A new species of Hyphessobrycon Durbin ( Characiformes : Characidae ) from the middle rio São Francisco and upper and middle rio Tocantins basins , Brazil , with comments on its biogeographic history

A new species of Hyphessobrycon Durbin is described from tributaries of the rio Grande (rio São Francisco basin) draining east to the Serra Geral de Goiás, of the rio São Domingos (upper rio Tocantins basin) and rio do Sono basins (middle rio Tocantins basin). Hyphessobrycon diastatos can be diagnosed from its congeners by the absence of humeral spot, 15-18 branched analfin rays, 1-3 maxillary conical to tricuspid teeth, a relatively well-defined dark caudal-peduncle spot, and elongation of dorsaland anal-fin rays in mature males. The biogeographical significance of the distribution of the new species is evaluated and discussed.


Introduction
Hyphessobrycon Durbin is one of the most species-rich genera of the Characidae, comprising approximately 130 valid species (Carvalho & Langeani, 2013;García-Alzate et al., 2013a, 2013b;Ingenito et al., 2013).The genus is distributed from Southern Mexico to the rio de La Plata in Argentina, and most of its diversity occurs east of the Andes.Hyphessobrycon was proposed by Durbin in Eigenmann (1908) as a subgenus of Hemigrammus Gill, differing from the latter by the absence of scales covering the caudal-fin lobes.The two genera were revised by Eigenmann (1917) who raised Hyphessobrycon to full generic status.Eigenmann's accounts are still the single most comprehensive review of the group.
During a recent expedition to upper and middle portions of the rio Tocantins and middle rio São Francisco, a new species of Hyphessobrycon was found to occur in part of the two basins.The new species is herein described and its particular biogeographical significance is discussed.

Material and Methods
Counts and measurements follow Fink & Weitzman (1974), except for number of horizontal scale rows below lateral line, which are counted to the pelvic-fin insertion, not including the small scale at pelvic-fin insertion, and with the addition of head depth, measured at vertical through the posterior end of supraoccipital spine and pelvic-fin origin to anal-fin origin measured at origin of pelvic-fin through the anal-fin origin.Standard length (SL) is expressed in millimeters (mm) and all other measurements are expressed as percentage of SL, except subunits of head, which are expressed as percentage of head length.Meristic data are given in the description, with the frequency of each count provided in parentheses after the respective count.An asterisk indicates counts of the holotype.Counts of maxillary tooth cusps, number and cusps of small dentary teeth, supraneurals, branchiostegal rays, gill rakers, vertebrae, and procurrent caudal-fin rays are taken from cleared and stained specimens (c&s) prepared according to Taylor & Van Dyke (1985).Vertebrae of the Weberian apparatus are counted as four elements and the compound caudal centra (PU1+U1) as a single element.The positive correlation between sex and fin elongation was confirmed on fourteen specimens, by direct examination of gonads.Color in life was described on the basis of photographs of five live specimens taken in the field.In specimen list, catalog numbers are followed by the number of specimens in alcohol, their SL range, and if any, the number of c&s specimens and their respective SL range.Subdivisions of the rio Tocantins basin follow Ribeiro et al. (1995)
Scales cycloid, with 3-5 radii on posterior border, and conspicuous circulii anteriorly.Lateral line incomplete, with 5(1), 6(10), 7*(12), or 8(7) perforated scales, and 31(9), 32*(17),  33(2), or 34(2  Color in alcohol.Overall ground coloration pale (Fig. 1).Infraorbital, opercular, and gular areas retaining some guanine.Dorsal portion of head and body dark.Dark chromatophores concentrated at upper and lower jaws and upper portion of opercle.Upper and lower lips with a dark line.Some specimens with dark chromatophores scattered at infraorbital series.Humeral spot absent.A thin longitudinal line formed by embedded dark pigmentation along horizontal septum, approximately from vertical through pelvic-fin origin to caudal peduncle.No evident longitudinal stripe, some specimens from rio Tocantins basin with more intense concentration of chromatophores along the midlateral body line.Body pigmented by small dark chromatophores, more intense at its dorsolateral portion, fading ventrally.Some specimens with slight reticulated pattern on first two horizontal scale rows, formed by concentration of chromatophores on the posterior portion of scales.Abdominal region devoid of chromatophores.Distal portion of dorsal and anal fins with dark pigmentation on interadial membranes, more intense in males than in females (Figs.1b-c, respectively).A well-defined black round spot extending from posterior half of caudal peduncle to base of middle caudal-fin rays (Figs. 1c;6a,c), or reaching their tips (Figs. 1a,b;6b).All fins with dark chromatophores along edge of lepidotrichia.
Color in life.Coloration in life similar to described above for preserved specimens, except for overall body coloration silver to yellowish.Infraorbitals, preopercle, and opercle silvery.Dorsal portion of iris yellow to orange.Pectoral, pelvic, and anal fins slightly yellowish to almost hyaline.Some specimens with distal portion of first anal-fin rays distinctly darker, especially males (Fig. 3a).Dorsal and adipose fins orange-to slightly yellowish.Conspicuous black blotch over caudal peduncle and median caudal-fin rays.Caudal fin orange-to slightly yellowish (Figs.3a, b).

