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Ecomorphological differences between Rhamdia (Bleeker, 1858) populations from the Iguaçu River basin

Abstracts

Morphological and genetic evidences suggest that Rhamdia branneri and Rhamdia voulezi, currently considered synonymous of Rhamdia quelen, are in fact two valid species. Furthermore, in the taxonomic revision of R. quelen, no exemplars from the Iguaçu River were examined, which makes the synonymy doubtful. Considering the two species as valid, it was hypothesized that R. branneri and R. voulezi have ecomorphological differences, with the objective to verify if they can be considered ecologically distinct. Ecomorphological characterization was conducted using ecomorphological indices. For statistical analysis, a Principal Component Analysis (PCA), a Multiresponse Permutation Procedure (MRPP), and a Discriminant Analysis (DA) were performed. The ordination provided by the PCA evidenced ecomorphological separation, with R. branneri having morphological aspects related to benthic fishes, and R. voulezi having morphological characteristics related to pelagic and lentic habitats. The DA results confirmed the morphological tendencies found in the PCA, and the MRPP showed significant statistical differences between the ecomorphology of Rhamdia species. In this way, the initial hypothesis can be corroborated. These results allied to information about diet, genetics, and reproduction can be helpful for the elucidation of the taxonomic status of R. branneri and R. voulezi.

endemism; Heptapteridae; Rhamdia voulezi; Rhamdia branneri; Rhamdia quelen; ecomorphology


Evidências morfológicas e genéticas sugerem que Rhamdia branneri e Rhamdia voulezi, atualmente consideradas sinônimas de Rhamdia quelen, são, de fato, duas espécies válidas. Adicionalmente, na revisão taxonômica de R. quelen nenhum exemplar do rio Iguaçu foi examinado, o que torna a sinonímia duvidosa. Considerando as duas espécies como válidas, foi testada a hipótese de que R. branneri e R. voulezi possuem diferenças ecomorfológicas, com o objetivo de verificar se elas podem ser consideradas ecologicamente distintas. A caracterização ecomorfológica foi conduzida utilizando os índices ecomorfológicos. Para a análise estatística foram feitas Análise de Componentes Principais (ACP), Procedimento de Permutação Multiresposta (PPMR) e Análise Discriminante (AD). A ordenação proveniente da ACP evidenciou separação ecomorfológica, com R. branneri possuindo aspectos morfológicos relacionados a peixes bentônicos e R. voulezi possuindo características morfológicas relacionadas a habitats pelágicos e lênticos. Os resultados da AD confirmaram as tendências morfológicas encontradas na ACP, e o PPMR mostrou diferenças estatísticas significativas entre as espécies de Rhamdia. Dessa maneira, a hipótese inicial pôde ser corroborada. Esses resultados, aliados a informações sobre a dieta, genética e reprodução, podem ser úteis para a elucidação do status taxonômico de R. branneri e R. voulezi.

endemismo; Heptapteridae; Rhamdia voulezi; Rhamdia branneri; Rhamdia quelen; ecomorfologia


