Dl. Larson et al., Effects of the herbicide atrazine on Ambystoma tigrinum metamorphosis: Duration, larval growth, and hormonal response, PHYSL ZOOL, 71(6), 1998, pp. 671-679
We exposed larval tiger salamanders (Ambystoma tigrinum) reared in the labo
ratory from eggs collected from a prairie wetland in North Dakota to three
concentrations of atrazine (0, 75, and 250 mu g/L) in a static renewal test
to determine the pesticide's effect on (1) plasma corticosterone and thyro
xine concentrations, (2) larval size, and (3) days-to-stage at stages 2 and
4 of metamorphic climax. We found significant effects of atrazine on each
of these response variables. Plasma thyroxine was elevated in both atrazine
-exposed groups compared with the control group; plasma corticosterone was
depressed in the 75 mu g/L treatment compared with both the control and 250
mu g/L treatment. Larvae exposed to 75 mu g/L atrazine reached stage 4 lat
er but at a size and weight comparable to the control group. By contrast, l
arvae in the 250 mu g/L treatment progressed to stage 4 at the same time bu
t at a smaller size and lower weight than larvae in the control group. Thes
e results indicate that the herbicide has the potential to influence tiger
salamander life history. We present a model consistent with our results, wh
ereby corticosterone and thyroxine interact to regulate metamorphosis of ti
ger salamanders based on nutrient assimilation and adult fitness.