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17 results for “Sex determination system”
Assembled chromosomes of the blood fluke Schistosoma mansoni provide insight into the evolution of its ZW sex-determination system
<p><em>Schistosoma mansoni </em>has a diploid genome of approximately 380 MB, organized in 7 pairs of autosomes and 2 sex chromosomes. The original <em>Schistosoma mansoni </em>Genome Project was completed by the Wellcome Sanger Institute in collaboration with The Institute for Genome Research using a Whole Genome Shotgun sequencing strategy. The draft assembly was subsequently improved first by incorporating Illumina reads from a clonal (single-miracidial) infection and more recently by incorporating long PacBio reads, HiC, and optical mapping data.</p> <p>Associated manuscript can be found at https://www.biorxiv.org/content/10.1101/2021.08.13.456314v1</p>
Epistatic interactions between sex chromosomes and autosomes can affect the stability of sex determination systems
<p>Sex determination (SD) is an essential and ancient developmental process, but the genetic systems that regulate this process are surprisingly variable. Why SD mechanisms vary so much is a longstanding question in evolutionary biology. SD genes are generally located on sex chromosomes which also carry genes that interact epistatically with autosomes to affect fitness. How this affects the evolutionary stability of SD mechanisms is still unknown. Here, we explore how epistatic interactions between a sexually antagonistic (SA) non-SD gene, located on either an ancestral or novel sex chromosome, and an autosomal gene affect the conditions under which an evolutionary transition to a new SD system occurs. We find that when the SD gene is linked to an ancestral sex chromosomal gene which engages in epistatic interactions, epistasis enhances the stability of the sex chromosomes so that they are retained under conditions where transitions would otherwise occur. This occurs both when weaker fitness effects are associated with the ancestral sex chromosome pair or stronger fitness effects associated with a newly-evolved SD gene. However, the probability that novel SD genes spread is unaffected if they arise near genes involved in epistasis. This discrepancy occurs because on autosomes, SA allele frequencies are typically lower than on sex chromosomes. In our model, increased frequencies of these alleles contribute to a higher frequency of epistasis which may therefore more readily occur on sex chromosomes. Because sex chromosome-autosome interactions are abundant and can take several forms, they may play a large role in maintaining sex chromosomes.</p>
Epistatic interactions between sex chromosomes and autosomes can affect the stability of sex determination systems
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Multiple paternity is related to adult sex ratio and sex determination system in reptiles
<p><span>The adult sex ratio (ASR, the proportion of males in the adult population) is an emerging predictor of reproductive behaviour, and recent studies in birds and humans suggest it is a major driver of social mating systems and parental care. ASR may also influence genetic mating systems. For instance, male-skewed ASRs are expected to increase the frequency of multiple paternity (defined here as a clutch or litter sired by two or more males) due to higher rates of coercive copulations by males and/or due to females exploiting the opportunity of copulation with multiple males to increase genetic diversity of their offspring. Here we evaluate this hypothesis in reptiles that often exhibit high frequency of multiple paternity, although its ecological and life-history predictors have remained controversial. Using a comprehensive dataset of 81 species representing all four non-avian reptile orders, we show that increased frequency of multiple paternity is predicted by more male-skewed ASR, and this relationship is robust to simultaneous effects of several life-history predictors. Additionally, we show that the frequency of multiple paternity varies with the sex determination system: species with female heterogamety (ZZ/ZW sex chromosomes) exhibit higher levels of multiple paternity than species with male heterogamety (XY/XX) or temperature-dependent sex determination. Thus, our across-species comparative study provides the first evidence that genetic mating system depends on ASR in reptiles. We call for further investigations to uncover the complex evolutionary associations between mating systems, sex determination systems and ASR.</span></p>
Multiple paternity is related to adult sex ratio and sex determination system in reptiles
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An investigation of ZZ/ZW and XX/XY sex determination systems in North African catfish (Clarias gariepinus)