Introduction

The Iguaçu River drainage is the largest basin among the rivers of Paraná State (Eletrosul 1978ELETROSUL. 1978. O impacto ambiental da ação do homem sobre a natureza – rio Iguaçu, Paraná, Brasil: reconhecimento da ictiofauna, modificações ambientais e usos múltiplos dos reservatórios. Florianópolis, p.33.), and is known by its high endemism, estimated in 69.7% of the total of species (Baumgartner et al. 2012BAUMGARTNER, G., PAVANELLI, C.S., BAUMGARTNER, D., BIFI, A.G., DEBONA, T. & FRANA, V.A. 2012. Peixes do Baixo Rio Iguaçu. Eduem, Maringá, p.203.). This unique condition is probably caused by the basin isolation propitiated by the Iguaçu falls (Baumgartner et al. 2012BAUMGARTNER, G., PAVANELLI, C.S., BAUMGARTNER, D., BIFI, A.G., DEBONA, T. & FRANA, V.A. 2012. Peixes do Baixo Rio Iguaçu. Eduem, Maringá, p.203.) and a series of smaller falls on its main channel. Thus, the river has great hydroelectric potential, which has been explored for over thirty years, resulting in a large sequence of dams, whose reservoirs occupy at least 41% of its total extension (Júlio-Junior et al. 1997JÚLIO-JUNIOR, H.F., BONECKER, C. & AGOSTINHO, A.A. 1997. Reservatório de Segredo e sua inserção na bacia do rio Iguaçu. In Reservatório de Segredo: bases ecológicas para o manejo (A.A. Agostinho & L.C. Gomes, eds.). Eduem, Maringá, p.1-17.). Although its geomorphological and hydrographical features provide a high ecological importance for the basin, its fish fauna has been relatively poorly studied, since most studies are generally restricted to the lower Iguaçu River basin (Universidade... 2002, Baumgartner et al. 2012BAUMGARTNER, G., PAVANELLI, C.S., BAUMGARTNER, D., BIFI, A.G., DEBONA, T. & FRANA, V.A. 2012. Peixes do Baixo Rio Iguaçu. Eduem, Maringá, p.203.).

Rhamdia branneri (Haseman, 1911) and Rhamdia voulezi (Haseman, 1911) are two endemic catfish species of Iguaçu River, currently considered synonymous with Rhamdia quelen (see Silfvergrip 1996SILFVERGRIP, A.M.C. 1996. A systematic revision of the Neotropical catfish genus Rhamdia (Teleostei, Pimelodidae). Pp. 156. Stockholm: Department of Zoology, Stockholm University and Department of Vertebrate Zoology: Swedish Museum of Natural History.). Silfvergrip (1996)SILFVERGRIP, A.M.C. 1996. A systematic revision of the Neotropical catfish genus Rhamdia (Teleostei, Pimelodidae). Pp. 156. Stockholm: Department of Zoology, Stockholm University and Department of Vertebrate Zoology: Swedish Museum of Natural History. considered these two species synonymous with R. quelen, however, no exemplar from Iguaçu basin was examined by the author, as mentioned by Baumgartner et al. (2012)BAUMGARTNER, G., PAVANELLI, C.S., BAUMGARTNER, D., BIFI, A.G., DEBONA, T. & FRANA, V.A. 2012. Peixes do Baixo Rio Iguaçu. Eduem, Maringá, p.203.. On the other hand, genetic studies conducted by Abucarma & Martins-Santos (2001)ABUCARMA, M. & MARTINS-SANTOS, I.C. 2001. Karyotype and B chromosome of Rhamdia species (Pisces, Pimelodidae) endemic in the River Iguaçu basin. Cytologia 66:299-306. http://dx.doi.org/10.1508/cytologia.66.299
http://dx.doi.org/10.1508/cytologia.66.2...
demonstrated karyotypic differences between the species of Rhamdia of Iguaçu River basin.

Recently, Baumgartner et al. (2012)BAUMGARTNER, G., PAVANELLI, C.S., BAUMGARTNER, D., BIFI, A.G., DEBONA, T. & FRANA, V.A. 2012. Peixes do Baixo Rio Iguaçu. Eduem, Maringá, p.203. provided an identification manual of fishes from the lower Iguaçu River basin. The authors considered both species of Rhamdia valid based on the morphological divergences like length of the dorsal-fin rays, which is bigger in R. voulezi, touching the adipose-fin when adpressed, allied to the endemic condition of Iguaçu River and their genetic difference (Abucarma & Martins-Santos 2001ABUCARMA, M. & MARTINS-SANTOS, I.C. 2001. Karyotype and B chromosome of Rhamdia species (Pisces, Pimelodidae) endemic in the River Iguaçu basin. Cytologia 66:299-306. http://dx.doi.org/10.1508/cytologia.66.299
http://dx.doi.org/10.1508/cytologia.66.2...
). Despite a minor superposition, the general body shape, mainly the relative body depth, can be also useful to identify the two species (Baumgartner et al. 2012BAUMGARTNER, G., PAVANELLI, C.S., BAUMGARTNER, D., BIFI, A.G., DEBONA, T. & FRANA, V.A. 2012. Peixes do Baixo Rio Iguaçu. Eduem, Maringá, p.203.). Additionally, differences in standard length (SL) at first maturation between R. branneri and R. voulezi are conspicuously different (Suzuki & Agostinho 1997SUZUKI, H.I. & AGOSTINHO, A.A. 1997. Reprodução de peixes do reservatório de Segredo. In Reservatório de Segredo: bases ecológicas para o manejo (A.A. Agostinho & L.C. Gomes, eds.). Eduem, Maringá, p.163-182.).

