Development of scleral ossicles in Podocnemis expansa (Testudines: Podocnemididae) embryos exposed to atrazine.

Understanding the effects of atrazine exposure on embryo development in oviparous animals may provide important data regarding the impacts of agrochemical use on wildlife and the ecosystem. This study set out to determine the effects of embryonic atrazine exposure on the development of osseous and cartilaginous components of scleral ossicles in Podocnemis expansa. Eggs were collected at the Environmental Protection Area Meandros do Rio Araguaia, Brazil, and artificially incubated in sand treated with solutions containing 2, 20 or 200 µg/L of atrazine. Sixty embryos were collected per treatment throughout the incubation period. Embryos were diaphanized with potassium hydroxide (KOH) and stained with Alizarin Red S and Alcian blue (bone and cartilage tissue respectively). Scleral ossicles were then counted and examined for skeletal abnormalities at different stages of embryonic development. Scleral ossicle counts were significantly reduced in P. expansa embryos treated with 200 µg/L atrazine solution. Rudimentary ossicles and gaps were also noted in embryos exposed to atrazine concentrations of 2 µg/L or 200 µg/L. Findings of this study emphasize the relevance of ecotoxicological investigations in determining the impacts of agrochemicals on native fauna.

Ontogeny of the plastron of the giant Amazon River turtle, Podocnemis expanse (Schweigger, 1812) (Testudines, Podocnemididae).

Podocnemis expanse, known popularly as the giant Amazon river turtle, is widely exploited. This makes specimens available for various studies, and we used this opportunity to investigate aspects of the development of the plastron. We examined several stages of pre- and post- hatching development in embryos and hatchlings collected starting from day 18 of natural incubation. Embryos and hatchlings were cleared and double stained for cartilage and bone. The epiplastron, endoplastron, hyoplastron, hypoplastron, xiphiplastron, and mesoplastron bones form the complete plastron of this turtle. In stage 16, bone centers become visible in most of the bones of the plastron. Alizarin Red stain retention indicated that the sequence of bone ossification is as follows: first the hyoplastron and the hypoplastron, then the endoplastron followed by the xiphiplastron, and lastly the mesoplastron. The epiplastron bone shows an ossification center only in stage 20. All these elements have independent ossification centers and join together only later. The plastron closes completely seven months after hatching.