Morphology and DNA Barcoding highlights the presence of a cryptic skate species in the South-west Atlantic Ocean

VALERIA GABBANELLI, FRANCISCO JAVIER CONCHA, DIEGO MARTÍN VAZQUEZ,; GONZÁLEZ CASTRO., M.; , JUAN MARTÍN DÍAZ DE ASTARLOA & EZEQUIEL MABRAGAÑA

Conferencia; Sharks Internacional Conference; 2018

The yellownose skate Zearaja chilensis inhabits the continental shelf and slope of Chile to Southern Brazil. It is a large skate that has been intensively exploited during decades due to international commercial demand. The species was firstly described from Chilean waters and has a complex nomenclatural history, which is not fully resolved. Additionally, molecular studies have shown some differences between individuals from the Atlantic and Pacific oceans. Due to its biological traits and exploitation is assessed by the IUCN as vulnerable. Under this scenario, is crucial to determine whether more than one species are included within Z. chilensis. In the present study, we compared specimens of Zearaja chilensis from Argentinean waters (AW, n=50) and Chilean waters (CHW, n=22) in order to determine if they correspond to the same nominal species. The study included both morphological (external morphology, spinulation patterns, clasper, egg cases) and molecular (Cytochrome oxidase subunit I) analyses. Despite its external similarity, several morphological features were noticeably different between AW and CHW specimens. Main differences were found in clasper morphology (both outer and inner components shape). For instance, distal lobe of clasper from AW was straight and only the tip was rounded, while clasper from CHW was expanded and rounded; clasper apophysis of ventral terminal cartilage was shorter in individuals from AW than that of specimens from CHW. Moreover, first gill openings to disc length-distance was shorter in AW specimens than that found in CHW individuals. Mostly, specimens from AW presented 3-5 raws of tail thorns, while specimens in CHW had only one raw. Denticles were more conspicuous in the snout tip of specimens from AW, whereas in CHW individuals the surface of disc was mostly covered with denticles, being smooth only the centre of the pectoral fins. Differences in egg cases morphology were also observed. Those from AW specimens had wider lateral keels than those from CHW individuals. Molecular analysis showed that sequences were grouped in two well defined cohesive clusters, corresponding to AW and CHW samples respectively. Average K2P distance between groups was 3.4%, a value significatively higher than expected for intraspecific differences. Indeed, the analysis of BINs (an algorithm that clusters barcode sequences into OTUs) assigned the sequences to different BINs. These integrative results strongly support that specimens from Argentinean waters known as Z. chilensis correspond to a different nominal species than those from Chilean waters.