Based on these arguments, the present study sought to investigate ecomorphological differences between the two species of Rhamdia from the Iguaçu River basin. Trying to corroborate the previous studies that considered R. branneri and R. voulezi as distinct species, we expect that these fishes have some differences in their ecology since they coexist in the Iguaçu River basin. Despite their morphological similarities that resulted in taxonomical problems, ecomorphological studies can elucidate morphological aspects that might favor the coexistence of these fishes.

The principal idea in ecomorphology is that different morphologies can result in distinct ecological aspects, influencing the use of food resources, habitat occupation, and the species' fitness (Norton et al. 1995NORTON, S.F., LUCZKOVICH, J.J. & MOTTA, P.J. 1995. The role of ecomorphological studies in the comparative biology of fishes. Environ. Biol. Fish 44:287-304. http://dx.doi.org/10.1007/BF00005921
http://dx.doi.org/10.1007/BF00005921...
). Studies comparing congeneric and sympatric species may provide valuable evolutionary insights (Douglas & Matthews 1999). Thus, the morphological aspects evidenced can be considered adaptive, showing divergences or convergences between the species.

In this way, we hypothesize that these closely related species show morphological differences that can be linked to differences in habitat use and feeding behavior, evidencing that R. branneri and R. voulezi, both from the Iguaçu River basin, are ecologically distinct and, therefore, are valid species. Furthermore, these aspects can provide useful information in explaining their coexistence in the Iguaçu River basin.

