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233 results for “sex determination”
Adult sex-ratio bias does not lead to detectable adaptive offspring sex allocation via nest-site choice in a turtle with temperature-dependent sex determination
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Data from: The sex determination pattern in crocodilians: a systematic review after three decades of research
1. Sex in crocodilians is not determined by chromosomes, but by egg incubation temperature, where different temperatures produce different clutch sex ratios. Two patterns have been proposed to describe these changes in sex ratios: a 100% female proportion at low and high temperatures with male predominance at intermediate ones (FMF) or a simpler pattern with a single female to male transition (FM). Over the last three decades, researchers have provided empirical information to support either of these two patterns in different species; however, no consensus has been reached partly because data has not been analyzed as a whole. 2. Here, we aimed at gathering the existing data on these patterns to provide models of temperature-driven sex-determination in those crocodilians studied so far. 3. A preliminary literature search allowed us to integrate a glossary of terms related with the phenomenon under study. With this, we created search queries that were entered into Web of Knowledge, Scopus, Scielo and Science Direct. Studies that reported results on the sexual identity of cocodrilian hatlings obtained from constant-temperature incubation treatments were considered. Using statistical models varying in their underlying assumptions, we evaluated which sex-determination pattern was best supported for the studied crocodilians and constructed species-specific and latitud-specific models. 4. Based on the 9030 sexed hatchlings studied throughout 30 studies, we show that the evidence supports a shared FMF pattern in all the crocodilian species thus far studied. We find that such pattern changes both at the species and population levels, but not at higher taxonomical ones. We provide single-species models of the FMF pattern, along with their variation at different latitudes. 5. These results suggest a lability of the FMF crocodilian sex determination pattern, a key feature under the present climate change scenario.
Data from: Sex is determined by XY chromosomes across the radiation of dioecious Nepenthes pitcher plants
Species with separate sexes (dioecy) are a minority among flowering plants, but dioecy has evolved multiple times independently in their history. The sex determination system and sex-linked genomic regions are currently identified in a limited number of dioecious plants only. Here, we study the sex-determination system in a genus of dioecious plants that lack heteromorphic sex chromosomes and are not amenable to controlled breeding: <i>Nepenthes</i> pitcher plants. We genotyped wild populations of flowering males and females of three <i>Nepenthes</i> taxa using ddRAD-seq, and sequenced a male inflorescence transcriptome. We developed a statistical tool (privacy rarefaction) to distinguish true sex-specificity from stochastic noise in read coverage of sequencing data from wild populations and identified male-specific loci and XY-patterned SNPs in all three <i>Nepenthes</i> taxa, suggesting the presence of homomorphic XY sex chromosomes. The male-specific region of the Y chromosome showed little conservation among the three taxa, except for the essential pollen development gene DYT1 which was confirmed as male-specific by PCR in additional <i>Nepenthes</i> taxa. Hence, dioecy and part of the male-specific region of the <i>Nepenthes</i> Y-chromosomes likely have a single evolutionary origin.
Determinants of offspring sex in kangaroos: a test of multiple hypotheses
When the fitness costs and benefits of sons and daughters differ, offspring sex ratio manipulation could be an important reproductive tactic. We explored the effects of environment and maternal caring ability on offspring sex to test four adaptive sex ratio modification hypotheses: the Extrinsic Modification (EMH), Carrying Capacity (CCH), Trivers-Willard (TWH) and Cost-of-Reproduction (CRH) hypotheses. The EMH and CCH propose that environmental conditions shape offspring sex ratios, directly or in interaction with maternal condition. The TWH and CRH predict a positive relationship between maternal condition and production of the costlier sex. The TWH predicts that mothers with superior caring ability should produce more of the sex that can provide the greatest fitness returns from additional maternal allocation, and the CRH proposes that females with limited caring ability should reduce fitness costs by producing the cheaper sex. Repeated measures on 83 known-age eastern grey kangaroos, polygynous marsupials with strong sexual dimorphism, revealed that offspring sex ratio was independent of per capita forage, supporting neither the EMH nor CCH, but was dependent on maternal mass, consistent with the TWH and CCH. Our results, however, cannot clearly identify the ultimate cause of the relationship between maternal mass and greater production of sons. One of the three assumptions of the TWH could not be verified, and mothers of sons suffered only marginal additional fitness costs. Sex ratios in higher vertebrates are likely not solely explained by factors dependent on maternal control.
