Effects of pH on embryo tolerance and adult behavior in the tiger salamander, Ambystoma tigrinum tigrinum

We examined adult discrimination ability and embryo performance under different pH conditions in the eastern tiger salamander, Ambystoma tigrinum tigrinum. We collected individuals from three populations in habitats that differed naturally in pH, thus allowing interpretation of population-specific responses in embryos and adults. We conducted pool-choice experiments in the field using two pH treatments to determine adult pH discrimination ability and controlled laboratory toxicity tests using eight pH treatments to evaluate embryo performance. Adult discrimination ability differed among source populations. Male salamanders from the locality with the highest pH were more likely to stay in neutral-pH pools and more likely to leave acidic ones. Males from the locality with the lowest pH were also more likely to remain within neutral pools, but their rates of staying and leaving acidic ones did not differ. These results suggest that the pH of the source-population habitat may influence breeding-habitat discrimination by adults. Decreasing pH produced similar patterns of lethal (survival) and sublethal (date and size at hatching) effects on embryos from the three populations, with reduced performance at low pH. Survival of embryos was more than 70% at pH 4.5 and above, but decreased dramatically at lower pH levels. The pH at which 50% mortality occurs (LC50) was estimated as 4.2, suggesting that tiger salamanders from our populations were relatively acid tolerant compared with congeners. However, significant sublethal effects could reduce the subsequent success of surviving hatchlings. Our results are consistent with the hypothesis that adult discrimination ability depends on pH levels in the breeding habitat. This suggests that adult behavior patterns could influence the success of population reintroductions to previously acidified areas. Thus, data on pH responses at all stages in the amphibian life cycle should contribute to management decisions.