多繁殖的基因也会导致寿命缩短。 如果这一理论正确，则支持这样的观点：衰老具有遗传基础，并且衰老是正常过程的结果，该正常过程有利于增加繁殖，但代价是缩短寿命。 此外，该理论原则上指出了一种通过基因改造来改变生育能力和寿命的方法。 虽然一些实验观察结果支持这种权衡预期，但许多实验观察结果并不支持。 许多实验研究中缺乏权衡可能是在不适应的环境中对生物体进行测试的结果，就像将野生捕获的生物体带入实验室时的情况一样。 根据这个假设，一些个体会偶然携带在新环境中有利的基因。 这些个体通常比其他偶然携带不适合新环境的基因的个体更有活力。 这种情况将产生生活史特征之间的正相关模式，而不是权衡模式。 然而，积极的关联应该是一种短暂的现象，随着人们适应新的环境，预期的权衡模式应该被重新建立。 这些实验将测试生命周期等特征进化基础理论的稳健性，以及该理论在新环境（例如全球气候变化期间发生的环境）中的预测价值。

Ecological and genetic theory predict that there should be trade-offs between life history traits such as reproductive output and lifespan. Genes that result in greater reproduction should also produce shortened life span. This theory, if correct, supports the idea that senescence has a genetic basis and that senescence is a consequence of normal processes that favor increased reproduction at the expense of shortened lifespan. Furthermore, this theory points a way, in principle, to genetic modification of fertility and lifespan. While some experimental observations support this expectation of trade-offs, many do not. The absence of trade- offs in a number of experimental studies may be a consequence of the testing of organisms in environments to which they are not adapted, as would be the case when wild-caught organisms are brought into the laboratory. Under this hypothesis, some individuals will carry genes that fortuitously are favorable in a new environment. Those individuals will be generally more vigorous than other individuals that by chance carry genes that are not favorable in the new environment. This situation will produce a pattern of positive associations between life history traits, rather than a pattern of trade-offs. However, the positive associations should be a transient phenomenon, and as populations adapt to their new environment, the expected pattern of trade-offs should be reestablished. These experiments will test the robustness of basic theories underlying the evolution of characters such as lifespan, and the predictive value of the theory in novel environments, such as would occur during global climate change.