A new species of Gymnogeophagus from the río Negro and río Tacuarí basins , Uruguay ( Teleostei : Perciformes )

The new cichlid species Gymnogeophagus tiraparae is described from the río Negro and río Tacuarí basins (Uruguay). The new species is distinguished from other Gymnogeophagus species by the unique presence of the following characters: adipose hump on head deeper than the dorsal-fin upper border, adipose hump with anterior profile vertical, extending from the upper lip to the dorsal-fin origin, absence of transversal bands on body; two horizontal series of moderately elongated light blue dots between dorsal fin spines, and a series of light blue stripes between soft rays, sometimes merged with the second series of elongated dots, always with a red ground color between series of dots, and caudal fin with dots vertically aligned on its distal border. According to these characters and a recent molecular phylogenetic analysis, the new species is closely related to G. gymnogenys.


Introduction
The Neotropical cichlid genus Gymnogeophagus Ribeiro can be distinguished from other cichlids by the presence of a forward directed spine on top of the first pterygophore and by the absence of bony supraneurals (Winberberg et al., 1998).Its monophyly has been corroborated by morphological (Reis & Malabarba, 1988) and molecular (Winberberg et al., 1998;López-Fernández et al., 2005a, b;Pereyra & García, 2008) analyses.However, as occurs in other Neotropical Cichlidae (Kullander, 2003), species level taxonomy, distribution patterns and reproductive behavioral evolution are still unclear (Winberberg et al., 1998).Part of this confusion possibly arises from the existence of many undescribed species present in the distribution range of the genus.
Endemic to the río de La Plata basin, laguna dos Patos system and rio Tramandaí drainage (Reis & Malabarba, 1988), Gymnogeophagus was hypothesized to be composed of two monophyletic lineages (Winberberg et al., 1998).One of them is composed of substrate spawning species: G. rhabdotus Hensel, G. meridionalis Reis & Malabarba, G. che Casciotta, Gómez & Toresanni, and two undescribed species (unpublished data).The other lineage is composed of the basal substrate spawning G. setequedas Reis, Malabarba & Pavanelli, and the mouth brooding G. balzanii Perugia, G. lacustris Reis & Malabarba, G. labiatus Hensel, G. gymnogenys Hensel, G. australis Eigenmann, G. caaguazuensis Staeck, and at least five undescribed taxa (Winberberg et al., 1998).Pereyra & García (2008), using citochrome b sequences from specimens of mouth brooding species (G.labiatus, G. gymnogenys, and two undescribed taxa) distributed in the lower río Uruguay and laguna Mirim tributaries, found three well supported monophyletic lineages from which G. gymnogenys would be the sister species.In this article we describe a new species of Gymnogeophagus from the río Negro and río Tacuarí basins (Uruguay), that belongs to the dimorphic mouth breeders group, and that corresponds to one of the monophyletic clades found by Pereyra & García (2008).

Materials and Methods
Examined material of the new species and comparative material from other Gymnogeophagus species came from the fish collection of the Facultad de Ciencias de la Universidad de la República, Montevideo (ZVC-P), and Museo Nacional de Historia Natural y Antropología (MNHN), Montevideo, and Universidade Federal do Rio Grande do Sul, Porto Alegre (UFRGS).Additional comparisons where done using published data from Reis & Malabarba (1988) and Staeck (2006).Counts and measurements were taken according to Reis & Malabarba (1988), with the addition of seven extra morphometric measures taken in straight line: snout to dorsal-fin origin length, snout to pelvic-fin origin length, snout to anal-fin origin length; and dorsal-, pelvic-, anal-and caudal-fin base lengths.

Gymnogeophagus tiraparae, new species
Figs. 1-2 Diagnosis.The new species can be distinguished from all others Gymnogeophagus species by the presence of the following unique characters: adipose hump on head deeper than the dorsal-fin upper border, adipose hump with anterior profile vertical, extending from the upper lip to the dorsal-fin origin, absence of transversal bands on body, two horizontal series of moderately elongated light blue dots between dorsal-fin spines, and a series of light blue stripes between soft rays, sometimes merged with the second series of elongated  Reproductive males with adipose hump on top of head from dorsal-fin origin to upper lip, deeper than dorsal-fin upper border and with anterior profile vertical.Mouth terminal and jaws isognathus.Body contour at dorsal-fin base slightly arched, decreasing from anterior part to caudal peduncle.Caudal peduncle rectangular, longer than deeper, dorsal and ventral profiles slightly concave.Body contour slightly convex between lower lip and last anal-fin ray, with straight segment between pelvic and anal fins.Body scales moderately large and ctenoid except for small cycloid and ctenoid scales in preventral area.Small ctenoid scales on opercle; scales on preopercle, when present, small and cycloid.Small ctenoid scales on base of hump (in adult reproductive males only) to approximately vertical line passing on center of eye.
Proximal third to half of caudal fin with small scales in single series between rays.Dorsal-fin without scales and its origin posterior to vertical line through posterior bony margin of opercle.Large males with sixth dorsal-fin soft ray longest, reaching proximal third of caudal fin.Pectoral fin reaching anal-fin origin.Anal fin reaching caudal-fin base.Caudal fin truncated or slightly concave; lyrate in large reproductive males; very deep distally, from distal edge of extended dorsal fin to distal edge of extended anal fin.
Color in life.Ground color of dorsal region of body in adults, brownish to light olivaceous, with one large dark spot on nape and two large dark spots on body flank, just below dorsal-fin base, first between eighth and twelfth dorsal-fin spine and second from first to sixth dorsal-fin soft ray.Well defined dark, circular, lateral spot just below upper portion of lateral line; often with three or four dark blotches on sides of body, anterior dark blotch larger and extending through lateral spot, other blotches smaller and aligned on sides, reaching caudal peduncle.Ventral portion of body yellowish in adult males and light olivaceus in adult females.Six or more lateral, parallel, bright green to pale blue bands from posterior part of pectoral-fin base to caudal-fin base.
Numerous small bright blue dots usually present on cheeks, bright green colored lips usually present in reproductive males.Adipose hump, when present, with brownish ground coloration without dark line anterior to eye, suborbital stripe usually absent or diffuse in reproductive males.Dorsal fin yellowish on base and reddish between two horizontal series of elongated, hyaline to light blue dots, and third distal series in posterior part of fin, often fused with proximal series; small proximal circular dots very close to dorsal-fin base often present, from the fifth or sixth dorsal-fin soft ray, to its distal end.Caudal fin with red ground color in adults and entirely covered with numerous circular hyaline dots, arranged into horizontal series between rays.Distal dots smaller, vertically aligned.Pectoral fin hyaline, pelvic fin with light blue stripes between fin rays; anal fin yellowish in proximal portion and reddish distally between many small light blue dots spread along fin.
Color in alcohol.Ground color turns paler.Reddish and yellowish pigmentations turn light brown or gray and light blue fin pigmentation turns hyaline.Dark spots turn darker and lateral parallel light green bands turn clearer, almost invisible.

