Male Viability Research Articles

Relationships between male secondary sexual traits, physiological state and offspring viability in the three-spined stickleback

BackgroundSexual signals produced by males play a central role in sexual selection, but the relationship between these traits and the quality of the bearer are often ambiguous. Secondary sexual traits may represent genetic quality of the bearer, resulting in positive relationships with physiological state, or may be costly to produce, showing trade-off with physiological state. A number of studies have explored the relationships between secondary sexual traits and other functional traits, but few have studied their fitness consequences. We studied the link between diverse physiological traits and both morphological and behavioural sexual traits and examined how their interplay influences offspring viability in the three-spined stickleback.ResultsMale sticklebacks showing nest building and courtship behaviour were smaller than those not investing in reproductive activities. There was no evidence that the expression of red nuptial colouration and the quality of courtship behaviour of males are positively related to their metabolic rates, swim ability, oxidative damage and mtDNA copy number. However, individuals showing larger red nuptial colour areas had higher levels of oxidative DNA damage in their sperm. Male courtship behaviour and aggressiveness, but not red colour area, were good predictors of offspring hatching and survival.ConclusionsOur results suggest that, in our study population at the southern edge of the species’ distribution, sexual colouration of male sticklebacks was not a good indicator of their body state, but both courtship quality and aggressiveness during the courtship are reliable cues of their gamete quality, influencing the viability of their offspring. Thus, females that choose mates based on their courtship behaviour will have high fitness. In the study population, which represents a fast pace-of-life with high reproductive rate and short lifespan, sexual ornaments of males may not honestly signal their physiological and physical state because they invest at maximum in a single reproductive season despite high costs.

Inbreeding, male viability, and the remarkable evolutionary stability of the aphid X chromosome.

Inbreeding, male viability, and the remarkable evolutionary stability of the aphid X chromosome.

Teach Us How: Love, Relationships, Resistance

The purpose of this conceptual paper is to examine Black love in the historical, contemporary cultural, and political context. The goal of this paper is to illustrate the importance of choosing love as a means of resistance and as a practice for teaching transdisciplinary praxis. Historically, scholarship conducted on Black love did not incorporate the multidimensionality that blackness spans. It placed a focus on the relationships between Black males and females through a sociocultural lens examining factors such as Black male viability, Black male scarcity, and the impact systemic structures have on Black males. This emphasis placed on the Black male experience does not allow us to examine Black love from a heterosexual relationship standpoint. This in turn creates hegemonic narratives leading towards the development of assigned gendered/sexed roles. It is important to understand that Black love exists beyond the gender binary. bell hooks’ (2000) writing on the subject illuminates the struggle that has been created by both the lack of discourse around love and individuals articulating love in a means that could potentially emphasize their experience with lovelessness. Combining this with work by Frankfurt (2004) and Kierkegaard (1847), a framework can be created and then further expanded conceptually, utilizing various theories such as Critical Race Theory, Black Feminist Thought, Lens Theory, and narrative inquiry by forming connections where applicable. The importance of this concept is grounded in understanding notions of love in relation to Black love; this lies in its capacity to build community, connection, and inspire social action.

Probing the Function of Metazoan Histones with a Systematic Library of H3 and H4 Mutants

Replication-dependent histone genes often reside in tandemly arrayed gene clusters, hindering systematic loss-of-function analyses. Here, we used CRISPR/Cas9 and the attP/attB double-integration system to alter numbers and sequences of histone genes in their original genomic context in Drosophila melanogaster. As few as 8 copies of the histone gene unit supported embryo development and adult viability, whereas flies with 20 copies were indistinguishable from wild-types. By hierarchical assembly, 40 alanine-substitution mutations (covering all known modified residues in histones H3 and H4) were introduced and characterized. Mutations at multiple residues compromised viability, fertility, and DNA-damage responses. In particular, H4K16 was necessary for expression of male X-linked genes, male viability, and maintenance of ovarian germline stem cells, whereas H3K27 was essential for late embryogenesis. Simplified mosaic analysis showed that H3R26 is required for H3K27 trimethylation. We have developed a powerful strategy and valuable reagents to systematically probe histone functions in D.melanogaster.

RNA-on-X 1 and 2 in Drosophila melanogaster fulfill separate functions in dosage compensation.