Material and Methods

1. Morphological measurements and ecomorphological indices. In order to characterize the ecomorphology of the specimens, linear measures and areas were obtained. Only aspects related to feeding behavior, habitat occupation and body hydrodynamics were analyzed (Gatz Jr. 1979, Winemiller 1991WINEMILLER, K.O. 1991. Ecomorphological diversification in lowland freshwater fish assemblages from five biotic regions. Ecol. Monogr. 61:343-365. http://dx.doi.org/10.2307/2937046
http://dx.doi.org/10.2307/2937046...
, Peres-Neto 1999PERES-NETO, P.R. 1999. Alguns métodos e estudos em ecomorfologia de peixes de riacho. In Oecologia Brasiliensis Ecologia de peixes de riachos (E.P. Caramaschi, R. Mazzoni & P.R. Peres-Neto, eds.). Universidade Federal do Rio de Janeiro, Rio de Janeiro, vol. 6, p.209-236.). The morphological measurements adopted were: standard length, maximum body height, body midline height, maximum body width, caudal peduncle's length, height and width, head's length, height and width, mouth's width and height, eye's height, fins length and height and areas of the eyes and fins. Linear measures were obtained using a digital caliper to the nearest 0.01mm. The software AutoCad 2009 was used to compute areas of the fins and eyes from drawings of the structures that were previously digitalized. Ecomorphological indices were calculated using data obtained from linear measures and areas. The indices and their respective formulae were adopted according to previous studies (Gosline 1971GOSLINE, W.A. 1971. Functional Morphology and Classification of Teleostean Fishes. University Press of Hawaii, Honolulu, p.208., Gatz Jr. 1979, Watson & Balon 1984WATSON, D.J. & BALON, E.K. 1984. Ecomorphological analysis of fish taxocenes in rainforest streams of northern Borneo. J. Fish Biol. 25:371-384. http://dx.doi.org/10.1111/j.1095-8649.1984.tb04885.x
http://dx.doi.org/10.1111/j.1095-8649.19...
, Wikramanayake 1990WIKRAMANAYAKE, E.D. 1990. Ecomorphology and biogeography of a tropical stream fish assemblage: evolution of assemblage structure. Ecology 71:1756-1764. http://dx.doi.org/10.2307/1937583
http://dx.doi.org/10.2307/1937583...
, Norton & Brainerd 1993NORTON, S.F. & BRAINERD, E.L. 1993. Convergence in the feeding mode of ecomorphologically similar species in the Centrarchidae and Cichlidae. J. Exp. Biol. 176:11-29., Casatti & Castro 1998CASATTI, L. & CASTRO, R.M. 1998. A fish community of the São Francisco River headwater riffles, southeastern Brazil. Ichthyol. Explor. Freshw. 9:229-242., Pouilly et al. 2003POUILLY, M., LINO, F., BRETENOUX, J.G. & ROSALES, C. 2003. Dietary-morphological relationship in a fish assemblage of the Bolivian Amazonian floodplain. J. Fish Biol. 62:1137-1158. http://dx.doi.org/10.1046/j.1095-8649.2003.00108.x
http://dx.doi.org/10.1046/j.1095-8649.20...
, Breda et al. 2005BREDA, L., OLIVEIRA, E.F. & GOULART, E. 2005. Ecomorfologia de locomoção de peixes com enfoque para espécies neotropicais. Acta Sci. Biol. Sci. 27:371-381. http://dx.doi.org/10.4025/actascibiolsci.v27i4.1271
http://dx.doi.org/10.4025/actascibiolsci...
, Hulsey & García de León 2005HULSEY, C.D. & GARCÍA DE LEÓN, F.J. 2005. Cichlid jaw mechanics: linking morphology to feeding specialization. Funct. Ecol. 19:487-494. http://dx.doi.org/10.1111/j.1365-2435.2005.00987.x
http://dx.doi.org/10.1111/j.1365-2435.20...
, Kerfoot Jr. & Schaefer 2006, Cochran-Biederman & Winemiller 2010COCHRAN-BIEDERMAN, J.L. & WINEMILLER, K.O. 2010. Relationships among habitat, ecomorphology and diets of cichlids in the Bladen River, Belize. Environ. Biol. Fish 88:143-152. http://dx.doi.org/10.1007/s10641-010-9624-y
http://dx.doi.org/10.1007/s10641-010-962...
, Oliveira et al. 2010OLIVEIRA, E.F., GOULART, E., BREDA, L., MINTE-VERA, C.V., PAIVA, L.R.S. & VISMARA, M.R. 2010. Ecomorphological patterns of the fish assemblage in a tropical floodplain: effects of trophic, spatial and phylogenetic structures. Neotrop. Ichthyol. 8:569-586.).

2. Biological material. Examined specimens are hosted in the Coleção Ictiológica do Núcleo de Pesquisas em Limnologia, Ictiologia e Aqüicultura (NUP) - Universidade Estadual de Maringá (Figure 1). All specimens were collected in reservoirs or next to their influence area. Numbers in parentheses indicate the number of specimens analyzed in their respective localities: Rhamdia branneri: NUP 3733 (9, Santa Clara Reservoir); 569 (3, Salto do Vau Reservoir); 10849 (12, Pinhãozinho River); 149 (3, Chopin Reservoir), Rhamdia voulezi : NUP 5271 (2, Salto Caxias Reservoir); 3721 (1, Capivara River, tributary of Jordão River); 5300 (6, Jordão Reservoir); 2426 (7, Jordão Reservoir); 1596 (7, Segredo Reservoir); 5289 (1, Caxias Reservoir); 2763 (1, Foz do Areia Reservoir); 568 (1, Salto do Vau Reservoir); 2905 (4, Iguaçu River).

