Biological endpoints, enzyme activities, and blood cell parameters in two anuran tadpole species in rice agroecosystems of mid-eastern Argentina

Different biological variables of tadpoles, including survival, development and growth rates, and biomarkers [cholinesterases, glutathione-S-transferases (GST), and blood cell morphology] were evaluated in two anuran species, Scinax squalirostris (Hylidae) and Leptodactylus mystacinus (Leptodactylidae), using in situ experimental chambers in a rice field (RF) sprayed with insecticide Lambda-cyhalothrin (LTC) by aircraft in Santa Fe Province, Argentina. We found a significant decrease in body weight (0.62 +/- 0.04 g) of L. mystacinus and an increased development rate of S. squalirostris in individuals from RF (41 +/- 1; Gosner) with respect to individuals from the reference site (RS: 0.93 +/- 0.04 g and 37 +/- 0; respectively). In S. squalirostris, individuals from RF mean values of butyrylcholinesterase activities decreased at 48 (4.09 +/- 0.32 nmol min(-1) mg(-1) of TP) and 96 h (3.74 +/- 0.20 nmol min(-1) mg(-1) of TP), whereas inhibition of acetylcholinesterase was observed at 96 h (47.44 +/- 2.78 nmol min(-1) mg(-1) of TP). In L. mystacinus from RF, an induction of acetylcholinesterase activity was observed at 96 h (36.01 +/- 1.09 nmol min(-1) mg(-1) of TP). Glutathione-S-transferase levels varied between species, being higher in L. mystacinus individuals but lower in S. squalirostris from RF at 48 (272.29 +/- 11.78 and 71.87 +/- 1.70 nmol min(-1) mg(-1) of TP; respectively) and 96 h (279.25 +/- 13.06 and 57.62 +/- 4.58 nmol min(-1) mg(-1) of TP, respectively). Blood cell parameters revealed a lower number of mitotic cells (MC: 0.36 +/- 0.31%o for S. squalirostris and 0.08 +/- 0.05 %o for L. mystacinus) and higher number of eosinophils (E: 3.45 +/- 1.75 %o for S. squalirostris and 7.64 +/- 0.98 %o for L. mystacinus) in individuals from the RF than in individuals from the RS (MC: 2.55 +/- 0.74 %o for S. squalirostris and 1.87 +/- 0.72%o for L. mystacinus; and E: 0.13 +/- 0.09 for S. squalirostris and 3.20 +/- 0.80 for L. mystacinus). Overall, our results demonstrate the existence of apparent differences in sensitivity between species in a series of sublethal responses to short-term exposure in RF after the application of Lambda-cyhalothrin. We suggest that the integral use of biological endpoints (development and growth) together with biomarkers (cholinesterase, GST, and blood cell parameters) may be a promising integral procedure for investigating pesticide exposure in wild frog populations.