In Drosophila melanogaster, the male-specific lethal (MSL) complex plays a key role in dosage compensation by stimulating expression of male X-chromosome genes. It consists of MSL proteins and two long noncoding RNAs, roX1 and roX2, that are required for spreading of the complex on the chromosome and are redundant in the sense that loss of either does not affect male viability. However, despite rapid evolution, both roX species are present in diverse Drosophilidae species, raising doubts about their full functional redundancy. Thus, we have investigated consequences of deleting roX1 and/or roX2 to probe their specific roles and redundancies in D. melanogaster. We have created a new mutant allele of roX2 and show that roX1 and roX2 have partly separable functions in dosage compensation. In larvae, roX1 is the most abundant variant and the only variant present in the MSL complex when the complex is transmitted (physically associated with the X-chromosome) in mitosis. Loss of roX1 results in reduced expression of the genes on the X-chromosome, while loss of roX2 leads to MSL-independent upregulation of genes with male-biased testis-specific transcription. In roX1 roX2 mutant, gene expression is strongly reduced in a manner that is not related to proximity to high-affinity sites. Our results suggest that high tolerance of mis-expression of the X-chromosome has evolved. We propose that this may be a common property of sex-chromosomes, that dosage compensation is a stochastic process and its precision for each individual gene is regulated by the density of high-affinity sites in the locus.

No blokes Is Essential for Male Viability and X Chromosome Gene Expression in the Australian Sheep Blowfly

It has been hypothesized that the Drosophila 4thchromosome is derived from an ancient X chromosome [1]. In the Australian sheep blowfly, Lucilia cuprina, the heterochromatic X chromosome contains few active genes and orthologs of Drosophila X-linked genes are autosomal. Of 8 X-linked genes identified previously in L.cuprina, 6 were orthologs of Drosophila 4th-chromosome genes [2]. The X-linked genes were expressed equally in males and females. Here we identify an additional 51 X-linked genes and show that most are dosage compensated. Orthologs of 49 of the 59 X-linked genes are on the4thchromosome in D.melanogaster. Because painting of fourth (Pof) is important for expression ofDrosophila 4th-chromosome genes [3], we used Cas9 to make a loss-of-function knockin mutation in an L.cuprina Pof ortholog we call no blokes (nbl). Homozygous nbl males derived from homozygous nbl mothers die at the late pupal stage. Homozygous nbl females are viable, fertile, and live longer than heterozygous nbl females. RNA expression of most X-linked genes was reduced in homozygous nbl male pupae and to a lesser extent in nbl females compared to heterozygous siblings. The results suggest that NBL could be important for X chromosome dosage compensation in L.cuprina. NBL may also facilitate gene expression in the heterochromatic environment of the X chromosome in both sexes. This study supports the hypothesis on the origin of the Drosophila 4th chromosome and that a POF-like protein was required for normal gene expression on the ancient X chromosome.

On the possibility of death of new genes \u2013 evidence from the deletion of de novo microRNAs

BackgroundNew genes are constantly formed, sometimes from non-genic sequences, creating what is referred to as de novo genes. Since the total number of genes remains relatively steady, gene deaths likely balance out new births. In metazoan genomes, microRNAs (miRs) genes, small and non-coding, account for the bulk of functional de novo genes and are particularly suited to the investigation of gene death.ResultsIn this study, we discover a Drosophila-specific de novo miRNA (mir-977) that may be facing impending death. Strikingly, after this testis-specific gene is deleted from D. melanogaster, most components of male fitness increase, rather than decrease as had been expected. These components include male viability, fertility and males’ ability to repress female re-mating. Given that mir-977 has a negative fitness effect in D. melanogaster, this de novo gene with an adaptive history for over 60 Myrs may be facing elimination. In some other species where mir-977 is not found, gene death may have already happened.ConclusionThe surprising result suggests that de novo genes, constantly rising and falling during evolution, may often be transiently adaptive and then purged from the genome.

Increase in viability due to the accumulation of X chromosome mutations in Drosophila melanogaster males.

To increase our understanding of the role of new X-chromosome mutations in adaptive evolution, single-X Drosophila melanogaster males were mated with attached-X chromosome females, allowing the male X chromosome to accumulate mutations over 28 generations. Contrary to our hypothesis that male viability would decrease over time, due to the accumulation and expression of X-linked recessive deleterious mutations in hemizygous males, viability significantly increased. This increase may be attributed to germinal selection and to new X-linked beneficial or compensatory mutations, possibly supporting the faster-X hypothesis.

