Apistogramma sororcula , a new dwarf cichlid ( Teleostei : Cichlidae ) from the drainage of the rio Guaporé in Bolivia and Brazil

Apistogramma sororcula sp. n. is described from the drainage of the the rio Guaporé in Bolivia (Departamento Beni) and Brazil (Estado Mato Grosso). It can be distinguished from all the other described Apistogramma species by the following combination of characters of the males: upper pectoral spot present, chin with dark band just below lower lip, a suborbital stripe becoming ventrally much wider, on bases of anterior abdominal scales several short vertical streaks forming oblique stripes, small round caudal spot, lateral band reaching caudal fin or caudal spot, produced dorsal-fin lappets, truncate caudal fin with streamers and distinct pattern of narrow vertical stripes, filamentous extensions of the pelvic fins and only three infraorbital pores. It is most similar to Apistogramma staecki KoslowsKi, 1985, but differs from this species by the higher number of 10 to 12 vertical stripes on the caudal fin of adult males, a lateral band reaching caudal fin or caudal spot, short vertical abdominal stripes on bases of scales of the anterior body and produced dorsal-fin lappets.


Introduction
The South American cichlid genus Apistogramma Regan is extremely rich in species for at present there are 84 (VaRella & sabaj PéRez, 2014) valid taxa.In addition, more than 30 species not formally described are listed in the aquarium literature (KoslowsKi, 2002;staecK, 2003;RömeR, 2006;staecK & linKe, 2006).Most Apistogramma species are small fishes for the males, usually greater than females, generally have only a standard length of less than 50 mm.Pronounced sexual dimorphism in morphology, fin shape and colour patterns is common in the genus.Males of different species are usually more distinct from each other than females.
Many Apistogramma species have an extremely restricted geographical distribution and are confined to very small areas, sometimes only to the catchment of a single river basin or to the drainage of a few adjacent tributaries (e.g. staecK, 2003;RömeR, 2006;bRitzKe & mehanna 2010;mesa & lasso, 2011).This is especially a characteristic of species distributed in the tropical forests in the Orinoco and Amazon basins.
Three Apistogramma species have been recorded from the drainage of the rio Guaporé (referred to as río Iténez in Bolivia), viz. A. trifasciata (eigenmann & Kennedy, 1903), A. inconspicua KullandeR, 1983 andA. staecki KoslowsKi, 1985 (originally described from the Rio Mamoré basin).However, the record of A. staecki from the drainage of the rio Guaporé (KullandeR, 2003) probably goes back to a misidentification and refers to the species described here in the following.caRVajal-Vallejos et al. (2014) listed additional species of Api sto gramma occouring in the basin of the rio Guaporé.But this needs further investigation since several of their records are based on misidentifications.
The dwarf cichlid described below from the rio Guaporé drainage is an example of the many Api sto gramma species, which have become well-known in the aquarium literature long before the material for a scientific description was available.It was discovered in 1987 and in the aquarium literature later provisionally referred to by the name Apistogramma sp."Guaporé" or Apistogramma sp."Rio Guaporé" (staecK, 2003;RömeR, 2006;staecK & linKe, 2006).The objective of this paper is to present a formal description of this species.

Material and methods
The type specimens were fixed in formalin and later transferred into 75% ethanol.The holotype and the majority of paratypes are deposited in the fish collection of the Museum für Tierkunde Dresden, Germany (MTD F).Two paratypes are deposited in the Centro de Investigacíon de Recursos Aquáticos, Universidad Técnica del Beni, Trinidad, Bolivia (CIRA-UTB).
The techniques for taking measurements and meristic data follow those described in KullandeR (1980;1986).Measurements were made with an electronic digital calliper reading to the nearest 0.1 mm.Specimen lengths are given as standard length (SL).Scale rows are numbered as described in KullandeR (1990).Numbers in brackets after counts indicate the number of specimens examined with that condition.The number of the dark transverse bars on the caudal fin includes the last on its distal margin.
In accordance with current taxonomic publications on the genus Apistogramma (e.g.mesa & lasso, 2011; VaRella & sabaj PéRez, 2014), the new species is diagnosed on external characters.The species concept used here is the diagnostic variant of the phylogenetic species concept (cf. nixon & wheeleR, 1990).

