Análise de condrocrânio de Rhizoprionodon porosus (Poey, 1861) da costa nordeste do Brasil

Abstract

The genus Rhizoprionodon (Whitley, 1929) comprises seven species occurring in the Atlantic, Pacific and Indian Oceans; the species are small and medium-sized animals attaining about 150 cm, inhabiting coastal waters, estuaries and brackish waters and feeding mainly on mollusks, crustaceans and small fish. In Brazil the two species are found Rhizoprionodon porosus (Poey, 1861) and lalandi (Valenciennes, 1839). The use of morphometric approaches has limitations for this group due to lack of anatomical landmarks, since they have a continuous form without angles. This study will analyze the chondrocranium a structure that is considered species-specific, located at the base of the skull holding and protecting the brain, displaying a shape that exhibits numerous angles. The study aims to verify the hypothesis suggested in the literature of two populations of the species R. porosus off northeastern Brazil (Lessa et al. 2011; Lessa et al. 2008). One corresponds to the northern coast of the Northeast (RN) and the other to the eastern coast of this region (PE). For that we performed a comparative morphometric study of the chondrocranium of R. porosus between the indicated areas using multivariate analyses. Thus, there were differences both for adult and juvenile phases by regions of capture. The discriminant analysis and k-means yielded a hit rate of 100, 0%. In conclusion, there is indeed a difference between chondrocrania from Pernambuco and Rio Grande do Norte as showed by approaches used. These results are in accordance with the hypotheses recently suggested in the literature that indicates two populations on the coast of northeastern Brazil.