Neoplecostomus doceensis: a new loricariid species (Teleostei, Siluriformes) from the rio Doce basin and comments about its putative origin

Abstract A new species of Neoplecostomus is described from the rio Doce basin representing the first species of this genus in the basin. The new species is distinguished from its congeners by having enlarged, fleshy folds between dentaries, two or three series of developed papillae anterior to premaxillary teeth and a adipose-fin membrane present, and by lacking enlarged odontodes along snout lateral margins in mature males, a well-developed dorsal-fin spinelet wider than dorsal-fin spine base, lower number of lateral-line figs and developed membrane on the dorsal portion of the first, second and third pelvic-fin branched rays. Additionally, we present a brief discussion of biogeographic scenarios that may explain the distribution of the new species in the rio Doce basin. We suggested that the ancestral lineage of the new species reached the rio Doce from the upper portions of rio Paraná drainages about 3.5 Mya (95% HPD: 1.6–5.5) indicating a colonization route of the N. doceensis ancestral lineage from the south end of Serra do Espinhaço, probably as a result of headwater capture processes between the upper rio Paraná and rio Doce basins.


Introduction
Paulo, São Paulo, Brazil; (NUP) Coleção Ictiológica do Nupélia, Universidade Estadual de Maringá, Maringá, Brazil. The scientific names of the species follow the International Code of Zoological Nomenclature (International Commission on Zoological Nomenclature 1999).

Results
Neoplecostomus doceensis sp. n. http://zoobank.org/28057609-4191-4808-B6C0-7DABFD0E73D2 Figure 1; Table 1 "Neoplecostomus sp. 9" - Roxo et al. 2012a  Diagnosis. Neoplecostomus doceensis is distinguished from all other congeners by having enlarged, fleshy folds between dentaries in all specimens, more evident in mature males, Fig. 2a (vs. absence of the enlarged fleshy folds, Fig. 2b). The new species can also be distinguished from all congeners by the presence of two or three series of well-developed papillae anterior to premaxillary teeth, Fig. 2c (vs. papillae poorly developed or absent Fig. 2d). Additionally, the new species can be distinguished from N. botucatu and N. paranensis by the presence of a fully-developed adipose fin (vs. lacking or reduced adipose fin); from N. selenae by moderately-sized odontodes along lateral margins of snout and snout without swollen skin in mature males (vs. presence of large-sized odontodes surrounded by swollen skin along lateral margins of snout in mature males); from N. franciscoensis and N. ribeirensis by having a well-developed dorsal-fin spinelet, wider than dorsal-fin spine base (vs. absent or narrower than dorsalfin spine base); from N. microps and N. variipictus by a higher number of dentary teeth 12-35 (vs. 5-12 and 7 respectively); from N. granosus by having a lower number of lateral-line plates, 25-29 (vs. 34-43); from N. langeanii by the presence of a developed membrane on the dorsal portion of the first, second and third pelvic-fin branched rays (vs. lacking).
Description. Counts and measurements are presented in Table 1. Body robust, elongated and depressed, greatest width at cleithrum (25.8-28.7% SL), narrowing to caudal peduncle. Dorsal profile of the head elevating and gently convex from snout tip to posterior margin of nares, straight to slightly concave to posterior margin of parieto supraoccipital, straight to dorsal-fin origin. Dorsal profile of trunk slightly concave and descending from dorsal-fin origin to adipose-fin origin, almost straight and descending to first procurrent caudal-fin ray; greatest body depth at dorsal-fin origin (15.3-19.6% SL). Ventral profile slightly convex from snout tip to anal-fin origin; concave at analfin region, straight and ascending to lower caudal-fin ray. Trunk and caudal peduncle almost ellipsoid in cross-section, rounded laterally and almost flat dorsally and ventrally.
