Molecular phylogenetics, morphological variation and colony-form evolution in the family Hydrodictyaceae (Sphaeropleales, Chlorophyta)

Abstract

H.A. McManus and L.A. Lewis. 2005. Molecular phylogenetics, morphological variation and colony-form evolution in the family Hydrodictyaceae (Sphaeropleales, Chlorophyta). Phycologia 44: 582–595.

A phylogenetic analysis of 26S and internal transcribed spacer–2 ribosomal DNA (rDNA) data from members of the freshwater green algal family Hydrodictyaceae, including multiple taxa from both culture collections and new isolates, sets the stage to explore morphological variation and patterns of colony-form evolution within the family. These analyses particularly focus on Pediastrum boryanum, P. tetras, P. duplex, Hydrodictyon and Sorastrum. The genera Hydrodictyon and Sorastrum are derived from within Pediastrum in the individual and combined analyses, indicating a pattern of colony-form evolution within the family from two-dimensionality to three-dimensionality. In some cases the gene topologies reveal discrepancies in the morphological characters used to delimit species, varieties and forms within Pediastrum. Some isolates, such as those of H. reticulatum, exhibited little or no genetic variation between different geographic localities. Additional data and taxa are needed to better resolve and support these relationships, but the present results illustrate that some taxonomic revisions will be necessary.

ACKNOWLEDGMENTS

We thank M. Buchheim and T. Carlson for providing their 18S rDNA tree, P. Lewis and D. Vanderpool for assistance with phylogenetic analyses, F. Trainor, E. Jockusch, K. Ober and two anonymous reviewers for helpful comments on the manuscript, the UCONN Electron Microscopy personnel for technical assistance with SEM preparation and imaging, M. Faust for assistance with the SEM fixation protocol and the following people for supplying samples: D. Czarnecki, M. Fawley (NSF MCB-0084188), P. Novis, R. Wells, D. Hoover and J. Kelley. This research was partly funded by grants from the Ronald Bamford Endowment to the Department of Ecology and Evolutionary Biology at the University of Connecticut and the National Aeronautics and Space Administration to L.A.L. (EXB02-0042-0054).