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ZooKeys 406: 1–23, doi: 10.3897/zookeys.406.7011
New species of the Pseudancistrus barbatus group (Siluriformes, Loricariidae) with comments on its biogeography and dispersal routes
Gabriel de Souza da Costa e Silva 1,†, Fábio Fernandes Roxo 1,‡, Ricardo Britzke 1,§, Claudio Oliveira 1,|
1 Laboratório de Biologia e Genética de Peixes, Departamento de Morfologia, IB-UNESP, Campus de Botucatu, 18618-000, Botucatu, SP, Brazil
† http://zoobank.org/BDE10BBD-857F-4EBD-81C6-1837CC05E60F
‡ http://zoobank.org/EEB03ED0-6A3A-4E11-BE30-4F5642DE5632
§ http://zoobank.org/17DBD9E4-E37A-450A-B258-2CE34A42159C
| http://zoobank.org/2E448127-8820-4F7C-9208-E2AB42ED3153

Corresponding author: Gabriel de Souza da Costa e Silva (gabriel_biota@hotmail.com)

Academic editor: Editor

received 9 January 2014 | accepted 15 April 2014 | Published 29 April 2014
(C) 2014 Gabriel de Souza da Costa e Silva. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
For reference, use of the paginated PDF or printed version of this article is recommended.

Citation: Silva GSC, Roxo FF, Britzke R, Oliveira C (2014) New species of the Pseudancistrus barbatus group (Siluriformes, Loricariidae) with comments on its biogeography and dispersal routes. ZooKeys 406: 1–23. doi: 10.3897/zookeys.406.7011

Abstract

A new species of Pseudancistrus is described from the Tapajós Basin, and assigned to the P. barbatus group by having hypertrophied odontodes along the snout and lacking evertible cheek plates. The new species is distinguished from other species in that group (P. barbatus, P. corantijniensis, P. depressus and P. nigrescens) by its pattern of spots, length and color of snout odontodes, greater head depth, cleithral width, anal-fin spine length, peduncle depth and internares width. Molecular phylogenetic results corroborate placement of the new species in the Pseudancistrus barbatus group which is otherwise distributed in the Xingu Basin and rivers draining the Guyana Shield into the Atlantic Ocean. Topology tests strongly reject alternative hypotheses supporting close relationships with Guyanancistrus, Lithoxancistrus or the species Pseudancistrus pectegenitor, P. sidereus and P. genisetiger. Additionally, we propose two hypotheses on the distribution of the new species in the rio Tapajós, a Brazilian Shield drainage. The first one proposes that ancestral stock of the P. barbatus group was widely distributed throughout rivers draining the Guyana and Brazilian shields, and the species P. zawadzkii and Pseudancistrus sp. L17 are in the limit of the distribution for the group in Tapajós and Xingu rivers. The second hypothesis proposes that ancestral stock of the P. barbatus group was restricted to Guyana Shield rivers, and that headwater capture events permitted several dispersal routs through Guyana and Amazon rivers, permitted that the ancestral lineages of Pseudancistrus sp. L17 and P. zawadzkii reached the rivers of Amazon basin.

Keywords

Ancistrini, freshwater, molecular phylogeny, F-reticulon 4, Brazilian Shield

Introduction

Ancistrini is a highly diverse tribe of the subfamily Hypostominae, with 30 genera (Lujan and Armbruster 2011; Covain and Fisch-Muller 2012; Salcedo 2013) and 252 valid species (Eschmeyer and Fong 2013) widely distributed in the Neotropics from rivers in Panamá to the La Plata system in Argentina. Armbruster (2004a) provided morphological support for the monophyly of Ancistrini based on his extensive analysis of relationships within Loricariidae. Molecular data, however, suggested that Ancistrini is not monophyletic (Montoya-Burgos 1998; Covain and Fish-Muller 2012).

Species of the genus Pseudancistrus Bleeker, 1862 are distributed in the Orinoco, Amazon and Jaguaribe river systems, and rivers draining the Guyana Shield into the Atlantic Ocean. Armbruster (2004a) recognized Pseudancistrus as a monophyletic group and included Guyanancistrus Isbrücker, Seidel, Michels, Schraml & Werner, 2001 and Lithoxancistrus Isbrücker, Nijssen & Cala, 1988 in its synonymy. Based on molecular and morphological data, Chambrier and Montoya-Burgos (2008) defined a subgroup within Pseudancistrus called the Pseudancistrus barbatus group and composed of Pseudancistrus barbatus (Valenciennes, 1840), Pseudancistrus depressus (Günther, 1868), Pseudancistrus nigrescens Eigenmann, 1912, and Pseudancistrus corantijniensis De Chambrier & Montoya-Burgos, 2008. That group was morphologically defined by having hypertrophied odontodes along the snout and lacking evertible cheek plates. Recently, Covain and Fisch-Muller (2012) suggested that Pseudancistrus guentheri (Regan, 1904) and Pseudancistrus kwinti Willink, Mol & Chernoff, 2010 may be added to the Pseudancistrus barbatus group. Covain and Fisch-Muller (2012) also recognized Pseudancistrus as paraphyletic, and restricted the genus by the Pseudancistrus barbatus group. They revalidated the genera Guyanancistrus and Lithoxancistrus, and considered Pseudancistrus pectegenitor Lujan, Armbruster & Sabaj Pérez, 2007, Pseudancistrus sidereus Armbruster, 2004b, and Pseudancistrus genisetiger Fowler, 1941 to represent two separate lineages unrelated to Pseudancistrus. Covain and Fisch-Muller (2012) suggested that these two lineages represent undescribed genera.

In this paper, we present a formal description of a new species of Pseudancistrus from the Tapajós river basin. Additionally, we provide a phylogenetic context for the new species based on analysis of sequence data of F-reticulon 4 nuclear gene, and a brief discussion of biogeographic scenarios that may explain the distribution of the new species in the rio Tapajós and northern Brazilian Shield.