Geographic distribution.
Hyphessobrycon diastatos is known from tributaries of the rio Grande (rio São Francisco basin) draining east to the Serra Geral de Goiás, from the rio São Domingos (upper rio Tocantins basin) and rio do Sono basins (middle rio Tocantins basin) (Fig. 5).
Etymology.The specific name diastatos comes from the Greek, meaning divided, in reference to its geographic distribution in both the rio São Francisco and the rio Tocantins basins.
Habitat and ecological notes.Hyphessobrycon diastatos was collected in clear water streams running over submerged vegetation and sandy bottom, at altitudes ranging from 430 to 935m above sea level, with relatively swift water current.The riparian vegetation is mainly composed of grass, herbs, and shrubs.Analysis of stomach contents of four specimens revealed the presence of allochthonous and autochthonous items, composed of fragments of plants, organic debris, insect larvae (Diptera and Trichoptera: Hydroptilidae), fragments of adults of terrestrial insects (Hymenoptera: Formicidae, Orthoptera, and unidentified orders) and of other unidentified   arthropods.One specimen (MZUSP 114029) has a parasitc Isopoda attached to the inside its urogenital cavity.

Discussion
Hyphessobrycon diastatos is readily diagnosed from most congeners by the absence of humeral spot.In addition to the species mentioned in the diagnosis, three other species currently in Hyphessobrycon also lack a humeral spot, H. arianae Uj & Géry, H. iheringi Fowler, and H. latus Fowler.Hyphessobrycon latus is assigned as species inquirendae in Characidae (Reis et al., 2003) and H. arianae and H. iheringi are considered valid species (Lima et al., 2003).Hyphessobrycon arianae is prossibly junior synonym of Cheirodon stenodon Eigenmann (Malabarba, 1998) and the holotypes of H. iheringi and H. latus belong to the subfamily Cheirodontinae (H. A. Britski, pers. comm.;Carvalho, 2011), and thus these species are not representatives of Hyphessobrycon.
The absence of an adipose fin is uncommon within the Characiformes, and has evolved independently in different lineages of the Characidae (Mirande, 2010).Some such cases are possibly related with miniaturization events (Weitzman & Malabarba, 1999;Bührnheim et al., 2008).Despite the realization that reductive characters are unlikely to be useful in studies of phylogenetic relationships of characids, given their homoplastic nature (Weitzman & Fink, 1983), the absence or presence of an adipose fin remains in wide use as a criterion to separate genera in the family.The new species has a variably developed adipose fin (Fig. 6).Of 294 specimens examined, only one completely lacks the fin.The genus Hasemania Ellis was originally defined as "like a Hyphessobrycon, but without an adipose" (Ellis, 1911).Curiously, Hyphessobrycon taurocephalus, described in the same paper and also lacking an adipose fin, was not included in Hasemania.Intraspecific variation of this character within the genus was reported for Hyphessobrycon negodagua (adipose fin present in four specimens, absent in 158 according to Lima & Gerhard, 2001), H. eilyos (present in 163 specimens, absent in 52 according to Lima & Moreira, 2003), H. uaiso Carvalho & Langeani (adipose fin variably developed in 512 specimens, absent in 1 specimen, according to Carvalho & Langeani, 2013) and H. langeanii Lima & Moreira (adipose fin always present but vestigial in some specimens according to Lima & Moreira, 2003).Such intraspecific variation of adipose fin was also observed by Géry (1977) in Hasemania nana (Lütken) and by the present authors (present in 3, absent in 173 specimens; MZUSP 38040).These observations show that generic limits between Hyphessobrycon and Hasemania, so far based only on the differential presence or absence of adipose fin, should be reevaluated.In view of that, a comparison of Hyphessobrycon diastatos with all Hasemania species is in order.Regardless of the presence or absence of an adipose fin, Hyphessobrycon diastatos differs from all Hasemania species, except H. hanseni (Fowler)  caudal-peduncle blotch with inconspicuous border in H. hanseni and H. nana and as a prolongation of the midlateral band in H. nambiquara).Finally, it is distinguished from H. maxillaris by a well-defined black round spot extending from posterior half of caudal peduncle to middle caudal-fin rays (vs.faint caudal spot, not continued with the caudal-fin rays).
