Tetraploid Loach Misgurnus Anguillicaudatus Research Articles

Comparison of age and growth performance of diploid and tetraploid loach Misgurnus anguillicaudatus in the Yangtze River basin, China

Diploids and tetraploids of the cyprinid loach Misgurnus anguillicaudatus coexist in many natural habitats in Asia. However, little is known about the biological and ecological differences between these two ploidy forms. We examined age, body size and growth rates of fish in a mixed ploidy population of M. anguillicaudatus in the Yangtze River basin in China. The sex ratios of both diploid and tetraploid M. anguillicaudatus were highly skewed toward females, who tended to be larger than males. The age distributions of the collected specimens clearly indicated that tetraploids lived longer than diploids. For example, we found a substantial number of tetraploids that were 5+ years old, while the oldest diploids were 4+ years old. Tetraploids were also longer and heavier than diploids for both sexes. Using the empirical body size and age data, we inferred the growth patterns of these fish with the von Bertalanffy growth function. The estimated asymptotic body lengths (L ∞) indicated that tetraploids could indeed achieve larger body sizes than diploids. This difference was partially due to the increased growth rate, as demonstrated by lower growth coefficient (K) and higher growth performance index (φ’). In sum, we show that tetraploid M. anguillicaudatus exhibited significantly increased longevity and superior growth performance compared to diploids. These differences may contribute to the ecological competitiveness of tetraploid M. anguillicaudatus, thus enabling them to coexist with diploids in certain ecological settings.

Aneuploid progenies of triploid hybrids between diploid and tetraploid loach Misgurnus anguillicaudatus in China.

Triploid Chinese loach, Misgurnus anguillicaudatus, hybrids between tetraploids from Hubei Province and diploids from Liaoning Province were mated with either diploid wild-type or triploid hybrids to analyze viability and ploidy of the resultant progenies. Both triploid males and females generated fertile gametes, but progenies from the crosses using gametes of triploid hybrids did not survive beyond the larval stages. In crosses between wild-type diploid females and triploid hybrid males, embryos ranging from 2.2n to 2.6n were predominant with a mode of either 2.4n (chromosome numbers 59, 60, 61) or 2.5n (chromosome numbers 62, 63). Those from the crosses between triploid hybrid females and diploid males gave a modal ploidy level at approximately 2.5n in one case, but a shift to a higher ploidy level was observed in other embryos. In the progenies between triploid hybrid females and males, the ploidy level at approximately 3.0n (chromosome numbers 74, 75, 76) was most frequent. The cytogenetic results of the progenies suggest the production of aneuploid gametes with a modal ploidy level at approximately 1.5n in triploid hybrids. However, a shift to higher chromosome numbers in gametes was observed in certain cases, suggesting the involvement of mortality selection of gametes and/or zygotes with lower chromosome numbers.

Production of Tetraploid Gynogenetic Loach Using Diploid Eggs of Natural Tetraploid Loach, Misgurnus anguillicaudatus, Fertilized with UV-Irradiated Sperm of Megalobrama amblycephala without Treatments for Chromosome Doubling

The gynogenesis phenomenon in nature mainly appears in the reproduction of fish and invertebrates. So far, gynogenesis has been successfully induced in many fish species with the aid of some physical or chemical methods for chromosome doubling. However, few fish can produce gynogenetic progenies, genetically identical or similar to the somatic cells of the mothers, without a treatment for the doubling of chromosomes, which may be related to apomixis, premeiotic endoreduplication, or premeiotic endomitosis. At present, no studies are available about fish with normal ovarian structures producing gynogenetic progenies that could spontaneously double their chromosomes. According to the analyses of flow cytometry, chromosome number, and microsatellites, we found that, with the use of UV-irradiated sperm of blunt snout bream Megalobrama amblycephala, tetraploid loach Misgurnus anguillicaudatus produced tetraploid gynogenetic progenies without any treatments for the doubling of chromosomes. To determine the genetic relationships of gynogenetic progenies and their maternal parent, microsatellite genotyping was conducted. The results indicated that the reason for spontaneous chromosome duplication in gynogenetic progenies may be cytokinesis or inhibition of the extrusion of the second polar body. This is the first report on fish with normal ovarian structures that can produce gynogenetic progenies which spontaneously double their chromosomes and which are genetically identical or similar to the somatic cells of the mothers.

Meiotic chromosome configurations in triploid progeny from reciprocal crosses between wild-type diploid and natural tetraploid loach Misgurnus anguillicaudatus in China.

Here, we showed meiotic chromosome configurations prepared from oocyte germinal vesicles and spermatocytes of triploid loaches produced from reciprocal crosses between wild-type diploids (2n = 50) obtained from Dalian, Liaoning Province, China and natural tetraploids (4n = 100) from Chibi, Hubei Province, China. Major meiotic cells in triploids comprised 25 bivalents and 25 univalents, but cells with one to five trivalents were also observed. When three homologous chromosomes bearing nucleolar organizing regions (NOR) were identified with the detection of signals or positive sites by silver staining, chromomycin A3 staining and fluorescence in situ hybridization with a 5.8S + 28S rDNA probe, two third of selected triploid cells gave a configuration including one bivalent with two NORs (association of two homologous chromosomes) and one univalent with one NOR. However, other triploid cells showed three univalent each of which had one NOR, suggesting a failure of synapsis between homologous chromosomes. These results suggested that triploid female and male should produce aneuploid gametes with the theoretical mode at 1.5n (37 or 38 chromosomes).

Length-weight relationships of diploid and tetraploid loach Misgurnus anguillicaudatus (Cantor, 1842) from the Yangtze River basin, China

Summary Length-weight relationships (LWRs) of diploid and tetraploid loach Misgurnus anguillicaudatus from the Yangtze River basin, China were estimated and compared.

Mitochondrial genome of the natural tetraploid loach Misgurnus anguillicaudatus

The mitochondrial genome of the natural tetraploid loach Misgurnus anguillicaudatus is a circular molecule of 16,645 bp in length, containing 13 protein-coding genes, 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and two main noncoding regions (the control region and the origin of the light strand replication). Most of the genes are encoded on the heavy strand, except for ND6 and eight tRNAs. All the protein-coding genes are initiated with ATG except for COX1, which began with GTG instead. However, the termination codons of 13 protein-coding genes are varied with TAA, TA-, T-- or TAG. The control region is 917 bp in length and located between the tRNAPro and tRNAPhe genes, some typical conserved elements (TAS, CSB1-3 and CSB D-F) were found in this region. All these features reflect a typical vertebrate mitochondrial gene arrangement of the tetraploid M. anguillicaudatus.

Chromosome banding and FISH with rDNA probe in the diploid and tetraploid loach Misgurnus anguillicaudatus

The chromosomes of the diploid and tetraploid loach Misgurnus anguillicaudatus were analyzed by staining with Ag, chromomycin A3 (CMA3)/distamycin A (DA), and DA/4′,6-diamidino-2-phenylindole (DAPI), and using fluorescence in situ hybridization (FISH) with 5.8S + 28S rDNA as a probe. Nucleolus organizer regions (NORs) were mapped to the telomeric region of the short arms of the largest (first) metacentric chromosome pair in the diploid loach with 2n = 50 and the homologous quartet in the tetraploid loach with 4n = 100. The NORs were positive at the same region of the first metacentric chromosome for Ag and CMA3/DA stainings, but negative for DA/DAPI staining. Four signals at the homologs within the same quartet suggest the duplication of the entire genome from diploid to tetraploid status. However, a size difference was detected between the rDNA signals by FISH and CMA3 banding.