Data from: Is multifactorial sex determination in the house fly, Musca domestica (L.), stable over time?
Sex determination pathways evolve rapidly, usually because of turnover of master regulatory genes at the top of the developmental pathway. Polygenic sex determination is expected to be a transient state between ancestral and derived conditions. However, polygenic sex determination has been observed in numerous animal species, including the house fly, Musca domestica. House fly males carry a male-determining factor (M) that can be located on any chromosome, and an individual male may have multiple M factors. Females lack M and/or have a dominant allele of the Md-tra gene(Md-traD) that acts as a female-determining locus even in the presence of multiple copies of M. We found the frequency and linkage of M in house flies collected in Chino, CA (USA) was relatively unchanged between 1982 and 2014. The frequency of females with Md-traD in the 2014 collection was 33.6% (n=140). Analysis of these results, plus previously published data, revealed a strong correlation between the frequencies of Md-traD and multiple M males, and we find that these populations are expected to have balanced sex ratios. We also find that fitness values that allow for the invasion and maintenance of multiple sex determining loci suggest that sexually antagonistic selection could be responsible for maintaining polygenic sex determination in house fly populations. The stability over time and equilibrium frequencies within populations suggest the house fly polygenic sex determination system is not in transition, and provide guidance for future investigations on the factors responsible for the polymorphism.
Environmental, sex-specific, and genetic determinants of infant social behavior in a wild primate
<p>Affiliative social bonds are linked to fitness components in many social mammals. However, despite their importance, little is known about how the tendency to form social bonds develops in young animals, or if the timing of development is heritable and thus can evolve. Using four decades of longitudinal observational data from a wild baboon population, we assessed the environmental determinants of an important social developmental milestone in baboons—the age at which a young animal first grooms a conspecific—and we assessed how the rates at which offspring groom their mothers develops during the juvenile period. We found that grooming development differs between the sexes: female infants groom at an earlier age and reach equal rates of grooming with their mother earlier than males. We also found that age at first grooming for both sexes is weakly heritable (h<sup>2</sup> = 0.043, 95% CI: 0.002 – 0.110). These results show that sex differences in grooming emerge at a young age; that strong, equitable social relationships between mothers and daughters begin very early in life; and that age at first grooming is heritable and therefore can be shaped by natural selection.</p>
Data from: Limited evidence of a genetic basis for sex determination in the common creek chub, Semotilus atromaculatus
<p>Sexual reproduction is almost universal in vertebrates of the animal kingdom; therefore, each species which use it must have a mechanism for designating sex as male or female. Fish especially have a wide range of sex determining systems. In the present study, we aimed to identify a genetic basis for sex determination in the common creek chub (<em>Semotilus atromaculatus</em>) using genotyping-by-sequencing data. No sex-associated markers were found by RADSex or a GWAS using GEMMA, however, our Weir and Cockerham locus-specific F<sub>ST</sub> analysis and discriminant analysis of principal components revealed some genetic differentiation between the sexes at several loci. While no explicit sex determination mechanism has been yet discovered in creek chub, these loci are potential candidates for future studies. Incompatible systems are thought to increase reproductive isolation but interspecific hybridization is common among groups such as cyprinid minnows; thus, studies such as ours can provide insight into hybridization and evolutionary diversification of this clade. We also highlight technical challenges involved in studying sex determination in species with extremely variable mechanisms.</p>
Long-term resilience of primary sex ratios in a species with temperature dependent sex determination after decades of climate warming
