scholarly journals Haploid selection, sex ratio bias, and transitions between sex-determining systems

2018 ◽  
Author(s):  
Michael Francis Scott ◽  
Matthew Miles Osmond ◽  
Sarah Perin Otto
Keyword(s):  
Sex Ratio ◽  
Sex Determination ◽  
Sex Chromosomes ◽  
Pollen Competition ◽  
Diploid Males ◽  
Mendelian Segregation ◽  
Male And Female ◽  
Ratio Bias ◽  
Sex Ratio Bias ◽  
Haploid Selection

AbstractSex determination is remarkably dynamic; many taxa display shifts in the location of sex-determining loci or the evolution of entirely new sex-determining systems. Predominant theories for why we observe such transitions generally conclude that novel sex-determining systems are favoured by selection if they equalise the sex ratio or increase linkage with a locus that experiences different selection in males vs. females. We use population genetic models to extend these theories in two ways: (1) We consider the dynamics of loci very tightly linked to the ancestral sex-determining loci, e.g., within the non-recombining region of the ancestral sex chromosomes. Variation at such loci can favour the spread of new sex-determining systems in which the heterogametic sex changes (XY to ZW or ZW to XY) and the new sex-determining region is less closely linked (or even unlinked) to the locus under selection. (2) We consider selection upon haploid genotypes either during gametic competition (e.g., pollen competition) or meiosis (i.e., non-Mendelian segregation), which can cause the zygotic sex ratio to become biased. Haploid selection can drive transitions between sex-determining systems without requiring selection to act differently in diploid males vs. females. With haploid selection, we find that transitions between male and female heterogamety can evolve where linkage with the sex-determining locus is either strengthened or weakened. Furthermore, we find that sex-ratio biases may increase or decrease with the spread of new sex chromosomes, which implies that transitions between sex-determining systems cannot be simply predicted by selection to equalise the sex ratio. In fact, under many conditions, we find that transitions in sex determination are favoured equally strongly in cases where the sex ratio bias increases or decreases. Overall, our models predict that sex determination systems should be highly dynamic, particularly when haploid selection is present, consistent with the evolutionary lability of this trait in many taxa.Author summarySystems of sex determination are strikingly diverse and labile in many clades. This poses the question: what drives transitions between sex-determining systems? Here, we use models to derive conditions under which new sex-determining systems spread. Prevailing views suggest that new sex-determining systems are favoured when they equalize the sex ratio and/or when they are more closely linked to genes that experience differential selection in males and females. Our models include selection upon haploid genotypes (meiotic drive or gametic competition), which biases the sex-ratio and occurs differently in male and female gametes. Surprisingly, we find the two forces (selection to equalize the sex ratio and the benefits of hitchhiking alongside driven alleles that distort the sex ratio) will often be equally strong, and thus neither is sufficient to explain the spread of new sex-determining systems in every case. We also find that new sex-determining alleles can spread despite being less closely linked to selected loci as long as initial linkage is tight or haploid selection is present. Our models therefore predict that loci in previously unexpected genomic locations and/or experiencing various types of selection (including haploid selection) can now be implicated as drivers of transitions between sex-determining systems.

scholarly journals Flow cytometric sexing of spider sperm reveals an equal sperm production ratio in a female-biased species

2014 ◽  
Vol 10 (5) ◽  
pp. 20140159 ◽  
Author(s):  
B. Vanthournout ◽  
K. Deswarte ◽  
H. Hammad ◽  
T. Bilde ◽  
B. Lambrecht ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Sex Allocation ◽  
Evolutionarily Stable Strategy ◽  
General Rule ◽  
Sperm Cells ◽  
Sperm Production ◽  
Male And Female ◽  
Ratio Bias ◽  
Sex Ratio Bias ◽  
Production Ratio

Producing equal amounts of male and female offspring has long been considered an evolutionarily stable strategy. Nevertheless, exceptions to this general rule (i.e. male and female biases) are documented in many taxa, making sex allocation an important domain in current evolutionary biology research. Pinpointing the underlying mechanism of sex ratio bias is challenging owing to the multitude of potential sex ratio-biasing factors. In the dwarf spider, Oedothorax gibbosus , infection with the bacterial endosymbiont Wolbachia results in a female bias. However, pedigree analysis reveals that other factors influence sex ratio variation. In this paper, we investigate whether this additional variation can be explained by the unequal production of male- and female-determining sperm cells during sperm production. Using flow cytometry, we show that males produce equal amounts of male- and female-determining sperm cells; thus bias in sperm production does not contribute to the sex ratio bias observed in this species. This demonstrates that other factors such as parental genes suppressing endosymbiont effects and cryptic female choice might play a role in sex allocation in this species.

scholarly journals Seed sexing revealed female bias in two Rumex species

2011 ◽  
Vol 80 (2) ◽  
pp. 93-97 ◽  
Author(s):  
Dagmara Kwolek ◽  
Andrzej J. Joachimiak
Keyword(s):  
Sex Ratio ◽  
Sex Chromosomes ◽  
Dna Markers ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Ratio Bias ◽  
Sex Ratio Bias ◽  
Y Chromosomes ◽  
Sex Chromosome System ◽  
Female Bias

Sex-ratio bias in seeds of dioecious <em>Rumex</em> species with sex chromosomes is an interesting and still unsettled issue. To resolve gender among seeds of <em>R. acetosa</em> and <em>R. thyrsiflorus</em> (two species with an XX/XY1Y2 sex chromosome system), this work applied a PCR-based method involving DNA markers located on Y chromosomes. Both species showed female-biased primary sex ratios, with female bias greater in <em>R. acetosa</em> than in <em>R. thyrsiflorus</em>. The observed predominance of female seeds is consistent with the view that the female biased sex ratios in <em>Rumex </em>are conditioned not only postzygotically but also prezygotically.

scholarly journals Haploid selection, sex ratio bias, and transitions between sex-determining systems

PLoS Biology ◽  
2018 ◽  
Vol 16 (6) ◽  
pp. e2005609 ◽  
Author(s):  
Michael Francis Scott ◽  
Matthew Miles Osmond ◽  
Sarah Perin Otto
Keyword(s):  
Sex Ratio ◽  
Ratio Bias ◽  
Sex Ratio Bias ◽  
Haploid Selection

CULTURAL INHERITANCE AS A MECHANISM FOR POPULATION SEX-RATIO BIAS IN REPTILES

Evolution ◽  
2007 ◽  
Vol 55 (5) ◽  
pp. 1049-1055 ◽  
Author(s):  
Steven Freedberg ◽  
Michael J. Wade
Keyword(s):  
Sex Ratio ◽  
Cultural Inheritance ◽  
Ratio Bias ◽  
Sex Ratio Bias

scholarly journals Do male and female heterogamety really differ in expression regulation? Lack of global dosage balance in pygopodid geckos

2021 ◽  
Vol 376 (1833) ◽  
pp. 20200102 ◽  
Author(s):  
Michail Rovatsos ◽  
Tony Gamble ◽  
Stuart V. Nielsen ◽  
Arthur Georges ◽  
Tariq Ezaz ◽  
...  
Keyword(s):  
Sex Determination ◽  
Sex Chromosomes ◽  
Gene Dosage ◽  
Regulatory Mechanisms ◽  
Gene Copy ◽  
Male And Female ◽  
Gene Dose ◽  
Female Heterogamety ◽  
Dosage Balance ◽  
Male Heterogamety

Differentiation of sex chromosomes is thought to have evolved with cessation of recombination and subsequent loss of genes from the degenerated partner (Y and W) of sex chromosomes, which in turn leads to imbalance of gene dosage between sexes. Based on work with traditional model species, theory suggests that unequal gene copy numbers lead to the evolution of mechanisms to counter this imbalance. Dosage compensation, or at least achieving dosage balance in expression of sex-linked genes between sexes, has largely been documented in lineages with male heterogamety (XX/XY sex determination), while ZZ/ZW systems are assumed to be usually associated with the lack of chromosome-wide gene dose regulatory mechanisms. Here, we document that although the pygopodid geckos evolved male heterogamety with a degenerated Y chromosome 32–72 Ma, one species in particular, Burton's legless lizard ( Lialis burtonis ), does not possess dosage balance in the expression of genes in its X-specific region. We summarize studies on gene dose regulatory mechanisms in animals and conclude that there is in them no significant dichotomy between male and female heterogamety. We speculate that gene dose regulatory mechanisms are likely to be related to the general mechanisms of sex determination instead of type of heterogamety. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.

Behavioral variation in nesting phenology may offset sex-ratio bias in tuatara

2018 ◽  
Vol 329 (6-7) ◽  
pp. 373-381 ◽  
Author(s):  
Nicola J. Nelson ◽  
Susan N. Keall ◽  
Jeanine M. Refsnider ◽  
Anna L. Carter
Keyword(s):  
Sex Ratio ◽  
Behavioral Variation ◽  
Ratio Bias ◽  
Sex Ratio Bias

SEX-RATIO BIAS WITH ASYMMETRIC EXCHANGE OF POLLEN BETWEEN DEMES

Evolution ◽  
1995 ◽  
Vol 49 (6) ◽  
pp. 1119-1124
Author(s):  
Peter D. Taylor
Keyword(s):  
Sex Ratio ◽  
Ratio Bias ◽  
Sex Ratio Bias

The Effects of Polygyny and Domicility on Offspring Sex Ratio in Ghana

2007 ◽  
Vol 6 (4) ◽  
pp. 431-456
Author(s):  
Adansi Amankwaa
Keyword(s):  
Sex Ratio ◽  
Family Structure ◽  
Living Arrangements ◽  
Living Arrangement ◽  
Demographic And Health Surveys ◽  
Offspring Sex Ratio ◽  
Ratio Bias ◽  
Sex Ratio Bias ◽  
Offspring Sex ◽  
The Relationship

AbstractThis article explores how family structure and domicility influences offspring sex ratio bias, specifically living arrangements of husband in polygynous unions. Data from three Ghana Demographic and Health Surveys were used to examine the relationship between family structure and offspring sex ratio at birth, something that previous studies have not been able to do. This study estimate models of sex ratio offspring if the wives live together with husband present and wives live in separate dwellings and are visited by husband in turn. The results suggest that within polygynous marriages there are more male births, especially when husbands reside in the same dwelling as wives, than when husbands reside in separate dwellings from their wives. The analyses show that offspring sex ratio is related to the structure of living arrangement of husbands in polygynous unions. Indeed, the findings suggest that living arrangements and family structure among humans are important factors in predicting offspring sex ratio bias.

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