Figure 1.
Specimens of Rhamdia branneri (a) and Rhamdia voulezi (b), NUP 10849 (SL= 111.58 mm) and NUP 2426 (SL= 90.74 mm), respectively.

3. Data analysis. From the ecomorphological indices, a principal component analysis (PCA) with a correlation matrix was performed in order to verify morphological patterns in the species. The criterion adopted for the axes' interpretation was the broken-stick (Jackson 1993JACKSON, D.A. 1993. Stopping rules in principal components analysis: a comparison of heuristical and statistical approaches. Ecology 74:2204-2214. http://dx.doi.org/10.2307/1939574
http://dx.doi.org/10.2307/1939574...
). To test if there is a significant difference in morphology between the species, a multi response permutation procedure (MRPP – McCune & Grace 2002McCUNE, B. & GRACE, J.B. 2002. Analysis of ecological communities. MjM, Oregon, p.300.) was conducted. This is a non-parametric analysis that uses groups determined a priori and a distance matrix. Thus, each Rhamdia species was assigned as a group, and the distance measure adopted was Euclidean distance.

In addition, a discriminant analysis (DA) was made using the forward-stepwise method with the aim to verify which morphological indices maximize the differences between the species. Similarly to the MRPP, the DA has groups determined a priori, but differently, it provides a reclassification of the specimens according to morphology. The DA analysis can indicate if any individual show morphological features that can include it in another group.

All analyses were conducted using the software PcOrd (McCune & Mefford 1999McCUNE, B. & MEFFORD, M.J. 1999. PC-ORD: multivariate analysis of ecological data. version 4.01. MjM Software Design, Oregon.) except the DA that was performed in Statistica 7.0.

Results

The principal component analysis had two axes retained for interpretation, according to the broken-stick criterion. In general, there was a clear segregation between R. branneri and R. voulezi along the first axis (Figure 2). Some individuals of R. branneri had a separation in the second axis, and did not show evident segregation of R. voulezi in the first axis.

Figure 2.
Principal component analysis scatterplot, showing the indices correlated with each axis.

Most of the morphological characters that separated the Rhamdia species were related to body shape (Table 1). Therefore, the specimens of R. voulezi can be characterized by having more compressed and less depressed bodies (major values for this index indicates less depression of the trunk, according to Watson & Balon 1984WATSON, D.J. & BALON, E.K. 1984. Ecomorphological analysis of fish taxocenes in rainforest streams of northern Borneo. J. Fish Biol. 25:371-384. http://dx.doi.org/10.1111/j.1095-8649.1984.tb04885.x
http://dx.doi.org/10.1111/j.1095-8649.19...
), longer caudal peduncle, wider mouth, and larger aspect ratio of the anal fin. The individuals of R. branneri can be characterized by having a higher mouth opening and anal fin. The MRPP showed significant differences (A=0.12; p<0.001) in the ecomorphological indices between the groups (or species), validating the differences found in the ordination.

Table 1.
Eigenvalues and percentage of variation for each axis as well as the indices' loadings. The indices that were more important for interpretation are in bold.

The DA revealed only one axis for interpretation with R. branneri showing negative scores and R. voulezi positive ones (Figure 3). The morphological attributes that separated the species were a higher anal fin for R. branneri, and a longer caudal peduncle, larger head width and less depressed bodies for R. voulezi (Table 2). The reclassification of the individuals had an efficacy of 100%, showing that the analyzed species are ecomorphologically distinct.

Figure 3.
Histograms with the scores related to the first axis of the discriminant analysis.

Table 2.
Eigenvalue and standardized function's coefficients. Indices that were more important for interpretation are in bold.

