Multiple interspecies transmissions of human and simian T-cell leukemia/lymphoma virus type I sequences |
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Authors: | Crandall KA |
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Institution: | Department of Zoology, University of Texas at Austin 78712-1064, USA. |
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Abstract: | Using two sets of nucleotide sequences of the human and simian T-cell
leukemia/lymphoma virus type I (HTLV-I/STLV-I), one consisting of 522 bp of
the env gene from 70 viral strains and the other a 140-bp segment from the
pol gene of 52 viral strains, I estimated cladograms based on a statistical
parsimony procedure that was developed specifically to estimate
within-species gene trees. An extension of a nesting procedure is offered
for sequence data that forms nested clades used in hypothesis testing. The
nested clades were used to test three hypotheses relating to transmission
of HTLV/STLV sequences: (1) Have cross-species transmissions occurred and,
if so, how many? (2) In what direction have they occurred? (3) What are the
geographic relationships of these transmission events? The analyses support
a range of 11-16 cross-species transmissions throughout the history of
these sequences. Additionally, outgroup weights were assigned to haplotypes
using arguments from coalescence theory to infer directionality of
transmission events. Conclusions on geographic origins of transmission
events and particular viral strains are inconclusive due to small samples
and inadequate sampling design. Finally, this approach is compared directly
to results obtained from a traditional maximum parsimony approach and found
to be superior at establishing relationships and identifying instances of
transmission.
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