title: Thermal plasticity of growth and development varies adaptively among alternative developmental pathways.
abstract: Polyphenism, the expression of discrete alternative phenotypes, is often a consequence of a developmental switch. Physiological changes induced by a developmental switch potentially affect reaction norms, but the evolution and existence of alternative reaction norms remains poorly understood. Here, we demonstrate that, in the butterfly Pieris napi (Lepidoptera: Pieridae), thermal reaction norms of several life history traits vary adaptively among switch-induced alternative developmental pathways of diapause and direct development. The switch was affected both by photoperiod and temperature, ambient temperature during late development having the potential to override earlier photoperiodic cues. Directly developing larvae had higher development and growth rates than diapausing ones across the studied thermal gradient. Reaction norm shapes also differed between the alternative developmental pathways, indicating pathway-specific selection on thermal sensitivity. Relative mass increments decreased linearly with increasing temperature and were higher under direct development than diapause. Contrary to predictions, population phenology did not explain trait variation or thermal sensitivity, but our experimental design probably lacks power for finding subtle phenology effects. We demonstrate adaptive differentiation in thermal reaction norms among alternative phenotypes, and suggest that the consequences of an environmentally dependent developmental switch primarily drive the evolution of alternative thermal reaction norms in P. napi.
authors.affiliation: Department of Zoology, Stockholm University, SE-10691, Stockholm, Sweden. sami.m.kivela@gmail.com.|Department of Ecology, University of Oulu, 90014, Oulu, Finland. sami.m.kivela@gmail.com.
authors.forename: Sami M
authors.initials: SM
authors.lastname: Kivelä
authors.affiliation: Department of Zoology, Stockholm University, SE-10691, Stockholm, Sweden.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Svensson
authors.affiliation: Department of Zoology, Stockholm University, SE-10691, Stockholm, Sweden.
authors.forename: Alma
authors.initials: A
authors.lastname: Tiwe
authors.affiliation: Department of Zoology, Stockholm University, SE-10691, Stockholm, Sweden.
authors.forename: Karl
authors.initials: K
authors.lastname: Gotthard
mesh_terms: D000818:Animals; D002080:Butterflies / Q000254:growth & development*; D064666:Diapause, Insect; D005260:Female; D007814:Larva / Q000254:growth & development; D008018:Life Cycle Stages; D008297:Male; D010641:Phenotype; D017440:Photoperiod; D013548:Sweden; D013696:Temperature
keywords: Countergradient variation; Pieris napi, polyphenism; diapause; direct development; larval instar; reaction norm