Material and methods
Sampling and morphological analysis

After capture, fish were anesthetized using 1% benzocaine in water, and either preserved in 95% ethanol for molecular studies or fixed in 10% formaldehyde for morphological studies. Vouchers and tissues were deposited in the collection of the Laboratório de Biologia e Genética de Peixes (LBP) and Museu de Zoologia da Universidade de São Paulo (MZUSP), Brazil, Muséum d’histoire naturelle de la ville de Genève (MHNG), Switzerland, Academy of Natural Sciences of Philadelphia (ANSP) and Auburn University (AUM), U.S.A., and Smithsonian Tropical Research Institute (STRI), Panama. Measurements and counts were taken on left side of specimens. Measurements follow Armbruster (2003), and were taken point to point to the nearest 0.1 mm with digital calipers.

DNA sequencing

Total DNA was extracted from ethanol-preserved muscle, fin, and liver samples using the Wizard Genomic DNA Purification Kit (Promega, Madison, Wisconsin, U.S.A.). Partial sequences of F-reticulon 4 were amplified using polymerase chain reaction (PCR) with the following primers from Chiachio et al. (2008): Freticul4-D 5’-AGG CTA ACT CGC TYT SGG CTT TG-3’, Freticul4-R 5’-GGC AVA GRG CRA ART CCA TCT C-3’, Freticul4 D2 5’-CTT TGG TTC GGA ATG GAA AC-3’, Freticul4 R2 5’-AAR TCC ATC TCA CGC AGG A-3’, Freticul4 iR 5’-AGG CTC TGC AGT TTC TCT AG-3’.

Amplifications were performed in a total volume of 12.5 μl containing 1.25 μl of 10X PCR buffer (20 mM Tris-HCl, pH 8.0, 40 mM NaCl, 2 mM Sodium Phosphate, 0.1 mM EDTA, 1 mM DTT, stabilizers, 50% (v/v) glycerol), 0.375 μl MgCl2 (50nM), 0.25 μl dNTPs (2 nM), 0.25 μl (each 5 mM primer), 0.05 μl Platinum® Taq DNA Polymerase (Invitrogen), 1 μl template DNA (50 ng), and 9.075 μl ddH2O. The nuclear markers were amplified in two PCR experiments; the first amplification using the primers Freticul4-D and Freticul4-R for 37–40 cycles (30 sec at 95°C, 30 sec at 48°C, and 135 sec at 72°C); and the second amplification using the primers Freticul4 D2, Freticul4 R2, and Freticul4 iR for 37–40 cycles (30 sec at 95°C, 30 sec at 53–54°C, and 135 sec at 72°C).

The products were then identified on a 1% agarose gel. The PCR products were purified using ExoSap-IT® (USB, Affymetrix Corporation, Cleveland, Ohio) following the manufacturer’s instructions. The purified PCR products were used to make a sequencing PCR using the BigDyeTM Terminator v 3.1 Cycle Sequencing Ready Reaction Kit (Applied Biosystems- Life Technologies do Brasil Ltda, Vila Guarani, SP, Brazil). Subsequently, the amplified DNA was purified again and loaded onto a 3130-Genetic Analyzer automatic sequencer (Applied Biosystems), in the Instituto de Biociências, Universidade Estadual Paulista, Botucatu, São Paulo. Contigs were assembled and edited in BioEdit 7.0.9.0 (Hall 1999). Where uncertainty of nucleotide identity was detected, IUPAC ambiguity codes were applied. All sequences obtained in this study were deposited in GenBank (Table 3).

Sequence alignment and phylogenetic analyses

The DNA sequences were aligned using ClustalW program implemented in DAMBE 5.2.31 (Xia and Xie 2001) and edited in BioEdit 7.0.1 (Hall 1999), using default parameters. The alignments were inspected by eye for any obvious misalignments that were then corrected. Alignment errors only were changed where indels of 1 bp were added to introns of the reticulon gene. The sequence of F-reticulon 4 of the new species was sequenced twice, and a preliminary phylogenetic analysis was performed to control potential sequencing errors involving pseudogenes, paralogous copies or laboratory cross-contamination or mistakes during manipulations of samples. Nucleotide variation was examined using MEGA 5.0 (Tamura et al. 2007). To evaluate the occurrence of substitution saturation, we estimated the index of substitution saturation (Iss) in DAMBE 5.2.31 (Xia and Xie 2001), as described by Xia et al. (2003) and Xia and Lemey (2009).

Maximum-Likelihood (ML) analyses were performed using RAxML Web-Servers (Randomized Accelerated Maximum Likelihood, Stamatakis et al. 2008) which implements a faster algorithm of heuristic search with bootstrap pseudoreplicates (RBS). Bootstrap resampling (Felsenstein 1985) was applied to assess support for individual nodes using 1, 000 replicates. Random starting trees were used for each independent ML tree search and all other parameters were set on default values. The ML analysis was conducted under a Generalized Time Reversible (GTR) model, with Gamma distribution (G) and Invariable Sites according to Modeltest 3.7 results (Posada and Crandall 1998). Gaps were treated as missing data.

Alternative tree topologies were evaluated in the program Treefinder (Jobb et al. 2004) using the Shimodaira and Hasegawa (SH) test (Shimodaira and Hasegawa 1999), the Approximately Unbiased (AU) test (Shimodaira 2002), and the Expected Likelihood Weights (ELW) method (Strimmer and Rambaut 2002). All tests were conducted under ML with a GTR model and Gamma distribution.

Results
Pseudancistrus zawadzkii sp. n.

http://zoobank.org/F244A7A4-253A-49B8-B027-16B640FDBCCF

http://species-id.net/wiki/Pseudancistrus_zawadzkii

Figure 1, Table 1
Holotype.