Coloration in life.
Based on observations immediately after capture and on specimens kept in aquarium.Adult males of Apistogramma sororcula show a distinct polychromatism with a yellow and a bluish colour morph.Males of the yellow morph have bright yellow cheeks and gill covers.Blue males have a predominantly whitish or bluish lower region of the head.
Forehead, nape and dorsal region dark grey or yellowish-brown, rest of body light grey to whitish.With dark band covering chin just below lower lip.Lower portion of suborbital stripe ventrally much wider, often reduced to a conspicuous black spot in the corner of the opercle.Blackish pectoral spot at the base of the upper margin of the pectoral fin.Usually without lateral spot or vertical bars.Bases of anterior abdominal scales with short vertical streaks often forming 5 or 6 oblique abdominal stripes.Postorbital stripe continued as narrow lateral band, posteriorly running in a zigzag, approx.one scale deep, and terminating on the base of caudal fin.Small roundish caudal spot, not extended beyond lateral   Females usually beige coloured, frequently with yellow head and belly, with lateral band or sometimes a small roundish lateral spot not extending beyond the lateral band, conspicuous black suborbital stripe with much wider lower portion, midventral stripe and hyaline to grey fins.Caudal and posterior part of soft anal fin with pattern of vertical spot-stripes.First two anterior dorsal-    Vila Bela da Santissima Trinidade and in Bolivia in the drainage of the rio San Martin approx.5 km upstream of the village Bella Vista.In addition, the species is also said to be exported for the aquarium hobby from the Lago das Cobras in the drainage of the rio Pacaás Novos in the southeast of the town Guajará-Mirim in the Estado Rondonia, Brazil (KoslowsKi, 2002).

