Isolation and characterization of microsatellite loci in the goldfish Carassius auratus

Genotype data not consistent with clonal transmission of sea turtle fibropapillomatosis or goldfish schwannoma

Recent discoveries of transmissible cancers in multiple bivalve species suggest that direct transmission of cancer cells within species may be more common than previously thought, particularly in aquatic environments. Fibropapillomatosis occurs with high prevalence in green sea turtles ( Chelonia mydas) and the geographic range of disease has increased since fibropapillomatosis was first reported in this species. Widespread incidence of schwannomas, benign tumours of Schwann cell origin, reported in aquarium-bred goldfish (Carassius auratus), suggest an infectious aetiology. We investigated the hypothesis that cancers in these species arise by clonal transmission of cancer cells. Through analysis of polymorphic microsatellite alleles, we demonstrate concordance of host and tumour genotypes in diseased animals. These results imply that the tumours examined arose from independent oncogenic transformation of host tissue and were not clonally transmitted. Further, failure to experimentally transmit goldfish schwannoma via water exposure or inoculation suggest that this disease is unlikely to have an infectious aetiology.

CROSS-SPECIES AMPLIFICATION STUDY OF Tor douronensis AND Tor tambroides USING MICROSATELLITES FROM OTHER CYPRINIDS

This study examined twenty six microsatellite primers developed from three cyprinid fishes (Cyprinus carpio, Barbus barbus and Barbonymus gonionotus) in two indigenous mahseer, Tor douronensis and T. tambroides. A total of 10 (38%) and 12 (46%) primers were successfully amplified producing four and five polymorphic loci in T. douronensis and T. tambroides, respectively. The number of alleles per locus ranging from 2 to 5 and 2 to 7 in T. douronensis and T. tambroides, respectively. A significant deviation from Hardy-Weinberg equilibrium (HWE) was observed at three loci (Barb37, Barb59 and Barb62) in one or more populations in T. tambroides while two loci (Barb37 and Barb62) were deviated in T. douronensis population of Batang Ai. Bayesian cluster analysis performed with STRUCTURE showed that the most likely K value identified was K = 2 with no evidence of population substructuring, similar to those identified by the UPGMA dendrogram. The low genetic distances among populations were also supported by low interpopulation genetic differences (FST) among pairwise populations in both mahseer. Overall, the identified microsatellite loci exhibit promise for use in fine scale population structure analysis of T. douronensis and T. tambroides natural populations.

Application of microsatellite markers in conservation genetics and fisheries management: recent advances in population structure analysis and conservation strategies

Microsatellites are the most popular and versatile genetic marker with myriads of applications in population genetics, conservation biology, and evolutionary biology. These are the arrays of DNA sequences, consisting of tandemly repeating mono-, di-, tri-, and tetranucleotide units, which are distributed throughout the genomes of most eukaryotic species. Microsatellites are codominant in nature, highly polymorphic, easily typed, and Mendelian inherited, all properties which make them very suitable for the study of population structure and pedigree analysis and capable of detecting differences among closely related species. PCR for microsatellites can be automated for identifying simple sequence repeat polymorphism. Small amount of blood samples or alcohol preserved tissue is adequate for analyzing them. Most of the microsatellites are noncoding, and therefore variations are independent of natural selection. These properties make microsatellites ideal genetic markers for conservation genetics and fisheries management. This review addresses the applications of microsatellite markers in conservation genetics and recent advances in population structure analysis in the context of fisheries management.

Individual identification of goldfish from eye morphology: the eye mark method

We developed an individual identification method for goldfish based on morphological variation of the iris. Each goldfish has a few dark lines (eye marks) in the rostral and caudal portion of the iris, which are blood vessels underneath the silvery reflective layer. Through the blood vessels and the locally thin reflective layer, the pigment cell layer is partially visible as a dark line. The pattern of the blood vessels was found to be temporally stable and unique to each individual. Using this feature, we successfully identified 10 individual goldfish, each sampled three times within a 4-month time period. The eye mark identification method was confirmed for a further 20 goldfish by comparison with identification based on screening at polymorphic microsatellite loci. The eye mark method is 100% accurate and can be used for studies in which multiple observations of individually identified goldfish are needed over long time periods, to avoid invasive tagging or individual housing that may affect the behavior of the fish.

