LOCK AND DAM 19 AS A BARRIER TO GENE FLOW IN RED-EARED SLIDER
TURTLES, Trachemys scripta elegans.

James T. Lamer, Michael A. Romano, Richard V. Anderson, and Lara LaDage.  
Department of Biological Sciences, Western Illinois University, Macomb, IL 61455.

Two population samples of red eared slider turtles, Trachemys scripta elegans,  were live-trapped
from sites above (n = 14) and below (n = 26) Lock and Dam 19 only separated by approximately
5 km.  Blood was extracted from the scapular vein using a 25-gauge hypodermic needle and a 1
cm segment of tail was excised to provide a source of soluble enzymes.  From these tissues
allelic variation was quantified by starch gel electrophoresis at 14 enzyme loci to determine if the
dam was an effective barrier to gene flow.  Sliders often occupy isolated aquatic habitats but
males tend to have a high propensity for aquatic dispersal for reproductive purposes.  Average
heterozygosity above the dam was 0.021 and 0.031 below the dam; however, these levels were
not significantly different (p = 0.550).  Extremely high levels of inbreeding were exhibited in
both populations with f = 0.596 (X2 = 3.552, p = 0.063) above the dam and f = 0.459 (X2 =
5.477, p = 0.027) below the dam.  These alarming levels of inbreeding suggest potential
problems for the long term sustainability of these populations.  

The most significant finding was a Gpi144 allele that was found in moderate frequency (0.056)
above the dam but was completely absent below the dam.  The fact that this allele was found in a
relatively small sample of 10 turtles compared to the much larger sample of 26 turtles below the
dam strongly imply that the dam does act as a significant barrier to dispersal and gene flow.  The
potential impact on natural turtle populations by dams like Lock and Dam 19 will be discussed.

Keywords:  red eared sliders, electrophoresis, average heterozygosity, gene flow, inbreeding