Effects of low pH and aluminum on body size, swimming performance, and susceptibility to predation of green tree frog (Hyla cinerea) tadpoles

Abstract

Green tree frog (Hyla cinerea) tadpoles were exposed immediately after hatching to aluminum (nominally 0, 150, 250, 400 μg/L) at pH 4.5 or 5.5, plus a control (pH 7.0, 0 μg/L Al) for 96 h. Mortality increased with increasing Al concentration at pH 4.5 but not at pH 5.5. Among surviving tadpoles, body size was significantly reduced at higher Al concentrations at both pH 4.5 and 5.5. At pH 4.5, analysis of covariance indicated that maximal swimming speed was positively correlated with tadpole total length and differed among Al treatments; tadpoles at higher Al levels swam more slowly. Body Al and Na+concentrations also differed among treatments. In a second experiment, tadpoles exposed for 96 h to approximately 150 μg/L Al at 4.5 pH were preyed upon by dragonfly larvae (Libellulidae) at a higher rate than were tadpoles raised in pH 4.5 or 7.0 without Al. As in the first experiment, tadpoles exposed to Al were smaller and were slower swimmers. Sublethal concentrations of Al at low pH may result in lowered growth rates and hence reduced body size. Swimming performance is reduced by small body size, and size-adjusted performance is further reduced by Al and low pH, which might lead to higher predation on Al-stressed tadpoles.