Marshall Dustin J, Keough Michael J
School of Integrative Biology, The University of Queensland, Brisbane, Queensland 4072, Australia.
Ecology. 2009 Feb;90(2):487-95. doi: 10.1890/08-0320.1.
Offspring size is one of the most well-studied life-history traits, yet it is remarkable that few field studies have examined the manner in which the relationship between offspring size and performance (and thus, optimal offspring size) is affected by the local environment. Furthermore, while offspring size appears to be plastic in a range of organisms, few studies have linked changes in offspring size to changes in the relationship between offspring size and performance in the field. Interspecific competition is a major ecological force in both terrestrial and marine environments, but we have little understanding of its role in shaping selection on offspring size. Here we examine the effect of interspecific competition on the relationship between offspring size and performance in the field for the marine bryozoan Watersipora subtorquata along the south coast of Australia. Both interspecific competition and offspring size had strong effects on the post-metamorphic performance of offspring in the field, but importantly, they acted independently. While interspecific competition did not affect the offspring size-performance relationship, mothers experiencing competition still produced larger offspring than mothers that did not experience competition. Because larger offspring are more dispersive in this species, increasing offspring size may represent a maternal strategy whereby mothers produce more dispersive offspring when they experience high competition themselves. This study shows that, while offspring size is plastic in this species, post-metamorphic factors alone may not determine the size of offspring that mothers produce.
后代大小是研究最为充分的生活史特征之一，但值得注意的是，很少有实地研究考察过当地环境对后代大小与性能之间关系（进而对最优后代大小）的影响方式。此外，虽然在一系列生物体中后代大小似乎具有可塑性，但很少有研究将野外后代大小的变化与后代大小和性能之间关系的变化联系起来。种间竞争是陆地和海洋环境中的一种主要生态力量，但我们对其在塑造后代大小选择方面的作用了解甚少。在这里，我们研究了种间竞争对澳大利亚南海岸海洋苔藓虫亚扭旋水螅虫后代大小与野外性能之间关系的影响。种间竞争和后代大小对野外后代变态后的性能都有强烈影响，但重要的是，它们的作用是独立的。虽然种间竞争没有影响后代大小与性能的关系，但经历竞争的母体仍比未经历竞争的母体产生更大的后代。因为在这个物种中较大的后代更具扩散性，增加后代大小可能代表一种母体策略，即当母体自身经历高竞争时会产生更具扩散性的后代。这项研究表明，虽然该物种的后代大小具有可塑性，但仅变态后因素可能无法决定母体产生的后代大小。
