Sexual Conflict in Hermaphrodites

Schärer, Lukas; Janicke, Tim; Ramm, Steven A.

doi:10.1101/cshperspect.a017673

Cited by 105 publications

(148 citation statements)

References 203 publications

(266 reference statements)

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“…A fuller understanding of sexual conflict will provide insight into its contribution to adaptive evolution and will reveal the constraints it might impose on populations. In many sexually reproducing species, divergent reproductive interests can arise between the sexes over courtship, fertilization and offspring investment, and these conflicting interests can lead to substantially different optimal phenotypes in males and females [1][2][3] . In such cases, selection will act in opposing directions on the sexes, a situation referred to as sexual conflict or sexual antagonism.…”

Section: Introductionmentioning

confidence: 99%

Population genetics of sexual conflict in the genomic era

2017

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ABSTRACT:Sexual conflict occurs when selection acts in opposing directions on males and females. Case studies in both vertebrates and invertebrates indicate that sexual conflict maintains genetic diversity through balancing selection, which might explain why many populations show more genetic variation than expected. Recent population genomic approaches based on different measures of balancing selection have suggested that sexual conflict can arise over survival, not just reproductive fitness as previously thought. A fuller understanding of sexual conflict will provide insight into its contribution to adaptive evolution and will reveal the constraints it might impose on populations. In many sexually reproducing species, divergent reproductive interests can arise between the sexes over courtship, fertilization and offspring investment, and these conflicting interests can lead to substantially different optimal phenotypes in males and females [1][2][3] . In such cases, selection will act in opposing directions on the sexes, a situation referred to as sexual conflict or sexual antagonism. Sexual conflict over a given phenotypic trait can occur through the interaction of alleles at two or more loci (inter-locus sexual conflict) [4][5][6] . This form of sexual conflict has been somewhat difficult to study using molecular population genetic methods, as it lacks a clear evolutionary signature in DNA sequence. As a result, the majority of recent population genomic studies have focused on cases where there are genetic trade-offs for male and female fitness from alleles at a single locus (intra-locus sexual conflict). This situation arises when male and female phenotypes are underpinned by the same genetic architecture 7 . With the exception of sex-specific Y and W chromosomes, males and females within a species share the vast majority of their genome, which creates a high potential for intra-locus conflict when male and female reproductive interests are not aligned through strict monogamy. Indeed, classic work measuring reproductive fitness in Drosophila 8 has suggested that intra-locus sexual conflict occurs at many different loci throughout the genome. Intra-locus sexual conflict can be ultimately resolved via alleles or expression patterns that are sex-specific in their effects 9-13 .The persistence of sexual conflict, and the mechanism by which it occurs, have important implications for the nature and magnitude of genetic diversity within populations [14][15][16][17][18][19] .Positive selection and purifying selection deplete populations of genetic variation over time.Nevertheless, many populations display more genetic diversity for traits under strong selection than expected, possibly because of balancing selection generated by intra-locus sexual conflict 15,20 . Intra-locus sexual conflict produces balancing selection by selecting for or against different alleles at a specific locus depending on whether they are present in females or males. The resulting genetic diversity-and by implication sexual conflictshapes t...

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Section: Introductionmentioning

confidence: 99%

Population genetics of sexual conflict in the genomic era

2017

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“…[3][4][5][6][7][8]), and seems especially prevalent in simultaneous hermaphrodites (e.g. [9][10][11][12]; reviews in [1,13]). It is usually thought to evolve as a response to sexual conflict, as a means through which the sperm-donating individual may be able to enforce mating, and thus (unilateral) sperm donation, and/or regain some control over the fate of its donated sperm (i.e.…”

