Whole-genome resequencing infers genomic basis of giant phenotype in Siamese fighting fish(Betta splendens)

Understanding the genetic basis of phenotypes is of importance in evolutionary biology and for genetic improvement of economically valuable animals.The giant phenotype of the fighting fish,Betta splendens,provides a unique opportunity to explore the genetic architecture of overgrowth in body size.As such,we re-sequenced and analyzed the genomes of 54 fighting fish.Genome-wide FST and selective sweep analyses using 3582429 DNA variants revealed three genomic regions at chr1,chr9,and chr11 that were associated with the giant phenotype.With a total length of~3.5 Mb,these regions showed high divergence between the giant and non-giant bettas.In contrast,no signature of selection was detected in the wild-type fish.Transcriptome analysis of brain and muscle samples from giant and normal bettas identified 14 candidate genes that were likely responsible for the giant phenotype.Overall,our data provide novel insights into the genetic basis of body size variation.The genome sequences,transcriptome sequences,DNA sequence variants,and candidate genes for body size provide valuable resources for further biological and evolutionary studies,as well as for rapid improvement in growth-related traits.

Who eats whom,when and why?Juvenile cannibalism in fish Asian seabass

While juvenile cannibalism plays an important role in the evolution of organisms in natural populations,it is a serious problem in aquaculture.A number of genetic and environmental factors result in different rates of cannibalism.Whether there is kin recognition in juvenile cannibalism in fish is poorly understood.We studied cannibalism and kinship recognition in juveniles of Asian seabass using molecular parentage analysis with polymorphic microsatellites.In the three mass crosses,under an ordinary feeding scheme without size grading,the rate of juvenile loss due to cannibalism was 1.08% per day.In the group without feeding for 24 h,2.30%±0.43% of offspring per day were lost within 24 h due to cannibalism.We detected that juveniles avoided cannibalizing their siblings when they were not hungry,whereas cannibalism among siblings increased when they were hungry.These data suggest that there is kin discrimination in fish cannibalism.Raising genetically closely related offspring in the same tanks and appropriate levels of feeding may reduce the rate of cannibalism.We hypothesized that the chemical cues for kin discrimination might be secreted by fish skins.To test this hypothesis,we analyzed gene expression profiles in the skins of juveniles under slightly and very hungry conditions using RNA sequencing and bioinformatics analysis.Genes differently expressed under slightly and very hungry conditions were identified.Among them,genes from the trypsin family were significantly downregulated under starved conditions,suggesting that they may play a role in kin discrimination.