Pre-dispersal predation effect on seed packaging strategies and seed viability
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An increased understanding of intraspecific seed packaging (i.e. seed size/number strategy) variation across different environments may improve current knowledge of the ecological forces that drive seed evolution in plants. In particular, pre-dispersal seed predation may influence seed packaging strategies, triggering a reduction of the resources allocated to undamaged seeds within the preyed fruits. Assessing plant reactions to pre-dispersal seed predation is crucial to a better understanding of predation effects, but the response of plants to arthropod attacks remains unexplored. We have assessed the effect of cone predation on the size and viability of undamaged seeds in populations of Juniperus thurifera with contrasting seed packaging strategies, namely, North African populations with single-large-seeded cones and South European populations with multi-small-seeded cones. Our results show that the incidence of predation was lower on the single-large-seeded African cones than on the multi-small-seeded European ones. Seeds from non-preyed cones were also larger and had a higher germination success than uneaten seeds from preyed cones, but only in populations with multi-seeded cones and in cones attacked by Trisetacus sp., suggesting a differential plastic response to predation. It is possible that pre-dispersal seed predation has been a strong selective pressure in European populations with high cone predation rates, being a process which maintains multi-small-seeded cones and empty seeds as a strategy to save some seeds from predation. Conversely, pre-dispersal predation might not have a strong effect in the African populations with single-large-seeded cones characterized by seed germination and filling rates higher than those in the European populations. Our results indicate that differences in pre-dispersal seed predators and predation levels may affect both selection on and intraspecific variation in seed packaging.
KeywordsJuniperus thurifera Seed number Seed size Deceptive fruits
We are especially grateful to MD García-González for her valuable advice on nursery procedure and to R Heleno for the early review of the manuscript. We also thank D Caimel, M Esteve, L Lope and P Lorenzo for helping in the laboratory, and M Alifriqui for his help in the field work. The comments and suggestions of A Worley, KL Gross and three anonymous referees improved the manuscript.
Author contribution statement
LDS and RT originally formulated the idea. LDS, SRE and CN conceived and designed the experiments. LDS and DT performed the experiments. LDS analyzed the data. All the authors wrote the manuscript.
Compliance with ethical standards
This work was supported by Fundação para a Ciência e a Tecnologia (FCT) with the project MEDIATIC (PTDC/AAC-CLI/103361/2008). LDS and RT were supported by a postdoctoral fellowship from FCT (SFRH/BPD/70632/2010) and Spanish Ministry of Education (BVA 2010-0375) respectively.
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical approval statement
This article does not contain any studies with human participants or animals performed by any of the authors.
The experiments comply with the current laws of Portugal in which the experiments were performed.
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