Sex allocation predicts mating rate in a simultaneous hermaphrodite

Janicke, Tim; Schärer, Lukas

doi:10.1098/rspb.2009.1336

Cited by 45 publications

(65 citation statements)

References 33 publications

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“…We could show that worms in octets produced larger testes and smaller ovaries and that they were therefore more male-biased compared to individuals in pairs, as previously documented for M. lignano (e.g. Schärer and Ladurner 2003;Schärer et al 2005;Schärer and Vizoso 2007;Janicke and Schärer 2009b). Despite this increase in male reproductive investment, there was no effect of the level of sperm competition on any of the sperm morphology traits we did measure.…”

Section: Discussionsupporting

confidence: 77%

“…The remaining worms were used for another experiment (published elsewhere; Janicke and Schärer 2009b). Image acquisition was carried out from day 36 to 41 according to the standard protocol (Schärer and Ladurner 2003;Janicke and Schärer 2009b). Afterwards, we amputated the tail plate of each worm with a scalpel to make the sperm that is stored in the seminal vesicle accessible for imaging.…”

Section: Morphological Measurement Of Sex Allocation and Sperm Morphomentioning

confidence: 99%

“…We then assessed whether our treatment induced a phenotypically plastic response in sex allocation, as already shown for M. lignano (e.g., Schärer and Ladurner 2003;Janicke and Schärer 2009b). For this, we used analysis of covariances (ANCOVAs), with testis size and ovary size as dependent variables, social group size as a fixed factor, and body size as a covariate (because testis size and ovary size are usually correlated with body size).…”

Section: Statistical Analysesmentioning

confidence: 99%

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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: Discussionsupporting

confidence: 77%

Section: Morphological Measurement Of Sex Allocation and Sperm Morphomentioning

confidence: 99%

Section: Statistical Analysesmentioning

confidence: 99%

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

Janicke

Schärer

2010

Behav Ecol Sociobiol

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“…In fact, Schärer [34] suggests using genetically homogeneous individuals to investigate how environmental factors affect sex allocation, which is an indirect acknowledgement of the confounding effect of genetic variation in allocation patterns. Even in species with plastic sex allocation [47], it seems likely that there can be overall differences in allocation or in the shape/slope of the allocation reaction norm.…”

Section: Sex Allocation and Evolutionary Transitions In Simultaneous mentioning

confidence: 99%

Intra-locus sexual conflict and sexually antagonistic genetic variation in hermaphroditic animals

Abbott

2010

Proc. R. Soc. B.

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Intra-locus sexual conflict results when sex-specific selection pressures for a given trait act against the intra-sexual genetic correlation for that trait. It has been found in a wide variety of taxa in both laboratory and natural populations, but the importance of intra-locus sexual conflict and sexually antagonistic genetic variation in hermaphroditic organisms has rarely been considered. This is not so surprising given the conceptual and theoretical association of intra-locus sexual conflict with sexual dimorphism, but there is no a priori reason why intra-locus sexual conflict cannot occur in hermaphroditic organisms as well. Here, I discuss the potential for intra-locus sexual conflict in hermaphroditic animals and review the available evidence for such conflict, and for the existence of sexually antagonistic genetic variation in hermaphrodites. I argue that mutations with asymmetric effects are particularly likely to be important in mediating sexual antagonism in hermaphroditic organisms. Moreover, sexually antagonistic genetic variation is likely to play an important role in inter-individual variation in sex allocation and in transitions to and from gonochorism (separate sexes) in simultaneous hermaphrodites. I also describe how sequential hermaphrodites may experience a unique form of intra-locus sexual conflict via antagonistic pleiotropy. Finally, I conclude with some suggestions for further research.

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“…Given that multiple mating might be beneficial for one sex function, but costly for the other function, a tradeoff between the optimal male and female mating strategies might arise within one individual, i.e. being eager to mate in one sex function versus being reluctant in the other sex function (Bedhomme et al 2009;Janicke and Schärer 2009b). Third, empirical data on female fitness consequences of multiple mating are crucial to resolve a longstanding debate on the preferred mating role in simultaneous hermaphrodites.…”

Section: Introductionmentioning

confidence: 99%

Determinants of female fecundity in a simultaneous hermaphrodite: the role of polyandry and food availability

2010

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Classical sexual selection theory assumes that the reproductive success of females is primarily limited by the resources available for egg production rather than by the number of mating partners. However, there is now accumulating evidence that multiple mating can entail fitness costs or benefits for females. In this study we investigated the effect of polyandry (i.e., the mating with different mating partners) and food availability on the reproductive output of the female sex function in an outcrossing simultaneous hermaphrodite, the free-living flatworm Macrostomum lignano. We exposed virgin worms to different group sizes, a treatment that has previously been shown to affect the level of polyandry in this species. Moreover, we manipulated the food availability throughout the subsequent egg laying period, during which the worms were kept in isolation. The number of offspring produced was used as an estimate of female fecundity. We found that food availability, but not group size, had a significant effect on female fecundity. Additionally, female fecundity was positively correlated with the number of stored sperm in the female sperm-storage organ at the time of isolation, but it was not correlated with body or ovary size of the worms. Our results suggest that female fecundity in M. lignano is primarily determined by the resources available for egg production, and not by the level of polyandry, confirming classic sexual selection theory for simultaneous hermaphrodites.

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Sex allocation predicts mating rate in a simultaneous hermaphrodite

Cited by 45 publications

References 33 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

Intra-locus sexual conflict and sexually antagonistic genetic variation in hermaphroditic animals

Determinants of female fecundity in a simultaneous hermaphrodite: the role of polyandry and food availability

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