Abstract
Lebiasinidae fishes have been historically neglected by cytogenetical studies. Here we present a genomic comparison in eleven Lebiasinidae species, in addition to a review of the ribosomal DNA sequences distribution in this family. With that, we develop ten sets of experiments in order to hybridize the genomic DNA of representative species from the genus Copeina, Copella, Nannostomus, and Pyrrhulina in metaphase plates of Lebiasina melanoguttata. Two major pathways on the chromosomal evolution of these species can be recognized: (i) conservation of 2n = 36 bi-armed chromosomes in Lebiasininae, as a basal condition, and (ii) high numeric and structural chromosomal rearrangements in Pyrrhulininae, with a notable tendency towards acrocentrization. The ribosomal DNA (rDNA) distribution also revealed a marked differentiation during the chromosomal evolution of Lebiasinidae, since both single and multiple sites, in addition to a wide range of chromosomal locations can be found. With some few exceptions, the terminal position of 18S rDNA appears as a common feature in Lebiasinidae-analyzed species. Altogether with Ctenoluciidae, this pattern can be considered a symplesiomorphism for both families. In addition to the specific repetitive DNA content that characterizes the genome of each particular species, Lebiasina also keeps inter-specific repetitive sequences, thus reinforcing its proposed basal condition in Lebiasinidae.
Highlights
Advanced molecular approaches have been widely applied in cytogenetic studies of many animal groups, providing useful insights into their karyotype differentiation and genome evolution
Two major pathways can be recognized in the chromosomal evolution of the family: (i) conservation of 2n = 36 and karyotype composed of exclusively bi-armed chromosomes in the Lebiasininae as a basal condition; (ii) high 2n and structural chromosomal rearrangements in the Pyrrhulininae, with karyotypes prominently dominated by acrocentric chromosomes (Figure 2)
These findings fit with the hypothesis that several derived fish clades predominantly possess mono-armed chromosomes, while basal ones have karyotypes dominated by bi-armed chromosomes [28]
Summary
Advanced molecular approaches have been widely applied in cytogenetic studies of many animal groups, providing useful insights into their karyotype differentiation and genome evolution. In fishes, such procedures have improved investigations as a whole, chromosomal analysis of several taxa is still emerging [1]. Dealing with chromosomes of miniature species, which reach a maximum length of 26 mm in maturity [2], is challenging, but possible [3,4,5,6,7]. Lebiasinidae is a freshwater characiform family comprising about 75 recognized species [8], distributed throughout Central and South America except Chile, which experienced body miniaturization along with their evolution [2].
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