PARENT SESSION
PS6 - Contaminant Effects on Amphibians & Reptiles
Sunday, 17 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P097) Actions of Methoprene Acid on Developmental Stability in a Urodele Amphibian, Ambystoma mexicanum.
Norris, David1, Lopez, Elena*,1, 1 University of Colorado, Boulder, CO, USA
ABSTRACT- The objective of this study was to characterize the biological actions of methoprene acid (MA), a natural metabolite of the insecticide methoprene, on the developing axolotl A. mexicanum, and to assess levels of developmental stability following treatment of embryos and hatchlings. The hypotheses tested include: (1) MA would produce effects on development similar to those produced by the positive control retinoic acid (RA); and (2) the degree of vulnerability to treatment would differ in exposed embryos versus hatchlings. Animals were exposed to 1 of 4 sub-lethal concentrations of MA (0, 30, 150, 300 ug/L) or RA (0, 0.3, 1.5, 3.0 ug/L). In addition, half were treated from blastula stage to hatching only (embryo phase), while the second half were treated beginning at hatching for the duration of the experiment (hatchling phase). The experiment was terminated when all animals reached full hindlimb development. Effects on morphometrics and bilateral symmetry (i.e., developmental stability) of eyes, forelimbs and hindlimbs were investigated. Morphometric effects on RA- and MA-treated animals were generally observed as reductions in the size of structures. Reductions in developmental stability were observed as fluctuating asymmetry of the forelimbs, hindlimbs, and overall body asymmetry in MA- and RA-treated animals. Additionally, embryo-phase animals were generally more vulnerable to the chemical treatments when examining morphometric parameters, whereas the hatchling-phase animals were generally more vulnerable when examining fluctuating asymmetry. These results demonstrate that MA and RA result in morphometric reductions in eye and limb size, and reduced developmental stability. Therefore, application of methoprene to ponds during critical periods of amphibian development may result in sub-optimal phenotypes in wild populations, and should be avoided until the risk posed by methoprene metabolites can be further investigated.
Key words: methoprene, amphibians, developmental stability