Genome-wide association study of host resistance to the ectoparasite Ichthyophthirius multifiliis in the Amazon fish Colossoma macropomum.

BACKGROUND: Tambaqui, Colossoma macropomum, is the most important native fish species farmed in South America, particularly in Brazil, where its production is limited in the southern and southeastern regions due to disease outbreaks caused by the parasite Ichthyophthirius multifiliis. Therefore, genome level analysis to understand the genetic architecture of the host resistance against I. multifiliis is fundamental to improve this trait in tambaqui. The objective of the present study was to map QTL (quantitative trait loci) associated with resistance to I. multifiliis in tambaqui by GWAS (genome-wide association study). METHODS AND RESULTS: Individuals belonging to seven families, which were previously submitted to an experimental challenge to assess the natural resistance to the parasite I. multifiliis, were used for genomic analysis. A total of 7717 SNPs were identified in this population by ddRAD (double digest restriction site associated DNA). GWAS revealed four SNPs significantly associated in the LGs (linkage groups) 2, 9, 11 and 20 for the traits time of death and parasite load. The SNPs explained a low proportion of the variance to I. multifiliis resistance for time of death and parasite load (about 0.622% and 0.375%, respectively). The SNPs were close to 11 genes related to the immune system: abcf3, znf830, ccr9, gli3, ackr4, tbata, ndr2, tgfbr3, nhej1, znf644b, and cldn10a. CONCLUSIONS: In conclusion, the resistance to I. multifiliis is probably under polygenic control in tambaqui, in which different QTLs of low variance can be involved in the immune responses against this ectoparasite.

Comparative eye and liver differentially expressed genes reveal monochromatic vision and cancer resistance in the shortfin mako shark (Isurus oxyrinchus).

The shortfin mako, Isurus oxyrinchus is an oceanic pelagic shark found worldwide in tropical and subtropical waters. However, the understanding of its biology at molecular level is still incipient. We sequenced the messenger RNA isolated from eye and liver tissues. De novo transcriptome yielded a total of 705,940 transcripts. A total of 3774 genes were differentially expressed (DEGs), with 1612 in the eye and 2162 in the liver. Most DEGs in the eye were related to structural and signaling functions, including nonocular and ocular opsin genes, whereas nine out of ten most overexpressed genes in the liver were related to tumor suppression, wound healing, and human diseases. Furthermore, DEGs findings provide insights on the monochromatic shark vision and a repertory of cancer-related genes, which may be insightful to elucidate shark resistance to cancer. Therefore, our results provide valuable sequence resources for future functional and population studies.

Development of a multi-species SNP array for serrasalmid fish Colossoma macropomum and Piaractus mesopotamicus.

Scarce genomic resources have limited the development of breeding programs for serrasalmid fish Colossoma macropomum (tambaqui) and Piaractus mesopotamicus (pacu), the key native freshwater fish species produced in South America. The main objectives of this study were to design a dense SNP array for this fish group and to validate its performance on farmed populations from several locations in South America. Using multiple approaches based on different populations of tambaqui and pacu, a final list of 29,575 and 29,612 putative SNPs was selected, respectively, to print an Axiom AFFYMETRIX (THERMOFISHER) SerraSNP array. After validation, 74.17% (n = 21,963) and 71.25% (n = 21,072) of SNPs were classified as polymorphic variants in pacu and tambaqui, respectively. Most of the SNPs segregated within each population ranging from 14,199 to 19,856 in pacu; and from 15,075 to 20,380 in tambaqui. Our results indicate high levels of genetic diversity and clustered samples according to their hatchery origin. The developed SerraSNP array represents a valuable genomic tool approaching in-depth genetic studies for these species.

Genetic Characterization of the Fish Piaractus brachypomus by Microsatellites Derived from Transcriptome Sequencing.

The pirapitinga, Piaractus brachypomus (Characiformes, Serrasalmidae), is a fish from the Amazon basin and is considered to be one of the main native species used in aquaculture production in South America. The objectives of this study were: (1) to perform liver transcriptome sequencing of pirapitinga through NGS and then validate a set of microsatellite markers for this species; and (2) to use polymorphic microsatellites for analysis of genetic variability in farmed stocks. The transcriptome sequencing was carried out through the Roche/454 technology, which resulted in 3,696 non-redundant contigs. Of this total, 2,568 contigs had similarity in the non-redundant (nr) protein database (Genbank) and 2,075 sequences were characterized in the categories of Gene Ontology (GO). After the validation process of 30 microsatellite loci, eight markers showed polymorphism. The analysis of these polymorphic markers in farmed stocks revealed that fish farms from North Brazil had a higher genetic diversity than fish farms from Southeast Brazil. AMOVA demonstrated that the highest proportion of variation was presented within the populations. However, when comparing different groups (1: Wild; 2: North fish farms; 3: Southeast fish farms), a considerable variation between the groups was observed. The FST values showed the occurrence of genetic structure among the broodstocks from different regions of Brazil. The transcriptome sequencing in pirapitinga provided important genetic resources for biological studies in this non-model species, and microsatellite data can be used as the framework for the genetic management of breeding stocks in Brazil, which might provide a basis for a genetic pre-breeding programme.

Microsatellite loci in the tiger shark and cross-species amplification using pyrosequencing technology.

The tiger shark (Galeocerdo cuvier) has a global distribution in tropical and warm temperate seas, and it is caught in numerous fisheries worldwide, mainly as bycatch. It is currently assessed as near threatened by the International Union for Conservation of Nature (IUCN) Red List. In this study, we identified nine microsatellite loci through next generation sequencing (454 pyrosequencing) using 29 samples from the western Atlantic. The genetic diversity of these loci were assessed and revealed a total of 48 alleles ranging from 3 to 7 alleles per locus (average of 5.3 alleles). Cross-species amplification was successful at most loci for other species such as Carcharhinus longimanus, C. acronotus and Alopias superciliosus. Given the potential applicability of genetic markers for biological conservation, these data may contribute to the population assessment of this and other species of sharks worldwide.

Structure and Genetic Variability of the Oceanic Whitetip Shark, Carcharhinus longimanus, Determined Using Mitochondrial DNA.

Information regarding population structure and genetic connectivity is an important contribution when establishing conservation strategies to manage threatened species. The oceanic whitetip shark, Carcharhinus longimanus, is a highly migratory, large-bodied, pelagic shark listed by the IUCN (International Union for Conservation of Nature) Red List as "vulnerable" throughout its range and "critically endangered" in the western north Atlantic. In 2014, the species was protected globally under Appendix II of CITES (Convention on International Trade in Endangered Species), limiting and regulating trade. This study used partial sequences of mitochondrial DNA (mtDNA) control region to determine the population genetic structure of oceanic whitetip sharks across the Atlantic and Indian Oceans. 724 base pairs were obtained from 215 individuals that identifed nine polymorphic sites and defined 12 distinct haplotypes. Total nucleotide diversity (π) was 0.0013 and haplotype diversity (h) was 0.5953. The Analysis of Molecular Variance (AMOVA) evidenced moderate levels of population structure (ɸST = 0.1039) with restricted gene flow between the western and eastern Atlantic Ocean, and a strong relationship between the latter region and the Indian Ocean. Even though the oceanic whitetip is a highly migratory animal the results presented here show that their genetic variability is slightly below average of other pelagic sharks. Additionally, this study recommends that at least two populations in the Atlantic Ocean should be considered distinct (eastern and western Atlantic) and conservation efforts should be focused in areas with the greatest genetic diversity by environmental managers.