Critical period of sensitivity for effects of cadmium on frog growth and development

Abstract

Cadmium is a ubiquitous pollutant in aquatic environments that can alter organismal physiology and ecology. Previous experiments found that ecological Cd exposures increased the growth and development of two North American anurans. However, the generality of these effects among species, the time period over which they occur, and the mechanisms responsible remain conjectural. The goal of the present study was to determine the critical period of sensitivity of Rana pipiens exposed to ecologically relevant levels of Cd. We exposed tadpoles to Cd (0 [control], 1.0, and 10.0 microg/L) from Gosner stage (GS) 25 to metamorphic climax. We assessed effects of Cd on amphibian length, survival, and development during premetamorphosis (GS 25-30) and prometamorphosis (GS 31-42). After 14 d of exposure, we staged tadpoles and recorded snout-vent length. Tadpoles were then pooled according to treatment and stage (GS < or =29 or GS > or =30) and allowed to undergo metamorphic development. Tadpoles exposed to 10 microg/L were significantly larger and more advanced in development by 14 d. Survival to forelimb emergence exceeded 90% in all treatments, and time to metamorphic climax was not different from that in controls. Body burdens of Cd were positively correlated with increasing treatment. Early amphibian development (premetamorphosis) was shown to be the critical period of sensitivity for growth and development. Whereas the freshwater criterion for Cd appears to be protective for survival, a lack of knowledge remains about the sublethal effects of chronic exposures of metal pollutants, especially as they relate to tissue concentrations at various stages of amphibian life history.

Heavy metals, hematology, plasma chemistry, and parasites in adult hellbenders (Cryptobranchus alleganiensis)

“…Leeches have been known to contribute to pathogen transmission in salamanders [27]. Desserobdella cryptobranchii (an aquatic leech) was found in Ozark hellbenders [28], but not in eastern hellbenders in Missouri (J. Briggler, personal Functional descriptions of hematology and plasma chemistry in various amphibian and reptilian species can be found in our previous study [13]. Lymphocytes, monocytes, eosinophils, and basophils are responsive to pathogenic infections.…”

“…Cadmium is widely distributed in the aquatic environment and can act as an endocrine disruptor in aquatic organisms [9,10]. Cadmium can also alter growth and development in amphibians [11][12][13]. Although Pb and Hg were below the detection limits in this single hellbender tested, Pb has been found at elevated levels in surface and groundwater from certain areas in the Ozarks region in Missouri [14].…”

Acute Toxic Effects of Cadmium in Larvae of the Green Toad, Pseudepidalea Variabilis (Pallas, 1769) (Amphibia: Anura)

“…James and Little (13) reported that 540 μg L -1 of chronically applied cadmium reduced survival and extended the metamorphosis period in Bufo americanus larvae, but prematurely induced metamorphosis at 5 and 54 μg L -1 . Cadmium exposure at 0.25-5 μg L -1 stimulated growth and metamorphosis in Rana pipiens larvae (16,32). In another study (15), chronic exposure to 0-855 μg L -1 of cadmium did not affect the survival rate of X. laevis larvae.…”

“…Among these, the destruction of habitats and increased pollution significantly threaten the survival of amphibians, which spend their embryonic and larval stages exclusively in water and play a significant role in biomonitoring programmes (9)(10)(11). That is why amphibian larvae are among the preferred bioindicators for aquatic toxicology studies (12)(13)(14)(15)(16).…”

“…Its biomagnification poses threats for human health as well as the ecosystem as a whole. Therefore, cadmium has recently become the subject of many investigations (16,(21)(22)(23)(24)(25). The toxic effects of cadmium investigated in freshwater fish include development abnormalities detected in many teleost species (26)(27)(28).…”