MZUSP 115056, male, 116.4 mm SL. Brazil: Pará State: municipality of Itaituba: rio Tapajós (Amazon basin), 04°33'09.7"S, 56°17'59.6"W, 11 June 2012, R. Britzke and CEPTA’s team.

Paratypes.

Brazil: Pará State: municipality of Itaituba: LBP 15045 (2 females, 97.9−128.7 mm SL), LBP 17724 (1 female, 87.5 mm SL), collected with holotype; LBP 16195 (1 male, 116.4 mm SL), rio Tracuá (trib. rio Tapajós), 04°28'11.2"S, 56°17'01.1"W.

Diagnosis.

Pseudancistrus zawadzkii is distinguished from all congeners, except species of the Pseudancistrus barbatus group, by presence of hypertrophied odontodes along the snout margin and the lack of evertible cheek plates. It further differs from two members of that group, Pseudancistrus barbatus and Pseudancistrus depressus, by having whitish spots that abruptly increase in size between the head (diameter 1.1−1.3 mm) and body (diameter 2.6−3.0 mm) (vs. whitish spots very small on whole body less than 1 mm), and snout odontodes yellowish (vs. snout odontodes reddish-brown). The new species differs from the other two members of the Pseudancistrus barbatus group, Pseudancistrus corantijniensis and Pseudancistrus nigrescens, by having odontodes along margin of snout increasing gradually in length from posterior of snout tip to cheek (vs. length of snout odontodes more uniform, smaller on tip of snout) and by having odontodes relatively longer on the most posterior portion of the nonevertible check plates (Fig. 1) (vs. odontodes shorter) (see fig. 3 in Chambrier and Montoya-Burgos 2008 for comparison of both characters). Additionally, Pseudancistrus zawadzkii differs from Pseudancistrus nigrescens by having rounded spots that do not cover more than one plate along the body (vs. whitish spots that become hazier along the body and can cover more than one plate, see Pseudancistrus nigrescens in fig. 3 in Chambrier and Montoya-Burgos (2008). Moreover, Pseudancistrus zawadzkii is distinguished by having a greater head depth, 67.0−72.7% of HL (vs. 38.3−44.9% of HL in Pseudancistrus barbatus; 40.6−53.0% of HL in Pseudancistrus corantijniensis, data based on original description; and 52.5−56.6% of HL in Pseudancistrus nigrescens); greater cleithral width, 35.2−38.0% of SL (vs. 31.1−32.7% of SL in Pseudancistrus nigrescens and 29.7−33.4% of SL in Pseudancistrus barbatus); shorter distance between posteromedial margin of supraoccipital and origin of dorsal-fin, 6.7−9.2% of SL (vs. 10.4−11.6% of SL in Pseudancistrus nigrescens); greater anal-fin spine length, 11.9−13.8% of SL (vs. 7.3−10.4 of SL in Pseudancistrus barbatus); greater peduncle depth, 12.5−14.2% of SL (vs. 9.3−10.4 of SL in Pseudancistrus barbatus); and wider internares distance, 12.7−16.6% of HL (vs. 9.9−11.8% of HL in Pseudancistrus barbatus). Pseudancistrus zawadzkii differs from Pseudancistrus kwinti and Pseudancistrus guentheri, two probable members of Pseudancistrus barbatus group by having whitish spots of the body (vs. body mottled or with bars, in Pseudancistrus kwinti and body plates dark at the base and pale along the edges, in Pseudancistrus guentheri).

Figure 1.

Pseudancistrus zawadzkii, MZUSP 115056, holotype, male, 116.4 mm SL; Pará State, Tapajós river basin, Brazil.

Figure 2.

Maximum-likelihood tree based on nuclear gene sequence F-reticulon 4 (-lnL = 11470.59). Numbers next to nodes are bootstrap values based on 1, 000 pseudoreplicates. Values below 50% are not shown.

Description.

Morphometric data presented in Table 1. In lateral view, dorsal profile convex from snout tip to dorsal-fin origin; straight, gradually descending from dorsal-fin origin to posterior insertion of adipose fin; straight, steeply ascending to insertion of caudal fin; ventral profile flat from snout tip to anal-fin origin; shallowly concave from anal-fin insertion to lower caudal-fin spine; greatest body depth at dorsal-fin origin. In dorsal view, greatest body width across cleithral region; snout broadly elliptical; body progressively narrowed from opercular region to caudal fin. Cross-section of body between pectoral and pelvic fins rounded dorsally and flattened ventrally; cross-section of caudal peduncle ellipsoid.

Table 1.

Morphometric data for Pseudancistrus zawadzkii.

Pseudancistrus zawadzkii n = 5
Holotype Range Mean SD
Standard length (SL) 116.4 128.7−87.5 109.5
Percents of SL
Predorsal length 43.3 43.1−46.1 44.5 1.3
Head length 36.6 32.9−37.8 36.3 1.9
Head-dorsal length 6.7 6.7−9.2 8.1 1.2
Cleithral width 35.2 35.2−38.0 36.7 1.2
Head pectoral length 30.5 29.6−32.2 30.9 0.9
Thorax length 23.5 21.2−23.5 22.5 1.1
Pectoral-spine length 31.5 31.3−33.2 31.9 0.7
Abdominal length 24.2 22.6−26.1 24.3 1.3
Pelvic-spine length 28.4 25.6−28.4 27.2 1.2
Post-anal length 31.2 29.6−31.2 30.5 0.7
Anal-fin spine length 12.5 11.9−13.8 12.6 0.7
Dorsal pectoral depth 27.3 26.6−30.7 28.6 1.7
Dorsal spine length 24.7 24.7−29.9 27.5 2.3
Dorsal pelvic depth 22.9 22.1−26.4 24.1 1.7
Dorsal-fin base length 31.2 29.1−31.2 30.0 1.0
Dorsal-adipose distance 11.2 10.5−13.7 11.6 1.2
Adipose-spine length 7.8 6.79−8.78 7.8 0.7
Dorsal adipose caudal distance 11.7 11.7−15.6 13.7 1.7
Caudal peduncle depth 12.5 12.5−14.2 13.3 0.6
Ventral adipose caudal distance 22.9 22.9−25.3 23.9 1.0
Adipose anal distance 21.3 18.5−21.3 19.8 1.0
Dorsal-anal distance 16.0 15.8−17.8 16.8 0.8
Pelvic-dorsal distance 29.5 22.0−29.5 22.5 2.7
Percents of head length (HL)
Head-eye length 29.4 28.1−30.1 29.1 0.8
Orbital diameter 14.6 14.5−18.8 15.8 1.7
Snout length 63.2 63.2−70.5 66.8 3.1
Internares width 14.4 12.7−16.6 14.4 1.4
Minimal interorbital distance 28.8 28.8−35.7 32.2 2.5
Mouth length 53.8 52.0−60.6 55.7 3.5
Barbel length 14.0 7.6−14.0 10.6 2.6
Dentary tooth cup length 17.6 17.0−19.6 18.5 1.1
Premaxillary tooth cup length 17.8 17.2−19.2 18.2 0.7
Head depth 68.9 67.0−72.7 68.8 2.3

