Premise of the study— Bet-hedging strategies maximize long term -geometric fitness at the cost of reduced arithmetic fitness by offsetting different mortality risks. Heterocarpic systems accomplish this through the production of two or more fruit types that vary in dormancy and dispersal ability. It is unknown whether heterocarpy also offsets pre-dispersal mortality risks. To address this, we investigated whether heterocarpy in Grindelia ciliata (Asteraceae) also offsets mortality risks posed by a seed predator Schinia mortua (Noctuidae) to increase plant fitness.
Methods—We conducted two manipulative experiments to quantify critical life history components of this plant-insect interaction. We measured pre-dispersal achene mortality from herbivory, post-dispersal achene mortality in the seed bank, and seedling emergence. These measurements were then used in deterministic models to evaluate evolutionary consequences of pre-dispersal seed mortality in G ciliata.
Key Results—Dormant achene types were less vulnerable to herbivory but more susceptible to mortality in the seed bank due to delayed seed emergence. Non-dormant achene types experienced high pre-dispersal seedling mortality but low seed bank mortality due to rapid germination. Our herbivore dependent model improved fit between observed and expected proportions of dormant and non-dormant G. ciliata achene proportions, and shows that heterocarpy could evolve in the absence of post-germination mortality.
Conclusions—Our study provides empirical support of how pre-dispersal herbivory can be equally important to post-dispersal seed mortality risks in the evolution and maintenance of a heterocarpic reproductive system, and expands understanding of how bet-hedging theory can be used to understand this unique reproductive strategy.
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