SummaryThis review reports on the processes associated with costs of reproduction, including some theoretical considerations, definitions and methodological aspects, followed by a list of the situations where costs are difficult to find. Despite some exceptions, case studies, examined by trade-offs between reproduction and other life-history traits, generally support the predictions of the cost of reproduction hypothesis. The cost of reproduction as an evolutionary determinant of sexual dimorphism in life history traits in dioecious species was specifically tested, considering that the higher cost of reproduction in females has driven the life history traits related to sexual dimorphism. Females of woody dioecious species were consistently smaller than males supporting the costs of reproduction hypothesis. By contrast, females of herbaceous perennials were generally the larger sex, which did not fit the expectations of the hypothesis. Finally, the mechanisms that enable the compensation of the reproductive costs are detailed, including the plastic responses of photosynthesis and growth, the effects of the timing of investment, plant architecture and plant physiological integration.
I. IntroductionLife history traits, such as growth, survival and reproduction, are linked through constraining relationships, implying that to be the best in all ecological situations is not biologically possible and to be well fitted to even one situation requires a compromise. We refer to these compromises as tradeoffs or costs between life history variables (Reznick, 1985). The concept of costs has taken on an important role in the development of many fields in evolutionary biology since the introduction of cost-benefit analyses into biology and it has been closely linked to the notion of evolutionary trade-offs and constraints (Williams, 1966a,b; Levins, 1968;Roff, 1992). Specifically, the costs of reproduction are defined in terms of losses in the potential future reproductive success caused by current investments in reproduction ( Jönsson, 2000). In a historical perspective, the idea that reproduction competes with other functions is as old as the study of natural history itself ( Jönsson & Tuomi, 1994). The historical development of this idea was mainly due to animal ecologists but a number of works by plant ecologists were compiled by Harper (1977) who concluded that perennial polycarpic plants often show an inverse correlation between vegetative growth and the production of fruit and seed which suggests that fecundity and vegetative activity are not wholly compatible. If reproduction carries no costs either in terms of future survival or fecundity an organism should begin reproducing at the earliest possible age (Roff, 1992). The fact that this does not seem to happen (most plants need to achieve a minimum size for reproduction) suggests that reproduction costs exist. The question of whether this threshold minimum size for reproduction mainly reflects the cost of reproduction or, alternatively, is a reflection of some allom...
