Title

Evidence of early insect pollination in the Arecaceae: A palynological investigation and a new palm flower from the Paleocene/Eocene of the Mississippi embayment

Date of Completion

January 1990

Keywords

Biology, Botany|Paleobotany|Palynology

Degree

Ph.D.

Abstract

Modern pollen from species of Arecaceae with known pollination mechanisms was examined using scanning electron, transmission electron, and light microscopy in an attempt to determine which variation in pollen characters could be related to any of the different methods of pollen transport. Three set of micromorphological pollen exine features showed marked differences at the level wind vs. insect vector. The following were associated exclusively with pollination systems: (1a) the presence of exine processes, (2a) a highly uneven exine, and (3a) densely perforate, reticulate, or intectate pollen. Conversely, the pollen exine in all wind pollinated species studied was: (1b) devoid of processes, (2b) smooth and even, and (3b) had extremely minute and sparsely distributed tectal perforations. A greater percentage of tectal area was present in all wind transported palm pollen (mean tectal area present 98.5%) relative to insect transported palm pollen (mean 70.9%). These differences suggest that these exine features evolved in response to divergent selective pressures associated with wind vs. insect pollination.^ The above demonstrated relationship between pollen exine features and pollination system in the Arecaceae allows another critical question to be addressed: what was the mode of pollination in primitive palms? This long unresolved issue was approached by evaluating the unequivocal fossil record of palm reproductive parts. This included newly discovered Paleocene palm flowers with in situ pollen, described here for the first time. The new fossil flowers represent the earliest floral remains of palms, have a suite of characters restricting their affinities to the tribe Areceae, and have pollen characters suggesting insect pollination. A review of the well-documented fossil record of dispersed palm pollen also suggests early pollination not by wind, but by insects. In contrast to the traditionally held belief that wind pollination was primitive in the family, results from this study suggest that insects were the original pollen dispersers in the Arecaceae. ^