Moenkhausia hysterosticta, Paulo H. F. Lucinda, Luiz R. Malabarba & Ricardo C. Benine, 2007

Paulo H. F. Lucinda, Luiz R. Malabarba & Ricardo C. Benine, 2007, On a new species of the genus Moenkhausia Eigenmann (Ostariophysi: Characidae)., Zootaxa 1525, pp. 61-68 : 62-67

Moenkhausia hysterosticta , new species

Figs. 1-3, Tables 1 and 2

Holotype. (Fig. 1). MCP 32559 , 43.1 mm SL, Rio Tocantins, Ipueiras , approximately 11°19’S 48°28’W, Tocantins, Brazil, 24 Oct 1999, Núcleo de Estudos Ambientais - Universidade Federal do Tocantins (NEAMB).

Paratypes. Brazil. Tocantins. MCP 32560 , 2 (40.5-45.3 mm SL), and UNT 4475 , 2 (42.3-43.4 mm SL), collected with the holotype. MCP 32561 , 19 (4 c&s) (39.2-45.0 mm SL), and UNT 4476 , 12, (39.4-45.4 mm SL), Lageado, Funil, Rio Tocantins , 09°45’02”S 48°21’56”W, 17 Oct 1999, NEAMB. UNT 3887 , 15 (34.7- 41.5 mm SL), Rio Tocantins, Ipueiras , approximately 11º19’S 48º28’W, 26 Jul 2004, NEAMB. UNT 4474 , 7 (36.8-40.2 mm SL), Rio Tocantins, Porto Nacional , 10°43’15”S 48°25’14”W, 18 Nov 1999, NEAMB.

Non-type specimens: Venezuela. Apure. MCNG 45346 , 12, (36.8-43.5 mm SL), Rio Apure, Modulo Fernando Corrales UNELLEZ, dique Noreste 07°34’40”N 69°32’40”W, 3 Feb 1981, D. Taphorn, C. Lilyestron, and S. Reid.

Diagnosis. Moenkhausia hysterosticta is distinguished from congeners by the presence of a dark spot in the upper caudal-fin lobe and by the large and irregularly shaped humeral spot located above the fifth to ninth perforated scale of the lateral line.

Description. Morphometric data in Table 1. Body short and compressed. Predorsal and preventral profiles nearly equally convex. Greatest depth at dorsal-fin origin. Body profile along anal-fin base nearly straight to slightly convex. Caudal peduncle short, nearly square. Dorsal and ventral profiles of caudal peduncle concave. Head small. Eyes large, corresponding to almost half head length. Maxilla positioned at angle of approximately45 degrees relative to long body axis. Maxilla short; posterior tip extending beyond vertical line crossing at anterior border of eyes.

Two series of premaxillary teeth. Teeth of outer series tricuspid, smaller than inner series, numbering 3 to 5. Five teeth, pentacuspid, in inner series. One or two maxillary teeth; anterior teeth tricuspidate, and second tooth, when present, smaller and conical. Four or five anterior large, pentacuspid, dentary teeth posteriorly followed by slightly smaller and usually tricuspid teeth, and 4 to 10 much smaller ones, conical (Fig.2).

Dorsal-fin rays ii, 9 (n = 58). First unbranched ray about one-half length of second. Dorsal-fin origin at midlength of body. Entire adipose-fin base located above posterior portion of anal-fin base. Anal-fin rays iv, 24-27 ([[mean]] = 25.6, n = 57). Anal-fin origin at or slightly posterior to vertical line through insertion of last dorsal-fin ray. Anteriormost portion of anal fin concave; last unbranched and anterior 4 branched rays gradually decreasing in size; remaining portion of anal-fin rays shorter and with equal lengths giving smooth profile to remaining fin. No hooks observed. Pectoral-fin rays i, 10-13 ([[mean]] = 11.1, n = 57), reaching to or near pelvic-fin origin. Pelvic-fin rays i, 7 (n = 56). Pelvic-fin origin anterior to vertical through dorsal-fin origin; longest ray falls short of anal-fin origin. Lower lobe of caudal fin slightly longer than upper lobe. Scales cycloid. Lateral line complete; 29-35 scales ([[mean]] = 31.2, n = 36). Scale rows between dorsal-fin origin and lateral line 5 (n = 58). Scale rows between lateral line and pelvic-fin origin 4 (5 in one specimen; n = 58). Predorsal scales 8 or 9 ([[mean]] = 8.8, n = 58), arranged in regular series. Scale sheath on anal-fin base consisting of one row of small scales, covering approximately anterior half of anal-fin base. Small and deciduous scales covering approximately half length of dorsal caudal-fin lobe and third proximal length of ventral caudal-fin lobe. Precaudal vertebrae 13 or 14 ([[mean]] = 13.3); caudal vertebrae 19 or 20 ([[mean]] = 19.3); total vertebrae 32-34 ([[mean]] = 32.6) (counts taken in four c&s specimens).