Body almost entirely covered by plates; ventral portions of head and abdomen and dorsal-fin base naked. Five lateral rows of dermal plates, dorsal plates 21−24, lateral mid-dorsal plates 19−21, lateral median plates 22−24, lateral mid-ventral plates 21−24, lateral ventral plates 18−20. Three predorsal plates; eight plates below dorsal-fin base; four plates between dorsal fin and adipose fin; five rows of plates on caudal peduncle. Dorsal spinelet present.

Body plates and cleithrum have minute odontodes. Odontodes slightly hypertrophied on pectoral-fin spines, becoming gradually larger towards tips. Numerous yellowish hypertrophied odontodes along lateral margins of head including snout; odontodes small on tip of snout, increasing gradually in length from anterolateral margin of snout to cheeks; longest odontodes on posterior most portion of non-evertible cheek plates. Eyes small (orbital diameter 14.5−18.8% of HL), dorsolaterally positioned. Oral disk transversely ellipsoid. Lower lip not reaching transverse line between gill openings. Lower lip covered with numerous small papillae. Maxillary barbel developed. Mouth relatively large. Premaxillary teeth 40−61 per ramus; dentary teeth 28−69 per ramus. Teeth bifid, medial cusp large and rounded, lateral cusp minute and pointed. Wide jaws, dentary bones forming an oblique angle, premaxillary bones almost co-linear.

Dorsal fin II, 7, origin approximately at midpoint between pectoral- and pelvic-fin origins, last dorsal-fin ray reaching adipose fin when depressed. Pectoral fin I, 6, spine tip curved inward, covered with enlarged odontodes distally; depressed tip reaching one-third length of pelvic-fin spine. Pelvic fin I, 5, spine tip curved inward, almost reaching anal-fin origin when depressed. Anal fin I, 5, spine tip straight, reaching seventh plate posterior to its origin. Caudal fin I, 7−I, 7, distal margin concave, inferior lobe longer than superior. Adipose fin with lightly curved spine, preceded by single median preadipose plate.

Color in life.

Ground color dark greenish-brown on dorsum and sides of body, becoming dark brown posteriorly, and lighter brown ventrally. Anterior portion of head to posterior margin of orbits with many small, crowded, yellow spots; spots becoming abruptly larger on posterior portion of head, continuing on body, becoming slightly and gradually larger towards caudal peduncle. Dorsal plate series usually with two large spots per plate. Mid-dorsal plates usually with one large spot per plate. Lateral median plates with one large spot per plate. Mid-ventral plates and ventral plates with one large spot per plate. Dorsal-fin spine, rays and membranes with large round large spots. Adipose-fin with two large spots on spine and membrane. Pectoral, pelvic, anal and caudal fin with numerous and similarly sized yellow spots. Hypertrophied odontodes along head margin yellowish (Fig. 3).

Figure 3.

Pseudancistrus zawadzkii, live specimen, LBP 15045, paratype, female, 128.7 mm SL, Tapajós river, Pará State, Brazil.

Color in alcohol.

Similar to pattern described for living individuals, but with ground color dark brown, and spots pale tan (Fig. 1).

Sexual dimorphism.

Males possess a papilla posterior to urogenital opening, an attribute absent in females. Both sexes in Pseudancistrus zawadzkii exhibit highly hypertrophied odontodes along snout margin, similar to others species of Pseudancistrus (Armbruster 2004b). In some loricariid species of genus Pareiorhaphis those hypertrophied odontodes may be sexually dimorphic (Pereira et al. 2007), an attribute not observed in the new species Pseudancistrus zawadzkii.

Etymology.

Specific name is in honor of Cláudio Henrique Zawadzki, professor at Universidade Estadual de Maringá (UEM), Maringá, Paraná State, Brazil, in recognition of his dedication and remarkable contributions to the study of the family Loricariidae.

Distribution.

Pseudancistrus zawadzkii is known from rio Tapajós (04°33'10"S, 56°18'W) and rio Tracuá (04°28'11"S, 56°17'01"W), municipality of Itaituba, all from rio Tapajós basin, Pará State, Brazil. (see Fig. 4 for distribution map of type species localities).

Figure 4.

Map showing the type locality (red square) of Pseudancistrus zawadzkii at rio Tapajós, 04°33'09.7"S, 56°17'59.6"W, and paratype locality (black circle) at rio Tracuá, Tapajós river basin, 04°28'11.2"S, 56°17'01.1"W.

Ecological notes.

The rio Tapajós, and rio Tracuá where Pseudancistrus zawadzkii occurs are clear water rivers, varying from medium to large size, with rocky outcrops forming small waterfalls and substrates of rocks and sand (Fig. 5).