Probing the Function of Metazoan Histones with a Systematic Library of H3 and H4 Mutants

Replication-dependent histone genes often reside in tandemly arrayed gene clusters, hindering systematic loss-of function analyses. Here we used CRISPR/Cas9 and the attP/attB double-integration system to alter the numbers and sequences of the histone genes in their original genomic context in Drosophila. As few as 8 copies of histone gene suffices to support embryo development and adult viability, whereas flies with 20 copies are indistinguishable from WT flies. Using a hierarchical assembly method, 40 alanine substitution mutations, covering all known modified residues on histone H3 and H4, were introduced and characterized. Mutations at multiple residues compromise viability, fertility, and DNA damage responses. In particular, H4K16 is necessary for expression of male X-linked genes, male viability and maintenance of ovarian germline stem cells, whereas H3K27 is essential for late embryogenesis. Finally, using simplified mosaic analysis, we found that H3R26 is required for H3K27 trimethylation. Taken together, we have developed a powerful strategy and valuable reagents for systematically probing histone functions in the fly.

Replacing the Y chromosome

Sex Chromosome The mammalian Y chromosome encodes a specialized set of genes that are essential for male viability and fertility. In particular, the sex-determining region Y (SRY) protein is necessary to initiate male sex determination. However, Yamauchi et al. show that the functions of the entire Y chromosome can be replaced with only two genes. In mice, two transgenes, Sox9 and Eif2s3x , compensated for the absence of all Y chromosome genes to allow successful sperm formation. Science , this issue p. [514][1] [1]: /lookup/doi/10.1126/science.aad1795

The evolutionary dynamics of haplodiploidy: Genome architecture and haploid viability.

Haplodiploid reproduction, in which males are haploid and females are diploid, is widespread among animals, yet we understand little about the forces responsible for its evolution. The current theory is that haplodiploidy has evolved through genetic conflicts, as it provides a transmission advantage to mothers. Male viability is thought to be a major limiting factor; diploid individuals tend to harbor many recessive lethal mutations. This theory predicts that the evolution of haplodiploidy is more likely in male heterogametic lineages with few chromosomes, as genes on the X chromosome are often expressed in a haploid environment, and the fewer the chromosome number, the greater the proportion of the total genome that is X‐linked. We test this prediction with comparative phylogenetic analyses of mites, among which haplodiploidy has evolved repeatedly. We recover a negative correlation between chromosome number and haplodiploidy, find evidence that low chromosome number evolved prior to haplodiploidy, and that it is unlikely that diplodiploidy has reevolved from haplodiploid lineages of mites. These results are consistent with the predicted importance of haploid male viability.

Within-population Y-linked genetic variation for lifespan in Drosophila melanogaster.

The view that the Y chromosome is of little importance for phenotypic evolution stems from early studies of Drosophila melanogaster. This species' Y chromosome contains only 13 protein-coding genes, is almost entirely heterochromatic and is not necessary for male viability. Population genetic theory further suggests that non-neutral variation can only be maintained at the Y chromosome under special circumstances. Yet, recent studies suggest that the D.melanogaster Y chromosome trans-regulates hundreds to thousands of X and autosomal genes. This finding suggests that the Y chromosome may play a far more active role in adaptive evolution than has previously been assumed. To evaluate the potential for the Y chromosome to contribute to phenotypic evolution from standing genetic variation, we test for Y-linked variation in lifespan within a population of D.melanogaster. Assessing variation for lifespan provides a powerful test because lifespan (i) shows sexual dimorphism, which the Y is primarily predicted to contribute to, (ii) is influenced by many genes, which provides the Y with many potential regulatory targets and (iii) is sensitive to heterochromatin remodelling, a mechanism through which the Y chromosome is believed to regulate gene expression. Our results show a small but significant effect of the Y chromosome and thus suggest that the Y chromosome has the potential to respond to selection from standing genetic variation. Despite its small effect size, Y-linked variation may still be important, in particular when evolution of sexual dimorphism is genetically constrained elsewhere in the genome.

Context-dependent effects of Y chromosome and mitochondrial haplotype on male locomotive activity in Drosophila melanogaster.