Color in alcohol. Eye black with greenish brown pupil. Ground color pale brown, darker in upper half. Border of scales and underlying skin of dorsal half of trunk replete with light brown chromatophores, conferring a very light reticulate pattern to this region. Inner surface of opercle and associated bones covered with dark chromatophores; patch formed by these chromatophores visible externally through opercle and preopercle. Weak, dark brown oblique line of chromatophores on body side above anal-fin base. Dorsal fin weakly pigmented; more pigmented specimens with series of brown chromatophores along both sides of each dorsalfin ray. Pectoral, pelvic and anal fins hyaline. A dark spot in the half proximal length of the upper caudal-fin lobe; remaining portions of the upper and all lower caudal-fin lobe scattered pigmented with dark chromatophores, not forming conspicuous spot. Humeral spot highly variable in size and shape; in less pigmented specimens located nearly over sixth scale of second scale row above lateral line; in more pigmented specimens covering fifth to eighth lateral line scales and extending two rows above and one row below lateral line. Wide dark midlateral band along flank from vertical passing through dorsal-fin origin to base of caudal-fin rays.

Sexual dimorphism. No apparent sexual dimorphism was observed.

Etymology. From the Greek hysteros-, after or posterior, and stictus, spot; refers to the humeral spot, which is located posteriorly on body side.

Distribution. Moenkhausia hysterosticta is currently known from middle portions of the Rio Tocantins in Porto Nacional, Ipueiras, and Lageado (Fig. 3).

Comments. Moenkhausia hysterosticta occurs in Rio Tocantins, but morphologically similar specimens were found far to the west in the Río Apure, Río Orinoco drainage, Venezuela. The population from the Río Apure differs from the Rio Tocantins population mainly in the number of branched anal-fin rays (26-29, mean = 27.5 versus 24-27, mean = 25.6) and dentary teeth (13-17, mean = 14 versus 9-15, mean = 12.7), but present much overlapping in the remaining morphometric and meristic traits (Tables 1 and 2). In the lack of comparative material from intermediate regions between the two river basins, we prefer to identify the population from the Río Apure tentatively as M. hysterosticta .

Discussion

Questions related to the definition and monophyly of Moenkhausia , based on the generic diagnosis proposed by Eigenmann (1903), have been discussed in several papers (Fink, 1979; Géry, 1977; 1992; Costa, 1994; Weitzman & Palmer, 1997; Lucena & Lucena, 1999; Lima & Toledo-Piza, 2001; Benine, 2002; Bertaco & Lucinda, 2006), but none has found or proposed a solution for the recognition or diagnosis of a monophyletic Moenkhausia . Instead, some of these papers discussed the likely relationships of species of Moenkhausia to species belonging to other characid genera.

Fink (1979) pointed out the possible relationships of his new species, M. phaeonota , with species of the genus Hyphessobrycon Durbin . More recently, Weitzman & Palmer (1997) suggested that M. pittieri Eigenmann and M. hemigrammoides Gery might be more closely related to the proposed “rosy tetras clade”, including Hyphessobrycon eques (Steindachner) and related species, instead of being closely related to Moenkhausia .

As a distinct example, Costa (1994) proposed the recognition of a monophyletic group of Moenkhausia species based on color pattern characters, including his new species, M. pyrophthalma with M. sanctaefilomenae (Steindachner) and M. oligolepis ( Guenther) , although M. pyrophthalma does not present all characters used by Eigenmann (1903) to define Moenkhausia (complete lateral line) and would fit in Eigenmann’s diagnosis for the genus Hemigrammus Gill (incomplete lateral line). Lima & Toledo-Piza (2001) repeated Costa’s procedure, describing M. diktyota in the genus Moenkhausia , although it should be placed in Hemigrammus according to Eigenmann concepts, further discussing its relationships to the group proposed by Costa (1994). Finally, Benine (2002) described M. levidorsa , proposing that it is likely related to M. sanctaefilomenae , M. oligolepis , M. cotinho Eigenmann , and M. grandisquamis ( Mueller & Troschel) , although the new species could also be described in the genus Gymnocorymbus Eigenmann based on the lack of scales along the predorsal region.

Besides these efforts to hypothesize relationships of new species, we mention the proposal of Géry (1977), who divided the genus in three distinct groups, on the basis of body depth and counts of scales: M. lepidura-group , M. grandisquamis-group and M. chrysargyrea-group . Later, Géry (1992) redefined the M. lepidura-group as those species bearing a black or gray spot on the upper caudal lobe.

