Sibly Richard M, Kodric-Brown Astrid, Luna Susan M, Brown James H
School of Biological Sciences, University of Reading, Reading, UK.
Biology Department, University of New Mexico, Albuquerque, NM, USA.
R Soc Open Sci. 2018 Aug 15;5(8):180453. doi: 10.1098/rsos.180453. eCollection 2018 Aug.
Teleosts such as tunas and billfish lay millions of tiny eggs weighing on the order of 0.001 g, whereas chondrichthyes such as sharks and rays produce a few eggs or live offspring weighing about 2% of adult body mass, as much as 10 000 g in some species. Why are the strategies so extreme, and why are intermediate ones absent? Building on previous work, we show quantitatively how offspring size reflects the relationship between growth and death rates. We construct fitness contours as functions of offspring size and number, and show how these can be derived from juvenile growth and survivorship curves. Convex contours, corresponding to Pearl Type 1 and 2 survivorship curves, select for extremes, either miniscule or large offspring; concave contours select for offspring of intermediate size. Of particular interest are what we call critical straight-line fitness contours, corresponding to log-linear Pearl Type 3 survivorship curves, which separate regimes that select for opposite optimal offspring sizes.
金枪鱼和旗鱼等硬骨鱼会产下数百万颗重量约为0.001克的微小鱼卵，而鲨鱼和鳐鱼等软骨鱼则只产出几颗鱼卵或活体后代，其重量约为成年个体体重的2%，某些物种可达10000克。为什么繁殖策略如此极端，为什么没有中间类型的策略呢？基于之前的研究，我们定量地展示了后代大小如何反映生长率和死亡率之间的关系。我们构建了作为后代大小和数量函数的适应度等值线，并展示了这些等值线如何从幼体生长和存活曲线推导得出。对应于珀尔第1型和第2型存活曲线的凸等值线会选择极端情况，即极小或极大的后代；凹等值线则选择中等大小的后代。特别值得关注的是我们所称的临界直线适应度等值线，它对应于对数线性珀尔第3型存活曲线，该曲线分隔了选择相反最优后代大小的区域。
