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Diapause and maintenance of facultative sexual reproductive strategies.

ABSTRACT: Facultative sex combines sexual and asexual reproduction in the same individual (or clone) and allows for a large diversity of life-history patterns regarding the timing, frequency and intensity of sexual episodes. In addition, other life-history traits such as a diapause stage may become linked to sex. Here, we develop a matrix modelling framework for addressing the cost of sex in facultative sexuals, in constant, periodic and stochastically fluctuating environments. The model is parametrized using life-history data from Brachionus calyciflorus, a facultative sexual rotifer in which sex and diapause are linked. Sexual propensity was an important driver of costs in constant environments, in which high costs (always > onefold, and sometimes > twofold) indicated that asexuals should outcompete facultative sexuals. By contrast, stochastic environments with high temporal autocorrelation favoured facultative sex over obligate asex, in particular, if the penalty to fecundity in 'bad' environments was large. In such environments, obligate asexuals were constrained by their life cycle length (i.e. time from birth to last reproductive adult age class), which determined an upper limit to the number of consecutive bad periods they could tolerate. Nevertheless, when facultative asexuals with different sexual propensities competed simultaneously against each other and asex, the lowest sex propensity was the most successful in stochastic environments with positive autocorrelation. Our results suggest that a highly specific mechanism (i.e. diapause linked to sex) can alone stabilize facultative sex in these animals, and protect it from invasion of both asexual and pure sexual strategies.This article is part of the themed issue 'Weird sex: the underappreciated diversity of sexual reproduction'.

SUBMITTER: Stelzer CP

PROVIDER: S-EPMC5031621 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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Diapause and maintenance of facultative sexual reproductive strategies.

Stelzer Claus-Peter CP Lehtonen Jussi J

Philosophical transactions of the Royal Society of London. Series B, Biological sciences 20161001 1706

Facultative sex combines sexual and asexual reproduction in the same individual (or clone) and allows for a large diversity of life-history patterns regarding the timing, frequency and intensity of sexual episodes. In addition, other life-history traits such as a diapause stage may become linked to sex. Here, we develop a matrix modelling framework for addressing the cost of sex in facultative sexuals, in constant, periodic and stochastically fluctuating environments. The model is parametrized u ...[more]

PMID: 27619700

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Project description:BackgroundMany of the 35 million women and girls aged 15-49 requiring humanitarian assistance have inadequate access to the sexual and reproductive health (SRH) services to which they are entitled. Ensuring accountability is critical to realizing their SRH and reproductive rights (RR).ObjectivesThis scoping review examines the extent and nature of existing evidence on accountability strategies for SRH in humanitarian settings in different geographical scopes/contexts, and contextualizes these findings in the larger thematic literature. This review seeks to answer the following questions: What accountability strategies are employed to address the availability, accessibility, acceptability, and quality of SRH in humanitarian settings? What do we know about the successes and challenges of the given strategies? What are the implications for practice?MethodsWe consulted public health, social science, and legal databases including SCOPUS, PubMed, ProQuest, and LexisNexis for peer-reviewed articles, as well as Google Advanced search for grey literature; the search was conducted in March 2019. We searched for relevant articles and documents relating to accountability, humanitarian, and SRH and/or RR. To identify key challenges not reflected in the literature and additional grey literature, 18 key informants from international NGOs, local government bodies, academia, and donor agencies were interviewed from March-June 2019.ResultsA total of 209 papers and documents were identified via our literature searches and interviews for review. We identified three categories of approaches to accountability in our background reading, and we then applied these to the papers reviewed a priori. We created a fourth category based on our findings. The categories include: (1) humanitarian principles, codes of conduct, and legal instruments; (2) technical, performance, and impact standards; (3) efforts to solicit and address the rights and needs of the affected populations, or "listening and responding," and, (4) accountability demands made by affected populations themselves. Almost all papers identified referred to challenges to realizing accountability in humanitarian contexts. There are promising accountability approaches - some specific to SRH and some not - such as open-ended feedback from affected populations, quality improvement, and practical application of standards. Reflecting a largely top down orientation, papers concentrate on accountability mechanisms within humanitarian work, with much less focus on supporting affected populations to deepen their understanding of structural causes of their position, understand their entitlements, or access justice.ConclusionIn the last 20 years, there has been increasing standard and guideline development and program experiences related to accountability in humanitarian settings. Yet, the emphasis is on tools or mechanisms for accountability with less attention to changing norms regarding SRH and RR within affected communities, and to a lesser extent, among implementers of humanitarian programs or to institutionalizing community participation.

Project description:Fluctuating environments threaten fertility and viability. To better match the immediate, local environment, many organisms adopt alternative phenotypic states, a phenomenon called "phenotypic plasticity." Natural populations that predictably encounter fluctuating environments tend to be more plastic than conspecific populations that encounter a constant environment, suggesting that phenotypic plasticity can be adaptive. Despite pervasive evidence of such "adaptive phenotypic plasticity," gene regulatory mechanisms underlying plasticity remains poorly understood. Here we test the hypothesis that environment-dependent phenotypic plasticity is mediated by epigenetic factors. To test this hypothesis, we exploit the adaptive reproductive arrest of Drosophila melanogaster females, called diapause. Using an inbred line from a natural population with high diapause plasticity, we demonstrate that diapause is determined epigenetically: only a subset of genetically identical individuals enter diapause and this diapause plasticity is epigenetically transmitted for at least three generations. Upon screening a suite of epigenetic marks, we discovered that the active histone marks H3K4me3 and H3K36me1 are depleted in diapausing ovaries. Using ovary-specific knockdown of histone mark writers and erasers, we demonstrate that H3K4me3 and H3K36me1 depletion promotes diapause. Given that diapause is highly polygenic, that is, distinct suites of alleles mediate diapause plasticity across distinct genotypes, we also investigated the potential for genetic variation in diapause-determining epigenetic marks. Specifically, we asked if these histone marks were similarly depleted in diapause of a genotypically distinct line. We found evidence of divergence in both the gene expression program and histone mark abundance. This study reveals chromatin determinants of phenotypic plasticity and suggests that these determinants may be genotype-dependent, offering new insight into how organisms may exploit and evolve epigenetic mechanisms to persist in fluctuating environments.

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Diapause and maintenance of facultative sexual reproductive strategies.

Publications

Diapause and maintenance of facultative sexual reproductive strategies.

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