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

CONCHA, J. F.; DÍAZ DE ASTARLOA, J. M.; GABBANNELLI, V.; GONZALEZ CASTRO M.; VAZQUEZ, D.M.; MABRAGAÑA E.

Joao Pessoa

Conferencia; Sharks International Conference; 2018

The yellownose skate, Zearaja chilensis, is a large skate that has been reported from thecoasts of Chile in the Southeastern Pacific to Southern Brazil in the Southwestern Atlantic.Due to its geographical range, biological traits, and levels of exploitation, this species waslisted as vulnerable by the IUCN. Recent molecular studies have called into question theconspecificity between specimens from these opposite coasts of South America, which canhave implications for the conservation status of the species. The aim of this study is toverify the identity of specimens identified as Z. chilensis in Argentina with respect tospecimens from Chile. A total of 50 specimens from Argentinean waters (AW) and 22 fromChilean waters (CHW) were examined in order to compare their external morphology,spinulation pattern, clasper, and egg capsules. Tissue samples (AW=12, CHW=2) wereobtained and sequence data for the Cytochrome Oxidase Subunit I (COI) gene weregenerated. Additionally, public sequences were obtained from BOLD (AW=25, CHW=8).Despite its external similarity, several traits were consistently different between specimensfrom both regions. Adults from AW presented longer preorbital length and shorter distancebetween first gill openings than those from CHW. AW specimens presented 3-5 rows ofcaudal thorns, whereas most specimens from CHW had only one row. Dermal denticleswere restricted to the rostral area in AW skates, whereas in CHW skates most of the dorsalsurface of the disc was covered with denticles, with a smooth area in the centre of pectoralfins. Major differences in clasper morphology were also found. For instance: in AWspecimens, terminal bridge (tb) is straight towards tip of dorsal terminal 2 cartilage (dt2)and sentinel (st) does not reach tb, whereas in CHW specimens tb is curved towards tip ofdt2 and st reach tb; ventral terminal cartilage of CHW has a longer apophysis and the outeredge is wider than those from AW. Egg capsules of AW skates had wider lateral keels thanthese of their Chilean counterparts. Molecular analysis revealed two well defined cohesiveclusters, corresponding to AW and CHW specimens, respectively. Average K2P distancebetween groups was 3.4%, a value substantially higher than expected for intraspecificdifferences. Indeed, BINs analysis (algorithm that clusters barcode sequences into OTUs)assigned the sequences to different BINs. These integrative results strongly support thatspecimens from Argentinean waters known as Z. chilensis correspond to a differentnominal species than those from Chilean waters.