Growth rate affects body size, and larger body sizes are often associated with the capacity to produce more surviving offspring. However, the assumption that growth rate should positively relate to fitness is rarely tested, especially in colonial marine invertebrates where size and age can be decoupled. We measured growth, survival, and reproduction through repeated census of 97 colonies from two populations of a marine bryozoan in the field from settlement to the end of their reproductive season in the northern Gulf of Mexico. Despite large population differences in fitness when grown in a common garden setting, selection within populations on variation in relative growth rate prior to reproduction was similar. In both populations, colonies that grew faster early after settlement, hence were larger, did not consistently have higher fitness than colonies that grew slower after settlement. Instead, early juvenile growth was uncorrelated to later juvenile growth, and colonies that grew faster just prior to the onset of reproduction had higher fitness than colonies that grew slower during this time. Growth rates then declined with the onset of reproduction. Our results show that, rather than being a simple consequence of selection on body size, growth rate can directly affect variation in fitness in ways that are not directly attributable to juvenile size. Colony size and growth rate in modular animals are not always reliable surrogates for direct estimates of survival and reproduction, without identifying when and how growth affects fitness.

中文翻译：

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增长率何时会影响殖民地海洋无脊椎动物的健康？

增长率会影响体型，而较大的体型通常与产生更多存活后代的能力有关。然而，增长率应该与适应度呈正相关的假设很少得到检验，尤其是在大小和年龄可以分离的殖民地海洋无脊椎动物中。我们通过对来自墨西哥湾北部的两个海洋苔藓动物种群的 97 个殖民地的重复普查来测量其生长、存活和繁殖，从定居到繁殖季节结束。尽管在普通花园环境中生长时种群的适应度存在很大差异，但繁殖前种群内相对增长率变化的选择是相似的。在这两个种群中，定居后早期增长更快的殖民地，因此更大，并不总是比定居后生长缓慢的群体具有更高的适应度。相反，早期的幼虫生长与后期的幼虫生长无关，并且在繁殖开始前生长得更快的菌落比在此期间生长较慢的菌落具有更高的适应性。随着繁殖的开始，增长率随后下降。我们的结果表明，生长率不是体型选择的简单结果，而是可以直接影响适合度的变化，而不直接归因于幼年体型。模块化动物的群体大小和增长率并不总是直接估计生存和繁殖的可靠替代指标，而没有确定生长何时以及如何影响健康。早期的幼虫生长与后期的幼虫生长无关，在繁殖开始前生长较快的菌落比在此期间生长较慢的菌落具有更高的适应性。随着繁殖的开始，增长率随后下降。我们的结果表明，生长率不是体型选择的简单结果，而是可以直接影响适合度的变化，而不直接归因于幼年体型。模块化动物的群体大小和增长率并不总是直接估计生存和繁殖的可靠替代指标，而没有确定生长何时以及如何影响健康。早期的幼虫生长与后期的幼虫生长无关，在繁殖开始前生长较快的菌落比在此期间生长较慢的菌落具有更高的适应性。随着繁殖的开始，增长率随后下降。我们的结果表明，生长率不是体型选择的简单结果，而是可以直接影响适合度的变化，而不直接归因于幼年体型。模块化动物的群体大小和增长率并不总是直接估计生存和繁殖的可靠替代指标，而没有确定生长何时以及如何影响健康。随着繁殖的开始，增长率随后下降。我们的结果表明，生长率不是体型选择的简单结果，而是可以直接影响适合度的变化，而不直接归因于幼年体型。模块化动物的群体大小和增长率并不总是直接估计生存和繁殖的可靠替代指标，而没有确定生长何时以及如何影响健康。随着繁殖的开始，增长率随后下降。我们的结果表明，生长率不是选择对体型的简单结果，而是可以直接影响适合度的变化，而不是直接归因于幼年体型。模块化动物的群体大小和增长率并不总是直接估计生存和繁殖的可靠替代指标，而没有确定生长何时以及如何影响健康。