A Molecular Perspective on Systematics, Taxonomy and Classiﬁcation Amazonian Discus Fishes of the Genus Symphysodon

SAGE-Hindawi Access to Research International Journal of Evolutionary Biology Volume 2011, Article ID 360654, 16 pages doi:10.4061/2011/360654 Research Article A Molecular Perspective on Systematics, Taxonomy and Classification Amazonian Discus Fishes of the Genus Symphysodon Manuella Villar Amado,1, 2 Izeni P. Farias,1 and Tomas Hrbek1, 3 1 Laboratorio´ de Evoluçao˜ e Genética Animal, Departamento de Biologia, Universidade Federal do Amazonas, Avenida Rodrigo Octavio´ Jordao˜ Ramos, 3000, 69077-000 Manaus, AM, Brazil 2 Instituto Federal de Educaçao,˜ Ciência e Tecnologia do Esp´ırito Santo, Unidade Vitoria,´ Avenida Vitoria,´ 1729, 29040-780 Vitoria, ES, Brazil 3 Biology Department, University of Puerto Rico—Rio Piedras, 00931 San Juan, PR, Puerto Rico Correspondence should be addressed to Tomas Hrbek, [email protected] Received 21 December 2010; Accepted 2 May 2011 Academic Editor: Martin J. Genner Copyright © 2011 Manuella Villar Amado et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. With the goal of contributing to the taxonomy and systematics of the Neotropical cichlid fishes of the genus Symphysodon, we analyzed 336 individuals from 24 localities throughout the entire distributional range of the genus. We analyzed variation at 13 nuclear microsatellite markers, and subjected the data to Bayesian analysis of genetic structure. The results indicate that Symphysodon is composed of four genetic groups: group PURPLE—phenotype Heckel and abacaxi; group GREEN—phenotype green; group RED—phenotype blue and brown; and group PINK—populations of Xingu´ and Cameta.´ Although the phenotypes blue and brown are predominantly biological group RED, they also have substantial contributions from other biological groups, and the patterns of admixture of the two phenotypes are different. The two phenotypes are further characterized by distinct and divergent mtDNA haplotype groups, and show differences in mean habitat use measured as pH and conductivity. Differences in mean habitat use is also observed between most other biological groups. We therefore conclude that Symphysodon comprises five evolutionary significant units: Symphysodon discus (Heckel and abacaxi phenotypes), S. aequifasciatus (brown phenotype), S. tarzoo (green phenotype), Symphysodon sp. 1 (blue phenotype) and Symphysodon sp. 2 (Xingu´ group). 1. Introduction have been reported; for example, see [10–14]. This makes it difficult to apply the phylogenetic species concept in species Tropical regions contain many more species than do tem- discovery and diagnosis. The delimitation of species of the perate and polar regions; however, explanations as to why genus Symphysodon has also been problematic in part due to remain unclear; for example, see [1, 2]. The Amazon Basin sharing of mitochondrial DNA haplotypes between species is particularly species rich and harbors arguably the world’s [15–17] and a complete lack of resolution with nuclear DNA greatest terrestrial [3, 4]andfreshwater[5] biodiversity. haplotypes [15, 17]. Numerous potential processes generating this diversity The discus fishes (genus Symphysodon)haveanatural within the Amazon basin have been proposed; for example, distribution is the Amazon basin. Traditionally, five principal see [6–8]. Testing of processes that have generated Amazo- phenotypic, largely allopatrically distributed groups are nian biodiversity depends on solid taxonomy, since species recognized in popular literature [18, 19].Thesegroupsare are the operational units in all studies of biodiversity; for (1) green phenotype—found in the western Amazon basin, example, see [9]. The taxonomy of many Amazonian groups (2) blue phenotype—found in the central Amazon basin, (3) is still poorly known [3, 5] and at least in fishes a number of brown phenotype—found in the eastern Amazon basin, (4) instances of haplotype sharing between closely related species Heckel phenotype—found in the Negro and Trombetas River 2 International Journal of Evolutionary Biology basins, and (5) abacaxi phenotype—found in the Abacaxis but have found no consistent karyotype differences between River, a blackwater tributary of the lower Madeira River. different species and populations of Symphysodon. Since the description of the type species and the genus by In spite all of these studies, the taxonomy of this group Heckel in 1840, there has been taxonomic uncertainty and remains elusive. Genetic characterization of Symphysodon confusing classification related to the genus Symphysodon. and identification of biological populations are essential for Considering descriptions and taxonomic revisions until the the understanding of evolutionary processes operating on year 