Ecological notes. Our field observations revealed that
Apistogramma sororcula is a lentic-adapted species capable of dealing with a comparatively wide range of physicochemical environmental conditions.The fish live in clear water and white water habitats or a mixture of these two water types.Water data of several collecting sites in the drainages of the Guaporé and the San Martin are: pH 6.2 -6.7, total and temporary hardness <l °dH, electrical conductivity 5 -20 µS/cm, water temperature 24 -28 °Celsius.
Apistogramma sororcula lives along the banks of lagoons and rivers in the littoral zones with extremely shallow water, i.e. in a water depth between approximately 5 and 40 cm.We found it either in a thick layer of dead leaves covering the bottom of the bank sides or among aquatic and submerged terrestrial vegetation.There is a distinct positive correlation between the available shelter and the abundance of the species.The highest population density occurs where a thick layer of dead leaves provides plenty of cover and protection.At the collection sites in the drainage of rio San Martin the associated fish fauna includes A. trifasciata and A. inconspicua.
In the rio San Martin the seasonal fluctuation of the water level is considerable.The normal seasonal difference between high and low water is eight meters.In the high-water season the river water floods into the ripar-ian forest and inundates the vegetation.Apistogramma sororcula apparently breeds in the flooded riparian forest during the high-water season.At the beginning of the dry season, the water level rapidly falls and the river water returns into its main channel.At that time, the still subadult fishes leave the riparian forests, which mostly dry up.
Reproductive behaviour.Observations under aquarium conditions revealed that Apistogramma sororcula is a polygynous cave spawner.Males defend a territory containing several potential spawning sites.Each of them may serve as the focus of a smaller territory occupied by a female.Like most cave brooders these dwarf cichlids place their eggs on the bottom side of a horizontal surface.The preferred spawning site is the underside of a stout plant leaf.
At 27 °C hatching occurs about three days postspawning.The fry attempt swimming approximately five days thereafter.After spawning the female drives the male energetically from the close proximity of the spawning site.Parental care is exclusively maternal in this species, although the male may indirectly assist by defending the territory against predators.
Etymology.The species epithet is a Latin noun which means 'little sister'.It refers to the similarity and the close relationship with Apistogramma staecki.
Discussion.Apistogramma sororcula is a member of the A. cacatuoides species complex (KullandeR, 1986;Kos-lowsKi, 2002;staecK, 2003;RömeR, 2006;bRitzKe & mehanna, 2010).Species of this complex are characterized by only three infraorbital pores and both a distinct sexual dimorphism and dichromatism.Adult males have a dark marking on the chin just below the lower lip, a lyrate caudal fin with dorsal and ventral streamers and a pattern of spot-stripes, a dorsal fin with two black anterior membranes and produced lappets, a lateral spot, a longitudinal band usually extending to the base of the caudal fin and abdominal markings in the anterior body region.Females possess a pectoral spot and a midventral stripe.KoslowsKi (1985) counts among the diagnostic characters of A. staecki (closely related to A. sororcula) the low number of tube-bearing scales in the lower lateral line.However, the data obtained from the specimens of A. so rorcula we examined revealed that their number increases during ontogenesis, i.e. there is a positive correlation between the size of the fish and the number of tube-bearing scales in its lower lateral line (fig.9).Their number, therefore, depends on the age of the fish (KullandeR, 1980).Apistogramma sororcula is most similar to its probable sister species A. staecki, but differs from it by the higher number of (usually) 11 to 12 (or even 13) vertical stripes on the caudal fin of adult males (versus up to 8, rarely 9 in male specimens of A. staecki; see figs. 1 -4 and 10), a lateral band reaching the caudal fin or caudal spot (versus not continuous with caudal spot), short vertical abdominal stripes on the bases of the anterior scales (fig.6), distinctly produced dorsal-fin lappets (versus only lappets 4 -6 produced) and a dark marking on its chin (versus no dark mark in comparative material of A. staecki).Additionally, bars 4 and 5, which are vertically divided in A. staecki, are usually not split into two narrow stripes in Apistogramma sororcula (refer to fig. 4 and photographs in KoslowsKi, 2002;staecK, 2003;RömeR, 2006;staecK & linKe, 2006 for a comparison).
Apistogramma sororcula and A. staecki have a vicariant distribution in the rivers draining the Bolivian lowlands (see below).Such allopatric species pairs may pose problems because morphological differences are often small and hence discrimination and classification difficult (mayR, 1969).However, minor deviations in the coloration or the patterns of dark markings may be of biological significance.For in cichlids mating preferences and mate choice are based on visual factors (e. g. couldRidge & alexandeR, 2002;blais et al., 2009), and the females of Apistogramma species can discriminate between conspecific and heterospecific courting males even if they are closely related and look very similar (RömeR & beisenheRz, 2005).As the males display their caudal with an intensified bar pattern in front of the females during courtship, the differences in the number of vertical bars in the caudal fin of male Apistogramma so rorcula and A. staecki may be a reproductive barrier.
The Bolivian lowlands, where A. sororcula and A. staecki occour, are part of the Amazonian ichthyographic province (géRy, 1969;hubeRt & Renno, 2006).Its Bolivian subbasin is a semi-isolated region separated from the adjacent main Amazon Basin by the rapids and waterfalls of the upper rio Madeira (saRmiento et al., 2014).The major rivers of this subbasin, which encompasses the southern portion of the Madeira drainage, are the rio Madre de Dios, the rio Beni, the rio Mamoré and in the east the rio Guaporé.
The rio Guaporé forming the border between Bolivia and Brazil drains the southeastern edge of this ichthyographic province.Unlike other right bank tributaries of the Madeira draining the Bolivian lowlands, it is the only river that originates on the Brazilian Shield.This results in distinctly different chemical and physical characteristics.The rio Madeira and the rivers draining the Beni plains are characterized by nutrient rich, sediment laden turbid whitewater (pH up to 7.6; usually between 70 and >100µS/cm (baRbosa & et al., 1999;Roche & FeRnandez, 1988, staecK pers. obs.).In contrast, the rio Guaporé is a nutrient poor, clearwater river with relatively high transparency, slightly acid pH (usually 6.3 -6.8), a negligible or moderate concentration of solutes and, consequently, low (usually 20 -34 µS/cm) electric conductivity (Roche & FeRnandez, 1988;saRmiento & Killeen, 1998;saRmiento et al., 2014;staecK pers. obs.).
These differences in the physicochemical environmental conditions combine with other evolutionary fac-    tors to produce significant differences in the ichthyofauna of the the rio Guaporé drainage when compared to the rest of Bolivia (saRmiento, 1998).Although it appears that there are no physical barriers between the rio Mamoré basin and the adjacent drainage of the rio Guaporé, there is a number of sister species of dwarf cichlids, which have like Apistogramma sororcula and A. staecki a marked allopatric distribution, with one species distributed in rivers draining the western parts of the Bolivian lowlands and the other limited to the rio Guaporé basin.
Thus the dispersal of Apistogramma sororcula and A. staecki is no exception, but agrees with the distribution patterns of several other dwarf cichlid species occurring in the Bolivian lowlands.
band.Black midventral stripe and vent region.Iris dark red.Dorsal fin dark grey or bluish, with two black anterior membranes, usually with a dark base and two or three vertical rows of dark dots on posterior part of soft fin.Caudal fin hyaline, but with a distinct reticulate pattern of up to twelve (13 in one specimen) narrow dark transverse bars on caudal fin.Pelvic fins blue or greyish.Anal fin bright blue, with up to nine vertical rows of dark dots on posterior part of soft fin.Pectoral fins colourless and hyaline.

Fig. 4 .
Fig. 4. Apistogramma staecki from the drainage of rio Manuripi in the vicinity of Puerto Rico (approx.5 cm TL) in a photo tank immediately after capture.

Fig. 5 .
Fig. 5. Female of Apistogramma sororcula sp.n. from Rio San Martin during brood care in the aquarium.

Fig. 7 .
Fig. 7. Collecting site of Apistogramma sororcula sp.n. at the rio Guaporé in the vicinity of Vila Bela da Santissima Trinidade.