title: Modulation of the heat shock response is associated with acclimation to novel temperatures but not adaptation to climatic variation in the ants Aphaenogaster picea and A. rudis.
abstract: Ecological diversification into thermally divergent habitats can push species toward their physiological limits, requiring them to accommodate temperature extremes through plastic or evolutionary changes that increase persistence under the local thermal regime. One way to withstand thermal stress is to increase production of heat shock proteins, either by maintaining higher baseline abundance within cells or by increasing the magnitude of induction in response to heat stress. We evaluated whether environmental variation was associated with expression of three heat shock protein genes in two closely-related species of woodland ant, Aphaenogaster picea and A. rudis. We compared adult workers from colonies collected from 25 sites across their geographic ranges. Colonies were maintained at two different laboratory temperatures, and tested for the independent effects of environment, phylogeny, and acclimation temperature on baseline and heat-induced gene expression. The annual maximum temperature at each collection site (Tmax) was not a significant predictor of either baseline expression or magnitude of induction of any of the heat shock protein genes tested. A phylogenetic effect was detected only for basal expression of Hsp40, which was lower in the most southern populations of A. rudis and higher in a mid-range population of possible hybrid ancestry. In contrast, a higher acclimation temperature significantly increased baseline expression of Hsc70-4, and increased induction of Hsp40 and Hsp83. Thus, physiological acclimation to temperature variation appears to involve modulation of the heat shock response, whereas other mechanisms are likely to be responsible for evolutionary shifts in thermal performance associated with large-scale climate gradients.
authors.affiliation: Department of Biology, University of Vermont, Burlington, VT 05405, USA. Electronic address: scahan@uvm.edu.
authors.forename: Sara
authors.initials: S
authors.lastname: Helms Cahan
authors.affiliation: Department of Biology, University of Vermont, Burlington, VT 05405, USA.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Nguyen
authors.affiliation: Department of Biology, University of Vermont, Burlington, VT 05405, USA.
authors.forename: John
authors.initials: J
authors.lastname: Stanton-Geddes
authors.affiliation: Department of Applied Ecology, Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC 27695, USA.
authors.forename: Clint A
authors.initials: CA
authors.lastname: Penick
authors.affiliation: Department of Biology, University of Vermont, Burlington, VT 05405, USA.
authors.forename: Yainna
authors.initials: Y
authors.lastname: Hernáiz-Hernández
authors.affiliation: Department of Entomology, Smithsonian Institution, Washington, DC 20013, USA.
authors.forename: Bernice B
authors.initials: BB
authors.lastname: DeMarco
authors.affiliation: Department of Biology, University of Vermont, Burlington, VT 05405, USA.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Gotelli
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001000:Ants / Q000502:physiology*; D057231:Climate Change; D015870:Gene Expression; D006360:Heat-Shock Proteins / Q000235:genetics; D018869:Heat-Shock Response
chemical_list: D006360:Heat-Shock Proteins
keywords: Ants; Heat shock proteins; Heat shock response; Hsc70-4; Hsp40; Hsp70; Hsp90