Intraspecific variation in Hydrogen Ion and Aluminum Toxicity inBufo americanusandAmbystoma maculatum

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Abstract
Variation in hydrogen ion and aluminum toxicity was measured among clutches in one Bufo americanus population from a pond with pH 5.96 and both among clutches and ponds in four Ambystoma maculatum populations from ponds with pH levels from 4.44 to 6.19. There was significant variation among clutches, but in general, B. americanus hatching success was reduced at pH 4.1 compared with pH6.0. At pH 4.1,200 μg Al/L caused even greater embryonic mortality. Aluminum toxicity did not vary among clutches; however, variation in acid tolerance was such that clutches with the highest hatching success at pH 6.0 had the lowest hatching success at pH 4.1. Hatching success of A. maculatum also varied among clutches, but in general, hatching success was lower at pH 4.3 than at pH 6.0, and 200 μg Al/L at pH 4.3 increased hatching success compared with when no aluminum was present. Variation in acid tolerance among pond populations was so large that one population had higher hatching success at pH 4.3 than at pH 6.0. Ambystoma maculatum hatching success was not related to diameter of the perivitelline space just prior to hatch. The wide variation in acid tolerance among clutches of B. americanus and among populations of A. maculatum suggests that laboratory studies using small numbers of clutches may not adequately represent the response of the natural populations.