Relationships of Basal Sarcopterygians: A Total Evidence
Analysis
The coelacanth, Latimeria
chalumnae.
Description of Project:
The phylogenetic relationships of basal sarcopterygians have long
been in question. Specifically in doubt are the relationships of
actinistians (coelacanths) and dipnoans (lungfishes) to tetrapods. Three
possibilities exist: (Actinistia (Dipnoi + Tetrapoda)), (Dipnoi
(Actinistia +Tetrapoda)) and ((Dipnoi + Actinistia) Tetrapoda). Multiple
morphological and molecular studies have attempted to give resolution to
this question, but no particular hypothesis seems overwhelmingly well
supported (see Schultze, 1994, for a general review of morphological
studies; Zardoya et al., 1998; Zardoya and Meyer, 1997; Zardoya and
Meyer, 1996; Meyer, 1995; Hedges et al., 1993; Hillis et al., 1991;
Meyer and Dolven, 1992; Joss et al., 1991; Stock et al., 1991; Forey,
1991; Gorr et al., 1991). Also of great interest and importance to this
issue are the relationships of basal sarcopterygian fossils:
Panderichthyida, Osteolepiformes, Porolepiformes and Diabolepis
(Schultze, 1994).
With no absolute corroboration between studies, the relationships
of these taxa remain in doubt. It is my intent to perform an unweighted
meta-analysis, consistent with idea of total evidence (Kluge, 1989).
Total evidence analysis will make the results of the individual studies
irrelevant, as the analysis of the combined data will provide resolution.
Any "noise" from mixed phylogenetic signal or random human error will not
overwhelm the most parsimonious phylogeny.
Professor Arnold Kluge is serving as my principal faculty advisor.
Dr. Mark Siddall and Jennifer Ast are providing technical assistance with
gene sequence alignment and analysis.
Basic external morphology of the coelacanth.
Regional map of coelacanth specimen records. Also note that two
specimen were recovered off the coast of Indonesia!
The South American Lungfish
The Australian Lungfish
The African Lungfish
Research Methodology:
An extensive literature review will be performed, including all
relevant morphological, molecular and paleontological publications. A
general search of genbank for relevant gene sequences will also be done.
All available data accumulated at the end of this search will be entered
into a large data matrix comparing all relevant extant and extinct taxa
and partitioned according to type of evidence (subsets of morphological,
separate genes, etc.). Each partition will not in any way be weighted,
nor will any character within each partition receive more weight. Any
grossly incomplete data set will be reevaluated and the missing data will
be personally investigated, and included in the matrix. The final
analysis will be done using unweighted parsimony on the Macintosh computer
program PAUP*.
Budget:
The only expense for this project is the immense cost of
photocopying. My preliminary bibliography is well over 100 sources, many
of which are of 10 pages and more of length.
References:
Forey, P.L. 1991. Latimeria-chalumnae and its pedigree. Environ. Biol.
Fish. 32(1-4):75-97.
Gorr, T., T. Kleinschmidt, and H. Fricke. 1991. Close tetrapod
relationships of the coelacanth Latimeria indicated by hemoglobin
sequences. Nature: 351(6325):394-397.
Hedges, S.B., C.A. Hass, and L.R. Maxson. 1993. Relations of fish and
tetrapods. Nature. 363(6429):501-502.
Hillis, D.M., M.T. Dixon, and L.K. Ammerman. 1991. The relationships of
the coelacanth Latimeria-chalumnae - evidence from sequences of vertebrate
28S ribosomal-RNA genes. Environ. Biol. Fish. 32(1-4):119-130.
Joss, J.M.P., N. Cramp, P.R. Baverstock, and A.M. Johnson. 1991. A
phylogenetic comparison of 18S-ribsomal RNA sequences of lungfish with
those of other chordates. Aust. J. Zool. 39(5):509-518.
Kluge, A.G. 1989. A concern for evidence and a phylogenetic hypothesis
of relationships among Epicrates (Boidae, Serpentes). Syst.
Zool. 38:7-25.
Meyer, A. 1995. Molecular evidence on the origin of tetrapods and the
relationships of the coelacanth. Trend. Ecol. Evolut. 10(3):111-116.
Meyer, A. and S.I. Dolven. 1992. Molecules, fossils, and the origins of
tetrapods. J. Mol. Evol. 35(2):102-113.
Schultze, H.-P. 1994. Comparison of hypothesis of the relationships of
sarcopterygians. Syst. Biol. 43(2):155-173.
Stock, D.W., K.D. Moberg, L.R. Maxson, and G.S. Whitt. 1991. A
phylogenetic analysis of 18S ribosomal-RNA sequence of
the coelacanth Latimeria-chalumnae. Environ. Biol. Fish. 32(1-4):99-117
Zardoya, R. and A. Meyer. 1996. Evolutionary relationships of the
coelacanth, lungfishes, and tetrapods based on the 28S ribosomal RNA gene.
Proc. Nat. Acad. Sci. USA. 93(11):5449-5454.
Zardoya, R. and A. Meyer. 1997. Molecular phylogenetic information on
the identity of the closest living relative(s) of land vertebrates.
Naturwissenschaften. 84(9):389-397.
Zardoya, R., Y. Cao, M. Hasegawa, and A. Meyer. 1998. Searching for the
closest living relative(s) of tetrapods through evolutionary analysis of
mitochondrial and nuclear data. Mol. Biol. Evol. 15(5):506-517.
A coelacanth receives a bit of respiratory therapy from well
intensioned divers.
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