Temporal patterns of land plant evolution suggest extensive polyphyly
Syvanen, M.
School of Medicine, University of California, Davis, California, USA
Fritz Went, in 1972 [1], pointed out the widespread occurrence of parallel developments between angiosperm families that are restricted to the same geographical areas and proposed that this is most easily explained by horizontal gene transfer. This suggests that horizontal gene transfer among plants is much more widespread than it is among animals. In the current work, I have examined this hypothesis through an analysis of ribosomal RNA and have focused on divergence times between major plant clades. A trifurcation rate test is employed whereby it is unnecessary to assume constant molecular clocks in the different lineages being compared. This test led to divergence times between major plant clades that are consistently earlier than suggested from the fossil record. For example, the molecular divergence time for monocots and dicots is about 210 MYA [2] while the fossil record shows that the angiosperm radiation occurred 110 MYA. Similar discrepancies are seen between molecular time of divergence and the fossilrecord when the lineages being compared include angiosperms, gymnosperms, filicophyta and bryophyta. This discrepancy between molecular time estimates and paleontological estimates is not generally seen with animals. This forces the conclusion that the major land plant clades are polyphyletic, as has been suggested by Krassilov [3] for the angiosperms and has been generally recognized for the gymnosperms. A single simple explanation for these widespread parallelisms, ambiguous higher taxonomic categories and polyphyly is that asexual transfer of genetic information between remotely related plants is a major factor in shaping the macroevolutionary patterns of plants.
[1] F.W. Went (1972) Parallel evolution. Taxon, 20:197-226.
[2] L. Savard, et al. (1994) Chloroplast and nuclear gene sequences indicate late Pennsylvanian time for the last common ancestor of extant seed plants. Proc. Nat. Acad. Sci. USA, 91:5163-7.
[3] V.A. Krassilov (1977) The origin of angiosperms. Bot. Rev., 43:143-76.
| LOCATION |
DATE |
TIME |
| Lecture Hall I |
Thursday, April 9 |
03:05 pm |