<p class="CxSpFirst">Sex-specific loci are powerful tools for identifying sex determination systems. They offer a molecular biotechnological approach for producing all‐male or all-female fish for commercial breeding. The North African catfish has been widely adopted for aquaculture, because its superior growth and disease resistance render the species suitable for hybridization with other catfish, to improve the productivity and quality of fish meat. North African catfish have either a ZZ/ZW or XX/XY sex determination system. Here, we investigate and characterize these systems using high-throughput genome complexity reduction sequencing. This approach was effective for identifying sex-specific loci with both single-nucleotide polymorphisms (SNPs) and restriction fragment presence/absence (PA) markers in 30 phenotypic sex assignments of North African catfish. In total, 41 male-linked loci met the criteria of moderately sex-linked loci (70:30, male:female; 80:20, male:female). By contrast, only 25 female-linked loci were detected from moderately sex-linked loci, and no perfectly male- or female-specific sex-linked loci were observed. Several male-linked loci were partially homologous to transposable element and functional genes, and most also showed partial homology with several amniote sex chromosomal linkages. This suggests that an ancestral amniote super-sex chromosome with overlaps of partial sex chromosomal linkages was also found in teleosts, and that the male heterogametic XX/XY sex determination system should exist in North African catfish. The putative Y chromosome is young and the non-recombination region is highly cryptic. In addition, the ZW type of North African catfish exhibits heteromorphic sex chromosomes, whereas the two other groups of North African catfish have different sex determination systems. Thus, turnover of sex chromosome systems might have occurred stochastically in ancestral homomorphic sex chromosomes. The XY group has been introduced into Thailand for commercial breeding. This approach using sex-specific loci provides a solid baseline for revealing sex determination mechanisms and identify potential sex determination regions in catfish, allowing further investigation of genetic improvements in breeding programs.</p>
Climate change, sex reversal, and lability of sex determining systems
Sex reversal at high temperatures during embryonic development (e.g. ZZ females) provides the opportunity for new genotypic crosses (e.g. ZZ male x ZZ female). This raises the alarming possibility that climatic warming could lead to the loss of an entire chromosome – one member of the sex chromosome pair (the Y or W) – and the transition of populations to environmental sex determination (ESD). Here we examine the evolutionary dynamics of sex-determining systems exposed to climatic warming using theoretical models. We found that the loss of sex chromosomes is not an inevitable consequence of sex reversal. A large frequency of ZZ sex reversal (50% reversal from male to female) typically divides the outcome between loss of the ZW genotype and the stable persistence of ZZ males, ZW females, and ZZ females. The amount of warming associated with sex chromosome loss depended on several features of wild populations – environmental fluctuation, immigration, heritable variation in temperature sensitivity, and differential fecundity of sex-reversed individuals. Chromosome loss was partially or completely buffered when sex-reversed individuals suffered a reproductive fitness cost, when immigration occurred, or when heritable variation for temperature sensitivity existed. Thus, under certain circumstances, sex chromosomes may persist cryptically in systems where the environment is the predominant influence on sex.
Data from: Within-population polymorphism of sex-determination systems in the common frog (Rana temporaria)
In sharp contrast with birds and mammals, the sex chromosomes of ectothermic vertebrates are often undifferentiated, for reasons that remain debated. A linkage map was recently published for Rana temporaria (Linnaeus, 1758) from Fennoscandia (Eastern European lineage), with a proposed sex-determining role for linkage group 2 (LG2). We analysed linkage patterns in lowland and highland populations from Switzerland (Western European lineage), with special focus on LG2. Sibship analyses showed large differences from the Fennoscandian map in terms of recombination rates and loci order, pointing to large-scale inversions or translocations. All linkage groups displayed extreme heterochiasmy (total map length was 12.2 cM in males, versus 869.8 cM in females). Sex determination was polymorphic within populations: a majority of families (with equal sex ratios) showed a strong correlation between offspring phenotypic sex and LG2 paternal haplotypes, whereas other families (some of which with female-biased sex ratios) did not show any correlation. The factors determining sex in the latter could not be identified. This coexistence of several sex-determination systems should induce frequent recombination of X and Y haplotypes, even in the absence of male recombination. Accordingly, we found no sex differences in allelic frequencies on LG2 markers among wild-caught male and female adults, except in one high-altitude population, where nonrecombinant Y haplotypes suggest sex to be entirely determined by LG2. Multifactorial sex determination certainly contributes to the lack of sex-chromosome differentiation in amphibians.
Data from: Within-population polymorphism of sex-determination systems in the common frog (Rana temporaria)
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Climate change, sex reversal, and lability of sex determining systems
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An investigation of ZZ/ZW and XX/XY sex determination systems in North African catfish (Clarias gariepinus)
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Data from: Restriction site-associated DNA sequencing (RAD-seq) reveals an extraordinary number of transitions among gecko sex-determining systems
Sex chromosomes have evolved many times in animals and studying these replicate evolutionary "experiments" can help broaden our understanding of the general forces driving the origin and evolution of sex chromosomes. However this plan of study has been hindered by the inability to identify the sex chromosome systems in the large number of species with cryptic, homomorphic sex chromosomes. Restriction site-associated DNA sequencing (RAD-seq) is a critical enabling technology that can identify the sex chromosome systems in many species where traditional cytogenetic methods have failed. Using newly generated RAD-seq data from twelve gecko species, along with data from the literature, we reinterpret the evolution of sex-determining systems in lizards and snakes and test the hypothesis that sex chromosomes can routinely act as evolutionary traps. We uncovered between 17 and 25 transitions among gecko sex-determining systems. This is approximately ½ to ⅔ of the total number of transitions observed among all lizards and snakes. We find support for the hypothesis that sex chromosome systems can readily become trap-like and show that adding even a small number of species from understudied clades can greatly enhance hypothesis testing in a model-based phylogenetic framework. RAD-seq will undoubtedly prove useful in evaluating other species for male or female heterogamety, particularly the majority of fish, amphibian, and reptile species that lack visibly heteromorphic sex chromosomes, and will significantly accelerate the pace of biological discovery.
Genome-wide SNP analysis of male and female rice field frogs, Hoplobatrachus rugulosus, supports a non-genetic sex determination system
<p>Sex determination systems (SDSs) in anurans are diverse and have undergone independent evolutionary transitions among species. The mode of sexual reproduction of the rice field frog (<i>Hoplobatrachus rugulosus</i>), an economically viable edible amphibian species, is not well known. Previous studies have proposed that threshold temperature conditions may determine sex in these frogs. To elucidate the SDS in <i>H. rugulosus</i>, we karyotyped 10 male and 12 female frogs, and performed fluorescence <i>in situ</i> hybridization combined with<b> </b>sequencing analyses using DArTseq™. Our results revealed a highly conserved karyotype with no sex chromosome heteromorphism, and the sequencing analyses did not identify any consistent sex-linked loci, supporting the hypothesis of temperature-dependent sex determination. The results of this study, and others, on SDSs in the rice field frog and related species also provides support for the theory that heteromorphic sex chromosomes may lead to an evolutionary trap that prevents variable SDSs. These findings add important information to the body of knowledge on <i>H. rugulosus</i> and are likely to have a significant impact on the productivity and economic success of rice field frog farming.</p>
Data from: Sex matters in massive parallel sequencing: Evidence for biases in genetic parameter estimation and investigation of sex determination systems
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Genome-wide SNP analysis of male and female rice field frogs, Hoplobatrachus rugulosus, supports a non-genetic sex determination system
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Data from: Restriction site-associated DNA sequencing (RAD-seq) reveals an extraordinary number of transitions among gecko sex-determining systems
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Chromatin landscape associated with sexual differentiation in a UV sex determination system
GEO Series GSE160087. Ectocarpus sp. Ec457; Ectocarpus sp. Ec460. 44 samples. Type: Expression profiling by high throughput sequencing; Genome binding/occupancy profiling by high throughput sequencing.
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