Section: Introductionmentioning

confidence: 99%

Hypodermic self-insemination as a reproductive assurance strategy

et al. 2015

Self Cite

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Self-fertilization occurs in a broad range of hermaphroditic plants and animals, and is often thought to evolve as a reproductive assurance strategy under ecological conditions that disfavour or prevent outcrossing. Nevertheless, selfing ability is far from ubiquitous among hermaphrodites, and may be constrained in taxa where the male and female gametes of the same individual cannot easily meet. Here, we report an extraordinary selfing mechanism in one such species, the free-living flatworm Macrostomum hystrix. To test the hypothesis that adaptations to hypodermic insemination of the mating partner under outcrossing also facilitate selfing, we experimentally manipulated the social environment of these transparent flatworms and then observed the spatial distribution of received sperm in vivo. We find that this distribution differs radically between conditions allowing or preventing outcrossing, implying that isolated individuals use their needle-like stylet (male copulatory organ) to inject own sperm into their anterior body region, including into their own head, from where they then apparently migrate to the site of (self-)fertilization. Conferring the ability to self could thus be an additional consequence of hypodermic insemination, a widespread fertilization mode that is especially prevalent among simultaneously hermaphroditic animals and probably evolves due to sexual conflict over the transfer and subsequent fate of sperm.

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“…By contrast, if the number of potential males is low, investing heavily in male function is unprofitable. Thus, even if male function usually benefits more from an additional mating, the actual fitness benefits will depend on a range of factors such as mating history, mate availability, fecundity, survival and sex-allocation decisions made by the mating partner (reviewed in [14]). Because it seems unlikely that selection can optimize both male and female functions in the same individual, simultaneous hermaphrodites need to trade-off male and female roles and investment into each role.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, it pays to increase a partner's investment into female function, as that will increase the number of eggs that can be fertilized provided the organism stores sperm for later fertilization [17]. 'Love darts', found in many species of land snails, are thought to manipulate the reproductive physiology of the recipient, either by increasing the fertilization success of the sperm that is transferred at the same time as the love dart, or by functioning as an anti-aphrodisiac (see Schärer et al [14] for a recent review). Likewise the seminal fluid of the freshwater snail Lymnaea stagnalis contains proteins that reduce both sperm transfer and fertilization success of a subsequent mating by the inseminated partner while at the same time manipulating female investment of that partner [18], similar to the anti-aphrodisiac found in seminal fluid of, for example, Drosophila [19].…”

Section: When You Are Both Male and Femalementioning

confidence: 99%

Sexual selection in hermaphrodites, sperm and broadcast spawners, plants and fungi

Beekman

Nieuwenhuis

Ortiz‐Barrientos

et al. 2016

Phil. Trans. R. Soc. B

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One contribution of 15 to a theme issue 'Weird sex: the underappreciated diversity of sexual reproduction'. Darwin was the first to recognize that sexual selection is a strong evolutionary force. Exaggerated traits allow same-sex individuals to compete over access to mates and provide a mechanism by which mates are selected. It is relatively easy to appreciate how inter-and intrasexual selection work in organisms with the sensory capabilities to perceive physical or behavioural traits that signal mate quality or mate compatibility, and to assess the relative quality of competitors. It is therefore not surprising that most studies of sexual selection have focused on animals with separate sexes and obvious adaptations that function in the context of reproductive competition. Yet, many sexual organisms are both male and female at the same time, often lack sexual dimorphism and never come into direct contact at mating. How does sexual selection act in such species, and what can we learn from them? Here, we address these questions by exploring the potential for sexual selection in simultaneous hermaphrodites, sperm-and broadcast spawners, plants and fungi. Our review reveals a range of mechanisms of sexual selection, operating primarily after gametes have been released, which are common in many of these groups and also quite possibly in more familiar (internally fertilizing and sexually dimorphic) organisms.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.

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Sexual Conflict in Hermaphrodites

Cited by 105 publications

References 203 publications

Population genetics of sexual conflict in the genomic era

Population genetics of sexual conflict in the genomic era

Hypodermic self-insemination as a reproductive assurance strategy

Sexual selection in hermaphrodites, sperm and broadcast spawners, plants and fungi

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