title: Spatially heterogeneous selection in nature favors phenotypic plasticity in anuran larvae.
abstract: Theory holds that adaptive phenotypic plasticity evolves under spatial or temporal variation in natural selection. I tested this prediction in a classic system of predator-induced plasticity: frog tadpoles (Rana temporaria) reacting to predaceous aquatic insects. An outdoor mesocosm experiment manipulating exposure to Aeshna dragonfly larvae revealed plasticity in most characters: growth, development, behavior, and external morphology. I measured selection by placing 1927 tadpoles into enclosures within natural ponds; photographs permitted identification of the survivors six to nine days later. Fitness was defined as a linear combination of growth, development, and survival that correlates with survival to age 2 in another anuran species. In enclosures with many predators, selection-favored character values similar to those induced by exposure to Aeshna in mesocosms. The shift in selection along the predation gradient was strongest for characters that exhibited high predator-induced plasticity. A field survey of 50 ponds revealed that predator density changes over a spatial scale relevant for movement of individual adults and larvae: 17% of variation in predation risk was among ponds separated by tens to thousands of meters and 81% was among sites ≤10 m apart within ponds. These results on heterogeneity in the selection regime confirm a key tenant of the standard model for the evolution of plasticity.
authors.affiliation: Department of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH-8057, Zurich, Switzerland.
authors.forename: Josh
authors.initials: J
authors.lastname: Van Buskirk
mesh_terms: D000818:Animals; D001001:Anura; D005075:Biological Evolution; D007814:Larva; D063191:Odonata; D010641:Phenotype; D011235:Predatory Behavior; D011896:Rana temporaria; D012306:Risk; D012641:Selection, Genetic
keywords: Adaptive landscape; amphibian; fitness; natural selection; phenotypic plasticity; predation