Discussion

The ecomorphological differences found in Rhamdia species are mostly related to swimming ability and habitat occupation. For example, R. voulezi had longer caudal peduncles and more compressed and less depressed bodies. The first characteristic indicates a better swimming performance mainly for short distance propulsion (Watson & Balon 1984WATSON, D.J. & BALON, E.K. 1984. Ecomorphological analysis of fish taxocenes in rainforest streams of northern Borneo. J. Fish Biol. 25:371-384. http://dx.doi.org/10.1111/j.1095-8649.1984.tb04885.x
http://dx.doi.org/10.1111/j.1095-8649.19...
, Blake 2004BLAKE, R.W. 2004. Fish functional design and swimming performance. J. Fish Biol. 65:1193-1222. http://dx.doi.org/10.1111/j.0022-1112.2004.00568.x
http://dx.doi.org/10.1111/j.0022-1112.20...
). Compressed bodies indicate fishes that occupy habitats with slow water velocity and swimming capacity to explore many levels in the water column, performing vertical movements (Gatz Jr. 1979, Watson & Balon 1984WATSON, D.J. & BALON, E.K. 1984. Ecomorphological analysis of fish taxocenes in rainforest streams of northern Borneo. J. Fish Biol. 25:371-384. http://dx.doi.org/10.1111/j.1095-8649.1984.tb04885.x
http://dx.doi.org/10.1111/j.1095-8649.19...
). On the other hand, R. branneri showed a higher anal fin, and more depressed bodies. The first is an ecomorphological characteristic related to stabilization in swimming, and the second indicates occupation of benthic habitats. Thus, based on the interpretation of ecomorphological indices, these results suggest a spatial segregation between the species, with R. branneri having morphological characteristics to occupy benthic habitats, and R. voulezi to occupy lentic and possibly pelagic habitats.

Studies concerning the feeding habits of these species are most focused on variations related to impoundments. Cassemiro et al. (2005)CASSEMIRO, F.A.S., HAHN, N.S. & DELARIVA, R.L. 2005. Estrutura trófica da ictiofauna, ao longo do gradiente longitudinal do reservatório de Salto Caxias (rio Iguaçu, Paraná, Brasil), no terceiro ano após o represamento. Acta Sci. Biol. Sci. 27:63-71. http://dx.doi.org/10.4025/actascibiolsci.v27i1.1362
http://dx.doi.org/10.4025/actascibiolsci...
verified that, in Salto Caxias Reservoir, Rhamdia species fed exclusively on fishes after the impoundment, differently from the previous phases when invertebrates and crustaceans were also consumed. Other authors recorded significant differences in diet in the impoundment phases with R. voulezi consuming fishes, and R. branneri feeding on crustaceans and terrestrial insects (Loureiro-Crippa & Hahn 2006LOUREIRO-CRIPPA, V. E & HAHN, N.S. 2006. Use of food resources by the fish fauna of a small reservoir (rio Jordão, Brazil) before and shortly after its filling. Neotrop. Ichthyol. 4:357-362. http://dx.doi.org/10.1590/S1679-62252006000300007
http://dx.doi.org/10.1590/S1679-62252006...
, Novakowski et al. 2007NOVAKOWSKI, G.C., HAHN, N.S. & FUGI, R. 2007. Alimentação de peixes piscívoros antes e após a formação do reservatório de Salto Caxias, Paraná, Brasil. Biota Neotrop. 7:149-157. http://dx.doi.org/10.1590/S1676-06032007000200017
http://dx.doi.org/10.1590/S1676-06032007...
). The dietary changes can be certainly related to environmental changes caused by impoundments, since fishes and insects are abundant food resources in reservoirs (Hahn & Fugi 2007HAHN, N.S. & FUGI, R. 2007. Alimentação de peixes em reservatórios brasileiros: Alterações e conseqüências nos estágios iniciais de represamento. Oecol. Bras. 11:469-480. http://dx.doi.org/10.4257/oeco.2007.1104.01
http://dx.doi.org/10.4257/oeco.2007.1104...
).

