Hu, Shusheng , Dilcher, David , Jarzen, David , Taylor, David W. .
Early steps of angiosperm-pollinator coevolution.
Early steps in angiosperm-pollinator coevolution have been best understood through the research on Cretaceous fossil flowers and pollen. A widely accepted hypothesis is that insect pollination was the dominant mode of angiosperm pollination during the Early Cretaceous with specialization increasing by the mid-Cretaceous, although the quantification of pollination modes has been difficult. We have taken two new approaches to examine pollination systems in early angiosperms and their subsequent specialization. First, we looked at the phylogenetic distribution of pollination syndromes in the basally placed dicots, basal monocots and basal eudicots. These data show that initially angiosperms were insect pollinated (86%, 38% specialized) while in derived clades such as monocots and eudicots wind and specialized pollination syndromes were more common (up to 78%). Second, we examined pollen clumps from the mid-Cretaceous. Pollen clumps are found in zoophilous flowers in extant angiosperms and a major step in angiosperm-pollinator coevolution. A novel approach combining pollen morphology characteristics previously shown to be associated with generalized pollination modes, and the frequency and morphology of dispersed pollen grains and single species clumps, allow us to quantify the pollination modes of angiosperms during the Cenomanian. In this study 22% of the pollen species are found in clumps that ranging in size and number of grains, and 37% of Cenomanian angiosperm pollen species show specialized pollination. Although the majority of the species appear to be pollinated by insect generalist (39%), others appear to be adapted for pollen reward (27%), wind (24%), or other specialized modes (10%). These data support the hypotheses of widespread zoophilous pollination modes during the Cretaceous, but also quantify the degree of specialized pollination by the mid-Cretaceous.
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1 - Indiana University Southeast, Biology, 4201 Grant Line Rd, New Albany, IN, 47150, USA
2 - University of Florida, Florida Museum of Natural History, P.O. Box 117800, Gainesville, Florida, 32611-7800, USA
3 - University of Florida, Department of Botany, Florida Museum of Natural History, P.O. Box 117800, Gainesville, Florida, 32611-7800, USA
4 - Indiana University Southeast, Biology, 4201 Grant Line Rd, New Albany, IN, 47150
Presentation Type: Oral Paper:Papers for Sections
Location: Lake Erie/Hilton
Date: Tuesday, July 10th, 2007
Time: 9:30 AM