Systematic review of the costs of reproduction in flowering plants

Costs of reproduction are frequently invoked to explain the phenotypic effects of reproductive trade-offs. There is abundant evidence that reproductive trade-offs have important effects on plant growth, survival and reproduction. Accordingly, our main objective was not to evaluate whether such trade-offs exist or are important. Instead, we aimed to highlight progress in the understanding of the costs of reproduction since a comprehensive review by Obeso published more than 20 years ago [@obesoCostsReproductionPlants2002b]. We outline the conceptual understanding of reproductive costs and its relation to plant fitness, link this conceptual understanding to sex-allocation theory, and then review the literature on reproductive costs with a focus on studies of flowering plants published since 2002. To do this, we searched the Web of Science Core Collection and used machine-learning software to screen studies for eligibility to mitigate biases in study inclusion. We scored studies in terms of species, methodologies, and the types of reproductive trade-offs examined. Experiments are now commonly used to study the costs of reproduction in plants but reproductive costs are not always apparent when they are studied in natural populations, regardless of whether an experimental manipulation was used. For dioecious plants, reproductive costs tended to be higher for females regardless of plant growth form, but this pattern may have been influenced by the preponderance of studies that measured costs as growth-reproduction trade-offs. There was also evidence indicating that reproductive costs can be size dependent, with a tendency for lower costs in larger plants. Ecological costs of reproduction, variation in the expression of somatic costs of reproduction within seasons and how they scale up to affect demographic costs, and the contribution of the male sex role to somatic and demographic costs of reproduction remain poorly understood.