A hierarchical perspective in allocation to reproduction from whole plant to fruit and seed level

Allocation to reproduction is often examined at the whole plant level from an allometric perspective; however, investment in reproduction is a hierarchical process which represents the integration of adjustments at different hierarchical levels. This essay review presents some key issues in reproductive allocation by examining problems of allocation at different hierarchical levels within plant. At the whole plant level, the application of 'Rensch's rule' to plants is discussed as a mechanism that might explain size differences in relation to gender in dioeclous species. At branch level, the existence of vegetative branches may be explained by hypotheses on branch specialization and costs of reproduction. However, vegetative branches might also constitute an 'assurance' for reproduction in variable environments. At a lower hierarchical level, fruit abortion is a process widely observed in plants that impose limits to our capacity to estimate and develop general laws about reproductive allocation in plants. The question of whether fruit abortion can be used by the parent to produce a more homogeneous progeny that limits asymmetric competition among sibs is discussed. Finally, it seems that in some cases the allocation within seeds is in accordance with some predictions of kin selection theory. Most of these topics contain open questions that deserve further research.