title: Floral scent of Joshua trees (Yucca brevifolia sensu lato): Divergence in scent profiles between species but breakdown of signal integrity in a narrow hybrid zone.
abstract: OBJECTIVE
  The role of floral scent in facilitating reproductive isolation between closely related plants remains poorly understood. Yucca brevifolia and Yucca jaegeriana are pollinated by different moth species in allopatry, but in a narrow contact zone, pollinator-host specificity breaks down, resulting in hybridization between species. We explored the chemical basis for reproductive isolation and hybridization in these Joshua trees by characterizing the floral scent of each species in allopatry, analyzing scent profiles from trees in the contact zone, and matching these data with genotypic and phenotypic data.
  
  
  METHODS
  We analyzed floral volatiles using gas chromatography-mass spectrometry, tested for species divergence of scent profiles and classified trees in the contact zone as hybrid or either parental species. We used floral and vegetative morphological data and genotypic data to classify trees and analyzed whether certain trait combinations were more correlated than others with respect to assignment of trees and whether frequencies of classified tree types differed depending on which data set was used.
  
  
  RESULTS
  The Joshua tree floral scent included oxygenated 8-carbon compounds not reported for other yuccas. The two species differed (P < 0.001) in scent profiles. In the contact zone, many hybrids were found, and phenotypic traits were generally weakly correlated, which may be explained by extensive gene flow between species or by exposure to different selection pressures.
  
  
  CONCLUSIONS
  Although the two Joshua tree species produce distinct floral scent profiles, it is insufficient to prevent attraction of associated pollinators to both hosts. Instead, floral morphology may be the key trait mediating gene flow between species.
authors: Department of Biology, Lund University, Solvegatan 37, SE-22362 Lund Sweden glenn.svensson@biol.lu.se.
authors: Glenn P
authors: GP
authors: Svensson
authors: Department of Neurobiology and Behavior, 215 Tower Road, Cornell University, Ithaca, New York 14853 USA.
authors: Robert A
authors: RA
authors: Raguso
authors: Department of Biology, Willamette University, 900 State Street, Salem, Oregon 97301 USA.
authors: Ramona
authors: R
authors: Flatz
authors: Department of Biology, Willamette University, 900 State Street, Salem, Oregon 97301 USA.
authors: Christopher I
authors: CI
authors: Smith
mesh_terms: D035264:Flowers / Q000033:anatomy & histology / Q000737:chemistry / Q000502:physiology; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats; D009505:Nevada; D009812:Odorants / Q000032:analysis; D010675:Pheromones / Q000032:analysis; D060047:Reproductive Isolation; D027623:Yucca / Q000033:anatomy & histology / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
chemical_list: D010675:Pheromones
keywords: Tegeticula; Yucca brevifolia; Yucca jaegeriana; floral scent; hybridization; mutualism; pollinator host specificity; signal integrity; trait mosaic