Figure 5.

a Habitat at type locality of Pseudancistrus zawadzkii: rio Tapajós, municipality of Itaituba, Pará State, Brazil b habitat at paratype locality: rio Tracuá, Tapajós river basin, municipality of Itaituba, Pará State, Brazil.

Phylogenetic analysis

Partial sequences of the nuclear gene F-reticulon 4 (RTN4) were obtained in this study and from GenBank for 44 specimens representing 35 Loricariidae species and the new species Pseudancistrus zawadzkii (Table 3). We included samples of the four lineages of Pseudancistrus proposed by Covain and Fisch-Muller (2012) to test whether Pseudancistrus zawadzkii is part of the Pseudancistrus barbatus group. Corydoras oiapoquensis Nijssen, 1972 (Callichthyidae) was used to root the phylogeny. Additionally, samples of Delturinae (Hemipsilichthys gobio Lutken, 1874) and Loricariinae (Harttia guianensis Rapp Py-Daniel & Oliveira, 2001) were included in the analysis as additional outgroups. The combined sequence data resulted in a matrix with 2, 318 base pairs (bp), out of which 1, 079 were conserved and 896 were variable. The estimated index of substitution saturation (Iss) performed in DAMBE 5.2.31 (Xia and Xie 2001) showed that the data was not saturated (i.e. Iss.c value greater than Iss).

Evolutionary relationships among species of Pseudancistrus sensu lato and other members of Otothyrini are similar between our ML phylogenetic tree (-lnL = 11470.59) and the one proposed by Covain and Fisch-Muller (2012). In our analysis, the genus Pseudancistrus is paraphyletic with species assigned to three different lineages. The first lineage is monotypic, composed of Pseudancistrus genisetiger, sister to Hemipsilichthys gobio, an outgroup taxon. Covain and Fisch-Muller (2012) suggested that Pseudancistrus genisetiger represents an undescribed genus within Delturinae. The second lineage of Pseudancistrus (Pseudancistrus sidereus + Pseudancistrus pectegenitor) is sister to a species of Lithoxus Eigenmann, 1910; Covain and Fisch-Muller (2012) suggested that the two species represent an undescribed genus or may be included in Lithoxus. The third lineage is composed of members of the Pseudancistrus barbatus group (Pseudancistrus depressus, Pseudancistrus barbatus, Pseudancistrus corantijniensis, Pseudancistrus nigrescens, the new species Pseudancistrus zawadzkii and an undescribed species from the rio Xingu known as L17 among hobbyists). The Pseudancistrus barbatus group forms a polytomy with almost all species analyzed in the ingroup (Fig. 3), and was recognized by Covain and Fisch-Muller (2012) as true Pseudancistrus since this group includes the type species Pseudancistrus barbatus. Additionally, Covain and Fisch-Muller (2012) revalidated two genera for several species previously assigned to Pseudancistrus, − Lithoxancistrus (for Pseudancistrus orinoco (Isbrücker, Nijssen & Cala, 1988)) and Guyanancistrus (for Pseudancistrus sp., Pseudancistrus brevispinis (Heitmans, Nijssen & Isbrücker, 1983), Pseudancistrus longispinis (Heitmans, Nijssen & Isbrücker, 1983) and Pseudancistrus niger (Norman 1926)). Our analysis also supports the recognition and composition of those two genera.

Discussion
Taxonomy and phylogenetic comparison

The new species Pseudancistrus zawadzkii possesses hypertrophied odontodes along the snout margin and lacks evertible cheek plates. Armbruster (2004b) identified that among Ancistrini, only Pseudolithoxus, Lithoxancistrus, and some members of Guyanancistrus and Pseudancistrus share the presence of hypertrophied odontodes along the snout in both sexes. Armbruster (2004b) also suggested that the species of Pseudancistrus that present this characteristic are derived; those species correspond to the Pseudancistrus barbatus group proposed by Chambrier and Montoya-Burgos (2008). Therefore, the new species described herein is a typical member of this group sensu Covain and Fisch-Muller (2012). Our phylogenetic analysis (Fig. 3) supports that hypothesis, and places the new species in a polytomy with Pseudancistrus corantijniensis, Pseudancistrus sp. L17 (undescribed species) and Pseudancistrus nigrescens, within the Pseudancistrus barbatus group. Our likelihood-based tests strongly rejected alternative topologies placing the new species in Lithoxancistrus, Guyanancistrus or with other species of Pseudancistrus apart from the Pseudancistrus barbatus group (see Table 2).

Table 2.

Likelihood-based tests for alternative topologies. SH and AU are probability values obtained from the Shimodaira-Hasegawa and the Approximately Unbiased tests (Shimodaira 2002). Asterisks denote significant values (P<0.05 for SH and P<0.01 for AU and ELW) that imply the topology is rejected.

Test Topology - Ln L ∆ - Ln L ELW SH AU
ML 11910.81
1 Pseudancistrus zawadzkii sister group to Pseudancistrus pectegenitor + Pseudancistrus sidereus a 11952.41 41.60 <0.001* 0.021* <0.001*
2 Pseudancistrus zawadzkii sister group to Guyanancistrus members a 11962.24 51.43 <0.001* 0.011* <0.001*
3 Pseudancistrus zawadzkii sister group to Lithoxancistrus members a 11966.25 55.44 <0.001* <0.001* <0.001*
4 Pseudancistrus zawadzkii sister group to Pseudancistrus genisetiger a 12033.30 122.49 <0.001* <0.001* <0.001*

a The alternative topology was defined as the ML tree forcing the desired relationship.

Table 3.

Taxa list, specimen and sequence data analyzed in the present study (n=44). Institutional acronyms follow Fricke and Eschmeyer (2013).