It seems clear, following the accounts presented above, that monophyly of Moenkhausia remains questionable and that relationships of its included species depends on the relationships of at least two other highly speciose characid genera, namely Hyphessobrycon and Hemigrammus . Nevertheless, this goes beyond the scope of this paper.

We herein describe our new species in Moenkhausia since it better conforms to the current definition of the genus (sensu Eigenmann, 1917). Moenkhausia hysterosticta , however, does not fit in any of the groups proposed by Costa (1994), Lima & Toledo-Piza (2001), and Benine (2002), lacking, among the few characters discussed by these authors, the dense reticulate pattern found in body scales and a caudal spot preceded by a light area. Although some specimens have a large humeral spot, resembling those species of the “rosy tetra clade” (Weitzman & Palmer, 1997), M. hysterosticta specimens do not have the complex color pattern, with black and red color marks, characteristic of the species of this clade, as well as any clearly discernible sexual dimorphism that is observable in the rosy tetras, such as the larger dorsal fin of males.

The presence of a black mark in the dorsal lobe of the caudal fin in M. hysterosticta allows it to be compared to other species of Moenkhausia . Among the groups defined by Géry (1977), the new species would fit in the M. grandisquamis-group by possessing 5 scales above, and 3-4 below the lateral line and a deep body (body depth less than 2.66 in SL; dorsal-fin origin to anal-fin origin 2.1-2.6 in SL in M. hysterosticta ), but none of the species of this group have caudal marks similar to that described for M hysterosticta .

Géry (1992) redefined the M. lepidura-group based on the presence of black or gray marks in the upper caudal-fin lobe, but clearly stated that this did not imply any phylogenetic relationship. Géry (1992) also considered that this caudal mark could be used as a recognition signal among protective associations between these species of Moenkhausia and other characids such as some species of Bryconops Kner . Moenkhausia hysterosticta fits into Géry ’s (1992) definition of the M. lepidura-group , despite that the monophyly of this group has not been tested. We were unable, however, to identify any closely related member of this group to M. hysterosticta . Moenkhausia hysterosticta can be readily distinguished from the remaining species of M. lepidura-group by the presence of a larger humeral spot, irregularly shaped and located more posteriorly along body side (above 6th to 9th lateral line scales). Representatives of the M. lepidura-group have a smaller humeral spot, located closer to the opercle than that in M. hysterosticta .

Three other species of Moenkhausia have been described from the Tocantins-Araguaia drainage: M. pyrophthalma , M. tergimacula Lucena & Lucena , and M. pankilopteryx Bertaco & Lucinda . Ten species of Moenkhausia occur in the Rio Orinoco basin and three of them - M. pittieri , M. eigenmanni , and M. miangi - were originally described from this drainage. Nonetheless, these species, both from Tocantins-Araguaia and Orinoco drainages, clearly differ from M. hysterosticta by lacking its characteristic humeral spot and upper caudal-fin lobe mark.

The intrageneric phylogenetic relationships of Moenkhausia species are not known. Although the lack of phylogenetic information precludes unambiguous assertions, some tentative biogeographical remarks on the distribution of M. hysterosticta are outlined below.

Moenkhausia hysterosticta inhabits Venezuelan coastal drainages and the Brazilian Rio Tocantins drainage. The lack of records of M. hysterosticta between the Venezuelan coastal drainages and the Brazilian Rio Tocantins drainage may due to the lack of sampling in this extensive area. Several taxa are distributed in the drainages along the north coast of South America east of the Andes from the Río Orinoco System to the Rio Tocantins drainage, including cyprinodontiforms, e.g. Fluviphylax Whitley , Micropoecilia Hubbs , and Tomeurus gracilis Eigenmann (Poeciliidae) (Lucinda & Reis, 2005), and characiforms, e.g. Curimata cyprinoides (Linnaeus) (Curimatidae) (Vari, 1989), Roeboexodon geryi Myers and Exodon paradoxus Mueller & Troschel (Characidae) (Lucena & Lucinda, 2004). This region has been proposed as an area of endemism for the Neotropical freshwater fishes by Lucinda & Reis (2005: 51), and the distribution pattern of M. hysterosticta seems to corroborate this hypothesis. However a complete comprehension of such a pattern of distribution is far from known. The proposition of a consistent hypothesis of historical biogeographical relationships among these areas depends on further taxonomic and phylogenetic studies concerning several subsets of the Neotropical ichthyofauna, which will demand much effort from fish systematists.