title: The ecology, evolution, and biogeography of dioecy in the genus Solanum: with paradigms from the strong dioecy in Solanum polygamum, to the unsuspected and cryptic dioecy in Solanum conocarpum.
abstract: •
  
  
  OBJECTIVE
  Island plants are over-exploited and "under-explored." Understanding the reproductive biology of plants, especially rare species, is fundamental to clarifying their evolution, estimating potential for change, and for creating effective conservation plans. Clarification of sexual systems like dioecy, and unusual manifestations of it in specific studies within Solanum, helps elucidate evolutionary patterns and genetic and ecological control of sex expression.•
  
  
  METHODS
  Studies of reproductive systems of two Caribbean endemics, S. polygamum and S. conocarpum, combined multifaceted analyses of field populations and of multiple generations of greenhouse plants.•
  
  
  RESULTS
  The dioecy in both species is, like that in other solanums, largely cryptic, although the gender of S. polygamum flowers is obvious. The rare S. conocarpum is recognized as dioecious; floral gender is not obvious. Variation in sex expression facilitated experiments and promoted hypotheses on control and significance of morphological features and sex expression.•
  
  
  CONCLUSIONS
  Confirmed dioecy in at least 15 solanums is distributed across the genus, with perhaps 6 independent origins, and with crypticity in the form of morphologically hermaphroditic, but functionally unisexual, flowers characterizing all species. Dioecy is not more strongly associated with islands. Inaperturate pollen in pistillate flowers characterizes almost all, but not the two dioecious species studied herein. Dioecy in both species indicates leakiness (rare hermaphroditic flowers on male plants) that helps explain island colonization and radiation. Leakiness allowed confirmation-usually impossible for dioecious species-of self-compatibility for S. polygamum, and thus support for the hypothesis that dioecy evolved to promote outcrossing.
authors.affiliation: Ecology and Evolutionary Biology, University of Connecticut, Storrs, Connecticut 06268-3043 USA.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Anderson
authors.affiliation: Linguistics, University of Connecticut, Storrs, Connecticut 06268-1145 USA.
authors.forename: Mona K J
authors.initials: MK
authors.lastname: Anderson
authors.affiliation: Nikisha Patel, Department of Plant Biology, 111 Jeffords Hall, 63 Carrigan Drive, University of Vermont, Burlington, Vermont 05405 USA.
authors.forename: Nikisha
authors.initials: N
authors.lastname: Patel
mesh_terms: D005075:Biological Evolution; D035264:Flowers / Q000033:anatomy & histology; D063148:Plant Dispersal; D011647:Puerto Rico; D012098:Reproduction; D032322:Solanum / Q000033:anatomy & histology / Q000502:physiology*; D014767:United States Virgin Islands
keywords: Baker’s Law; Solanum; compatibility; conservation and endemics; cryptic/functional dioecy; island colonization; leaky dioecy; pollinator deception; sexual system evolution; underlying synapomorphy