Species Catalog Number Field Number GenBank Nº F-RTN4 Ref.
Corydoras oiapoquensis MHNG 2682.023 GF06-186 GU210997 Alexandrou et al. (2011)
Hemipsilichthys gobio LBP 2368 15363 EU817547 Chiachio et al. (2008)
Harttia guianensis MHNG 2643.016 GF00–351 FJ013232 Chiachio et al. (2008)
Hypostomus sp. MHNG 2721.062 PE08-198 JN855790 Covain and Fisch-Muller (2012)
Hypostomus boulengeri (Eigenmann & Kennedy, 1903) MHNG 2519.23 ASU7 EU817560 Chiachio et al. (2008)
Hypostomus gymnorhynchus (Norman, 1926) MHNG 2621.098 SU01-160 JN855789 Covain and Fisch-Muller (2012)
Ancistrus cirrhosis (Valenciennes, 1836) MHNG 2645.037 MUS 202 HM623638 Rodriguez et al. (2011)
Dekeyseria picta (Kner, 1854) MHNG 2588.046 MUS 162 JN855755 Covain and Fisch-Muller (2012)
Dekeyseria scaphirhyncha (Kner, 1854) AUM 43874 V5528 JN855756 Covain and Fisch-Muller (2012)
Hemiancistrus medians (Kner, 1854) MHNG 2664.078 GF00-084 JF747011 Fisch-Muller et al. (2012)
Guyanancistrus brevispinis MHNG 2725.099 GF00-103 JN855772 Covain and Fisch-Muller (2012)
Guyanancistrus brevispinis MHNG 2621.073 SU01-121 JN855773 Covain and Fisch-Muller (2012)
Guyanancistrus longispinis MHNG 2725.100 GF99-204 JN855757 Covain and Fisch-Muller (2012)
Guyanancistrus niger MHNG 2722.089 GF99-185 JN855759 Covain and Fisch-Muller (2012)
Guyanancistrus sp. MHNG 2679.099 MUS 300 JN855774 Covain and Fisch-Muller (2012)
Hopliancistrus tricornis Isbrücker & Nijssen, 1989 MHNG 2588.051 MUS 146 JN855765 Covain and Fisch-Muller (2012)
Lasiancistrus aff. caucanus MHNG 2586.043 MUS 118 JN855786 Covain and Fisch-Muller (2012)
Lasiancistrus heteracanthus (Günther, 1869) MHNG 2613.037 CA 013 JN855787 Covain and Fisch-Muller (2012)
Lasiancistrus planiceps (Meek & Hildebrand, 1913) STRI-01805 Stri 3526 JN855785 Covain and Fisch-Muller (2012)
Lasiancistrus saetiger Armbruster 2005 MHNG 2602.016 BR98-148 JN855754 Covain and Fisch-Muller (2012)
Lasiancistrus schomburgkii (Günther, 1869) MHNG 2651.009 PE08-719 JN855782 Covain and Fisch-Muller (2012)
Lasiancistrus schomburgkii MHNG 2651.068 GY04-308 JN855783 Covain and Fisch-Muller (2012)
Lasiancistrus schomburgkii MHNG 2710.055 PE08-277 JN855784 Covain and Fisch-Muller (2012)
Lasiancistrus tentaculatus Armbruster, 2005 MhnG uncat. MUS 573 JN855788 Covain and Fisch-Muller (2012)
Lithoxus lithoides Eigenmann, 1912 MHNG 2651.087 GY04-136 JN855777 Covain and Fisch-Muller (2012)
Lasiancistrus pallidimaculatus Boeseman, 1982 MHNG 2621.066 SU01-096 JN855778 Covain and Fisch-Muller (2012)
Lasiancistrus planquettei Boeseman, 1982 MHNG 2722.060 GF03-055 JN855779 Covain and Fisch-Muller (2012)
Lithoxancistrus orinoco AUM 43725 V5246 JN855766 Covain and Fisch-Muller (2012)
Lithoxancistrus orinoco AUM 42179 P4527 JN855767 Covain and Fisch-Muller (2012)
Pseudancistrus barbatus MHNG 2653.059 GF00-074 JN855761 Covain and Fisch-Muller (2012)
Pseudancistrus corantijniensis MHNG 2672.092 SU05-296 JN855781 Covain and Fisch-Muller (2012)
Pseudancistrus depressus MHNG 2674.026 SU05-020 JN855780 Covain and Fisch-Muller (2012)
Pseudancistrus genisetiger MHNG 2593.061 MUS 173 JN855764 Covain and Fisch-Muller (2012)
Pseudancistrus nigrescens MHNG 2651.069 GY04-313 JN855770 Covain and Fisch-Muller (2012)
Pseudancistrus nigrescens MHNG 2650.087 GY04-260 JN855771 Covain and Fisch-Muller (2012)
Pseudancistrus pectegenitor AUM 42202 V5363 JN855769 Covain and Fisch-Muller (2012)
Pseudancistrus pectegenitor ANSP 182801 V5433 JN855768 Covain and Fisch-Muller (2012)
Pseudancistrus sidereus AUM 43443 P4871 JN855775 Covain and Fisch-Muller (2012)
Pseudancistrus sidereus AUM 42180 P4537 JN855776 Covain and Fisch-Muller (2012)
Pseudancistrus zawadzkii LBP 15045 61628 KJ028080 Present study
Pseudancistrus sp. L17 MHNG 2586.046 MuS 132 JN855763 Covain and Fisch-Muller (2012)
Pseudolithoxus cf. kelsorum MHNG 2679.043 MUS 260 JN855762 Covain and Fisch-Muller (2012)
Pseudancistrus dumus (Armbruster & Provenzano, 2000) MHNG 2708.080 MUS 288 JN855760 Covain and Fisch-Muller (2012)
Pseudancistrus tigris (Armbruster & Provenzano, 2000) AUM 42215 V5292 JN855758 Covain and Fisch-Muller (2012)

