Morphological and Molecular Evidence Reveals the Longnose Skate Zearaja brevicaudata (Marini, 1933) to be a Senior Synonym of Dipturus lamillai Concha, Caira, Ebert & Pompert 2019

Abstract

Longnose skates have great economic importance in South American fisheries, and in order to preserve them, it is important to have a well-defined taxonomic status of their species. Dipturus lamillai was recently described for Malvinas Islands waters based on morphological and molecular comparisons with Zearaja chilensis. Although D. lamillai has been compared with several congeneric species, it was not properly compared with the morphologically similar Zearaja brevicaudata, the most abundant longnose skate in the Southwest Atlantic. Here, these species were compared by morphological and molecular analyses in order to evaluate their conspecificity. Linear morphometric variables of holotype and paratypes of D. lamillai and 69 specimens of Z. brevicaudata were compared and investigated using Principal Component Analysis. In addition, thorn patterns, denticle distributions, color, and clasper morphology were compared. No body proportions or other single character that could differentiate D. lamillai from Z. brevicaudata were found. Molecular analyses comprised of the comparison of the Cytochrome oxidase subunit I (COI) and the NADH dehydrogenase subunit 2. The results of the Maximum Likelihood (ML) carried out for each molecular marker showed that sequences from D. lamillai clustered together with those of Z. brevicaudata, and the molecular distance determined by Kimura two-parameter were lower than the expected for different species. Additionally, the Automatic Barcode Gap Discovery method and the Bayesian implementation of the Poisson tree processes were carried out with COI sequences to explore species limits, and their results were consistent with ML analyses. In summary, the results obtained showed that there are no morphological or molecular differences between these nominal species of the valid skate genus Zearaja, leading to the conclusion that they are conspecific. Therefore, we designated Z. brevicaudata as a senior synonym of D. lamillai.

Keywords: Integrative taxonomy; Longnose skates; Rajiformes; Southwest Atlantic; Synonyms.

Fig. 1.

Principal component analysis based on morphological data expressed as percentage of total length. a) PC1 vs PC2 b) PC2 vs PC3. PC1: first principal component, PC2: second principal component, PC3: third principal component. ▲, ellipse with whole line: Zearaja brevicaudata; ■, holotype of Raia brevicaudata; ●, ellipse with dotted line: Z. chilensis; ◊, ellipse with dashed line: Dipturus lamillai.

Fig. 2.

Dorsal spinulation pattern of an adult female of Zearaja brevicaudata (RM 170, 943 mm TL). White arrows point the dorsal thorns. Scale bar = 50 mm.

Fig. 3.

Female specimen of Zearaja brevicaudata (RM 317, 427 mm TL) showing the same coloration pattern as female paratype of Dipturus lamillai (cf. Concha et al., 2019, fig. 7B). Scale bar = 50 mm.

Fig. 4.

External components of the clasper of a mature male of Zearaja brevicaudata (RM 186, 783 mm TL). Cl: cleft, Dl: distal lobe, P: pocket, Pr: pseudorhiphidion, Rh: rhiphidion, Sh: shield, Sl: slit, Sp: Spike, Sr: spur, Tb: terminal bridge. Scale bar = 30 mm.

Fig. 5.

Maximum Likelihood tree, produced with Cytochrome oxidase subunit I (COI) sequences of Dipturus argentinensis, D. lamillai, Zearaja brevicaudata, Z. chilensis, Z. nasuta and Amblyraja doellojuradoi as outgoup. Barcode Index Number assigned by Barcode of Life Datasystem (A) and the results of species delimitation analyses using bPTP (B) and ABGD (C) algorithms are shown as vertical bars on the right. Dipturus lamillai sequences are marked in bold.

Fig. 6.

Maximum Likelihood tree produced with NADH dehydrogenase subunit 2 (NADH2) sequences of Dipturus argentinensis, D. lamillai, Zearaja brevicaudata, Z. chilensis, Z. nasuta and D. olseni as outgroup. Dipturus lamillai sequences are marked in bold and sequences corresponding to the description of the species (Concha et al. 2019) are indicated with *.