<p><span>Species with environmental sex determination (ESD) have persisted through deep time, despite massive environmental perturbation in the geological record. Understanding how species with temperature-dependent sex determination (TSD), a type of ESD, persist through climate change is particularly timely given the current climate crisis, as highly biased sex ratios and extinction are predicted. Since 1982, we have studied primary sex ratios of a reptile with TSD (<em>Chelydra serpentina</em></span><span>). Primary sex ratios remained unchanged over time, despite warming in the environment. Resilience of the primary sex ratio occurred via a portfolio effect, realized through remarkable intra-annual variation in nest-level sex ratios, leading to a relatively consistent mean annual sex ratio. Intra-annual variation in nest-level sex ratios was related to variation in egg burial depth coupled with large clutch sizes, creating thermal gradients in the nest, and promoting mixed-sex clutches. Further, both locally and globally, sustained increases in nighttime air temperature contribute more to warming than increases in daily maximum temperature, but development rate was affected more strongly by maximum daily air temperature, conferring additional resilience to overall warming. Our study suggests that some TSD species may be resilient to warming and provides an example of how ESD may persist under environmental change.</span><span><br></span></p>
Supplemental data files: XY sex determination in a cnidarian
<p><strong>Project Abstract:</strong></p> <p>Sex determination occurs across animal species, but most of our knowledge about the mechanisms of sex determination comes from only a handful of bilaterian taxa. This limits our ability to infer the evolutionary history of sex determination within animals. In this study, we generated a linkage map of the genome of the colonial cnidarian <em>Hydractinia symbiolongicarpus</em> and used this map to determine that this species has an XX/XY sex determination system. We delineate the pseudoautosomal and non-recombining regions of the Y chromosome and show that the latter encodes a number of genes with male gonad-specific expression. These findings establish Hydractinia as a tractable non-bilaterian model system for the study of sex determination. </p> <p> </p> <p>This archive contains supplemental data files for "XY sex determination in a cnidarian" by Chen et. al. The manuscript will be submitted to bioRxiv. </p> <ul> <li><strong>Hsym_primary_v1.0.fa.gz: </strong><em>Hydractinia </em>reference genome assembly</li> <li><strong>160429_CRATOS_HKM5MBCXX.lane1.12268798.read1.DOWNSAMPLE_0.2.fq.gz: </strong>Illumina reads for paternal genome downsampled with seqtk.</li> <li><strong>160429_CRATOS_HKM5MBCXX.lane1.12268798.read2.DOWNSAMPLE_0.2.fq.gz: </strong>Illumina reads for paternal genome downsampled with seqtk.</li> <li><strong>rawvariants.90f1.vcf.gz: </strong>Raw genotypes for all 90 offspring and the two parents, called by GATK HaplotypeCaller</li> <li><strong>GATKBP-passed.vcf.gz: </strong>Genotypes quality filtered according to GATK best practices and custom critera.</li> <li><strong>GATKBP-passed.femaleHet.abxabRemoved.vcf.gz: </strong>Genotypes suitable for mapping the maternal genome with a pseudo-testcross strategy.</li> <li><strong>GATKBP-passed.maleHet.abxabRemoved.vcf.gz: </strong>Genotypes suitable for mapping the paternal genome with a pseudo-testcross strategy.</li> </ul>
Genome-wide DNA methylation patterns harbor signatures of hatchling sex and past incubation temperature in a species with environmental sex determination
<p>Conservation of thermally sensitive species depends on monitoring organismal and population-level responses to environmental change in real time. Epigenetic processes are increasingly recognized as key integrators of environmental conditions into developmentally plastic responses, and attendant epigenomic datasets hold potential for revealing cryptic phenotypes relevant to conservation efforts. Here, we demonstrate the utility of genome-wide DNA methylation (DNAm) patterns in the face of climate change for a group of especially vulnerable species, those with temperature-dependent sex determination (TSD). Due to their reliance on thermal cues during development to determine sexual fate, contemporary shifts in temperature are predicted to skew offspring sex ratios and ultimately destabilize sensitive populations. Using reduced-representation bisulfite sequencing, we profiled the DNA methylome in blood cells of hatchling American alligator (<em>Alligator mississippiensis</em>), a TSD species lacking reliable markers of sexual dimorphism in early life-stages. We identified 120 sex-associated differentially methylated cytosines (DMCs; FDR < 0.1) in hatchlings incubated under a range of temperatures, as well as 707 unique temperature-associated DMCs. We further developed DNAm-based models capable of predicting hatchling sex with 100% accuracy (in 20 training samples and 4 test samples) and past incubation temperature with a mean absolute error of 1.2˚C (in 4 test samples) based on the methylation status of 20 and 24 loci, respectively. Though largely independent of epigenomic patterning occurring in the embryonic gonad during TSD, DNAm patterns in blood cells may serve as non-lethal markers of hatchling sex and past incubation conditions in conservation applications. These findings also raise intriguing questions regarding tissue-specific epigenomic patterning in the context of developmental plasticity. </p>
Pleistocene divergence in the absence of gene flow among populations of a viviparous reptile with intraspecific variation in sex determination
<p>Polymorphisms can lead to speciation if there is differential mating success among conspecifics divergent for a trait. Polymorphism for sex determining system might be particularly expected to isolate gene pools, given strong selection for the production of viable males and females and the low success of heterogametic hybrids when sex chromosomes differ (Haldane's rule). We investigated this question using a rare example of a species exhibiting polymorphism for sex determination: the viviparous snow skink <i>Carinascincus ocellatus</i>. While a coparatively high elevation population has entirely genotypic sex determination, in a lower elevation population there is an additional environmental component to sex determination. These systems also exhibit minor differences in sex-linked genotypes. Using 'Isolation with Migration' analysis of neutral loci, we estimated that these populations and their sex determining systems diverged in the absence of gene flow, across multiple periods of geographic proximity during Pleistocene glaciations. Our analysis suggests that populations of <i>C. ocellatus</i> with divergent sex determining systems are likely reproductively isolated, even though they are presently underlined by only subtle DNA differences. Given the influence of temperature on sex in one lineage, we also discuss the implications for the persistence of this polymorphism under climate change.</p>
Genetic sex determination, sex chromosome size and sex-specific lifespan across tetrapods
<p>Sex differences in lifespan are ubiquitous across the tree of life and exhibit broad taxonomic patterns that remain a puzzle, such as males living longer than females in birds and <em>vice</em> <em>versa</em> in mammals. The prevailing "unguarded-X" hypothesis explains sex differences in lifespan by differential expression of recessive mutations <span>o</span>n the X or Z chromosome of the heterogametic sex but has only received indirect support to date. An alternative hypothesis is that the accumulation of deleterious mutations and repetitive elements on the Y or W chromosome might lower the survival of the heterogametic sex ("toxic Y" hypothesis). Here, we use a new database to report lower survival of the heterogametic relative to the homogametic sex across 136 species of birds, mammals, reptiles and amphibians, as expected if sex chromosomes shape sex-specific lifespans, and consistent with previous findings. We also found that the relative sizes of both the X and the Y chromosomes in mammals (but not the Z or the W chromosomes in birds) are associated with sex differences in lifespan, as predicted by the "unguarded-X" and the "toxic Y". Furthermore, we report that the relative size of the Y is negatively associated with male lifespan in mammals, so that small Y size correlates with increased male lifespan. In theory, toxic Y effects are expected to be particularly strong in mammals, and we did not find similar effects in birds. Our results confirm the role of sex chromosomes in explaining sex differences in lifespan across tetrapods and further suggest that, at least in mammals, "toxic Y" effects may play an important part in this role.</p>
Data from: Context-dependent thermolability of sex determination in a lacertid lizard with heteromorphic sex chromosomes
<p>Developmental conditions can profoundly impact key life history traits of the individual. In cases where offspring sex is driven by developmental reaction norms, permanent changes to the phenotype can fundamentally alter life history trajectories. Sex determination mechanisms in reptiles are remarkable diverse including well-characterized genetic and temperature-dependent sex determination. In rarer, but increasingly more commonly documented cases, sex can also be determined by a combination of the two, with temperature overriding the genetically determined sex. Thus, sex-by-temperature interactions is a mechanism that can be contextually labile, where reaction norms of sex against developmental environment might