Description of a new killifish of the genus Rivulus (Teleostei: Cyprinodontiformes: Rivulidae) from south eastern Peru

Rivulus parlettei spec. nov. from south eastern Peru (Departamento Cusco) is described. It is a member of the R. limoncochae group (as diagnosed by Costa, 2010) and differs from all the other species of this assemblage by its unique colour pattern and different morphology. It is distinguished from its geographic neighbour R. christinae by irregular interrupted lines of dots wider than the interspaces on body sides (versus longitudinal rows of dots forming stripes narrower than the interspaces). The infl uence of the occupation of distinct microhabitats for the radiation of the clades and the possible process of speciation of the new species are briefl y discussed.

During a killifi sh survey in October 2004 through the south-east of Peru C. Parlette and L. Peck collected R. christinae and another Rivulus species of the R. limoncochae group, which could not be attributed to either of the hitherto known species.This in the vicinity of Vitobamba (departemento Cusco) collected new species is described here.

Material and methods
Measurements and counts were taken as described in Amiet (1987), Huber (1992) and Valdesalici (2010).Measurements were made with a digital calliper, under a dissecting microscope, and rounded to the nearest 0.1 mm.All measurements are presented as percentages of standard length (SL), except for eye diameter and snout length, which are given as percentage of head length (HL).Terminology of the cephalic neuromast series follows Costa (2001).Terminology of the frontal squamation as described in Hoedeman (1958) and Huber (1992).Osteological preparations (cleared and stained, C&S) were made according to Taylor & Van Dyke (1985), but not stained for cartilages.
Data from Huber (1992) and Costa (2006) were used for comparisons.

Rivulus parlettei spec. nov.
Figs. 1 -2 Diagnosis.Males of Rivulus parlettei are distinguished from males of the remaining members of the R. limoncochae group by irregular interrupted lines of dots wider than the interspaces (versus longitudinal rows of dots, sometimes coalescing to form stripes narrower than the interspaces), by an inferior lip without distinctive colouration (versus red inferior lip), a dorsal and anal fi n without a dark posterior tip (versus presence of dark tip), a light blue venter (versus yellow in R. christinae and white in the remaining species of R. limoncochae group) and a yellowish anal fi n with a whitish basal region (versus yellow with light blue basal region).Females of R. parlettei can be distinguished from females of the other species of the R. limoncochae by the presence of variable shaped orange spots on body sides (mainly above anal fi n) forming oblique bars (versus absence of spots or spots forming stripes), by a yellow-orange ventral parts of head, venter and caudal peduncle (versus light blue to light brown) and by having orange to yellow paired fi ns (versus yellowish hyaline or hyaline paired fi ns).An additional distinguishing feature of R. parlettei is the position of its dorsal-fi n origin (dorsal fi n origin above base of 7th or 8th of anal-fi n ray versus 9th or 12th anal-fi n ray in R. christinae, R. erberi, R. iridescens, R. rubrolineatus, and R. taeniatus).
Description.Measurements are summarised in Table 1.Largest examined male 37.7 mm SL; largest examined female 33.2 mm SL.Dorsal profi le slightly convex from snout to end of dorsal fi n base, about straight at caudal peduncle.Ventral profi le slightly convex from lower jaw to anal fi n origin; approximately straight from anal fi n to posterior end of caudal peduncle.Body slender, subcylindrical anteriorly, compressed posteriorly, greatest body depth at midlength between pectoral fi n base and anal fi n origin.Snout short, rounded.Dorsal and anal fi n rounded, without fi laments in both sexes.Pectoral fi ns rounded.Pelvic fi ns small, reaching anus.Caudal fi n rounded.Dorsal fi n origin above base of the 7th or the 8th anal fi n ray.Dorsal fi n rays 8 -9; anal fi n rays 13 -14; caudal-fi n rays 24; pectoral-fi n rays 13 -14; pelvic-fi n rays 6. Scales large, cycloid.Body and head entirely scaled.No scales on dorsal-fi n and anal-fi n base.Frontal squamation E-patterned.Longitudinal series of scales 37 -40.Cephalic neuromasts: supraorbital 3 + 3. Lateral line interrupted.Basihyal subtriangular.Second pharyngobranchial with two teeth.Vomerine teeth 2. Lateral process of post-temporal short.Bifi d antero-dorsal process of urohyal.Total vertebrae 30.
Vertebrate Zoology ■ 61 (3) 2011 ish with three transverse dark brown to black stripes.Anal fi n yellow, base whitish with red spots.Caudal fi n hyaline, with 5 narrow brown to black bars, yellow on ventral portion; close to its dorsal margin with small, vertically elongate black spot, proximal margin with a small light yellow zone.Pelvic fi ns and pectoral fi ns yellow.
Distribution.Currently known only from the type locality, a small stream belonging to the río Araza in the vicinity of Vitobamba, at an altitude of about 820 m asl, Departamento Cusco, south eastern Peru (Fig. 3).
Habitat notes.Type specimens were collected in a small forest stream (Fig. 4) and in an adjacent shallow pool with mud and leaf litter on its ground.The water was clear and transparent; temperature about 25 °C, pH approx.7 and electric conductivity about 15 μS/cm.No other fi sh species was found there.
Etymology.Named after Casey Parlette, who collected the type specimens.Costa (2006), is characterised by the presence of yellow stripes on the dorsal and ventral caudal-fi n margin in males.This character state is often inconspicuous or even absent in some members (Costa, 2006).In a cladistic sense this character state is consequently ambiguous and taxonomically doubtful to constitute Cyno do nich thys.Nevertheless, we recognise and endorse Cyno do nichthys in the sense of Costa (2006Costa ( , 2008Costa ( , 2010) ) as a convenient assemblage because no contrary phy logenetical analysis is available.Rivulus parlettei is considered to be a member of the subgenus Cyno donichthys.

