Post-K/T Boundary Expansion Of Polyphyletic Geniculate Coralline Red Algae Is Correlated With Multiple Polyploidy Events

DF Kapraun and JC Bailey

Department of Biological Sciences, University of North Carolina-Wilmington,601 South College Road, Wilmington, NC 28403-5915, USA
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Coralline red algae deposit calcite in their cell walls and are represented by an extensive fossil record4. Crustose (nongeniculate) taxa appear to extend back to the mid-Mesozoic and beyond. Articulated (geniculate) taxa appeared following the Cretaceous/Tertiary extinction (K/T event) and experienced subsequent rapid and substantial radiation1,2.
Recent molecular studies provide evidence that genicula are nonhomologous structures that evolved independently in several families3. When these 2C nuclear DNA content data are superimposed on a phylogeny inferred from 18S rRNA gene sequence analysis, it becomes apparent that the polyphyletic geniculate clades are represented by species with larger nuclear genomes (0.6 - 1.3 pg) while nongeniculate clades contain species with relatively small nuclear genomes (0.1- 0.4 pg). Analysis of nuclear DNA contents suggest a pattern of discontinuous discrete values consistent with polyploidy events. Proposed polyploidy events must have occurred independently in these several lineages following the K/T event. The strong correlation between the geniculate/nongeniculate morphotype and a ‘polyploid’ nucleotype is remarkable as it implies a significant role for the nucleotype (in addition to a substantial genotype role) in the expression of this morphotype.

1. Adey WH, Johansen HW. (1972). Phycologia 11: 159-180.
2. Adey WH, Macintyre IG. (1973). Bulletin of the Geologic Society of America 84: 883-904.
3. Bailey JC, Chapman RL. (1998). Journal of Phycology 34: 692-705.
4. Wray JL (1977). Calcareous Algae. Elsevier, Amsterdam, 185 pp.