Miller, Jill S. , Levin, Rachel , Feliciano, Natalie M. .
A tale of two continents: Bakerís law and the maintenance of self-incompatibility in Lycium (Solanaceae) following long distance dispersal.
Over 50 years ago, Baker suggested that self-compatible species were more likely than self-incompatible species to establish new populations following oceanic dispersal. His logic rested on the assumption that colonization was infrequent and selection favored the establishment of self-fertilizing individuals. In support of Bakerís Law, many have documented high frequencies of self-compatibility on islands, and recent work has solidified the generality of Bakerís ideas. Lycium (Solanaceae) has 85 species worldwide. Phylogenetic studies suggest the genus originated in South America, dispersing to the Old World once. Previous analyses of the S-RNase gene, which controls the stylar component of self-incompatibility, have shown that self-incompatibility is ancestral in Lycium, making it a good model for investigating Bakerís assertions. Lycium is also useful for investigations of reproductive evolution given that species vary in sexual expression and the presence of self-incompatibility. A model for the evolution of gender dimorphism suggests that polyploidy breaks down self-incompatibility leading to the evolution of gender dimorphism, which arises as an alternative outcrossing mechanism. There is a perfect association of dimorphic gender expression, polyploidy, and self-fertility (versus cosexuality, diploidy, and self-incompatibility) supporting this model. Although the association between ploidy and gender holds for African Lycium, no studies of mating systems have been initiated in Old World species. Here, we document strong self-incompatibility in two species of African Lycium using controlled pollinations. We also sequence the S-RNase gene from five African species and recover 24 alleles. Genealogical analyses indicate reduced trans-generic diversity in Old World, compared to New World, S-RNases. We suggest that allelic diversity was reduced as a result of a founder event but, despite the bottleneck, self-incompatibility was maintained in the Old World. The present data provide an exception to Bakerís Law, and are consistent with previously hypothesized models for the evolution of gender dimorphism.
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Miller Lab website
1 - Amherst College, Department of Biology, Mcguire Life Sciences Building, Amherst, Massachusetts, 01002, USA
2 - University of Massachusetts, Amherst, Plant Biology Graduate Program, 217 Morrill Science Center South, 611 North Pleasant Street, Amherst, MA, 01003, United States
Presentation Type: Oral Paper:Papers for Topics
Location: Lake Ontario/Hilton
Date: Tuesday, July 10th, 2007
Time: 4:45 PM