only be observable under certain conditions. We examine the effects of incubation temperature on hatchling sex in an oviparous lizard with clearly defined heteromorphic sex chromosomes presumed to determine sex solely on a genetic basis. We also test the repeatability of our results by replicating incubation experiments across three years. We show that warmer temperatures may override chromosomal sex and cause overproduction of daughters. However, this effect was inconsistent among years, with high temperature only resulting in a daughter-significant bias in one year. Warm-incubated daughters were more efficient at converting yolk into tissue, which would allow for greater resource allocation to other fitness-related processes, such as growth. This suggests that thermolabile sex determination could be a trait under selection. More energy-efficient embryos also produced faster-growing offspring, suggesting that energy utilization patterns of the embryo were maintained into the juvenile stage, which could have important implications for the ontogenetic development and evolution of life histories.</p>
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>
Data from: Differential early-life survival underlies the adaptive significance of temperature-dependent sex determination in a long-lived reptile
<p><span class="normaltextrun"><span>Many ectotherms rely on temperature cues experienced during development to determine offspring sex. The first descriptions of temperature-dependent sex determination (TSD) were made over 50 years ago, yet an understanding of its adaptive significance remains elusive, especially in long-lived taxa. </span></span><span class="normaltextrun"><span>One novel hypothesis predicts that TSD should be evolutionarily favored when two criteria are met – (a) incubation temperature influences annual juvenile survival and (b) sexes mature at different ages. Under these conditions, a sex-dependent effect of incubation temperature on offspring fitness arises through differences in age at sexual maturity, with the sex that matures later benefiting disproportionately from temperatures that promote juvenile survival.</span></span><span class="eop"><span><span> </span></span></span><span class="normaltextrun"><span>The American alligator (<em>Alligator mississippiensis</em>) serves as an insightful model in which to test this hypothesis, as males begin reproducing nearly a decade after females. Here, through a combination of artificial incubation experiments and mark-recapture approaches, we test the specific predictions of the survival-to-maturity hypothesis for the adaptive value of TSD by disentangling the effects of incubation temperature and sex on annual survival of alligator hatchlings across two geographically distinct sites.</span></span><span class="normaltextrun"><span><span> </span></span></span><span class="normaltextrun"><span>Hatchlings incubated at male-promoting temperatures consistently exhibited higher survival compared to those incubated at female-promoting temperatures. This pattern appears independent of hatchling sex, as females produced from hormone manipulation at male-promoting temperatures exhibit similar survival to their male counterparts.</span></span><span class="normaltextrun"><span><span> </span></span></span><span class="normaltextrun"><span>Additional experiments show that incubation temperature may affect early-life survival primarily by affecting the efficiency with which maternally transferred energy resources are used during development. </span></span><span class="normaltextrun"><span>Results from this study provide the first explicit empirical support for the adaptive value of TSD in a crocodilian <span>and point to developmental energetics as a potential unifying mechanism underlying persistent survival consequences of incubation temperature.</span></span></span></p>
Data from: Transitions in sex determination mechanisms through parental and sexual antagonism
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Data from: The sex determination pattern in crocodilians: a systematic review after three decades of research
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Brief exposure to warm temperatures reduces intron retention in Kdm6b in a species with temperature-dependent sex determination
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Data from: Differential early-life survival underlies the adaptive significance of temperature-dependent sex determination in a long-lived reptile
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Data from: Ecological and behavioral determinants of sex-biased predation of katydid prey by a bat predator
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