Morphology and microchemistry of the otoliths of the inner ear of anuran larvae.

To navigate in space most vertebrates need precise positional cues provided by a variety of sensors, including structures in the inner ear, which are exquisitely sensitive to gravity and linear acceleration. Although these structures have been described in many vertebrates, no information is available for anuran larvae. The purpose of our study was to describe, for the first time, the size, complexity and microchemistry of the saccular otoliths of the larva of 13 anuran species from central Argentina, using electron microscopy and X-ray spectroscopy (N = 65). We concluded that a) these structures differ in area, perimeter, otolith relative size and fractal dimension, but are similar in terms of their microchemistry when compared by spatial guilds, b) that nektonic species have larger otoliths than nektonic-benthic and benthic species and c) that benthic species have larger otolith relative size than nektonic-benthic and nektonic species.

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.