Sex allocation and sexual conflict in simultaneously hermaphroditic animals

Schärer, Lukas; Janicke, Tim

doi:10.1098/rsbl.2009.0100

Cited by 49 publications

(70 citation statements)

References 21 publications

(32 reference statements)

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“…Individuals of this species are capable of adjusting their sex allocation (i.e., the reproductive investment into the male versus the female sex function) in response to the social group size (i.e., the number of potential mates) that they experience. Such an adjustment is in agreement with a central prediction of sex allocation theory for simultaneous hermaphrodites (for a review, see Schärer 2009), and several studies have demonstrated for M. lignano that individuals that were raised in larger groups have bigger testes (e.g., Schärer and Ladurner 2003;Schärer et al 2005;Schärer and Vizoso 2007;Schärer and Janicke 2009).…”

Section: Communicated By T Mooresupporting

confidence: 56%

Sperm competition affects sex allocation but not sperm morphology in a flatworm

Janicke

Schärer

2010

Behav Ecol Sociobiol

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Sperm competition has been shown to be an important evolutionary agent affecting the behaviour, physiology, and morphology of both males and females. One morphological trait that is particularly likely to be affected by sperm competition is sperm size because it is thought to influence the competitiveness of sperm by determining sperm longevity, motility, and/or their ability to displace competing sperm. Most comparative studies across taxa have found a positive relationship between the level of sperm competition and sperm length, but very few studies have tested for a phenotypically plastic adjustment of sperm morphology in response to sperm competition. In this study, we experimentally tested for an effect of sperm competition on phenotypic plasticity in sperm morphology in an obligately outcrossing simultaneous hermaphrodite, the free-living flatworm Macrostomum lignano, by either raising worms in monogamous pairs (no sperm competition) or in promiscuous groups (intense sperm competition). Worms in groups produced larger testes and smaller ovaries as predicted by sex allocation theory and as previously documented in this species. However, we found no evidence for an effect of group size on sperm morphology, measured as total sperm length, sperm body length, and the length of two different sperm appendages. We conclude that M. lignano may either be incapable of adjusting the sperm morphology in a phenotypically plastic way and/or that there might be no benefit of phenotypic plasticity in sperm traits in this species.

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Section: Communicated By T Mooresupporting

confidence: 56%

Sperm competition affects sex allocation but not sperm morphology in a flatworm

Janicke

Schärer

2010

Behav Ecol Sociobiol

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“…Until recently, most models of sperm competition have treated the sperm recipients as a passive vessel in which sperm from different sperm donors compete for access to ova. However, as Charnov [18] pointed out in his seminal 1979 paper, reciprocal mating may lead to post-copulatory female choice (later termed cryptic female choice [74,75]; see also [76]). Cryptic female choice is expected to be prevalent in hermaphrodites because reciprocal mating strategies lead to the receipt of sperm from individuals that are unattractive as fathers.…”

Section: (C) Cryptic Female Choicementioning

confidence: 99%

Sex allocation and investment into pre- and post-copulatory traits in simultaneous hermaphrodites: the role of polyandry and local sperm competition

Schärer

Pen

2013

Phil. Trans. R. Soc. B

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Sex allocation theory predicts the optimal allocation to male and female reproduction in sexual organisms. In animals, most work on sex allocation has focused on species with separate sexes and our understanding of simultaneous hermaphrodites is patchier. Recent theory predicts that sex allocation in simultaneous hermaphrodites should strongly be affected by post-copulatory sexual selection, while the role of pre-copulatory sexual selection is much less clear. Here, we review sex allocation and sexual selection theory for simultaneous hermaphrodites, and identify several strong and potentially unwarranted assumptions. We then present a model that treats allocation to sexually selected traits as components of sex allocation and explore patterns of allocation when some of these assumptions are relaxed. For example, when investment into a male sexually selected trait leads to skews in sperm competition, causing local sperm competition, this is expected to lead to a reduced allocation to sperm production. We conclude that understanding the evolution of sex allocation in simultaneous hermaphrodites requires detailed knowledge of the different sexual selection processes and their relative importance. However, little is currently known quantitatively about sexual selection in simultaneous hermaphrodites, about what the underlying traits are, and about what drives and constrains their evolution. Future work should therefore aim at quantifying sexual selection and identifying the underlying traits along the pre- to post-copulatory axis.

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“…Hence, there will be much to gain from the consideration of kin structure across all studies of sexual conflict. Schärer & Janicke (2009) also do much to highlight the fact that the links between sex allocation and sexual conflict deserve further study across hermaphrodites and organisms with separate sexes. Similarly, Bedhomme et al (2009) initiate a discussion of the differences in how traits selected under the influence of sexual conflict will behave in hermaphrodites in comparison to plants and animals with separate sexes.…”

Section: (D) Sexual Conflict Coevolution Evolutionary Chases and Rementioning

confidence: 99%

“…Differences in variance between sex functions are also therefore important in species without separate sexes. Schärer & Janicke (2009) nicely extend this approach by examining conflicts over sex allocation between sperm donors and sperm recipients in hermaphrodites, and the importance of post-copulatory sexual selection. Sperm-trading and the influence of conflicts of interest between different hermaphrodite partners are themes that were also tackled by Charnov (1979).…”

Section: (D) Sexual Conflict Coevolution Evolutionary Chases and Rementioning

confidence: 99%

Sexual conflict and sex allocation

Chapman

2009

Biol. Lett.

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Sex allocation and sexual conflict in simultaneously hermaphroditic animals

Cited by 49 publications

References 21 publications

Sperm competition affects sex allocation but not sperm morphology in a flatworm

Sperm competition affects sex allocation but not sperm morphology in a flatworm

Sex allocation and investment into pre- and post-copulatory traits in simultaneous hermaphrodites: the role of polyandry and local sperm competition

Sexual conflict and sex allocation

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