Pseudancistrus zawadzkii, Pseudancistrus corantijniensis, and Pseudancistrus nigrescens share the presence of whitish colored snout odontodes and a dark colored body covered with white spots. The new species can be easily distinguished from Pseudancistrus corantijniensis and Pseudancistrus nigrescens by having large hypertrophied odontodes on the posteriormost portion of the non-evertible check plates, and marginal odontodes that increase gradually in length from tip of snout to cheeks. Pseudancistrus barbatus and Pseudancistrus depressus share reddish-brown snout odontodes, a probable synapomorphy, and are the sister group to Pseudancistrus zawadzkii, Pseudancistrus corantijniensis and Pseudancistrus nigrescens. Covain and Fisch-Muller (2012) suggested that Pseudancistrus guentheri and Pseudancistrus kwinti may be added to the Pseudancistrus barbatus group. However, those two species have a different body coloration pattern (Chambrier and Montoya-Burgos 2008; see fig. 3); in Pseudancistrus kwinti the body is either mottled or with bars, while in Pseudancistrus guentheri the body plates are dark at the base and pale along the edges (Willink et al. 2010).

Biogeography and dispersal routes

Named species of the Pseudancistrus barbatus group are distributed in rivers draining to Guyana Shield into the Atlantic Ocean, and the new species described herein is from Tapajós river draining of Brazilian Shield into the Amazon. In our phylogeny, species from the eastern Guyana Shield (Pseudancistrus barbatus and Pseudancistrus depressus) form a clade sister to a group composed of species from the western Guyana Shield (Pseudancistrus corantijniensis and Pseudancistrus nigrescens) and Amazon basin (Pseudancistrus zawadzkii and Pseudancistrus sp. L17) (Fig. 6). Therefore, based on this interpretation and our results of phylogenetic analysis, we suggested two hypotheses that could generate the distribution pattern of Pseudancistrus barbatus group extant-species. The first hypothesis is that the ancestral stock of the Pseudancistrus barbatus group was widely distributed through all Guyana Shield rivers and Amazon Brazilian Shield rivers, and the species Pseudancistrus zawadzkii and Pseudancistrus sp. L17 are in the limit of the distribution for the group in Tapajós and Xingu rivers, respectively. Gaston (1998) and Hubbell (2001) suggested that when allopatric divergence is the dominant mode of speciation, many daughter species are expected to arise from geographically widespread ancestral species. This is a reasonable interpretation given that named species of the group are widespread in rivers draining Guyana Shield into the Atlantic Ocean; the new species Pseudancistrus zawadzkii are from Tapajós river drainage of Amazon Brazilian Shield; the possible new and undescribed species Pseudancistrus sp. L17 are from Xingu river which also belongs to drainages of Amazon Brazilian Shield and others possible new and undescribed species of Pseudancistrus barbatus group may be present in drainages of Guyana Shield into Amazon (Pseudancistrus sp. L220 from rio Paru; Pseudancistrus sp. L251 from rio Cuminá (rio Erepecuru); Pseudancistrus sp. L383 from rio Trombetas; Pseudancistrus sp. L440 from rio Jatapu (Seidel 2008)). However, phylogenetic and taxonomic studies are necessary to confirm that the latter undescribed species belong to Pseudancistrus barbatus group.

Figure 6.

Distribution and phylogenetic relationships of species of the Pseudancistrus barbatus group based on F-reticulon 4 gene. Based in our first hypothesis of extand-species distribution of this group the ancestral was widespread through all Guyana Shield rivers and Amazon Brazilian Shield rivers, the species Pseudancistrus zawadzkii and Pseudancistrus sp. L17 are in the limited distribution of this group in Tapajós and Xingu rivers, drainages of Brazilian Shield into Amazon.

The second hypothesis suggests that the ancestral stock of Pseudancistrus barbatus group should have been distributed through Guyana Shield rivers and there existed several dispersal routes through Guyana and Amazon rivers, permitting that the ancestral lineages of Pseudancistrus sp. L17 and Pseudancistrus zawadzkii reached the rivers of Amazon basin (see Fig. 7 for dispersal routes). Therefore, examples of connections and areas of movement among Guyana drainages and the north tributaries of Amazon basin was reported by several authors: (1) the Rupununi portal, an example of seasonal connection among Takutu and Rupununi rivers (Armbruster and Werneke 2005; Lujan and Armbruster 2011; De Souza et al. 2012); (2) the corridor among Sipalawini (Corantijn river basin) and the Paru do Oeste (Amazon basin), also connected only in the rainy season (Nijssen 1972; Lujan and Armbruster 2011); (3) the Cassiquiare Canal, a large and permanently navigable corridor between the upper Orinoco and the upper Rio Negro (Amazon) (Chernoff et al. 1991; Buckup 1993; Schaefer and Provenzano 1993; Lovejoy and Araújo 2000; Turner et al. 2004; Moyer et al. 2005; Willis et al. 2007; Winemiller et al. 2008; Winemiller and Willis 2011); (4) Proto-Berbice, a river system which had its headwaters in an ancient mountain range draining northward to Guyana system (Rupununi and Essequibo rivers) and suffered a major sedimentation, erosion and/or corrosion of the highlands and at the end of the Pliocene had its head waters captured by the Amazon system; (5) the Atlantic coastal corridors resulted in a coastal marine corridor with reduced salinity due to the westerly Amazon River discharge, coastal junctions during times of marine regressions and expanded coastal plains, and stream captures (Eigenmann 1912; Boeseman 1968; Cardoso and Montoya-Burgos 2009; Lujan and Armbruster 2011).

Figure 7.

Hypothesized dispersal routs between basins of the Guiana Shield and Amazon Shield of ancestror of the Pseudancistrus barbatus group (based on Lujan and Armbruster 2011). Our second hypothesis of the Pseudancistrus barbatus group extent-species distribution is based on the assumption of a widespread ancestral through all Guyana Shield rivers and dispersal events enable the ancestor of Pseudancistrus zawadzkii (red star) and Pseudancistrus sp. L17 (yellow star) to colonize the Amazon Brazilian Shield rivers in Tapajós and Xingu rivers.

