Wright, Michael , Ianni, Michael , Costea, Mihai .
Diversity and evolution of floral morphology and pollen/ovule production in Cuscuta (dodder, Convolvulaceae).
Cuscuta (dodder, Convolvulaceae) is a genus of obligate stem parasites with around 200 species distributed across temperate, subtropical and tropical regions worldwide. In order to build a broad picture of floral and mating system evolution, the diversity of floral morphology and pollen and ovule production was surveyed in 128 species and ten varieties. Taxa were assigned to Cruden's mating system categories based on their pollen-ovule ratios. Variation and correlations among floral characters were analyzed using regression and ANOVA, while the mating system categories were subjected to a linear discriminant and canonical variates analysis to assess their cohesiveness. Our data suggest that most Cuscuta species possess one of a wide range of mixed-mating systems. Whereas four ovules develop in each flower, pollen production varies over three orders of magnitude between taxa. Several Cuscuta taxa appear to be highly outcrossing, but no species could be identified that are exclusively selfing. The role of herkogamy as a facilitator of outcrossing has decreased in two phases: first, the transition from the one-style flowers of subgenus Monogynella to the two-style flowers of subgenera Cuscuta and Grammica, and second from simultaneous to sequential maturation of the two stigmas in subgenus Grammica. These evolutionary changes are associated with an increase of species richness in subgenus Cuscuta, and especially in subgenus Grammica. Morphological features were not individually found to have a strong correlation to the mating system, but in general larger corollas and stigmas were associated with greater pollen-ovule ratios. When considered in light of the sex allocation theory, Cuscuta presents some puzzling results. Only some infrageneric lineages demonstrate the predicted pollen size-number tradeoff, while Cuscuta gracillima complex (in subgenus Grammica) displays an unexpected negative relationship between pollen size and style length. The relationship between host ranges and mating systems will be discussed, highlighting opportunities for further research into the co-evolution of pollination systems and life history traits between parasitic plants and their host species.
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Link to published paper.
1 - University of Toronto, Ecology & Evolutionary Biology/UTM Biology, 3359 Mississauga Road N, Mississauga, ON, L5L1C6, Canada
3 - Wilfrid Laurier University, Biology, 75 University Ave W, Waterloo, ON, N2L3C5, Canada
Presentation Type: Oral Paper:Papers for Sections
Location: Franklin A/Hyatt
Date: Tuesday, July 10th, 2012
Time: 9:45 AM