First record and extended distribution of Otothyropsis piribebuy (Loricariidae: Hypoptopomatinae) in Brazil

Cascudinhos are a group of small benthic fishes included in the Hypoptopomatinae subfamily, inhabiting small to moderate streams and rivers within the Neotropical region, from Venezuela to Northern Argentina. Until now, Otothyropsis piribebuy originally described from the rio Paraguay basin, in Paraguay, is the only species of the genus not recorded in Brazil. Recent samples in the rio Tererê, rio Paraguay basin, Brazil, revealed a population of Otothyropsis with uncertain taxonomic identity. Therefore, the study aimed to unveil the distribution of Otothyropsis within Brazilian territory. External morphology, osteology, measurements, and counts (plates, teeth, and rays) of these specimens from rio Tererê were compared to data from the original description of O. piribebuy, and also with specimens of O. piribebuy sampled in Paraguayan territory. Observations indicated no differences among the analyzed specimens. Furthermore, a Principal Component Analysis (PCA), carried out using log-transformed measures from Brazilian and Paraguayan specimens, showed no separation of these populations, also indicating that all analyzed specimens pertain to the same species. Based on this, a prediction map of distribution, using Maximum Entropy, was produced. The correct identification of spatial range of occurrence is an essential step to ensure the conservation of species, and the extended distribution of Otothyropsis piribebuy was confirmed, enhancing the list of neotropical fish from Brazil. Key-Words. Cascudinhos; Pantanal; Upper Paraguay basin; Chaco; Ichthyofauna.


INTRODUCTION
Cascudinhos are a group of small benthic fishes included in the Hypoptopomatinae subfamily, inhabiting small to moderate streams and rivers within the Neotropical region, from Venezuela to Northern Argentina (Schaefer, 2003). Within the group, Otothyropsis Ribeiro, Carvalho & Melo, 2005 was described to allocate O. marapoama Ribeiro, Carvalho, Melo, 2005, a species from the rio Paraná basin. Currently, there are six valid species for the genus, belonging to the rio Paraná and the rio Paraguay basins: O. alicula Lippert, Calegari, Reis, 2014, O. biamnicus Calegari, Lehmann, Reis, 2013, O. dialeukos Calegari, Molis, Reis, 2017, O. marapoama, O. piribebuy Calegari, Lehmann, Reis, 2011, and O. polyodon Calegari, Lehmann, Reis, 2013 Otothyropsis piribebuy, from rio Paraguay basin, is known exclusively from Paraguayan territo-ry ( Fig. 1 -star, square and triangle). This species is distinguished from the congeners by possessing the lateral middle series of plates truncated before the caudal fin; the inner margin of pectoral spine fin smooth; the distal tip of the first ceratobranchial accessory flange pointed; and abdomen with unplated areas in adults (Calegari et al., 2011). Recent examination of specimens sampled in the rio Tererê, rio Paraguay basin, Mato Grosso do Sul, Brazil ( Fig. 1 -circles), revealed the first record of O. piribebuy in Brazilian territory, extending the occurrence area of the species.