Ecology.
Localities where the new species was collected are large rivers, higher than stream order 6, with clear water, sandy or rocky bottoms, and little vegetation.Specimens were collected using cast nets, seine and electro fishing device.Females holding juveniles in their mouths were collected at the end of spring and summer.
Etymology.Gymnogeophagus tiraparae takes its name from María Luisa Tirapare, a Guaraní woman who founded the now disappeared town of San Borja del Yí (close to the first locality where the new species was found), the last native town in Uruguayan land, where natives, fugitive African slaves, gauchos, and other outsiders lived together.

Discussion
According to the molecular data presented by Pereyra & García (2008), the new species described herein is assigned to the "gymnogenys-like" group of Gymnogeophagus.This is in agreement with the morphological analysis of the present description.Gymnogeophagus tiraparae shares with other members of the derived "gymnogenys-like" group the following characters: conspicuous secondary sexual dimorphism (including development of nuchal hump in reproductive males), mouth brooding reproductive system, high E1 scale count (27-30, 96% with 28-30 scales), weak fin squamation, reduced sensory canal on caudal fin (Reis & Malabarba, 1988;Winberger et al., 1998).Pereyra and García (2008) found that G. tiraparae (clade 3 in fig. 3 of that article) is closely related to G. sp. 1, with both species forming the sister group of G. sp. 3. The three species together represent the sister group of G. gymnogenys specimens from Rio Grande do Sul (Brazil).However, only the clades G. sp. 3, G. sp. 2 and G. tiraparae were supported by parsimony bootstrap values.It is interesting to note that G. sp. 3 presents all the diagnostic characteristics of G. gymnogenys from type locality (Reis & Malabarba, 1988).For this reason further taxonomic work should include a revision of G. gymnogenys sensu stricto for a better understanding of the taxonomy and phylogeny of this group.
The new species is so far known from the río Negro and its tributaries (lower río Uruguay drainage), and río Tacuarí (laguna Merín drainage).This discontinuous distribution is shared, almost with the same pattern, with two species of the annual genus Austrolebias (Loureiro et al., 2004;Costa, 2006): A. arachan Loureiro, Azpelicueta & García, A. vazferreirai Berkenkamp, Etzel, Reichert & Salvia.Most populations of these species are present along río Negro basin, while their distribution in the laguna Merin drainage is restricted to a small area of highland wetlands (100 m above sea level) in the upper rio Tacuarí, that is geographically close to río Negro tributaries (as close as 10 km) (Loureiro et al. 2004).In a broader geographical scale the biogeographic relationship of these two areas has been proposed as a result of basin capture (Ribeiro, 2006) and marine transgressions and regressions (Loureiro, 2004;Loureiro & Garcia, 2006).Ribeiro (2006), reviewed the geological and geomorphological relationship between Atlantic coastal basins and their adjacent upland cristalline shield, and the concomitant fish distributions patterns that arose from this relationship, where headwaters of the cristalline shield rivers are constantly being captured by the Atlantic rivers.This author identified three different distribution patterns according to their time of occurrence.An ancient pattern exemplified by the presence of basal clades of Trichomicteridae and Doradidae in Atlantic rivers; an intermediate pattern exemplified by sister group relationships at the generic level as in the Aspidoradini (Callichthyidae), the sister group relationship of Lignobrycon and Triportheus (Characidae), and others (see Ribeiro, 2006); and a recent   (Loureiro & Silva, 2006;Giora et al., 2008).
The distribution of G. tiraparae and the Austrolebias species mentioned before correspond to that recent pattern and, based on the highly restricted distribution of these taxa in laguna Merín drainage (so far, only known from the Tacuarí River basin), it is likely to represent one the most recent events.