Zanata & Camelier (2010) proposed a putative close relationship among Hyphessobrycon brumado, H. negodagua, and H. parvellus on the basis mainly of a reduced muscle layer between the first and second ribs, the absence of humeral spot, and the sexually dimorphic caudal spot.Males of the aforementioned species have a poorly-defined caudalpeduncle, formed by pigmentation spread over inner portions of the caudal lobes (especially in H. negodagua and H. parvellus, Fig. 7).Respective females have a round and relatively well-defined caudal-peduncle blotch, not extending to the caudal-fin lobes.Hyphessobrycon diastatos shares these characters, except that its caudal-peduncle blotch is round, relatively well-defined, and does not extend to the caudal-fin lobes in either sex.Whether those species compose a monophyletic assemblage still requires independent confirmation.All aforementioned species are from Northeastern Brazilian coastal drainages, while H. diastatos is founded in both the rio São Francisco and rio Tocantins basins.
The presence of Hyphessobrycon diastatos in both middle rio São Francisco (rio Grande basin) and middle rio Tocantins (rio do Sono basin) may be a result of the common headwater ("água emendada") between the rio Sapão (rio São Francisco basin) and the rio Galheiros (rio Tocantins basin), which potentially allow current faunistic interchange (Lima & Caires, 2011).The presence of the species in both the middle rio São Francisco (rio Grande basin) and the upper rio Tocantins (rio São Domingos basin) have two alternative explanations.The distribution can be a result of the dispersal of the species from the middle to upper rio Tocantins, although this hypothesis seems to be less parsimonious.Another explanation is a putative headwater capture of a stretch of a stream from the rio São Francisco basin into the rio Tocantins.Geological evidence shows that the western border of the Serra Geral de Goiás plateau has been gradually eroded (Lima & Caires, 2011) and could potentially promote headwater capture events of the rio São Francisco basin by the rio Tocantins basin.The presence of Cichlasoma sanctifranciscense, a species widely distributed in the rio São Francisco basin, also in the rio São Domingos basin (upper rio Tocantins; MZUSP 114033) provides further evidence of such hypothesis.Stream capture occurs when part or all of a river flow is diverted to a neighboring drainage system, as a result of unequal rates of erosion or relative tectonic movements (Bishop, 1995;Wilkinson et al., 2006).As a consequence, the area upstream of the diversion drains to a new watershed and is then separated from its original watershed.Such captures potentially represent simultaneous vicariant and geodispersal events for the aquatic fauna.Headwater stream capture has been suggested as one of the main sources of vicariant events and, consequently, one main causes of diversification in the South American continent (cf.Ribeiro et al., 2006).Therefore, headwater captures enrich the ichthyofaunal composition, providing mix of previously isolated faunas of either side of a watershed divide.Some basins indeed present a mosaic of fish assemblages composed of elements from different origins recruited across different times and events (Hubert & Renno, 2006;Lima & Ribeiro, 2011).Cleary, this is the case of the rio São Domingos basin, which has a mixed ichthyofauna composed of typically Amazonian groups (e.g., Creagrutus spp.and Retroculus spp.) along with other taxa originally from the rio São Francisco basin (e.g., Cichlasoma sanctifranciscense and Hyphessobrycon diastatos).

Fig. 5 .
Fig. 5. Distribution of Hyphessobrycon diastatos in the middle rio São Francisco basin and upper and middle rio Tocantins basin, Brazil.Yellow dot represents the holotype and red dots the paratypes.Each dot may represent more than one collection event.