title: Yucca aloifolia (Asparagaceae) opts out of an obligate pollination mutualism.
abstract: •
  
  
  OBJECTIVE
  According to Cope's 'law of the unspecialized' highly dependent species interactions are 'evolutionary dead ends,' prone to extinction because reversion to more generalist interactions is thought to be unlikely. Cases of extreme specialization, such as those seen between obligate mutualists, are cast as evolutionarily inescapable, inevitably leading to extinction rather than diversification of participating species. The pollination mutualism between Yucca plants and yucca moths (Tegeticula and Parategeticula) would seem to be locked into such an obligate mutualism. Yucca aloifolia populations, however, can produce large numbers of fruit lacking moth oviposition scars. Here, we investigate the pollination ecology of Y. aloifolia, in search of the non-moth pollination of a Yucca species.•
  
  
  METHODS
  We perform pollinator exclusion studies on Yucca aloifolia and a sympatric yucca species, Y. filamentosa. We then perform postvisit exclusion treatments, an analysis of dissected fruits, and a fluorescent dye transfer experiment.•
  
  
  RESULTS
  As expected, Yucca filamentosa plants set fruit only when inflorescences were exposed to crepuscular and nocturnal pollinating yucca moths. In contrast, good fruit set was observed when pollinators were excluded from Y. aloifolia inflorescences from dusk to dawn, and no fruit set was observed when pollinators were excluded during the day. Follow up experiments indicated that European honeybees (Apis mellifera) were passively yet effectively pollinating Y. aloifolia flowers.•
  
  
  CONCLUSIONS
  These results indicate that even highly specialized mutualisms may not be entirely obligate interactions or evolutionary dead ends.
authors.affiliation: Department of Plant Biology, University of Georgia, Athens, Georgia 30602 USA.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Rentsch
authors.affiliation: Department of Plant Biology, University of Georgia, Athens, Georgia 30602 USA.
authors.forename: Jim
authors.initials: J
authors.lastname: Leebens-Mack
mesh_terms: D000818:Animals; D001516:Bees; D005075:Biological Evolution; D035264:Flowers; D005638:Fruit; D009036:Moths; D010802:Phylogeny; D054817:Pollination / Q000235:genetics*; D012098:Reproduction / Q000235:genetics; D013045:Species Specificity; D013559:Symbiosis / Q000235:genetics*; D027623:Yucca / Q000235:genetics* / Q000502:physiology
keywords: European honey bee; Yucca; obligate mutualism; yucca moth