Regarding the pre-impoundment phases, the diet of both Rhamdia species does not differ (Loureiro-Crippa & Hahn 2006LOUREIRO-CRIPPA, V. E & HAHN, N.S. 2006. Use of food resources by the fish fauna of a small reservoir (rio Jordão, Brazil) before and shortly after its filling. Neotrop. Ichthyol. 4:357-362. http://dx.doi.org/10.1590/S1679-62252006000300007
http://dx.doi.org/10.1590/S1679-62252006...
) with crustaceans and fish being consumed in similar proportions. On the other hand, other authors (Cassemiro et al. 2005CASSEMIRO, F.A.S., HAHN, N.S. & DELARIVA, R.L. 2005. Estrutura trófica da ictiofauna, ao longo do gradiente longitudinal do reservatório de Salto Caxias (rio Iguaçu, Paraná, Brasil), no terceiro ano após o represamento. Acta Sci. Biol. Sci. 27:63-71. http://dx.doi.org/10.4025/actascibiolsci.v27i1.1362
http://dx.doi.org/10.4025/actascibiolsci...
, Novakowski et al. 2007NOVAKOWSKI, G.C., HAHN, N.S. & FUGI, R. 2007. Alimentação de peixes piscívoros antes e após a formação do reservatório de Salto Caxias, Paraná, Brasil. Biota Neotrop. 7:149-157. http://dx.doi.org/10.1590/S1676-06032007000200017
http://dx.doi.org/10.1590/S1676-06032007...
) found dietary differences between R. branneri and R. voulezi. However, patterns in the diet of these fishes were not clearly defined, occurring local variations (Cassemiro et al. 2005CASSEMIRO, F.A.S., HAHN, N.S. & DELARIVA, R.L. 2005. Estrutura trófica da ictiofauna, ao longo do gradiente longitudinal do reservatório de Salto Caxias (rio Iguaçu, Paraná, Brasil), no terceiro ano após o represamento. Acta Sci. Biol. Sci. 27:63-71. http://dx.doi.org/10.4025/actascibiolsci.v27i1.1362
http://dx.doi.org/10.4025/actascibiolsci...
).

Despite the discrepancy found in the studies, differences in the diet composition between the studied species indicate that, besides food abundance, other variables influence the use of food resources. The ecomorphological indices related to occupation of lentic habitats probably favored R. voulezi to feed on prey that explore the bottom, such as Cyphocharax modestus (Fernández-Yépez 1948), and fishes that can forage in shallow waters, such as some species of Astyanax (Hahn et al. 2004HAHN, N.S., FUGI, R. & ANDRIAN, I.F. 2004. Trophic ecology of the fish assemblages. In The Upper Paraná River and its Floodplain: physical aspects, ecology and conservation (S.M. Thomaz, A.A. Agostinho & N.S. Hahn, eds.). Backhuys Publishers, Leiden, p.247-269.). These two prey types were the most consumed by piscivores in Salto Caxias Reservoir (Novakowski et al. 2007NOVAKOWSKI, G.C., HAHN, N.S. & FUGI, R. 2007. Alimentação de peixes piscívoros antes e após a formação do reservatório de Salto Caxias, Paraná, Brasil. Biota Neotrop. 7:149-157. http://dx.doi.org/10.1590/S1676-06032007000200017
http://dx.doi.org/10.1590/S1676-06032007...
). The ecomorphological characteristics related to benthic fishes (depressed body) in R. branneri may have favored the ingestion of benthic crustaceans as Aegla sp. Additionally, a higher anal fin that provides stabilization in swimming can propitiate the consumption of allochthonous food, which drift in the water column, such as terrestrial insects (Gosline 1971GOSLINE, W.A. 1971. Functional Morphology and Classification of Teleostean Fishes. University Press of Hawaii, Honolulu, p.208., Gatz Jr. 1979).