Dorsal body surface completely covered by dermal plates, except for a naked area around dorsal-fin base and a small naked area at snout tip. Ventral head surface naked except for a plate bearing odontodes in front of gill openings. Abdomen with conspicuous, small dermal platelets between insertions of pectoral and pelvic fins, forming a thoracic shield surrounded by naked areas. Abdominal platelets densely covered by backward-oriented odontodes, their tips round. Head wide (79.8-90.8% HL) and depressed (47.1-57.1% HL). Head and snout rounded in dorsal view; interorbital space straight to slightly concave in frontal view.
Snout tip with a weak ridge between nares, sometimes absent, more evident in larger specimens. A weak ridge from middle of snout to superior margin of orbit. Moderate-sized odontodes along lateral margins of snout, more evident in mature males. Eye moderately small (7.0-11.2% HL) and dorso-laterally placed; lips well developed and rounded; lower lip almost reaching pectoral girdle and covered with papillae, wider anteriorly. Enlarged fleshy folds among dentary, more evident in mature males (Fig. 2a). Two to three irregular and conspicuous rows of large and transversally flattened papillae along and posterior to dentary teeth and anterior to premaxillary teeth (Fig. 2c). Maxillary barbel very short, coalesced, usually its tip not free from lower lip. Teeth long, slender and bicuspid; mesial cusp longer than lateral; dentary ramus forming an angle of approximately 125-130°.
Dorsal fin II,7; origin slightly posterior to pelvic-fin origin; dorsal-fin spinelet semicircular and wider than dorsal-fin spine base (spinelet hardly visible in some specimens, but always present); dorsal-fin locking mechanism not functional; dorsal-fin posterior margin straight to slightly rounded, reaching end of pelvic-fin rays when adpressed. Adipose-fin well developed and always present, preceded by azygous plate. Pectoral-fin I,6; unbranched ray depressed and curved inward (more pronounced in larger specimens), shorter than longest branched ray; posterior margin slightly concave, almost reaching half pelvic-fin ray length when adpressed; unbranched ray anteroventrally covered with backward-oriented odontodes. Pelvic-fin I,5; posterior margin nearly straight, reaching anal-fin insertion when adpressed; pelvic-fin unbranched ray ventrally flattened, with dermal flap on its dorsal surface in males; first and second branched rays also with dermal flap on its dorsal surface in males; unbranched ray anteroventrally covered with backward-oriented odontodes. Anal-fin I,5; posterior margin nearly straight; unbranched ray ventrally covered with back-oriented odontodes. Caudal-fin I,7,7,I; bifurcated; lower spine longer than upper; pectoral spine and unbranched pelvic-fin rays with odontodes on lateral and ventral portions.
Color in alcohol. Ground color of dorsal surface of head and body dark brown to lighter brown in some specimens. Head with a pale spot on naked area of snout tip; orbital margin slightly lighter, mainly on its superior portion; small pale spot on interorbital space; lateral margin of snout usually lighter than rest of dorsal surface of head. Body dorsal color pattern in most specimens with four transverse light bands: first through supraoccipital, second in middle of dorsal-fin, third posterior to dorsalfin, fourth posterior to adipose-fin. Body lateral portion with an upper darker and a lower lighter, just below lateral line. Dorsal, pectoral, pelvic, anal and caudal fins with hard visible irregular series of dark spots on rays. Ventral surface of head and body light brown.
Sexual dimorphism. Males with papilla at the urogenital opening and a membrane along the dorsal portion of the unbranched pelvic-fin ray. Males seem to reach a greater length.
Distribution. Neoplecostomus doceensis is known from thirteen localities: one at rio Gualaxo do Norte, one at rio Gualaxo do Sul, one at rio José Pedro, one at rio Piranga, three at rio Manhuaçu, one at rio Suaçuí Pequeno and five at rio Xopotó, all in the rio Doce Basin, Minas Gerais State, Brazil (Fig. 3).
Ecological notes. Neoplecostomus doceensis is found in clear water rivers, varying from small to medium sized, with rocky outcrops forming small waterfalls and substrates of rocks and sand. The species is found at the bottom of the rivers among the rocks.
Etymology. The specific name doceensis is a Latin noun meaning being located or having connection with the rio Doce basin. This hydrographic system is located in the southeastern region of Brazil and comprises a drainage area of 83,400 km², on the border of Minas Gerais and Espirito Santo states.

Taxonomy
Neoplecostomus doceensis has a conspicuous series of enlarged papillae just posterior to the dentary teeth, which are larger than those on the remaining portions of the lower lip. The abdomen is covered with platelet shields of pentagonal, hexagonal or heptagonal shape. The canal bearing plate and the dorsal locking mechanism are absent, suggesting that this is a typical species of the genus Neoplecostomus, sensu Langeani (1990).
The main character used to distinguish the new species from its congeners is the enlarged fleshy folds between dentaries present in all specimens (Fig. 2a). Apparently, these folds can also be present in some large specimens of N. selenae, although it is poorly developed. Within N. doceensis, this character was observed in specimens of all sizes. However, it is more developed in mature males. Within N. yapo, we found variations of the folds between dentaries. In specimens of N. yapo of the rio Verde, municipality of Ponta Grossa (NUP 4300), this character is poorly developed, as in N. selenae and in specimens of the rio Atlântico, municipality of Mandaguaçu (NUP 4851), in which this character is absent. Several authors (e.g . Langeani 1990;Bizerril 1995;Zawadzki et al. 2008;Roxo et al. 2012c) have reported that the characters used to define the species of Neoplecostomus are influenced by both the sex and stage of ontogenetic development, which also occurs with the papillae between the dentary teeth.
The presence of two or three series of well-developed papillae anterior to the premaxillary teeth also distinguish the new species from its congeners (Fig. 2c). The presence of two or three series of conspicuous papillae just posterior to dentary teeth was previously discussed by Langeani (1990) and is used to diagnose the genus Neoplecostomus. Nevertheless, the papillae series anterior to premaxillary teeth have not previously been reported. Several species of Neoplecostomus such as N. bandeirante, N. corumba and N. ribeirensis have this character; however, it is best developed in N. doceensis. Apparently, this character is also influenced by sex and is enlarged in mature males. Roxo et al. (2012aRoxo et al. ( , 2012b, in a phylogenetic study of the Neoplecostominae species, suggested that Neoplecostomus originated within "interior running drainages" (i.e., drainages of the upper rio Paraná, rio Iguaçu, and rio São Francisco). An exception was found for N. ribeirensis, which appeared as a sister group to Isbrueckerichthys and originated in littoral drainages (i.e., Northeastern Mata Atlântica rivers, rio Paraíba do Sul, rio Ribeira de Iguape, Southeastern Mata Atlântica river, and Fluminense river). The new species, N. doceensis (cited as Neoplecostomus sp. 9 in Roxo et al. 2012a), is closely related to two undescribed species of Neoplecostomus, Neoplecostomus sp. 6 (from córrego do Sapateiro) and Neoplecostomus sp. 7 (from córrego Tamborete) both from streams in the rio Grande basin, an Atlantic coastal drainage. Roxo et al. (2012a) suggested that the ancestor of N. doceensis (cited as Neoplecostomus sp. 9) reached the rio Doce basin about 3.5 million years ago (95% HPD: 1.6-5.5) indicating a colonization route of the N. doceensis ancestral lineage from southern Serra do Espinhaço (Fig. 4), probably as a result of headwater capture processes between the upper rio Paraná and rio Doce basins. Ribeiro (2006) suggested that the south-eastern region of Brazil has undergone intensive geological activity and that the activations of ancient faults could have resulted in headwater captures between adjacent drainages during several periods of its geological history. The eastern Brazilian coastal drainages have probably resulted in the capture of several adjacent rivers, including the headwaters of the Tietê, Grande, São Francisco and Doce rivers. A river capture event at this approximate time and place is also consistent with the General Area Cladogram of fish taxa from tropical South America (Albert and Carvalho 2011). This process is likely to have influenced the movement of ancestral fish throughout the adjacent drainages, similar to the geodispersal of the ancestor of N. doceensis from the upper rio Paraná drainages to the rio Doce drainages about 3.5 Mya (95% HPD: 1.6-5.5).