MATERIAL AND METHODS
Sampling occurred in Pantanal floodplain, rio Tereré drainage, transition between the Nabileque subregion and Chaco domain. Fishes were collected on shaded rapids of temporary shallow streams, locally known as "vazantes", usually associated with submerged twigs, and co-occurring with shoals of another Hypoptopomatinae, Otocinclus bororo Schaefer, 1997. Comparison of specimens were based on counts and measurements following Schaefer (1997), and compilation proposed by Martins et al. (2014) with additional measurements from Calegari et al. (2011). Measurements were obtained using digital calipers (± 0.1 mm), point-to-point, under a stereomicroscope on the left side of 17 specimens [13 from Brazil (ZUFMS 5718) and 4 from Paraguay (MNRJ 26113)]. Morphometric data are expressed as a percent of standard length (SL) for body, or head length (HL) for cephalic subunits. For osteological examination, three specimens were cleared and stained (c&s), following Taylor & Van Dyke (1985) (2 from ZUFMS 5718 and one from MNRJ 26113). All obtained results were compared with data from the original description of Otothyropsis piribebuy. Principal Component Analysis (PCA) was carried out using log-transformed measures from the same specimens used in morphometrics analysis, in R environment (R Core Team, 2019), with ggbiplot (Vincent, 2011) and stats (R Core Team, 2019) packages.
Distribution map was produced using QGis (QGIS Development Team, 2019), with dataset from FAO Fisheries & Aquaculture Department (FAO Fisheries & Aquaculture Department, 2019). Prediction of the distribution of species were performed using Maximum Entropy -relying on probability of occurrence based of presence-only data from available sample sites (CZCEN 332, MCP 45754, MNRJ 26113, ZUFMS 5717, ZUFMS 5718) using MaxEnt (Phillips et al., 2019) and environmental datasets -maximum, average and minimum temperature and precipitation, besides a climatic biological dataset (see worldclim.com for detailed information) -from WorldClim (Fick & Hijmans, 2017

RESULTS
To compare the specimens of Otothyropsis collected in Brazilian portions of the Paraguay basin (ZUFMS 5718, Fig. 2), specimens of O. piribebuy sampled near the type-locality in the Paraguay were examined (MNRJ 11256), as well as the data from the original description given by Calegari et al. (2011). Based on comparison of meristic and morphometric data (Tables 1-2), external morphology, and osteological features the specimens were identified as Otothyropsis piribebuy.
Principal Component Analysis (PCA), based on populations of Otothyropsis piribeuy from Brazilian and Paraguayan portions of rio Paraguay basin, corroborated the conspecificity, indicating no differences between the two populations (Fig. 3). The two distinct groups showed on PCA result were separated based strictly on sexual dimorphism. The first group clustered all females specimens, while the second group united the males. Calegari et al. (2011) had already pointed the sexual dimorphism as an important feature of this species.
Considering the sampling locations and their morphoclimatic features, a prediction map was constructed (Fig. 4), which revealed a greater potential extent of occurrence for O. piribebuy. The orange areas on the map are regarded as the most probable of occurrence, representing putative sampling sites.

DISCUSSION
The majority of morphometric and meristic features of the specimens from rio Tererê, Brazil, were consistent with those of the type series of O. piribebuy, as given by Calegari et al. (2011). Also, considering the diagnostic features for O. piribebuy, the same patterns were observed in Brazilian specimens, such as the number and truncation of lateral series of plates, lack of serration in internal margin of the pectoral-fin spine, and abdominal pattern of plating. An osteological variation identified in one specimen was the fusion of infraorbitals 2 and 3, revealing an intraspecific exception.
The PCA showed no distinction between the two compared populations from Brazil and Paraguay, but was efficient to separate males and females (Fig. 3), corroborating the sexual dimorphism already known to O. piribebuy. Besides the two most common characteristics used to identify sexual dimorphism within Hypoptopomatinae (the fleshy flap above the first pelvic-fin ray and the urogenital papilla), the males also shared other secondary sexual dimorphism features, such as the enlarged nostril and smaller internarial distance as many other Hypoptopomatinae species (e.g., Calegari et al., 2011;Martins & Langeani, 2011).
It is noteworthy that the collections occurred six months apart within two distinct hydrological moments (flood and drought seasons), and despite the effort to locate the species on other habitats, specimens of O. piribebuy were only found on those two locations ( Fig. 1 -circles). Although the flooding is known as a driver of homogenization of fish communities of floodplain systems (Thomaz et al., 2007), the specificity of occupation observed on O. piribebuy emphasizes the need for further fieldworks in upper the rio Paraguay basin environments in order to fill gaps on the ichthyological knowledge of this drainage. This is corroborated by the prediction map of distribution to O. piribebuy (Fig. 4), according to which, the species probably exists in other portions of the basin.