Little evidence for a selective advantage of armour-reduced threespined stickleback individuals in an invertebrate predation experiment
The repeated colonization of freshwater habitats by the ancestrally marine threespined stickleback Gasterosteus aculeatus has been associated with many instances of parallel reduction in armour traits, most notably number of lateral plates. The change in predation regime from marine systems, dominated by gape-limited predators such as piscivorous fishes, to freshwater habitats where grappling invertebrate predators such as insect larvae can dominate the predation regime, has been hypothesized as a driving force. Here we experimentally test the hypothesis that stickleback with reduced armour possess a selective advantage in the face of predation by invertebrates, using a natural population of stickleback that is highly polymorphic for armour traits and a common invertebrate predator from the same location. Our results provide no compelling evidence for selection in this particular predator–prey interaction. We suggest that the postulated selective advantage of low armour in the face of invertebrate predation may not be universal.
KeywordsEda Stn382 Aeshna Dragonfly larvae Lateral plates
The experiments reported in this study were approved by the veterinary office of the Canton of Bern and complied with all legal requirements in Switzerland (permit no. BE51/09). We thank the members of the Eawag Fish Ecology and Evolution lab for constructive feedback and two anonymous reviewers of previous versions of the manuscript for their comments.
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