Developmental and Structural Section
Riviere, Stephanie , Clayson, Courtney , Dockstader, Kristy , Wright, Michael , Costea, Mihai .
To attract or to repel? Function, diversity and evolution of infrastaminal scales in Cuscuta(dodders, Convolvulaceae).
Cuscuta (dodder, Convolvulaceae) is a genus of about 200 species of obligate stem parasites with subcosmopolitan distribution. Infrastaminal scales (IFS) are staminode-like formations that surround the ovary in the flowers of dodders. Their morphological diversity has historically provided some of the most useful taxonomic characters at the species-level, however, their function had not been determined. We have performed a comparative study of the IFS in 147 taxa using light, scanning and transmission electron microscopy, and results were analyzed in relation to a Cuscuta phylogeny obtained from a combined analysis of rbcL and 26S rDNA gene sequences. To test the hypothesis that the role of IFS is to attract pollinators, we analyzed the correlations between IFS characters and the production of pollen/ovules in the flower as an indicator of breeding systems. With a few exceptions, the IFS exhibit numerous fimbriae that contain laticifer cells secreting a complex resin-glycoside latex. In subgenus Monogynella, the first diverged infrageneric lineage, laticifer cells are exposed and fimbriae are similar to uniseriate glandular hairs. In the derived subgenera Grammica and Cuscuta, laticifers are enclosed and protected by an epidermis but leaving the distal ends of the laticifers exposed. Ultrastructurally, epidermal cells are connected among themselves and with the laticifer cells through plasmodesmata. The slightest mechanical contact with the exposed part of the laticifer cells (for example by an insect) causes them to burst open and release the latex. However, their putative role in attracting pollinators is not confirmed because the IFS and pollen/ovule ratios are not correlated. From a developmental point of view, IFS are the last structures to form in the flower and they persist after the fertilization, which strongly suggests that they play a role in the protection of the developing ovary/capsule against herbivorous insects. In three of the fifteen clades of subgenus Grammica, IFS have undergone a reduction trend, and in some species they are completely absent. In Clade O from the same subgenus, we observed papillae on the fimbriae, a feature that appears to be an apomorphy. Our study further details the morphological diversity of the IFS in Cuscuta, confirming their significance for the species-level systematics.
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1 - Wilfrid Laurier University, Biology, 75 University Avenue West, Waterloo, ON, N2L3C5, CA
2 - Wilfrid Laurier University, 75 University Avenue West, Waterloo, ON, N2L3C5, CA
3 - University of Toronto, Ecology & Evolutionary Biology/UTM Biology, 3359 Mississauga Road N, Mississauga, ON, L5L1C6, Canada
4 - Wilfrid Laurier University, Biology, 75 University Ave W, Waterloo, ON, N2L3C5, Canada
Presentation Type: Poster:Posters for Sections
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM