Mechanism Of Sex Determination Research Articles

How to get rid of diploid bumblebee males – variability in wing size and shape does not allow within‐colony ploidy discrimination

AbstractThe bumblebee Bombus terrestris L. (Hymenoptera: Apidae) is an effective pollinator of both wild and cultivated plants and essential for the pollination of various important greenhouse crops. Because of its sex determination mechanism, homozygosity of the complementary sex determination (csd) locus due to inbreeding causes fertilized eggs to develop into diploid males, which represent a serious disadvantage for the colonies as their presence decreases colony growth and survival. The identification of diploid males is thus important from both ecological and economic points of view. In the present study, we applied the geometric morphometrics method on wing shape and size of B. terrestris diploid and haploid males at overall and intra‐colony levels to investigate wing changes between the two groups. We found that changes in wing shape concerned almost all cells investigated and male diploidy resulted in a narrower and slightly longer configuration. In addition, diploid male wings presented a very high variation both in size and shape, likely due to sub‐optimal temperature of incubation and food availability during their larval development. This strong variation of diploid male wings makes the ploidy discrimination by wing geometric morphometrics inaccurate based on small reference samples at the intra‐colony level even with allometric data correction, whereas it is accurate (precision >90%) at the overall level, in which sample size is high enough (i.e., 500 individuals). Therefore, our results indicated the need to create a large dataset to allow the analysis of few samples, as is the case with studies of wild bumblebee populations, small rearing companies, or preserved museum specimens. For this reason, we provide a large database of B. terrestris wing Procrustes coordinates (500 samples) to the bumblebee scientific community for use in the analysis of the determination of diploid male individuals.

Transcriptome analysis provides insights into differentially expressed long noncoding RNAs between the testis and ovary in golden pompano (Trachinotus blochii)

The golden pompano (Trachinotus blochii) is a warm water fish that is widely distributed in tropical and subtropical waters. T. blochii is one of the most important economic species in China where it is produced in marine cage culture; however, few studies have been performed on the mechanism of sex determination and differentiation, and there are no obvious morphological differences between males and females. To further understand the role of long non-coding RNAs (lncRNAs) in sex determination and gonadal development of T. blochii, we conducted a tran-scriptome analysis of T. blochii ovaries and testes. In this study, a total of 530,128,262 clean reads were produced from six cDNA libraries, after stringent filtering. The RNA-seq analysis yielded 13,509 novel lncRNAs, 2621 novel mRNAs, and 18,683 known mRNA transcripts with 4909 and 10,410 differentially expressed lncRNAs and mRNAs. The Gene Ontology (GO) enrichment patterns between the lncRNAs and mRNAs were different. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis confirmed that some of the differentially expressed mRNAs and target genes of the lncRNAs were mainly associated with several sex determination and gonadal development signaling pathways, including the GnRH signaling pathway, the Wnt signaling pathway, and the insulin signaling pathway. The lncRNA-mRNA co-expression network analysis showed that the lncRNA TCONS_00083175 may play a key role in the T. blochii sex differentiation. The findings broaden our understanding of lncRNAs and gonad genetics, and provide new insight into the function of lncRNAs in sex differentiation and highlight a key lncRNA for future studies.

Identification and Characterization of Dimorphic Expression of Sex-Related Genes in Rock Bream, a Fish With Multiple Sex Chromosomes.

The rock bream (Oplegnathus fasciatus) is a typical fish with a unique multiple sex chromosome system. In this study, we investigated the gene expression profiling in the gonads and brains of both males and females using RNA-Seq to identify sex-related genes and pathways. In accordance with the dimorphic expression profiles, combined with Gene ontology and KEGG enrichment analyses, a number of potential genes and pathways associated with sex determination were obtained from transcriptional analysis, especially some sex-biased genes and pathways. Next, we selected 18 candidate genes and analyzed their expression in different tissues and developmental stages. We found that the expression levels of Amh, Dmrt1, Sox9, Dmrtb1, and Nanos2 were significantly higher in the testis than those in the ovary or other tissues, whereas the expression levels of ZP4, Bouncer, RNF208, FoxH1, and TOB were significantly higher in the ovary than those in the testis. Furthermore, the expression levels of these genes in different developmental stages of gonads also showed sexually dimorphic patterns, suggesting that they might play important roles during gonadal development. These genes are useful markers for investigating sex determination and differentiation in rock bream. The findings of this study can provide insights into the molecular mechanisms of sex determination and differentiation in fish with multiple sex chromosome systems.

A feminizing switch in a hemimetabolous insect.

The mechanism of sex determination remains poorly understood in hemimetabolous insects. Here, in the brown planthopper (BPH), Nilaparvata lugens, a hemipteran rice pest, we identified a feminizing switch or a female determiner (Nlfmd) that encodes a serine/arginine-rich protein. Knockdown of Nlfmd in female nymphs resulted in masculinization of both the somatic morphology and doublesex splicing. The female-specific isoform of Nlfmd, Nlfmd-F, is maternally deposited and zygotically transcribed. Depletion of Nlfmd by maternal RNAi or CRISPR-Cas9 resulted in female-specific embryonic lethality. Knockdown of an hnRNP40 family gene named female determiner 2 (Nlfmd2) also conferred masculinization. In vitro experiments showed that an Nlfmd2 isoform, NlFMD2340, bound the RAAGAA repeat motif in the Nldsx pre-mRNA and formed a protein complex with NlFMD-F to modulate Nldsx splicing, suggesting that NlFMD2 may function as an RNA binding partner of the feminizing switch NlFMD. Our results provide novel insights into the diverse mechanisms of insect sex determination.

Sex-specific markers developed by genome-wide 2b-RAD sequencing confirm an XX/XY sex determination system in Chinese longsnout catfish (Leiocassis longirostris)

Longsnout catfish (Leiocassis longirostris), an important commercial fish in China, shows significant sexual size dimorphism. However, the sex determination system and mechanism of longsnout catfish remain unknown. In this study, an effective protocol of artificial gynogenesis using heterologous sperm was successfully developed and male heterogametic XX/XY sex determination system was revealed in longsnout catfish. Subsequently, sex-specific markers were developed based on isolated homologous X-specific and Y-specific sequences by 2b-RAD sequencing and PCR amplification. Finally, the Y-specific and XY-shared primers were developed and validated in a full-sib family, a gynogenetic population and two local populations, which further verify the sex determination system. Therefore, this study not only reveals XX/XY sex determination system in longsnout catfish, but also provides applicable sex-specific markers for production of all-male population for aquaculture in the future.

A single intronic single nucleotide polymorphism in splicing site of steroidogenic enzyme hsd17b1 is associated with phenotypic sex in oyster pompano, Trachinotus anak.

Teleosts show varied master sex determining (MSD) genes and sex determination (SD) mechanisms, with frequent turnovers of sex chromosomes. Tracing the origins of MSD genes and turnovers of sex chromosomes in a taxonomic group is of particular interest in evolutionary biology. Oyster pompano (Trachinotus anak), a marine fish, belongs to the family Carangidae, in which 17b-hydroxysteroid dehydrogenase 1 (hsd17b1) has repeatedly evolved to an MSD gene. Whole-genome resequencing identified a single nucleotide polymorphism (SNP) at chromosome 24 to be strictly associated with phenotypic sex, with females being the heterozygous sex. This SNP is located in a splicing site at the first exon/intron boundary of hsd17b1. The Z-linked SNP results in malfunction of all spliced isoforms, whereas the W-linked isoforms were predicted to have open reading frames that are conserved among vertebrates, suggesting that hsd17b1 is a female-determining gene. The differential alternative splicing patterns of ZZ and ZW genotypes were consistently observed both in undifferentiated stages and differentiated gonads. We observed elevated recombination around the SD locus and no differentiation between Z and W chromosomes. The extreme diversity of mutational mechanisms that hsd17b1 evolves to an MSD gene highlights frequent in situ turnovers between sex chromosomes in the Carangidae.

Chromosome-level assembly reveals a putative Y-autosomal fusion in the sex determination system of the Greenland Halibut (Reinhardtius hippoglossoides).

Despite the commercial importance of Greenland Halibut (Reinhardtius hippoglossoides), important gaps still persist in our knowledge of this species, including its reproductive biology and sex determination mechanism. Here, we combined single-molecule sequencing of long reads (Pacific Sciences) with chromatin conformation capture sequencing (Hi-C) data to assemble the first chromosome-level reference genome for this species. The high-quality assembly encompassed more than 598 Megabases (Mb) assigned to 1594 scaffolds (scaffold N50 = 25 Mb) with 96% of its total length distributed among 24 chromosomes. Investigation of the syntenic relationship with other economically important flatfish species revealed a high conservation of synteny blocks among members of this phylogenetic clade. Sex determination analysis revealed that similar to other teleost fishes, flatfishes also exhibit a high level of plasticity and turnover in sex determination mechanisms. A low-coverage whole-genome sequence analysis of 198 individuals revealed that Greenland Halibut possesses a male heterogametic XY system and several putative candidate genes implied in the sex determination of this species. Our study also suggests for the first time in flatfishes that a putative Y-autosomal fusion could be associated with a reduction of recombination typical of the early steps of sex chromosome evolution.

Application of SNP in Genetic Sex Identification and Effect of Estradiol on Gene Expression of Sex-Related Genes in Strongylocentrotus intermedius.

Sea urchin (Strongylocentrotus intermedius) is an economically important mariculture species in Asia, and its gonads are the only edible part. The efficiency of genetic breeding in sea urchins is hampered due to the inability to distinguish gender by appearance. In this study, we first identified a sex-associated single nucleotide polymorphism (SNP) by combining type IIB endonuclease restriction site-associated DNA sequencing (2b-RAD-seq) and genome survey. Importantly, this SNP is located within spata4, a gene specifically expressed in male. Knocking down of spata4 by RNA interference (RNAi) in male individuals led to the downregulation of other conserved testis differentiation-related genes and germ cell marker genes. We also revealed that sex ratio in this validated culture population of S. intermedius is not 1:1. Moreover, after a 58-day feeding experiment with estradiol, the expression levels of several conserved genes that are related to testis differentiation, ovary differentiation, and estrogen metabolism were dynamically changed. Taken together, our results will contribute toward improving breeding efficiency, developing sex-controlled breeding, and providing a solid base for understanding sex determination mechanisms in sea urchins.

Screening and characterization of sex-specific markers for the hybrid (Megalobrama amblycephala ♀ × Ancherythroculter nigrocauda ♂) based on 2b-RAD and transcriptome sequencing

Sex-specific molecular markers provide significant molecular basis for sex control breeding biotechnologies to produce mono-sex fish population in aquaculture breeding programs. “Xianfeng No. 2”, a new hybrid of Megalobrama amblycephala (M. amblycephala) (♀) × Ancherythroculter nigrocauda (A. nigrocauda) (♂), with the females growing faster than males, is one of an important aquaculture fish species in China. In order to avoid genetic contamination impact on the ecological environment, maintain gene purity and improve the economic value, it is greatly important to cultivate all-female strains. In this study, artificially induced gynogenesis was performed in the hybrid females and it was found that all progenies were females. Then, we used 2b-RAD-seq to screen the sex-specific markers of the hybrid species. Nine male-specific tags were firstly identified by the sequencing, and then two male-specific tags were screened and successfully validated by PCR amplification in both hybrid and paternal A. nigrocauda populations. Furthermore, one male-specific molecular marker ref57660–1 (326 bp) was validated by RNA-seq and quantitative interpretation from the gene expression level, which indicated the reliability of the marker. Together with the results of all females from gynogenesis population and the identified male-specific markers, it is suggested that this hybrid species is female homogametic (XX) with sex determination mechanism being XX/XY type. The identified sex-specific markers are of great value to improve the efficiency of all-male/all-female breeding practices for this hybird species as well as for paternal A. nigrocauda.

Identification of the sex-determining factor in the liverwort Marchantia polymorpha reveals unique evolution of sex chromosomes in a haploid system

SummarySex determination is a central process for sexual reproduction and is often regulated by a sex determinant encoded on a sex chromosome. Rules that govern the evolution of sex chromosomes via specialization and degeneration following the evolution of a sex determinant have been well studied in diploid organisms. However, distinct predictions apply to sex chromosomes in organisms where sex is determined in the haploid phase of the life cycle: both sex chromosomes, female U and male V, are expected to maintain their gene functions, even though both are non-recombining. This is in contrast to the X-Y (or Z-W) asymmetry and Y (W) chromosome degeneration in XY (ZW) systems of diploids. Here, we provide evidence that sex chromosomes diverged early during the evolution of haploid liverworts and identify the sex determinant on the Marchantia polymorpha U chromosome. This gene, Feminizer, encodes a member of the plant-specific BASIC PENTACYSTEINE transcription factor family. It triggers female differentiation via regulation of the autosomal sex-determining locus of FEMALE GAMETOPHYTE MYB and SUPPRESSOR OF FEMINIZATION. Phylogenetic analyses of Feminizer and other sex chromosome genes indicate dimorphic sex chromosomes had already been established 430 mya in the ancestral liverwort. Feminizer also plays a role in reproductive induction that is shared with its gametolog on the V chromosome, suggesting an ancestral function, distinct from sex determination, was retained by the gametologs. This implies ancestral functions can be preserved after the acquisition of a sex determination mechanism during the evolution of a dominant haploid sex chromosome system.

