Introduction:

Eublepharis macularius  is the leopard gecko, a chemosensory specialized lizard.  Leopard geckos in captivity will chose only one corner of their enclosure to defecate in. It is uncommon for many species of lizard to do this, but can be found as a trait in other geckos. In this experiment, these locations of fecal deposition are referred to as defecation stations.  This defecation can mark the presence and territories of male and female animals (Carpenter and Duvall 1995).  For some reason all of the individual geckos in one container will use the same corner as everyone else.  My hypothesis that the location of defecation corners is based on scent and pheromones, because they mark territories. I set up different containers to try to distinguish these territories and see if the defecation station added a chemosensory cue.

Materials and Methods:

     3 female Eublepharis macularius and 8 male Eublepharis macularius were used in this experiment. The 3 females and one male were studied in a 40 gallon breeder tank with paper towel roll hides, cork bark, a water dish, and a circular pink container holding eggs in the center for incubation. 3 males were kept separately in foot long plastic Tupperware with paper towel substrate and a water dish. One male was in the 40 gallon tank and the other 4 were in a 30 gallon  breeder tank together on sand and with a water dish, each with his own hide box. Two were in the 30 for the first month, then two more were introduced.  The location of the defecation station was was recorded after at least 3 of the animals grouped together used it, or after a week in the separated males. 
     After a definite location for defecation was established in the 40 gallon tank, the topography was flipped but the station itself was untouched.  The setup remained the same for this control until a station was established, afterwards, all the liner and tank objects were cleaned with dawn dish washing detergent and isopropyl alcohol and place back in the same arrangement.  When a station was distinguished, the liner and cage furniture were cleaned again and arranged with either the hide or the water dish mirroring its previous location. After 3 rearrangements of the 40 gallon tank, 3 arrangements of a large hide box location were added.
     After a week of  the foot long containers, the the defecation stations were determined and the males were relocated to circular containers with no corners but otherwise similar conditions.  Defecation stations were determined after another week had passed.
     Nothing was rearranged in the 30 gallon tank other than adding in two more males with two more hide boxes. The sand in their tank was sifted every week, but not washed.

Results:

Location of Defecation Stations

40 gallon tank with no hide box
Control- Male uses old defecation station, females use mirrored location., as shown in figure 2.
Arrangement 1- mirrored location used for all 4 animals, males first defecation in center as shown in figure 3
Arrangement 2- mirrored location used as shown in figure 4, same location relative to the placement of terrain
Arrangement 3- mirrored location used as shown in figure 4, same location relative to the placement of terrain


40 gallon tank with hide box
Defecation station is located wherever hide box is without any cleaning, regardless of previous location of defecation station.

30 gallon male tank
Defecation station was in bottom right hand corner at all times
Introduced males used same defecation station
Very seldom was there feces in the hides.

Tupperware containers
Defecation station was furthest away from the side with water in all cases

Round containers
Defecation station was on one half of the circle, less apparent.

Discussion:

My experimentation cannot support my hypothesis of a scent based defecation station.  The control of the 40 gallon group showed that despite any chemical markers or the actual feces still being present, they will defecate in a representative area that appears the same.  The all used the hide as a defecation station no matter where it was moved.  In the open, the defecation station was away from the water in  all the 40 gallon, 30 gallon, Tupperware and round container experiments.  An interesting side effect of the stations was that when I put another male in the 40 gallon tank, he would stay away from the areas that were used as defecation stations and the hides the other male and females used.  Also, when fecal samples were presented to conspecifics, there was a definite reaction.  The females all just did labial licks, where they flicked their tongues out a few times and rubbed it on the scent organs of their mouths.  The submissive males all labial licked, but waved their tails and shrunk close to the ground.  The one dominant male that was in with the females labial licked and vibrated his head.  There is a definite chemosensory function to the feces, supported by Carpenter and Duvall in their study on western banded geckos (Carpenter and Duvall 1995).  This is a desert species and water is precious.  A new hypothesis to test is whether or not the tidy defecation stations are a way to keep their water from becoming contaminated. 

References

Carpenter, G.C. Duvall, D. “Fecal Scent Marking in the Western Banded Gecko (Coleonyx variegatus)” Herpetologica, Vol. 51, No. 1 (Mar., 1995), pp. 33-38
Accessed:  <http://www.jstor.org/stable/3892782> 17/04/2011