title: Signal honesty and cost of pollinator rewards in Dalechampia scandens (Euphorbiaceae).
abstract: OBJECTIVE
  Most species of Dalechampia vines (Euphorbiaceae) attract bee pollinators with terpenoid resins secreted by a gland-like structure in the inflorescence. In some species, pollinating bees appear to preferentially visit inflorescences (blossoms) with large resin-producing glands, whereas in other species bees preferentially visit blossoms with large involucral bracts. In this study, the reliability of bract and gland size as signals of the quantity of resin produced in one species, D. scandens, was assessed. Whether resin secretion has a cost with respect to the number or mass of the seeds produced by a blossom was also examined.
  
  
  METHODS
  Measurements were made of bract size, gland size and the amount of resin secreted by blossoms of D. scandens maintained in a common environment, and the relationships between these traits were analysed. Resin production was also manipulated, and the effects of the manipulation were tested on seed set and seed mass.
  
  
  RESULTS
  The amount of resin produced was better predicted by the size of the gland than by the size of the bract. Furthermore, when the effect of gland size was accounted for, bract size only weakly predicted the amount of resin produced. Neither an increase in resin secretion (by daily removal of the resin) nor a decrease (by removal of the resin gland) affected seed set or seed mass detectably, but resin production correlated positively with mean seed mass at the individual level once the size of the resin gland was accounted for.
  
  
  CONCLUSIONS
  Gland size is a better indicator of the amount of reward than bract size, although the latter remained an honest signal of the quantity of resin produced. Resin secretion has no detectable cost in terms of seed production, but may be condition dependent, as suggested by a positive correlation with seed mass at the individual level.
authors.affiliation: Centre for Conservation Biology, Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway. christophe.pelabon@bio.ntnu.no
authors.forename: Christophe
authors.initials: C
authors.lastname: Pélabon
authors.forename: Patrick
authors.initials: P
authors.lastname: Thöne
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Hansen
authors.forename: W Scott
authors.initials: WS
authors.lastname: Armbruster
mesh_terms: D000818:Animals; D001516:Bees / Q000502:physiology*; D019665:Euphorbiaceae / Q000469:parasitology / Q000502:physiology*