Additionally, the mainstream of Amazon River can act as a permeable barrier for endemic taxa on the respective Guiana and Brazilian shields. Several genera known to tolerate more lowland conditions (e.g. Ancistrus Kner, 1854, Lasiancistrus, and Hypostomus Lacepéde, 1803) may be able to cross the Amazon basin, but such dispersal is unlikely among most species of Ancistrini (Lujan and Armbruster 2011). Also historically, epochs of cooler climate, as during glacial periods, could produce reduced precipitation, marine regressions, expansion of the coastal plain, and deepening of river channels. During such arid periods, rapids would have been more widespread, and deep-channel habitats that may currently work as barriers to fish dispersal would have been reduced (Schubert et al. 1986; Latrubesse and Franzinelli 2005; Lujan and Armbruster 2011). Drier climate will hardly change the Amazon river in a rapid, but can reduce its water flow allowing fish dispersal. Among Neotropical fishes Psectrogaster essequibensis Günther, 1864 (Characiformes: Curimatidae; see Vari (1987)), Parotocinclus aripuanensis Garavello, 1988, and Pseudancistrus britskii Boeseman, 1974 (Loricariidae: Hypoptopomatinae) are species known to support dispersal via the northern Brazilian Shield.

Also, the dispersal routes around adjacent drainages of southern and northern Guyana Shield and northern parts of the Brazilian Shield could allow the dispersal of the ancestral form of Pseudancistrus zawadzkii and Pseudancistrus sp. L17, as well as others ancestral species of the Pseudancistrus barbatus group and even species of Ancistrini (Lujan and Armbruster 2011). The movement of fish species around adjacent drainages could be explained by two hydrographic reconfiguration process: headwater capture events (geomorphological phenomenon) and marine regressions (sea level oscillation). Changes in the earth’s surface involving changes in the courses of rivers, as stream captures, portions of tributaries of a river in a watershed could be “captured” by adjacent basins resulting in isolated populations and at the same time letting species to move, or disperse, between adjacent drainages (Almeida and Carneiro 1998; Bishop 1995; Wilkinson et al. 2006, 2010; Roxo et al. 2012). Montoya-Burgos (2003) hypothesized that dispersal (followed by allopatric population divergence) among Amazon and North-eastern coastal rivers probably occurred by temporary connections between adjacent rivers during periods of lower sea level about 6–5 Ma (see fig. 5 in Montoya-Burgos 2003). Cardoso and Montoya-Burgos (2009) suggested the same process to explain dispersal of Pseudancistrus brevispinis along coastal rivers of the Guyana. Therefore, temporary lowland connections and headwater capture events, together with the previously related hypothesis of colonization routes, likely explain the widespread distribution of the Pseudancistrus barbatus group extant species on Guyana and Brazilian Shields, as well as how the ancestral lineages of Pseudancistrus zawadzkii and Pseudancistrus sp. L17 reached the drainages of the northern Brazilian Shield, in Tapajós and Xingu rivers.

Comparative material

Pseudancistrus barbatus (Valencienes, 1840): ANSP 177366, 2, 76.5−103.7 mm SL, Burro Burro river, Water Dog Falls, Essequibo river basin, Guyana. ANSP 189119, 3, 75.1−151.5 mm SL, Lawa river, Sipalawini, Suriname. Pseudancistrus brevispinis (Heitmans, Nijssen & Isbrücker, 1983): ANSP 189128, 3, 56.8−125.7 mm SL, Marowini river, Sipalawini, Suriname. Pseudancistrus nigrescens Eigenmann, 1912: ANSP 177379, 5, 96.4−133.5 mm SL, Burro Burro river, Water Dog Falls, Essequibo river basin, Guyana. Pseudancistrus orinoco (Isbrücker, Nijssen & Cala, 1988): ANSP 160600, 6, 68.0−78.5 mm SL, Orinoco river, Venezuela. Pseudancistrus pectegenitor Lujan, Armbruster & Sabaj, 2007: ANSP 190755, 1, 206, 2 mm SL, Ventuari river, Orinoco river basin, Venezuela. Pseudancistrus sidereus Armbruster, 2004b: ANSP 185321, 4, 148.6−154.1 mm SL, Casiquiari river, Venezuela. Pseudancistrus sp. L17: LBP 16551, 2, 75.3−101.0 mm SL; rio Xingu, Altamira, Pará State, Amazon river basin, Brazil. ANSP 193074, 3, 51.7−188.7 mm SL, Xingu river, Altamira, Pará State, Amazon river basin, Brazil. Pseudancistrus sp. ANSP 191153, 6, 49.2−75.7 mm SL, Ventuari river, Orinoco river basin, Venezuela.

Acknowledgements

We are grateful to M.H. Sabaj Pérez (Academy of Natural Sciences of Philadelphia) and J.S. Albert (University of Louisiana at Lafayette) for loans of specimens and curatorial assistance; to CEPTA’s team (Centro de Pesquisa Treinamento em Aquicultura - formerly Centro Nacional de Pesquisa e Conservação de Peixes Continentais) for help collecting specimens; B. Waltz and again to M.H. Sabaj Pérez for reading the manuscript and providing valuable suggestions. Fishes collected in accordance with Brazilian laws, under a permanent scientific collecting license issued to Dr. Claudio Oliveira by IcmBio/CEPTA. Research supported by Brazilian agencies FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, proc. 2010/01610-9 to FFR, proc. 2012/01622-2 to GSCS and proc. 2011/00269-4 to RB), MCT/CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) and CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior). Comparative material from rio Xingu made available by iXingu Project funded by the U.S. National Science Foundation (DEB-1257813).

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