Ecomorphological differences related to habitat occupation and use of food resources in congeneric species are well documented in the literature (e.g.Casatti et al. 2005CASATTI, L., ROCHA, F.C. & PEREIRA, D.C. 2005. Habitat use by two species of Hypostomus (Pisces, Loricariidae) in southeastern brazilian streams. Biota Neotrop. 5(2): http://www.biotaneotropica.org.br/v5n2/pt/abstract?article+bn02905022005 (último acesso em 15/01/2013).
http://www.biotaneotropica.org.br/v5n2/p...
, Balassa et al. 2004BALASSA, G.C., FUGI, R., HAHN, N.S. & GALINA, A.B. 2004. Dieta de espécies de Anostomidae (Teleostei, Characiformes) na área de influência do reservatório de Manso, Mato Grosso do Sul, Brasil. Iheringia, Ser. Zool. 94:77-82. http://dx.doi.org/10.1590/S0073-47212004000100014
http://dx.doi.org/10.1590/S0073-47212004...
, Santos et al. 2011SANTOS, F.L., CAMILO, F.L., ALBIERI, R.J. & ARAÚJO, F.G. 2011. Morphological patterns of five fish species (four characiforms, one perciform) in relation to feeding habits in a tropical reservoir in South-eastern Brazil. J. Appl. Ichthyol. 27:1360-1364. http://dx.doi.org/10.1111/j.1439-0426.2011.01801.x
http://dx.doi.org/10.1111/j.1439-0426.20...
). Resource partitioning is considered the principal factor in structuring the aquatic communities (Ross 1986ROSS, S.T. 1986. Resource partitioning in fish assemblages: a review of field studies. Copeia 1986:352-388. http://dx.doi.org/10.2307/1444996
http://dx.doi.org/10.2307/1444996...
). Hence, the coexistence of the species can be favored by ecomorphological differences. The MRPP and the Discriminant Analysis resulted respectively in significant differences and total separation in ecomorphological aspects that can enable the characterization of the Rhamdia species as distinct ecological units.

Thus, the morphological segregation found in the present study and evidences in diet, reproduction, and genetic segregation coupled with the known endemism of Iguaçu river basin (Baumgartner et al. 2012BAUMGARTNER, G., PAVANELLI, C.S., BAUMGARTNER, D., BIFI, A.G., DEBONA, T. & FRANA, V.A. 2012. Peixes do Baixo Rio Iguaçu. Eduem, Maringá, p.203.) reinforce the arguments to refute the synonymy proposed by Silfvergrip (1996)SILFVERGRIP, A.M.C. 1996. A systematic revision of the Neotropical catfish genus Rhamdia (Teleostei, Pimelodidae). Pp. 156. Stockholm: Department of Zoology, Stockholm University and Department of Vertebrate Zoology: Swedish Museum of Natural History.. However, the elucidation of the taxonomic status of R. branneri and R. voulezi can only be fulfilled with a complete taxonomic review, with morphological and molecular data, of populations attributed to R. quelen.

We express our appreciation to Nupélia (Núcleo de Pesquisas em Limnologia, Ictiologia e Aquicultura), to PEA (Programa de Pós-graduação em Ecologia de Ambientes Aquáticos Continentais), to PGB (Programa de Pós-graduação em Biologia Comparada) for their financial support and infrastructure, to Ichythyological Museum of Nupélia for the permission to carry out the research on their properties, Rosemara Fugi, Erivelto Goulart and Marlene Sofia Arcifa Froehlich for suggestions for the manuscript, and two anonymous referees for providing valuable suggestions. The authors also thank Coordenação de Aperfeiçoamento Pessoal de Nível Superior (CAPES/ Ministério da Educação) and CNPq (Conselho Nacional de Desenvolvimento Científico e Técnológico) for grants to FT Mise, LFC Tencatt, and F de Souza.

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Data availability

Data citations

CASATTI, L., ROCHA, F.C. & PEREIRA, D.C. 2005. Habitat use by two species of Hypostomus (Pisces, Loricariidae) in southeastern brazilian streams. Biota Neotrop. 5(2): http://www.biotaneotropica.org.br/v5n2/pt/abstract?article+bn02905022005 (último acesso em 15/01/2013).

Publication Dates

  • Publication in this collection
    Dec 2013

History

  • Received
    17 Jan 2013
  • Reviewed
    18 Sept 2013
  • Accepted
    1 Nov 2013
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