Relationships among developmental stage, metamorphic timing, and concentrations of elements in Bullfrogs (Rana catesbeiana)

Abstract

We collected bullfrog (Rana catesbeiana) larvae from a coal combustion waste settling basin to investigate the effects of developmental stage and timing of metamorphosis on concentrations of a series of trace elements in bullfrog tissues. Bullfrogs at four stages of development (from no hind limbs to recently metamorphosed juveniles) and bullfrogs that metamorphosed in the fall or overwintered in the contaminated basin and metamorphosed in the spring were analyzed for whole-body concentrations of Al, V, Cr, Ni, Cu, As, Pb, Cd, Zn, Ag, Sr, and Se. After the effects of dry mass were removed, tissue concentrations of six elements (Al, V, Cr, Ni, Cu, As, and Pb) decreased from the late larval stage through metamorphosis. Decreases in concentrations through metamorphosis ranged from 40% for Cu to 97% for Al. Tissue concentrations of these elements were also similar or higher in spring; Al and Cr concentrations were 34 and 90% higher in the spring, respectively, whereas As, Ni, Cu, and Pb concentrations were <10% higher. Concentrations of Cd, Se, and Ag varied among seasons but not among stages; Cd and Ag concentrations were 40 and 62% lower, respectively, and Se concentrations were 21% higher in spring. Concentrations of Zn varied only among stages; concentrations decreased gradually through late larval stage and then increased through metamorphosis. Concentrations of Sr varied among stages, but this variation was dependent on the season. Concentrations of Sr were higher in larval stages during the spring, but because concentrations of Sr increased 122% through metamorphosis in the fall and only 22% in the spring, concentrations were higher in fall metamorphs when compared with spring metamorphs. Our results indicate that metamorphosis and season of metamorphosis affects trace element concentrations in bullfrogs and may have important implications for the health of juveniles and the transfer of pollutants from the aquatic to the terrestrial environment.

Adverse effects of chronic copper exposure in larval northern leopard frogs (Rana pipiens)

“…For example, Cu concentration in the liver of Rana ridibunda collected in northern Greece was 1,041 mg/kg dry mass [34], which is close to whole‐body Cu concentration in our highest Cu treatment. In sites polluted by coal‐burning power plants near Aiken, South Carolina, USA, the highest whole‐body Cu concentration reported was about 125 mg/kg dry mass in larval Rana catesbeiana [35] and about 160 mg/kg in larval Bufo terrestris [36]. These whole‐body Cu concentrations are close to that in our medium treatment (154.5 mg/kg dry mass).…”

Mercury accumulation along a contamination gradient and nondestructive indices of bioaccumulation in amphibians

“…Although tadpoles are omnivorous grazers, this observation is consistent with the literature that many pond-breeding larvae are excellent accumulators of trace metals because they are closely associated with the benthos [16,44]. Although many metals, including some Hg, may be bound to the gut epithelium in tadpoles [17,18], evidence suggests that Hg becomes mobilized during metamorphic climax and is retained in amphibian tissues after metamorphosis is completed [4,18]. After metamorphosis, B. americanus juveniles and adults are highly terrestrial and mobile [25].…”

“…These characteristics also suggest that amphibians may have high rates of contaminant bioaccumulation compared with other animals of similar trophic positions. In addition, the complex life cycles of many amphibians potentially make them important in transferring contaminants from aquatic to terrestrial food chains [16,17], especially for Hg, because evidence suggests that most Hg accumulated by larvae is retained through metamorphosis [4,18].…”

Metamorphosis of two amphibian species after chronic cadmium exposure in outdoor aquatic mesocosms

“…Frog tadpoles reared outdoors in small aquatic mesocosms containing leaf litter, sand, algae, and zooplankton dosed once with 100 μg Cd/L contained an average of 2.2 μg Cd/g whole body wet weight after three weeks, and only 25% survived to metamorphosis [14]. Larval amphibians collected from contaminated field sites have possessed in excess of 13 μg Cd/g whole body dry mass [16], and those exposed in the laboratory can withstand at least 60 μg Cd/g [13].…”