Discussion
The taxon Rivulus is a diversifi ed and in a cladistic sense probably a non-monophyletic unit (Hrbek & Larson, 1999;Vermeulen & Hrbek, 2005;Costa, 2010, Costa & De Luca, 2011).The type species of the genus R. cylindraceus Poey 1860 belongs to a basal clade and is phylogenetically not closely related to the species treated herein (Hrbek & Larson, 1999;Costa, 2006).Nevertheless, we include the new species in Rivulus because it is in congruence with the re-descriptions and the current use of the genus (e.g.Costa, 1998Costa, , 2006Costa, , 2008Costa, , 2010;;Huber, 1992Huber, , 1999)).
The subgenus Cynodonichthys (recently re-de scribed by Costa, 2006) includes more than 60 species from Middle and South America.The species from the coastal river basins of eastern Brazil listed as Cynodonichthys were later transferred to the recently erected subgenus Atlantirivulus Costa (2008).middle of dorsal fi n (Costa, 2006).Whereas, Huber (1998Huber ( , 1999) ) found no diagnostic characters to separate species of the R. limoncochae group and the R. urophthalmus group.He mentioned that it is diffi cult to provide clear cut key characters to discriminate be-parts of the Amazonian drainage.He discriminated this group from the urophthalmus group by the possession of contact organs on the fl anks of males (versus contact organs absent) and by the presence (versus absence) of an oblique transverse stripe on the   ses of freshwater fi sh beta diversity have shown that neighbouring areas differing in altitude often harbour dissimilar sets of species (Leprieur et al., 2011).Such differences in species composition may refl ect an adaption to abiotic conditions by range shifts or by vicariance (Leprieur et al., 2011).A similar pattern of vicarious distribution as found for R. parlettei and R. christinae is known from Hemibrycon inambari, occurring only in the upper parts of the río Alto Madre de Dios and the río Inambari drainages, and H. jelskii, which inhabits the lower parts of these river systems (Bertaco & Malabarba, 2010).There are also vicarious species pairs in Cypridontiformes.For instance the evolutionary process of speciation and separation of species along an elevational gradient is well documented in some species pairs of the poeciliid genus Xiphophorus (e.g.X. malinche and X. birchmanni; X. clemenciae and X. helleri) from the Atlantic slopes of the Sierra Madre in Mexico (Kallman & Kazianis, 2006;Culumber et al., 2010).Thus, it is not unlikely that R. parlettei evolved from a peripherally isolated allopatric population of its putative sister species R. christinae.Speciation based on peripheral isolation is well known in evolutionary biology and tween these rivulids because of their phenotypically similarity and their variation even at population level.
In this study we recognise the R. limoncochae group as a taxonomic unit only because it allows a better handling of the subsets of the subgenus and we do not consider it as a phylogenetically robust clade.
In the R. limoncochae group, R. parlettei is hypothesised to be closely related to its geographic neighbour R. christinae (Figs. 5 -9).Both are differentiated by divergent character states mentioned in the diagnosis.Additionally the distribution of R. christinae is (so far known) limited to the plains at the western border of the Departamento Madre de Dios (Huber, 1992;Staeck, 1994;this study).It occurs in the río Madre de Dios drainage including río de las Piedras, río Marcapata, río Manuripi and río Tambopata.In contrast, R. parlettei occurs more to the west on the most eastern foothills of the Andes at a comparatively high altitude of about 820 m asl in the upper río Inambari system in the Departamento Cusco.The Inambari area is associated with the refuge hypothesis as a model of vertebrate speciation in Amazonia and is characterised by a high diversity of endemic species (Haffer, 2008).Furthermore, analy-  this manuscript.We are grateful to Casey Parlette (USA) for information about the type locality, for photographs (4)(5)(6)(7)(8) and donation of material, to Stefan van der Voort (the Netherlands) for correcting grammar and spelling, to Günter Gerlach (Germany) for providing the Spanish abstract and to Wolfgang Staeck (Germany) for fi sh photograph (Fig. 9), corrections and helpful suggestions.Thanks go out to Hernan Ortega Torres (MUSM), Jeffrey M. Clayton and Lynne Parenti (both USNM), Giuliano Doria, Roberto Poggi (both MSNG), and Axel Zarske (MTD) for access to collections under their care.is thought to be a major factor in the evolution of new species (Mayr, 1967).Huber (1998) discussed the relevance of a separation along elevational gradients, the signifi cance of refuge areas and the importance of isolated population at the periphery of distribution areas as factors in the speciation within the Killifi sh.He argued that such peripheral species (called 'frontier species' by Huber, 1998) are usually characterised by a restricted distribution (in comparison to their sister taxon), by a distinctive colour pattern (particularly on the body sides of males) and a divergent position of the dorsal-fi n origin in comparison to that of the anal fi n.With all these three requirements being met in R. parlettei (cf.fi gures 1 -2, 5 -9 for differences in colour pattern; dorsal fi n origin above base of the 7th or the 8th anal fi n ray in R. parlettei versus the 9th or 10th anal fi n ray in R. christinae), it is likely that it represents an independent lineage in the sense of the evolutionary species concept sensu Wiley (1978).
Field observation in the habitats of the Amazonian species of Rivulus revealed that different lineages occupy distinct kinds of biotops, suggesting a divergent specialisations during the evolution of the species clades (Costa, 2006).Subsequent studies (e.g.Schindler & Etzel, 2008;Schindler & Valdesalici, 2011) confi rm this observation for the subgenera Melanorivulus and Owiyeye.The tendency of species or groups of monophyletic clades to maintain the ancestral ecological traits of their lineages over time is discussed and known as 'phylogenetic niche conservatism' (Losos, 2008;Wiens et al., 2010).In the case of the cis-Andean Rivulus the retained ecological trait (as discussed in Costa, 2006) is the occupation of a similar habitat or microhabitat (resource utilisation) in related species.For example all the members of the Rivulus limoncochae group, including R. parlettei, prefer shallow creeks at sunny glades in forest areas.This may be regarded as phylogenetic niche conservatism.It seems to be a wellfounded hypothesis that the ancestral ecology played a role both during the evolution of the different groups and speciation (cf.Costa, 2006).However, habitat data of as many species of Rivulus as possible have to be compared in a phylogenetic framework (cf.Losos, 2008;Wiens et al., 2010) in order to confi rm the hypothesis that there is a tendency of species or monophyletic groups to maintain the ancestral ecological traits of their clade.
Colouration.Body sides of males (Fig.1) metallic green-yellow, dorsolateral portion of body between postorbital region and anterior portion of fl ank pale brownish with dark brown mottling; broad interrupted lines comprised of red dots on entire fl ank.Dorsum brownish.Venter light blue.Opercular region green-yellow.Ventral part of head light blue.Upper jaw light brown, lower jaw dark brown.Iris yellow.Dorsal fi n pale yellowish with a transverse red stripe and short oblique red bars on posterior portion.Anal fi n pale yellowish, base whitish with red spots on posterior portion.Caudal fi n pale yellowish to hyaline on posterior margin and with red spots on proximal portion.Pelvic fi ns yellowish.Pectoral fi ns yellowish to hyaline.Body sides of females (Fig.2) light yellow, with irregular dark brown mottling and orange spots and oblique marks of variable shape, forming three irregular lines on caudal peduncle.Dorsum brownish.Venter orange yellow.Opercular region with large dark brown blotch.Ventral part of head yellow.Upper jaw light brown; lower jaw yellow.Iris yellow.Dorsal fi n hyaline to pale yellow-

Table 1 .
Morphometric data of Rivulus parlettei.All measurements are presented as percentages of standard length, except eye diameter and snout length as percentages of head length, standard length in mm.