Evolutionary Relationships, Gynodioecy, and Polyploidy in the Galápagos Endemic Lycium minimum (Solanaceae)

• Published in: International journal of plant sciences Vol. 176; no. 2; pp. 197 - 210
• Main Authors: Levin, Rachel A., Keyes, Edmund M., Miller, Jill S.
• Format: Journal Article
• Language: English
• Published: Chicago University of Chicago Press 01.02.2015; University of Chicago, acting through its Press
• Subjects: Anthers; Biological taxonomies; Deoxyribonucleic acid; DNA; Endemic species; Evolution; Flow cytometry; Flowers; Flowers & plants; Gender; Gene expression; Genetic diversity; Haplotypes; Islands; Lycium; Plants; Pollen; Polyploidy; Population genetics; Population structure; Solanaceae; Species diversity; Tetraploidy; Galapagos Islands; South America; phylogenetics; Galápagos; Lycium; Solanaceae; gender dimorphism
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/679492

Premise of research. Whereas most Lycium species are diploid and hermaphroditic, an association across Lycium species has been demonstrated between higher ploidy levels and gender dimorphism. Previous monographic work, in combination with a single tetraploid chromosome count, suggested that the Galápagos endemic Lycium minimum may be dimorphic. If substantiated, this would be the only documented Lycium species from South America to be dimorphic in gender expression, which is especially notable given that species diversity is highest in South America. The goals of this study are to (1) test the monophyly, characterize population-level genetic diversity, and determine the closest mainland relatives of L. minimum; (2) infer the sexual system of L. minimum; and (3) assess/verify ploidy using DNA content measurements. Methodology. Phylogenetic, morphological, and cytometric approaches were used to document evolutionary affinities, gynodioecy, and polyploidy. Phylogenetic analyses were conducted with DNA sequence data from both plastid and nuclear regions. Plastid data were also subject to network analysis, and genetic diversity within and among islands was examined using nuclear data. To determine whether populations were dimorphic in gender expression, we made floral measurements and documented pollen presence/absence. DNA content was determined using flow cytometry for multiple individuals from four islands. Pivotal results. Our findings support a South American origin for the Galápagos endemic L. minimum, with the Argentine L. athium as the closest living relative. Island populations exhibit significant population structure, with geographic distance positively correlated with genetic distance. Populations of L. minimum are gynodioecious; plants vary in the presence of pollen, and those without pollen have reduced anther length, width, and height. Conclusions. Morphological evidence and DNA content data confirm gender dimorphism and polyploidy in L. minimum, the first documented instance of a dimorphic Lycium species in South America.