title: High metabolic and water-loss rates in caterpillar aggregations: evidence against the resource-conservation hypothesis.
abstract: Several hypotheses have been proposed for explaining animal aggregation, including energy or water conservation. However, these physiological hypotheses have not been well investigated. Here, we report the effects of aggregation on metabolic ( ) and evaporative water-loss rates ( ) of the gregarious caterpillar Eutricha capensis, by comparing individuals and groups of individuals (N=10-100). Contrary to findings from previous physiological studies, we did not find an advantage to aggregation: unexpectedly, and did not decrease with increasing group size. and generally remained constant or increased in larger groups relative to individuals. The amount of water lost per unit of CO2 exchanged ( : ratio) showed a marked increase in grouped caterpillars, particularly in larger groups. Other benefits of aggregation (e.g. reduced predation or increased growth rates) likely outweigh these potential costs, because individuals of E. capensis aggregate voluntarily despite no obvious energetic or hygric advantage, and other potentially confounding group effects (e.g. increased thermoregulatory advantage or whole-animal activity) are inconsequential. The results of this study provide an important exception to physiological studies reporting enhanced energy or water conservation in animal groups.
authors.affiliation: Centre for Invasion Biology, Department of Conservation Ecology and Entomology, Stellenbosch University, Matieland 7602, South Africa.
authors.forename: Ruben E
authors.initials: RE
authors.lastname: Schoombie
authors.forename: Leigh
authors.initials: L
authors.lastname: Boardman
authors.forename: Berlizé
authors.initials: B
authors.lastname: Groenewald
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Glazier
authors.forename: Corné E
authors.initials: CE
authors.lastname: van Daalen
authors.forename: Susana
authors.initials: S
authors.lastname: Clusella-Trullas
authors.forename: John S
authors.initials: JS
authors.lastname: Terblanche
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D004734:Energy Metabolism; D007814:Larva / Q000378:metabolism / Q000502:physiology; D009036:Moths / Q000378:metabolism / Q000502:physiology*; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water
keywords: desiccation; grouping; respiratory metabolism; scaling