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

生态学和遗传学理论预测，应该在繁殖产量和寿命等生活史特征之间进行权衡。导致更多繁殖的基因也应该缩短寿命。如果这一理论是正确的，它支持这样一种观点，即衰老有遗传基础，衰老是正常过程的结果，正常过程以缩短寿命为代价，有利于增加生殖。此外，这一理论在原则上为生育力和寿命的基因改造指明了一条道路。虽然一些实验观察支持这种权衡的预期，但许多人并不支持。在一些实验研究中缺乏权衡可能是在它们不适应的环境中测试生物体的结果，就像将野生捕获的生物体带进实验室一样。在这一假设下，一些个体将携带在新环境中幸运地有利的基因。这些个体通常会比其他碰巧携带了在新环境中不利的基因的个体更有活力。这种情况将产生一种生活史特征之间积极关联的模式，而不是一种权衡的模式。然而，积极的关联应该是一个暂时的现象，随着人们适应他们的新环境，应该重新建立预期的权衡模式。这些实验将测试字符进化的基本理论的稳健性，如寿命，以及该理论在新环境中的预测价值，例如在全球气候变化期间。

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.