2006, two species were recognized in scientific literature the genus Symphysodon and for delimitation of evolutionary [20, 21]: Symphysodon discus Heckel, 1840 and Symphysodon species. Neutral molecular markers with high mutation aequifasciatus Pellegrin, 1904, and four subspecies in popular rates have the greatest ability to record signatures of recent literature: S. discus willischwartzi Burgess, 1981 (phenotype evolutionary events. abacaxi), S. discus tarzoo Lyons, 1959 (phenotype green), S. Microsatellite loci have a mutation rate estimated at 2.5 × 10−3 in humans [28, 29]to5.6 × 10−4 [30] mutations aequifasciatus haraldi Schultz, 1960 (phenotype blue) and per generation with similar values observed in mice [31], S. aequifasciatus axelrodi Schultz, 1960 (phenotype brown), and are commonly used for intraspecific population studies, with the nominal sub-species S. discus discus Heckel, 1840 for example, [32–35]. Since microsatellite flanking regions (phenotype Heckel), and S. aequifasciatus aequifasciatus are generally conserved among closely related species, they Pellegrin, 1904 (phenotype green), being restricted to just are also often used for interspecific studies and studies of one major phenotype. Recently, Ready et al. [17] proposed species complexes, for example, see [36–41]. Microsatellite the existence of three species: S. discus (phenotype Heckel markers, thus, lend themselves well to delimiting taxonomic and abacaxi), S. aequifasciatus (phenotype blue and brown) boundaries and identifying cases of hybridization [42–44]. and S. tarzoo (green phenotype). Bleher et al. [16] also argued The aim of the present study was to use microsatel- for the existence of three species: S. discus (phenotype Heckel lite markers to genetically characterize phenotypic vari- and abacaxi), S. aequifasciatus (phenotype green) and S. ants of Symphysodon sampled throughout their area of haraldi (phenotype blue and brown), with S. aequifasciatus natural distribution and to investigate association between and S. haraldi occurring allopatrically but throughout the genetic variants, geographic distribution, and described Amazon basin (i.e., the species are not restricted to the species/subspecies. We also use the proxy variables of pH western, and central+eastern Amazon basin). Farias and and conductivity to test for differences in mean habitats Hrbek [15] on the other hand argued that the genus occupied by the different phenotypes and groups. Neither Symphysodon is probably a biological complex in the process pH nor conductivity are necessarily the primary agents of speciation. Farias and Hrbek [15] also reported the causing ecological separation, but they are likely to reflect existence of an additional deeply divergent mitochondrial differences in habitats occupied by the different phenotypes lineage from the Xingu´ River basin. as correlates of other important environmental variables or All three studies found individuals of the green phe- differences in the geological history of the areas occupied by notype to form a monophyletic mtDNA group. Farias and species of Symphysodon. Hrbek [15] also observed monophyly of the blue phenotype and the Xingu´ lineage. All three studies [15–17]observed 2. Material and Methods haplotype sharing between the Heckel, abacaxi, and brown phenotypes, with Bleher et al. [16] considering the brown 2.1. Samples. A total of 336 individuals were sampled from phenotype individuals to be blue phenotype individuals 24 localities (Figure 1) throughout the known geographic introgressed with Heckel phenotype mtDNA. distribution of the genus Symphysodon. All five principal Inclusion of nuclear DNA sequence data did not identify phenotypes (Heckel, abacaxi, brown, green, and blue) were monophyletic groups or clarify taxonomy of Symphysodon. sampled, with an average number of 13 individuals per Farias and Hrbek [15] analyzed the third exon the recom- sampled locality. Individuals were assigned to phenotype bination activation gene one (RAG1) observing extensive following Farias and Hrbek [15]. Fishes were collected by haplotype sharing among all phenotypes. Ready et al. [17] cutting and submerging branches in appropriate habitats included the Rhodopsin gene in their analysis; however, it on the margins of lakes and small rivers for approximately showed no sequence variation within Symphysodon. aweektoallowsufficient time for individuals to colonize The two published isozyme studies of Symphysodon [22, 23] could not find any diagnostic marker that would this habitat (popularly known as “galhada”). After the fish separate S. discus and S. aequifasciatus, and Kokoscha colonized this habitat, they were collected with nets. Samples and Greven [23] even observed that among-population

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