MiRNA target prediction of avian Z-linked DMRT1 gene during sex determination in chicken (G. Gallus)

Sex determination in dimorphic animal, such as chicken (G. Gallus), is controlled by the expression of doublesex and mab-3 related transcription factor 1 (DMRT1) gene. This gene act as sex determination switch by critically needed for testis differentiation and as antagonist of ovarian development. miRNA, is belongs to short noncoding RNA which modulate gene expression in specific or board targeted genes. This study was aimed to predict miRNA(s) candidate targeted to DMRT1 expression in chicken. In silico method was employed to mining miRNA targeted to DMRT1 using three online databases namely miRDB, TargetScan, and microT-CDS. Following prediction, clustering was performed to select common miRNA(s) in minimal two databases for gene ontology (GO) analysis. Totally 78 miRNAs were targeted to DMRT1 3’UTR, and eight miRNA(s) were found in minimal two databases. The GO analysis found seven distinct biological functions in membrane, cytoplasm, protein binding, nucleus, integral component of membrane and molecular function, and all are related to the cell growth namely cell proliferation. According to the result, it shows the possibility to use selected candidate of miRNA(s) targeted to DMRT1 to reveal the sex determination mechanism at early stage of chicken development.

Screening and identification of female-specific DNA sequences in octaploid sturgeon using comparative genomics with high-throughput sequencing

In this study, six candidate female-specific DNA sequences of octaploid Amur sturgeon (Acipenser schrenckii) were identified using comparative genomic approaches with high-throughput sequencing data. Their specificity was confirmed by traditional PCR. Two of these sex-specific sequences were also validated as female-specific in other eight sturgeon species and two hybrid sturgeons. The identified female-specific DNA fragments suggest that the family Acipenseridae has a ZZ/ZW sex-determining system. However, one of the two DNA sequences has been deleted in some sturgeons such as Sterlet sturgeon (Acipenser ruthenus), Beluga (Huso huso) and Kaluga (H. dauricus). The difference of sex-specific sequences among sturgeons indicates that there are different sex-specific regions among species of sturgeon. This study not only provided the sex-specific DNA sequences for management, conservation and studies of sex-determination mechanisms in sturgeons, but also confirmed the capability of the workflow to identify sex-specific DNA sequences in the polyploid species with complex genomes.

Construction of a high-density linkage map and detection of sex-specific markers in Penaeus japonicus.

Penaeus japonicus is one of the most important farmed shrimp species in many countries. Sexual dimorphism is observed in P. japonicus, in which females grow faster and larger than males; therefore, a unisexual female culture of P. japonicus could improve the efficiency of productivity. However, the genetic mechanisms underlying sex determination in P. japonicus are unclear. In this study, we constructed a high-density genetic linkage map of P. japonicus using genotyping-by-sequencing (GBS) technology in a full-sib family. The final map was 3,481.98 cM in length and contained 29,757 single nucleotide polymorphisms (SNPs). These SNPs were distributed on 41 sex-averaged linkage groups, with an average inter-marker distance of 0.123 cM. One haplotype, harboring five sex-specific SNPs, was detected in linkage group 1 (LG1), and its corresponding confidence interval ranged from 211.840 to 212.592 cM. Therefore, this high-density genetic linkage map will be informative for genome assembly and marker-assisted breeding, and the sex-linked SNPs will be helpful for further studies on molecular mechanisms of sex determination and unisexual culture of P. japonicus in the future.

Early embryonic transcriptomes of Zeugodacus tau provide insight into sex determination and differentiation genes.

