Trade-offs between larval survival and adult ornament development depend on predator regime in a territorial dragonfly
Trade-offs between juvenile survival and the development of sexually selected traits can cause ontogenetic conflict between life stages that constrains adaptive evolution. However, the potential for ecological interactions to alter the presence or strength of these trade-offs remains largely unexplored. Antagonistic selection over the accumulation and storage of resources could be one common cause of environment-specific trade-offs between life stages: higher condition may simultaneously enhance adult ornament development and increase juvenile vulnerability to predators. We tested this hypothesis in an ornamented dragonfly (Pachydiplax longipennis). Higher larval body condition indeed enhanced the initial development of its intrasexually selected wing coloration, but was opposed by viability selection in the presence of large aeshnid predators. In contrast, viability selection did not oppose larval body condition in pools when aeshnids were absent, and was not affected when we manipulated cannibalism risk. Trade-offs between larval survival and ornament development, mediated through the conflicting effects of body condition, therefore occurred only under high predation risk. We additionally characterized how body condition influences several traits associated with predator avoidance. Although body condition did not affect burst distance, it did increase larval abdomen size, potentially making larvae easier targets for aeshnid predators. As high body condition similarly increases vulnerability to predators in many other animals, predator-mediated costs of juvenile resource accumulation could be a common, environment-specific limitation on the elaboration of sexually selected traits.
KeywordsEcological agents of selection Ontogenetic conflict Natural selection
This work could not have been completed without technical assistance from C. Lis, L. Robinson, A. Wiecek, and H. Rollins. We thank A. Gilmore for generously sharing data on fat stores. We also thank A. Locci and the Squire Valleevue Farm staff, especially S. Brown and J. Miller, for providing access to all field sites and maintaining an exceptionally well-mowed area for our wading pools. Critical feedback from M. Dugas, S. Diamond, L. Chick, A. Perez, S. Peacor, several anonymous reviewers, and the Case Western Reserve University Ecology and Evolution reading group greatly improved the manuscript. MPM was funded in part by a GAANN fellowship.
Author contribution statement
MPM designed the experiment, collected and analyzed all data, and wrote the manuscript. RAM discussed experimental design, analyses, and manuscript revisions.
Compliance with ethical standards
All applicable institutional and/or national guidelines for the care and use of animals were followed.
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