Chromosomes of Asian cyprinid fishes: cytogenetic analysis of two representatives of small paleotetraploid tribe Probarbini

Pasakorn Saenjundaeng,Alongklod Tanomtong,Weerayuth Supiwong,Cassia Fernanda Yano,Maria João Collares-Pereira,Luiz Antonio Carlos Bertollo,Terumi Hatanaka,Sumalee Phimphan,Petr Ráb,Alexandr Sember,Ezequiel Aguiar De Oliveira,Thomas Liehr,Marcelo De Bello Cioffi

doi:10.1186/s13039-018-0399-8

Abstract

BackgroundPolyploidy, although still poorly explored, represents an important evolutionary event in several cyprinid clades. Herein, Catlocarpio siamensis and Probarbus jullieni - representatives of the paleotetraploid tribe Probarbini, were characterized both by conventional and molecular cytogenetic methods.ResultsAlike most other paleotetraploid cyprinids (with 2n = 100), both species studied here shared 2n = 98 but differed in karyotypes: C. siamensis displayed 18m + 34sm + 46st/a; NF = 150, while P. jullieni exhibited 26m + 14sm + 58st/a; NF = 138. Fluorescence in situ hybridization (FISH) with rDNA probes revealed two (5S) and eight (18S) signals in C. siamensis, respectively, and six signals for both probes in P. jullieni. FISH with microsatellite motifs evidenced substantial genomic divergence between both species. The almost doubled size of the chromosome pairs #1 in C. siamensis and #14 in P. jullieni compared to the rest of corresponding karyotypes indicated chromosomal fusions.ConclusionBased on our findings, together with likely the same reduced 2n = 98 karyotypes in the remainder Probarbini species, we hypothesize that the karyotype 2n = 98 might represent a derived character, shared by all members of the Probarbini clade. Besides, we also witnessed considerable changes in the amount and distribution of certain repetitive DNA classes, suggesting complex post-polyploidization processes in this small paleotetraploid tribe.

Highlights

Polyploidy, still poorly explored, represents an important evolutionary event in several cyprinid clades
The chromosome pairs #1 in C. siamensis and #14 in P. jullieni were almost doubled in size when compared to the rest of corresponding karyotypes
Chromosome mapping of 5S and 18S ribosomal DNA sequences In the genome of C. siamensis, the minor 5S rDNA class is located on a single chromosomal pair (#27), while the major 18S rDNA occurs in four chromosome pairs (#22, #23, #40, #41)

Summary

Introduction

Polyploidy, still poorly explored, represents an important evolutionary event in several cyprinid clades. Probarbini represents the most early-diverging group [9], with only two genera: (i) the monotypic Catlocarpio (C. siamensis Boulenger, 1898) being the largest known cyprinid species attaining a length of up to three meters [12, 13], and (ii) the genus Probarbus, with three valid species [14] (P. jullieni Sauvage, 1880, P. labeamajor Roberts, 1992 and P. labeaminor Roberts, 1992) These four potamodromous species from large river systems in Southeast Asia have been and are heavily declining in the sizes of populations due to fishery pressures, and due to Saenjundaeng et al Molecular Cytogenetics (2018) 11:51 habitat loss and degradation. Since extirpated from most of their native range, these species were considered as “threatened” following IUCN criteria (IUCN Red List of Threatened Species 2012) [15,16,17,18]

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Conclusion