title: Multifarious selection through environmental change: acidity and predator-mediated adaptive divergence in the moor frog (Rana arvalis).
abstract: Environmental change can simultaneously cause abiotic stress and alter biological communities, yet adaptation of natural populations to co-changing environmental factors is poorly understood. We studied adaptation to acid and predator stress in six moor frog (Rana arvalis) populations along an acidification gradient, where abundance of invertebrate predators increases with increasing acidity of R. arvalis breeding ponds. First, we quantified divergence among the populations in anti-predator traits (behaviour and morphology) at different rearing conditions in the laboratory (factorial combinations of acid or neutral pH and the presence or the absence of a caged predator). Second, we evaluated relative fitness (survival) of the populations by exposing tadpoles from the different rearing conditions to predation by free-ranging dragonfly larvae. We found that morphological defences (relative tail depth) as well as survival of tadpoles under predation increased with increasing pond acidity (under most experimental conditions). Tail depth and larval size mediated survival differences among populations, but the contribution of trait divergence to survival was strongly dependent on prior rearing conditions. Our results indicate that R. arvalis populations are adapted to the elevated predator pressure in acidified ponds and emphasize the importance of multifarious selection via both direct (here: pH) and indirect (here: predators) environmental changes.
authors.affiliation: Department of Zoology and Physical Anthropology, University of Murcia, , Murcia 30100, Spain, Eawag, Department of Aquatic Ecology, and ETH-Zurich, Institute of Integrative Biology, , Ueberlandstrasse 133, Duebendorf 8600, Switzerland, Animal Ecology/Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, , Norbyvägen 18D, Uppsala 75236, Sweden.
authors.forename: Andrés
authors.initials: A
authors.lastname: Egea-Serrano
authors.forename: Sandra
authors.initials: S
authors.lastname: Hangartner
authors.forename: Anssi
authors.initials: A
authors.lastname: Laurila
authors.forename: Katja
authors.initials: K
authors.lastname: Räsänen
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D004777:Environment; D010641:Phenotype; D011157:Population Dynamics; D011235:Predatory Behavior; D011898:Ranidae / Q000502:physiology*; D012641:Selection, Genetic; D013312:Stress, Physiological
keywords: acidification; amphibians; environmental stress; multiple stressors; natural selection; predator defences