Characterization of polymorphic microsatellite markers and genetic diversity in wild bronze featherback, Notopterus notopterus (Pallas, 1769)

Six polymorphic microsatellite DNA loci were identified in the primitive fish, bronze featherback, Notopterus notopterus for the first time and demonstrated significant population genetic structure. Out of the six primers, one primer (NN90) was specific to N. notopterus (microsatellite sequence within the RAG1 gene) and five primers were product of successful cross-species amplification. Sixty-four primers available from 3 fish species of order Osteoglossiformes and families Notopteridae and Osteoglossidae were tested to amplify homologous microsatellite loci in N. notopterus. Fifteen primer pairs exhibited successful cross-priming PCR product. However, polymorphism was detected only at five loci. To assess the significance of these six loci (including NN90) in population genetic study, 215 samples of N. notopterus from five rivers, viz Satluj, Gomti, Yamuna, Brahmaputra and Mahanadi were analyzed. The five sample sets displayed different diversity levels and observed heterozygosity ranged from 0.6036 to 0.7373. Significant genotype heterogeneity (P < 0.0001) and high FST (0.2205) over all loci indicated that the samples are not drawn from the same genepool. The identified microsatellite loci are promising for use in fine-scale population structure analysis of N. notopterus.

Molecular identification of hybrids of the invasive gibel carp Carassius auratus gibelio and crucian carp Carassius carassius in Swedish waters

Both mitochondrial DNA sequence and two nuclear microsatellite markers were used to confirm the identity of the first record of Carassius auratus gibelio in the western (Swedish) Baltic Sea region. A total of 49 fishes were analysed, where 22 were from three Swedish sites connected to the Baltic Sea. The D-loop mitochondrial DNA sequences showed that 16 of 22 Swedish fishes were related to C. a. gibelio. The phylogenetic analysis of these sequences showed that these fish are probably not native, but represent different lineages of C. a. gibelio from China, Japan and Russia. All except three of these 16 fishes had microsatellite alleles suggesting hybridization with Carassius carassius. These findings suggest that a cryptic invasion of C. a. gibelio might be in progress.

Attempt at cloning high-quality goldfish breed ‘Ranchu’ by fin-cultured cell nuclear transplantation

The viability of ornamental fish culture relies on the maintenance of high-quality breeds. To improve the profitability of culture operations we attempted to produce cloned fish from the somatic nucleus of the high-quality Japanese goldfish (Carassius auratus auratus) breed ‘Ranchu’. We transplanted the nucleus of a cultured fin-cell from an adult Ranchu into the non-enucleated egg of the original goldfish breed ‘Wakin’. Of the 2323 eggs we treated, 802 underwent cleavage, 321 reached the blastula stage, and 51 reached the gastrula stage. Two of the gastrulas developed until the hatching stage. A considerable number of nuclear transplants retained only the donor nucleus. Some of these had only a 2n nucleus derived from the same donor fish. Our results provide insights into the process of somatic cell nuclear transplantation in teleosts, and the cloning of Ranchu.

Cross-species amplification of 36 cyprinid microsatellite loci in Phoxinus phoxinus (L.) and Scardinius erythrophthalmus (L.)

Background

To conduct phylogeographic or population genetic studies, an adequate number of DNA markers for the focal species are required. Due to severe unavailability of genotype markers of any kind for the species Eurasian minnow (Phoxinus phoxinus L.) and rudd (Scardinius erythrophthalmus L.), we set out to attempt cross-amplification of a set of microsatellite loci from related species.

Findings

We tested 36 cyprinid microsatellite loci for cross-species amplification in minnow and rudd. Fifteen species-locus combinations produced amplifications in minnow, seven being polymorphic, while 18 combinations amplified in rudd, nine of these being polymorphic.

Conclusions

The positive cross-species amplifications present potential contributions to the establishment of genetic marker sets for population genetics studies of the two focal species.