Zeugodacus tau (Walker) is an invasive pest. The sterile insect technique is an environment-friendly method for pest control. Understanding the mechanism of sex determination will contribute to improving efficiency of this technique. In this study, we identified the transformer (tra) gene in Z. tau. One female-specific and two male-specific isoforms of tra were found in Z. tau, and the male-specific splicing pattern of tra was found to occur 5 h after egg laying. We performed transcriptome sequencing at 1 h (E1), 5 h (E5), and 9 h (E9) after egg laying and obtained high-quality transcriptome libraries of early embryo development. We identified 13297 and 11713 differentially expressed genes (DEGs) from E5 versus E1 and E9 versus E1 comparisons, respectively. To explore the potential functions of the DEGs during embryonic development, Gene Ontology, Clusters of Orthologous Groups of proteins, and Kyoto Encyclopedia of Genes and Genomes analyses were performed. Twenty-six genes potentially involved in sex determination or differentiation, including Maleness-on-the-Y (MoY), were identified in Z. tau. To verify the transcriptome results, 15 genes were selected for quantitative real-time PCR validation. The results were consistent with the transcriptome sequencing results. Moreover, U2 small nuclear riboprotein auxiliary factor (U2AF-50), female lethal d (fl(2)d), and virilizer (vir) were highly expressed at E5, indicating that they may be related to the sex-specific splicing of tra. Further functional analysis is needed to confirm this speculation. Our data provide an insight into the mechanism underlying sex determination and differentiation in tephritid species.

Absence of complementary sex determination in two Leptopilina species (Figitidae, Hymenoptera) and a reconsideration of its incompatibility with endosymbiont-induced thelytoky.

Complementary sex determination (CSD) is a widespread sex determination mechanism in haplodiploid Hymenoptera. Under CSD, sex is determined by the allelic state of one or multiple CSD loci. Heterozygosity at one or more loci leads to female development, whereas hemizygosity of haploid eggs and homozygosity of diploid eggs results in male development. Sexual (arrhenotokous) reproduction normally yields haploid male and diploid female offspring. Under asexual reproduction (thelytoky), diploidized unfertilized eggs develop into females. Thelytoky is often induced by bacterial endosymbionts that achieve egg diploidization by gamete duplication. As gamete duplication leads to complete homozygosity, endosymbiont‐induced thelytokous reproduction is presumed to be incompatible with CSD, which relies on heterozygosity for female development. Previously, we excluded CSD in four Asobara (Braconidae) species and proposed a two‐step mechanism for Wolbachia‐induced thelytoky in Asobara japonica. Here, we conclusively reject CSD in two cynipid wasp species, Leptopilina heterotoma and Leptopilina clavipes. We further show that thelytoky in L. clavipes depends on Wolbachia titer but that diploidization and feminization steps cannot be separated, unlike in A. japonica. We discuss what these results reveal about the sex determination mechanism of L. clavipes and the presumed incompatibility between CSD and endosymbiont‐induced thelytoky in the Hymenoptera.

Against the mainstream: exceptional evolutionary stability of ZW sex chromosomes across the fish families Triportheidae and Gasteropelecidae (Teleostei: Characiformes).

Teleost fishes exhibit a breath-taking diversity of sex determination and differentiation mechanisms. They encompass at least nine sex chromosome systems with often low degree of differentiation, high rate of inter- and intra-specific variability, and frequent turnovers. Nevertheless, several mainly female heterogametic systems at an advanced stage of genetic differentiation and high evolutionary stability have been also found across teleosts, especially among Neotropical characiforms. In this study, we aim to characterize the ZZ/ZW sex chromosome system in representatives of the Triportheidae family (Triportheus auritus, Agoniates halecinus, and the basal-most species Lignobrycon myersi) and its sister clade Gasteropelecidae (Carnegiella strigata, Gasteropelecus levis, and Thoracocharax stellatus). We applied both conventional and molecular cytogenetic approaches including chromosomal mapping of 5S and 18S ribosomal DNA clusters, cross-species chromosome painting (Zoo-FISH) with sex chromosome-derived probes and comparative genomic hybridization (CGH). We identified the ZW sex chromosome system for the first time in A. halecinus and G. levis and also in C. strigata formerly reported to lack sex chromosomes. We also brought evidence for possible mechanisms underlying the sex chromosome differentiation, including inversions, repetitive DNA accumulation, and exchange of genetic material. Our Zoo-FISH experiments further strongly indicated that the ZW sex chromosomes of Triportheidae and Gasteropelecidae are homeologous, suggesting their origin before the split of these lineages (approx. 40-70 million years ago). Such extent of sex chromosome stability is almost exceptional in teleosts, and hence, these lineages afford a special opportunity to scrutinize unique evolutionary forces and pressures shaping sex chromosome evolution in fishes and vertebrates in general.

