Abstract The concept of fitness is central to evolutionary biology, yet it is difficult to define and to measure. In plant biology, fitness is often measured as seed count. However, under an array of circumstances, seed count may be a biased proxy of fitness, for example when individuals vary in allocation to sexual versus asexual reproduction. A more subtle example, but also likely to be important in natural populations, is when interindividual variation in conditions during development results in variation in offspring quality among seed parents. In monocarpic (semelparous) plants, this is expected to result from variation in effective season length experienced among individuals that reach reproductive maturity at different times. Here, we manipulate growing season length to ask whether seed count is an accurate representation of parental fitness in the monocarpic herb Lobelia inflata. Simple seed count suggests a paradoxical fitness advantage under constrained‐season length. However, we find that the apparent fitness advantage of a constrained‐season length is overridden by low relative per‐seed fitness. Furthermore, the fitness deficit in the constrained environment is associated primarily with an accelerating decrease in viability and seedling survival in seeds derived from fruits produced progressively later in the season. In this study, the overall fitness value of a seed under a constrained season is 0.774 of that observed under a long season.

中文翻译：

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妄想：种子计数不是个体物候变化下的良好适应度指标

摘要 适应度的概念是进化生物学的核心，但很难定义和衡量。在植物生物学中，适应度通常以种子数来衡量。然而，在一系列情况下，种子数量可能是适应性的有偏见的代理，例如当个体对有性繁殖和无性繁殖的分配不同时。一个更微妙但在自然种群中也可能很重要的例子是，发育过程中条件的个体间差异导致种子亲本中后代质量的差异。在单果（半产）植物中，预计这是由于在不同时间达到生殖成熟的个体之间经历的有效季节长度的变化所致。这里，我们操纵生长季节长度来询问种子计数是否准确表示单果草半边莲中的亲本适应性。简单的种子计数表明在受限制的季节长度下存在矛盾的适应性优势。然而，我们发现受限季节长度的明显适应度优势被低相对种子适应度所覆盖。此外，受限环境中的适应性缺陷主要与来自本赛季后期逐渐生产的果实的种子的活力和幼苗存活率加速下降有关。在这项研究中，种子在受限季节下的整体适应度值是在长季节下观察到的 0.774。然而，我们发现受限季节长度的明显适应度优势被低相对种子适应度所覆盖。此外，受限环境中的适应性缺陷主要与来自本季逐渐后期生产的果实的种子的活力和幼苗存活率加速下降有关。在这项研究中，种子在受限季节下的整体适应度值是在长季节下观察到的 0.774。然而，我们发现受限季节长度的明显适应度优势被低相对种子适应度所覆盖。此外，受限环境中的适应性缺陷主要与来自本赛季后期逐渐生产的果实的种子的活力和幼苗存活率加速下降有关。在这项研究中，种子在受限季节下的整体适应度值是在长季节下观察到的 0.774。