Chromosomes of Asian cyprinid fishes: Novel insight into the chromosomal evolution of Labeoninae (Teleostei, Cyprinidae).

The Labeoninae subfamily is a highly diversified but demonstrably monophyletic lineage of cyprinid fishes comprising five tribes and six incertae sedis genera. This widely distributed assemblage contains some 48 genera and around 480 recognized species distributed in freshwaters of Africa and Asia. In this study, the karyotypes and other chromosomal properties of five Labeoninae species found in Thailand Labeo chrysophekadion (Labeonini) and Epalzeorhynchos bicolor, Epalzeorhynchos munense, Henicorhynchus siamensis, Thynnichthys thynnoides (´Osteochilini´) were examined using conventional and molecular cytogenetic protocols. Our results confirmed a diploid chromosome number (2n) invariably 2n = 50, but the ratio of uni- and bi-armed chromosomes was highly variable among their karyotypes, indicating extensive structural chromosomal rearrangements. Karyotype of L. chrysophekadion contained 10m+6sm+20st+14a, 32m+10sm+8st for H. siamensis, 20m+12sm+10st+8a in E. bicolor, 20m+8sm+8st+14a in E. munense, and 18m+24sm+8st in T. thynnoides. Except for H. siamensis, which had four sites of 5S rDNA sites, other species under study had only one chromosome pair with those sites. In contrast, only one pair containing 18S rDNA sites were found in the karyotypes of three species, whereas two sites were found in that of E. bicolor. These cytogenetic patterns indicated that the cytogenomic divergence patterns of these labeonine species largely corresponded to the inferred phylogenetic tree. In spite of the 2n stability, diverse patterns of rDNA and microsatellite distribution as well as their various karyotype structures demonstrated significant evolutionary differentiation of Labeoninae genomes as exemplified in examined species. Labeoninae offers a traditional point of view on the evolutionary forces fostering biological diversity, and the recent findings add new pieces to comprehend the function of structural chromosomal rearrangements in adaption and speciation

Microsatellite sequences mapped onto <i>L</i>. <i>chrysophekadion</i> chromosomes.

Distribution of microsatellite sequences (CA)15, (GC)15, (TA)15, (CAA)10 (GAA)10 (CAG)10 (CAT)10, and (CGG)10 onto L. chrysophekadion metaphase chromosomes.</p

Karyotypes of <i>Labeo chrysophekadion</i> and <i>Henicorhyncus siamensis</i>.

Karyotypes of L. chrysophekadion (A,C,E) and Henicorhyncus siamensis (B,D,F) organized from chromosomes after Giemsa-staining, Ag-NOR impregnation and FISH with 5S and 18S probes. Chromosomes were counterstained with DAPI (blue). Arrows indicate the positive FISH results. Bar = 5 μm.</p

Mapping of our cytogenetic results onto modified phylogenetic relationships of the Labeoninae based on nuclear and mitochondrial genes by Yang et al. [2] and classification of Tan and Armbruster [1].

The common names of the species are indicated under the scientific name. The position of Epalzeorhynchos munense was manually added to our figure, since it is not included in the [2] phylogeny, thus requiring confirmation.</p

Distribution of five Labeoninae species here investigated.

Thailand map showing the collection sites of the five species studied including 1. Labeo chrysophekadion (green circles); 2. Henicorhynchus siamensis (orange circles); 3. Epalzeorhynchos bicolor (pink circles); 4. Epalzeorhynchos munense (yellow circles); 5. Thynnichthys thynnoides (red circles). Scale bar = 1 cm.</p

Microsatellite sequences mapped onto <i>T</i>. <i>thynnoides</i> chromosomes.

Distribution of microsatellite sequences (CA)15, (GC)15, (TA)15, (CAA)10 (GAA)10 (CAG)10 (CAT)10 and (CGG)10 onto T. thynnoides metaphase chromosomes.</p

Microsatellite sequences mapped onto <i>E</i>. <i>munense</i> chromosomes.

Distribution of microsatellite sequences (CA)15, (GC)15, (TA)15, (CAA)10 (GAA)10 (CAG)10 (CAT)10 and (CGG)10 onto E. munense metaphase chromosomes.</p

Karyotypes of <i>Epalzeorhyncos bicolor</i>, <i>E</i>. <i>munense</i>, and <i>Thynnichthys thynnoides</i>.

Karyotypes of E. bicolor (A,C,E), E. munense (B,D,F), and T. thynnoides (G,H,I) arranged from Giemsa- and Ag-NOR-stained chromosomes and chromosomes after FISH with 5S (red) and 18S (green) rDNA probes. Chromosomes were counterstained with DAPI (blue). The positive FISH signals are indicated by arrows. Scale bar = 5 μm.</p

The collection sites of the five Labeoninae species and the number of analyzed individuals (n) per sex.

Individuals of E. bicolor and E. munense were gathered from Ban Pong Fish Market, Ratchaburi province (13°51’42.6"N 99°52’48.8"E).</p

Microsatellite sequences mapped onto <i>H</i>. <i>siamensis</i> chromosomes.

Distribution of microsatellite sequences (CA)15, (GC)15, (TA)15, (CAA)10 (GAA)10 (CAG)10 (CAT)10 and (CGG)10 onto H. siamensis metaphase chromosomes.</p