Sex-Determination Mechanisms among Populations within Cryptic Species Complex of Calotes (Squamata: Agamidae: Draconinae)

Sex-determination mechanisms and sex chromosomes are known to vary among reptile species and, in a few celebrated examples, within populations of the same species. The oriental garden lizard, Calotes versicolor, is one of the most intriguing species in this regard, exhibiting evidence of multiple sex-determination modes within a single species. One possible explanation for this unusual distribution is that in C. versicolor, different modes of sex determination are confined to a particular population or a species within a cryptic species complex. Here, we report on a population genetic analysis using SNP data from a methylation-sensitive DArT sequencing analysis and mitochondrial DNA data obtained from samples collected from six locations: three from Bangladesh and three from Thailand. Our aim was to determine whether C. versicolor is best described as a single species with multiple lineages or as multiple species, as well as if its sex-determination mechanisms vary within or between species. We present evidence that the latter possibility is the case and that C. versicolor comprises a complex of cryptic species. We also identify sex-linked markers within these species and use them to identify modes of sex determination. Overall, our results suggest that different sex-determination modes have evolved among closely related species and within populations of Agamid lizards.

Evolutionary Genomics of Sex-Related Chromosomes at the Base of the Green Lineage.

Although sex is now accepted as a ubiquitous and ancestral feature of eukaryotes, direct observation of sex is still lacking in most unicellular eukaryotic lineages. Evidence of sex is frequently indirect and inferred from the identification of genes involved in meiosis from whole genome data and/or the detection of recombination signatures from genetic diversity in natural populations. In haploid unicellular eukaryotes, sex-related chromosomes are named mating-type (MTs) chromosomes and generally carry large genomic regions where recombination is suppressed. These regions have been characterized in Fungi and Chlorophyta and determine gamete compatibility and fusion. Two candidate MT+ and MT− alleles, spanning 450–650 kb, have recently been described in Ostreococcus tauri, a marine phytoplanktonic alga from the Mamiellophyceae class, an early diverging branch in the green lineage. Here, we investigate the architecture and evolution of these candidate MT+ and MT− alleles. We analyzed the phylogenetic profile and GC content of MT gene families in eight different genomes whose divergence has been previously estimated at up to 640 Myr, and found evidence that the divergence of the two MT alleles predates speciation in the Ostreococcus genus. Phylogenetic profiles of MT trans-specific polymorphisms in gametologs disclosed candidate MTs in two additional species, and possibly a third. These Mamiellales MT candidates are likely to be the oldest mating-type loci described to date, which makes them fascinating models to investigate the evolutionary mechanisms of haploid sex determination in eukaryotes.

Identification of male-specific SNP markers and development of rapid PCR-based genetic sex identification method in channel catfish (Ictalurus punctatus)

Channel catfish (Ictalurus punctatus) is an important aquaculture species worldwide. Although studies of the sex determination mechanism of channel catfish began during the 1980s, the mechanism and sex-specific genes remain unclear. In this study, based on the results of sex-related quantitative trait locus (QTL) mapping and targeted next-generation sequencing (NGS) technique, 13 male-specific single nuclear polymorphisms (SNPs) were identified in the coding region of the zbtb38 gene of channel catfish by targeted next-generation sequencing. Among them, six substitutions resulted in changes in the amino acid coding in zbtb38 on both the X and Y chromosomes. It is speculated that zbtb38 on the Y chromosome has an important role in testicular differentiation and is an important candidate gene for sex determination in channel catfish. Subsequently, male-specific primers were designed according to male-specific nucleotides, which amplified an expected band from males but not from females. Thus, a rapid and effective method was successfully established to identify the genetic sex of channel catfish. Our study contributes to the study of the sex determination mechanisms and development of mono-sex populations in channel catfish.

The Snakeskin Gourami (Trichopodus pectoralis) Tends to Exhibit XX/XY Sex Determination

The snakeskin gourami (Trichopodus pectoralis) has a high meat yield and is one of the top five aquaculture freshwater fishes in Thailand. The species is not externally sexually dimorphic, and its sex determination system is unknown. Understanding the sex determination system of this species will contribute to its full-scale commercialization. In this study, a cytogenetic analysis did not reveal any between-sex differences in chromosomal patterns. However, we used genotyping-by-sequencing to identify 4 male-linked loci and 1 female-linked locus, indicating that the snakeskin gourami tends to exhibit an XX/XY sex determination system. However, we did not find any male-specific loci after filtering the loci for a ratio of 100:0 ratio of males:females. This suggests that the putative Y chromosome is young and that the sex determination region is cryptic. This approach provides solid information that can help identify the sex determination mechanism and potential sex determination regions in the snakeskin gourami, allowing further investigation of genetic improvements in the species.