60 



Fishery Bulletin 97(1), 1999 



validity of sequence data. Many molecular genetic 

 or phylogenetic studies (or both) are based on se- 

 quences sampled from only one individual of a spe- 

 cies. Discovery of erroneous sequence data in such 

 studies is becoming increasingly common (Derr et 

 al., 1992; Helbig and Seibold 1996; Ledje and 

 Arnason, 1996). PCR reactions are easily contami- 

 nated by carryover DNA from other organisms or by 

 other DNAs in the laboratory (Thomas, 1994). 

 Mislabeling of tubes also can lead to incorrect as- 

 signment of sequence data to species. We sequenced 

 the entire cyt h gene in tiger shark from Florida and, 

 in comparison with the "tiger shark" sequence re- 

 ported by Martin and Palumbi (1993), found one 

 nucleotide difference in the first (5'-most) 540 bp of 

 the gene and 64 nucleotide differences in the remain- 

 ing 606 bp of the gene. We hypothesize that the "ti- 

 ger shark" sequence of Martin and Palumbi (1993) 

 is a mixture that includes sequence data from an- 

 other species. The discrepancy between published 

 and newly determined sequences is similar to obser- 

 vations on published bird sequence by Helbig and 

 Seibold (1996) and on mammalian sequences re- 

 ported by Ledje and Arnason (1996). In each case, 

 the published sequences differed so greatly from 

 newly obtained sequences that conclusions of the 

 prior works were called into question. The free ex- 

 change of sequence data through Genbank also fa- 

 cilitates replication of errors. Validity of sequence 

 data can, and perhaps should, be tested by amplify- 

 ing DNA from several individuals of the same spe- 

 cies, and then by determining whether predicted re- 

 striction sites are present in all amplifications. 



Acknowledgments 



We thank Steve Branstetter, George Burgess, Mat- 

 thew Callahan, Bob Hueter, Chris Jensen. Chris 

 Lowe, Charlie Manire, and Craig Plizga for provid- 

 ing tissue samples. Andrew Martin provided valu- 

 able advice and assistance. This work research was 

 supported by the MARFIN Program of the U.S. De- 

 partment of Commerce (grant NA57FF0053). Part 

 of this work was carried out in the Center for Bio- 

 systematics and Biodiversity, a facility funded, in 

 part, by the National Science Foundation (award 

 DIR-8907006). 



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