Abstract
Insect pollination of flowers should change the within-season allocation of resources in plants. But the nature of this life-history response, particularly regarding allocation to roots, photosynthetic structures, and flowers, is empirically unresolved. This study uses a greenhouse experiment to investigate the effect of insect pollination on the reproductive output of 23 varieties of a globally important crop—canola (Brassica napus). Overall, insect pollination modified the functional characteristics (flower timing & effort, plant size & shape, seed packaging, root biomass) of canola, increasing seed production and quality, and pollinator dependence. Reproductive output and pollinator dependence were defined by strong trait trade-offs, which ranged from more pollinator-dependent plants favouring early reproductive effort, to less pollinator-dependent plants favouring a prolonged phenology with smaller plant size and lower seed quality. Seed production decreased with pollinator dependence in the absence of pollinators. The agricultural preference for hybrid varieties will increase seed production compared to open-pollinated varieties, but, even so, pollinators typically enhance seed production of both types. Our study elucidates how insect pollination alters the character and function of a globally important crop, supporting optimization of yield via intensification of insect pollination, and highlights the beneficial effects of insect pollination early in the season.
Highlights
The allocation of resources between growth and reproduction is a central theme in life history evolution[1], directly affecting age and size at maturity[2]
Differences among canola varieties (e.g.27) could explain these results regarding the effect of insect pollination on canola seed production, meriting a more thorough examination of pollinator dependence and its associated traits among canola varieties
To determine how insect pollination affects reproductive output and pollinator dependence of a globally important crop, as mediated by key vegetative and phenological traits, we experimentally evaluated the functional output to insect visitation of 23 commercially available canola varieties, comprising 8 open-pollinated and 15 hybrid varieties
Summary
The allocation of resources between growth and reproduction is a central theme in life history evolution[1], directly affecting age and size at maturity[2]. In the case of plant life histories, understanding this tradeoff is potentially important for global crop production. Plants, due to their sessile nature and constraints on dispersal, have evolved a variety of strategies that allow them to optimize fitness across a range of biotic and abiotic environments. Because 75% of seed and fruit production of the major global field crops relies, at least to some extent, upon insect pollination[17], it is important to understand the effects of insect pollination on resource allocation and plastic trait responses in crop plants. Has the transition from use of open-pollinated to use of hybrid varieties resulted in a change in pollinator dependence? considering the economic importance of canola crops globally, the global decline in wild pollinators[33], and the fact that human food security decreases with increased crop pollinator dependence[34], the importance of examining the traits and pollination dependencies of canola becomes apparent
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