Some regions of the genome exhibit sexual asymmetries in inheritance and are thus subjected to sex-biased evolutionary forces. Maternal inheritance of mitochondrial DNA (mtDNA) enables mtDNA mutations harmful to males, but not females, to accumulate. In the face of male-harmful mtDNA mutation accumulation, selection will favour the evolution of compensatory modifiers in the nuclear genome that offset fitness losses to males. The Y chromosome is a candidate to host these modifiers, because it is paternally inherited, known to harbour an abundance of genetic variation for male fertility, and therefore likely to be under strong selection to uphold male viability. Here, we test for intergenomic interactions involving mtDNA and Y chromosomes in male Drosophila melanogaster. Specifically, we examine effects of each of these genomic regions, and their interaction, on locomotive activity, across different environmental contexts--both dietary and social. We found that both the mtDNA haplotype and Y chromosome haplotype affected activity in males assayed in an environment perceived as social. These effects, however, were not evident in males assayed in perceived solitary environments, and neither social nor solitary treatments revealed evidence for intergenomic interactions. Finally, the magnitude and direction of these genetic effects was further contingent on the diet treatment of the males. Thus, genes within the mtDNA and Y chromosome are involved in genotype-by-environment interactions. These interactions might contribute to the maintenance of genetic variation within these asymmetrically inherited gene regions and complicate the dynamics of genetic interactions between the mtDNA and the Y chromosome.

Gametic selection, developmental trajectories, and extrinsic heterogeneity in Haldane's rule.

Deciphering the genetic and developmental causes of the disproportionate rarity, inviability, and sterility of hybrid males, Haldane's rule, is important for understanding the evolution of reproductive isolation between species. Moreover, extrinsic and prezygotic factors can contribute to the magnitude of intrinsic isolation experienced between species with partial reproductive compatibility. Here, we use the nematodes Caenorhabditis briggsae and C. nigoni to quantify the sensitivity of hybrid male viability to extrinsic temperature and developmental timing, and test for a role of mito-nuclear incompatibility as a genetic cause. We demonstrate that hybrid male inviability manifests almost entirely as embryonic, not larval, arrest and is maximal at the lowest rearing temperatures, indicating an intrinsic-by-extrinsic interaction to hybrid inviability. Crosses using mitochondrial substitution strains that have reciprocally introgressed mitochondrial and nuclear genomes show that mito-nuclear incompatibility is not a dominant contributor to postzygotic isolation and does not drive Haldane's rule in this system. Crosses also reveal that competitive superiority of X-bearing sperm provides a novel means by which postmating prezygotic factors exacerbate the rarity of hybrid males. These findings highlight the important roles of gametic, developmental, and extrinsic factors in modulating the manifestation of Haldane's rule.

X Chromosome and Autosome Dosage Responses in Drosophila melanogaster Heads.

X chromosome dosage compensation is required for male viability in Drosophila. Dosage compensation relative to autosomes is two-fold, but this is likely to be due to a combination of homeostatic gene-by-gene regulation and chromosome-wide regulation. We have baseline values for gene-by-gene dosage compensation on autosomes, but not for the X chromosome. Given the evolutionary history of sex chromosomes, these baseline values could differ. We used a series of deficiencies on the X and autosomes, along with mutations in the sex-determination gene transformer-2, to carefully measure the sex-independent X-chromosome response to gene dosage in adult heads by RNA sequencing. We observed modest and indistinguishable dosage compensation for both X chromosome and autosome genes, suggesting that the X chromosome is neither inherently more robust nor sensitive to dosage change.

Biased transmission of sex chromosomes in the aphid Myzus persicae is not associated with reproductive mode.

Commonly, a single aphid species exhibits a wide range of reproductive strategies including cyclical parthenogenesis and obligate parthenogenesis. Sex determination in aphids is chromosomal; females have two X chromosomes, while males have one. X chromosome elimination at male production is generally random, resulting in equal representation of both X chromosomes in sons. However, two studies have demonstrated deviations from randomness in some lineages. One hypothesis to account for such deviations is that recessive deleterious mutations accumulate during bouts of asexual reproduction and affect male viability, resulting in overrepresentation of males with the least deleterious of the two maternal X chromosomes. This hypothesis results in a testable prediction: X chromosome transmission bias will increase with time spent in the asexual phase and should therefore be most extreme in the least sexual aphid life cycle class. Here we test this prediction in Myzus persicae. We used multiple heterozygous X-linked microsatellite markers to screen 1085 males from 95 lines of known life cycle. We found significant deviations from equal representation of X chromosomes in 15 lines; however, these lines included representatives of all life cycles. Our results are inconsistent with the hypothesis that deviations from randomness are attributable to mutation accumulation.

Plumage Coverage is Related to Body Condition and Ectoparasitism in Blue-black Grassquits

Females may prefer elaborate sexual ornaments in males as these can be costly and may honestly indicate male viability. We used a wild population of the Blue-black Grassquit (Volatinia jacarina) in central Brazil to test whether more ornamented males have lower parasite loads (parasite-mediated sexual selection) and/or better body condition (condition-dependent sexual selection) compared with less ornamented males. We predicted that blue-black plumage coverage should be positively correlated to body condition (weight/tarsus) and negatively correlated to parasite load (Mallophaga lice). We found that blue-black plumage coverage of grassquit males was positively related to body condition score and negatively related to ectoparasite load. However, body condition was not correlated with ectoparasite load in these males. Our data are consistent with the hypothesis of sexual selection mediated by parasites as well as with the hypothesis of sexual selection mediated by body condition, indicating that nuptial plumage coverage can be an honest signal of male quality in Blue-black Grassquits, and could thus be used by females during mate choice.

Mammalian Y chromosomes retain widely expressed dosage-sensitive regulators

The human X and Y chromosomes evolved from an ordinary pair of autosomes, but millions of years ago genetic decay ravaged the Y chromosome, and only three percent of its ancestral genes survived. We reconstructed the evolution of the Y chromosome across eight mammals to identify biases in gene content and the selective pressures that preserved the surviving ancestral genes. Our findings indicate that survival was non-random, and in two cases, convergent across placental and marsupial mammals. We conclude that the Y chromosome's gene content became specialized through selection to maintain the ancestral dosage of homologous X-Y gene pairs that function as broadly expressed regulators of transcription, translation and protein stability. We propose that beyond its roles in testis determination and spermatogenesis, the Y chromosome is essential for male viability, and plays unappreciated roles in Turner syndrome and in phenotypic differences between the sexes in health and disease.

Male viability is positively related to multiple male ornaments in Asian Barn Swallows

The European Barn Swallow Hirundo rustica rustica is a model system for studying female mate choice for indirect benefits, as the long tail of males, the target of female mate choice, is positively related to male viability. However, situations may differ in other subspecies where male ornaments other than tail length are prominent and seem to be the targets of female choice. In this study, similar to previous studies on European populations, we determined the relationship between male viability and male ornaments, including tail length, in a Japanese population of the Asian Barn Swallow H. r. gutturalis, which have short tails, a whitish ventral plumage, and a large red throat patch. We observed that males with longer tails and larger and more colored (i.e., lower saturation values) throat patches were more likely to return to the study area than other males, independent of their age. Of these ornaments, information on viability of male tail length partially overlapped the information on viability by throat coloration. Because females choose mates, either directly or indirectly, based on their throat coloration, female mate preference for tail length had few benefits for the choosers. This may explain why female mate preference for tail length was not observed in this population. In addition, differing from a previous study in a European population, male throat patch size may serve as a good indicator of male viability, independent of tail length and throat coloration in this population. We discuss the possible explanations for the observed patterns.

Postzygotic isolation involves strong mitochondrial and sex-specific effects in Tigriopus californicus, a species lacking heteromorphic sex chromosomes

Detailed studies of the genetics of speciation have focused on a few model systems, particularly Drosophila. The copepod Tigriopus californicus offers an alternative that differs from standard animal models in that it lacks heteromorphic chromosomes (instead, sex determination is polygenic) and has reduced opportunities for sexual conflict, because females mate only once. Quantitative trait loci (QTL) mapping was conducted on reciprocal F2 hybrids between two strongly differentiated populations, using a saturated linkage map spanning all 12 autosomes and the mitochondrion. By comparing sexes, a possible sex ratio distorter was found but no sex chromosomes. Although studies of standard models often find an excess of hybrid male sterility factors, we found no QTL for sterility and multiple QTL for hybrid viability (indicated by non-Mendelian adult ratios) and other characters. Viability problems were found to be stronger in males, but the usual explanations for weaker hybrid males (sex chromosomes, sensitivity of spermatogenesis, sexual selection) cannot fully account for these male viability problems. Instead, higher metabolic rates may amplify deleterious effects in males. Although many studies of standard speciation models find the strongest genetic incompatibilities to be nuclear-nuclear (specifically X chromosome-autosome), we found the strongest deleterious interaction in this system was mito-nuclear. Consistent with the snowball theory of incompatibility accumulation, we found that trigenic interactions in this highly divergent cross were substantially more frequent (>6×) than digenic interactions. This alternative system thus allows important comparisons to studies of the genetics of reproductive isolation in more standard model systems.