title: Testing mechanisms and context dependence of costs of plastic shade avoidance responses in Impatiens capensis (Balsaminaceae).
abstract: OBJECTIVE
  Many plant species elongate their shoots in response to neighbor proximity and neighbor height. Although these plastic responses may be beneficial in terms of enhancing light interception, they also may have costs in terms of increased risk of mechanical failure (i.e., lodging or breaking) because of thinner stems. This trade-off between light acquisition and stability may shape the evolution of plastic elongation responses to foliage shade.
  
  
  METHODS
  In a field experiment manipulating elongation phenotypes and densities, we tested two hypotheses. We predicted that the risks of mechanical failure depend on plastic elongation and/or on characteristics of the immediate neighborhood, such as density and neighbor height. Further, we predicted that plants that fail mechanically would have reduced fitness.
  
  
  RESULTS
  Mechanical failure was earlier and more frequent at high density and showed a complex interaction with neighborhood characteristics such as relative height of the neighbors and the expression of early plasticity. Plants that broke earlier had shorter lifespan and lower reproductive output.
  
  
  CONCLUSIONS
  Our results show that depending on the height and density of the group, plastic elongation responses can remain advantageous despite costs of increased risk of mechanical failure of the taller stems, as mechanical failure was not associated with strong costs in terms of reduced lifespan or seed production. The overall benefits of elongation outweigh the costs resulting in selection for elongation at the population level.
authors.affiliation: Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island, USA. H.Huber@science.ru.nl
authors.forename: Heidrun
authors.initials: H
authors.lastname: Huber
authors.forename: Eric J
authors.initials: EJ
authors.lastname: von Wettberg
authors.forename: Anna
authors.initials: A
authors.lastname: Aguilera
authors.forename: Johanna
authors.initials: J
authors.lastname: Schmitt
mesh_terms: D001696:Biomechanical Phenomena; D004777:Environment; D029069:Impatiens / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D008027:Light; D010641:Phenotype