A map showing the places where the samples were collected.

<p>A map showing the places where the samples were collected.</p

Phylogeny of the genus <i>Gymnotus</i> adapted from [3] and [4] with chromosomal information cited in this paper.

<p>Phylogeny of the genus <i>Gymnotus</i> adapted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055608#pone.0055608-Albert2" target="_blank">[3]</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055608#pone.0055608-Lovejoy1" target="_blank">[4]</a> with chromosomal information cited in this paper.</p

18S rDNA probe FISH (green) and whole NOR-bearing chromosome probe FISH (red) in A) <i>G. capanema</i>; B) <i>G. sylvius</i> and C) <i>G. jonasi</i>. The ideogram on each image shows the position of NOR.

<p>18S rDNA probe FISH (green) and whole NOR-bearing chromosome probe FISH (red) in A) <i>G. capanema</i>; B) <i>G. sylvius</i> and C) <i>G. jonasi</i>. The ideogram on each image shows the position of NOR.</p

Table_2.docx

<p>Chromosome changes can perform an important role in speciation by acting as post-zygotic reproductive barriers. The Neotropical electric fish genus Brachyhypopomus (Gymnotiformes, Hypopomidae) has 28 described species, but cytogenetic data are hitherto available only for four of them. To understand karyotype evolution and investigate the possible role of chromosome changes in the diversification of this genus, we describe here the karyotype of eight species of Brachyhypopomus from a sympatric assemblage in the central Amazon basin. We analyzed cytogenetic data in the context of a phylogenetic reconstruction of the genus and known patterns of geographical distribution. We found a strong phylogenetic signal for chromosome number and noted that sympatric species have exclusive karyotypes. Additional insights into the role of chromosome changes in the diversification of Brachyhypopomus are discussed.</p

Optimization of the basic number (right) and the position of NORs (left) in Cophomantini on a condensed phylogenetic hypothesis resulting from the analyses of Faivovich et al. [21] and Duellman et al. [7].

<p>Optimization of the basic number (right) and the position of NORs (left) in Cophomantini on a condensed phylogenetic hypothesis resulting from the analyses of Faivovich et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192861#pone.0192861.ref021" target="_blank">21</a>] and Duellman et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0192861#pone.0192861.ref007" target="_blank">7</a>].</p

Triploid specimen of <i>Boana pulchella</i> (LGE 11504).

<p><b>A</b>. Giemsa stained karyotype. <b>B.</b> C banded pattern. <b>C.</b> Meiotic cell in metaphase I stage. <b>D.</b> Normal spermatid (<b>I</b>) and abnormal microspermatid (<b>II</b>).</p

Studied species and the cytogenetic techniques applied for each one.

<p>Studied species and the cytogenetic techniques applied for each one.</p

Karyotypes of three species of <i>Hyloscirtus</i>.

<p><i>Hyloscirtus alytolylax</i> (left), <i>H</i>. <i>palmeri</i> (center), and <i>H</i>. <i>larinopygion</i> (right). <b>A, B.</b> Giemsa staining. <b>C, D.</b> C-bands. <b>E, F.</b> CMA₃. <b>G, H.</b> DAPI. Squares show NOR-bearing chromosome pairs as stained by the silver impregnation technique (<b>I</b>), and with FISH using a 18S DNA probe (<b>II</b>).</p

Idiograms with DAPI-CMA₃ bands present in the species of <i>Boana</i> and <i>Hyloscirtus</i> studied in this paper.

<p>Scale indicates percentage relative size of chromosome pairs.</p

C banding pattern in karyotypes of the <i>Boana faber</i> and <i>B</i>. <i>pulchella</i> groups.

<p><b>A.</b><i>B</i>. <i>faber</i>. <b>B.</b><i>B</i>. <i>cipoensis</i>. <b>C.</b><i>B</i>. <i>curupi</i>. <b>D.</b><i>B</i>. <i>stellae</i>. <b>E.</b><i>B</i>. <i>albonigra</i>. <b>F.</b><i>B</i>. <i>riojana</i>. <b>G.</b><i>B</i>. <i>marianitae</i>. <b>H.</b><i>B</i>. <i>bischoffi</i>. <b>I.</b><i>B</i>. <i>cordobae</i>. <b>J.</b><i>B</i>. <i>pulchella</i>. <b>K.</b><i>B</i>. <i>caingua</i>.</p