Population genetics and management units of invasive common carp Cyprinus carpio in the Murray-Darling Basin, Australia

Common carp Cyprinus carpio were introduced into Australia on several occasions and are now the dominant fish in the Murray-Darling Basin (MDB), the continent's largest river system. In this study, variability at 14 microsatellite loci was examined in C. carpio (n = 1037) from 34 sites throughout the major rivers in the MDB, from 3 cultured populations, from Prospect Reservoir in the Sydney Basin and from Lake Sorrell in Tasmania. Consistent with previous studies, assignment testing indicated that the Boolara, Yanco and koi strains of C. carpio are present in the MDB. Unique to this study, however, the Prospect strain was widely distributed throughout the MDB. Significant genetic structuring of populations (Fisher's exact test, AMOVA and distribution of the different strains) amongst the MDB sub-drainages was detected, and was strongly associated with contemporary barriers to dispersal and population history. The distributions of the strains were used to infer the history of introduction and spread of C. carpio in the MDB. Fifteen management units are proposed for control programmes that have high levels of genetic diversity, contain multiple interbreeding strains and show no evidence of founder effects or recent population bottlenecks.

Microsatellite evolution in vertebrates: inference from AC dinucleotide repeats

We analyze published data from 592 AC microsatellite loci from 98 species in five vertebrate classes including fish, reptiles, amphibians, birds, and mammals. We use these data to address nine major questions about microsatellite evolution. First, we find that larger genomes do not have more microsatellite loci and therefore reject the hypothesis that microsatellites function primarily to package DNA into chromosomes. Second, we confirm that microsatellite loci are relatively rare in avian genomes, but reject the hypothesis that this is due to physical constraints imposed by flight. Third, we find that microsatellite variation differs among species within classes, possibly relating to population dynamics. Fourth, we reject the hypothesis that microsatellite structure (length, number of alleles, allele dispersion, range in allele sizes) differs between poikilotherms and homeotherms. The difference is found only in fish, which have longer microsatellites and more alleles than the other classes. Fifth, we find that the range in microsatellite allele size at a locus is largely due to the number of alleles and secondarily to allele dispersion. Sixth, length is a major factor influencing mutation rate. Seventh, there is a directional mutation toward an increase in microsatellite length. Eighth, at the species level, microsatellite and allozyme heterozygosity covary and therefore inferences based on large-scale studies of allozyme variation may also reflect microsatellite genetic diversity. Finally, published microsatellite loci (isolated using conventional hybridization methods) provide a biased estimate of the actual mean repeat length of microsatellites in the genome.

A test of the hypothesis of an autopolyploid vs. allopolyploid origin for a tetraploid lineage: application to the genus barbus (Cyprinidae)

A new method is described for determination of the origin of polyploid lineages. It tests the hypothesis that a tetraploid lineage originated via autopolyploidization vs. allopolyploidization. The method is based on the hypothesis that, in the case of autopolyploidy, any genetic marker in the first tetraploid ancestor is represented by two copies (one for each homoeologous chromosome of the haploid complement), whereas in allopolyploidy some markers absent from one of the hybridizing species will display one copy at most. The model requires knowledge of the phylogeny (topology and branch lengths) of a sample of species descending from the same tetraploidization event, together with the number of homoeologous copies present in each species for a set of neutral markers. The likelihood of a given proportion of the markers being present in both homoeologous chromosome pairs of the ancestral tetraploid is expressed as a function of the deletion rate of a marker. In the case of an autopolyploid origin, this proportion equals one. A likelihood-ratio test was carried out to test this hypothesis. The method was used to examine five microsatellite loci in eight species of Barbus (sensu lato). Assuming the validity of the hypotheses on phylogenetic relationships and evolutionary rates, the test rejects the possibility that European tetraploid barbs originated through autopolyploidy. This is the first test that can reject autopolyploidy, and it would appear particularly useful for phylogenetic studies in taxa where hybridization is known and where, consequently, undetected reticulate evolution may impair phylogenetic reconstruction.