THE EVOLUTIONARY DIVERSIFICATION OF SEED SIZE: USING THE PAST TO UNDERSTAND THE PRESENT

The Devonian origin of seed plants and subsequent morphological diversification of seeds during the late Paleozoic represents an adaptive radiation into unoccupied ecological niche space. A plant's seed size is correlated with its life-history strategy, growth form, and seed dispersal syndrome....

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Bibliographic Details
Published in:Evolution 2012-05, Vol.66 (5), p.1636-1649
Main Author: Sims, Hallie J.
Format: Article
Language:English
Subjects:
Angiosperms
Biological Evolution
Biological taxonomies
Correlation analysis
Cycadopsida - anatomy & histology
Cycadopsida - genetics
Evolution
Evolutionary trends
Fossils
Gymnosperms
Magnoliopsida - anatomy & histology
Magnoliopsida - genetics
morphospace
Ovules
paleozoic
Phylogeny
plant traits
Plants
Radiation
Seed size
Seeds
Seeds - anatomy & histology
Seeds - genetics
Selection, Genetic
Skewed distribution
Taxa
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Summary:The Devonian origin of seed plants and subsequent morphological diversification of seeds during the late Paleozoic represents an adaptive radiation into unoccupied ecological niche space. A plant's seed size is correlated with its life-history strategy, growth form, and seed dispersal syndrome. The fossil record indicates that the oldest seed plants had relatively small seeds, but the Mississippian seed size envelope increased significantly with the diversification of larger seeded lineages. Fossil seeds equivalent to the largest extant gymnosperm seeds appeared by the Pennsylvanian, concurrent with morphological diversification of growth forms and dispersal syndromes as well as the clade's radiation into new environments. Wang's Analysis of Skewness indicates that the evolutionary trend of increasing seed size resulted from primarily passive processes in Pennsylvanian seed plants. The distributions of modern angiosperms indicate a more diverse system of active and some passive processes, unbounded by Paleozoic limits; multiple angiosperm lineages independently evolved though the upper and lower bounds. Quantitative measures of preservation suggest that, although our knowledge of Paleozoic seeds is far from complete, the evolutionary trend in seed size is unlikely to be an artifact of taphonomy.
ISSN:0014-3820
1558-5646
DOI:10.1111/j.1558-5646.2011.01527.x