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22 results for “Facultative sex”
The presence of a guard vicariously drives split sex ratios in a facultatively social bee
<p>Split sex ratios provide broad insights into how reproductive strategies evolve and historically have special relevance to the evolution of eusociality. Yet almost no attention has been directed to situations where split sex ratios may potentially decrease the payoffs for worker-like behaviour, increasing selective thresholds for eusociality. We examined sex ratios in a facultatively social colletid bee, <em>Amphylaeus morosus</em>. Sex ratios in this bee vary strongly with the presence of a nest guard and in a pattern that does not conform to assumptions of previous models in which split sex ratios facilitate altruism. While the production of daughters was constant across social and solitary nests, mothers produced more brood when a non-reproductive guard was present, but these extra brood were all male. This leads to split sex ratios, vicariously driven by guards that are unable to manipulate sex ratios in their favour. Importantly, if guarding becomes more common in a population this would lead to an excess of males and lower the genetic value of these extra males to guards, effectively putting a brake on selection for worker-like behaviour.</p>
Differential sex allocation strategies between females and facultative hermaphrodites of Chamaelirium hisauchianum (Melanthiaceae)
<p><span>Species of <em>Chamaelirium</em> are known to be highly diversified in sexual characters, but there has been no detailed empirical approach to elucidate the mechanism and process of sexual diversification in the genus. This paper reports the results of population-based analyses on various sexual aspects of <em>C. hisauchianum</em> endemic to Japan. Of the 20 populations surveyed, eight (40%) were composed of facultative hermaphrodites highly labile in sexual expression, exhibiting a wide range of gradational variation from hermaphroditism through andromonoecy to male. The remaining 12 populations (60 %) consisted of females and facultative hermaphrodites. In them, 11.8–30.9% (mean 22.2%) of the individuals were female. With no reciprocal sex changes, females and facultative hermaphrodites were regarded as, plausibly genetically determined, discrete sex morphs. In contrast, sexual expression in both sex morphs appeared resource dependent. Besides the difference in floral sexual traits, the average ratio of ovuliferous flowers in females was higher than that in facultative hermaphrodites. The production of ovuliferous flowers by females was less susceptible to both field and cultivated conditions and tended to be significantly relatively higher under unfavorable growing conditions. Females were thus less plastic (or more persistent) in producing ovuliferous flowers (or female organs) than facultative hermaphrodites irrespective of internal and external conditions. In all populations, andromonoecious plants dominated (50.8–100%), which appeared to reflect the high plasticity in sex allocation of facultative hermaphrodites. The different modes of sex allocation were regarded as secondary sex characters and presumably stem from a difference in easiness or attainability of sexual reproduction between the two sex morphs. </span></p>
Differential sex allocation strategies between females and facultative hermaphrodites of Chamaelirium hisauchianum (Melanthiaceae)
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The presence of a guard vicariously drives split sex ratios in a facultatively social bee
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Sex differences in fearful personality traits are explained by facultative calibration to physical strength
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Data from: Sex at the margins: parthenogenesis vs. facultative and obligate sex in a Neotropical ant
Geographic parthenogenesis is a distribution pattern, in which parthenogenetic populations tend to live in marginal habitats, at higher latitudes and altitudes and island-like habitats compared with the sexual forms. The facultatively parthenogenetic ant Platythyrea punctata is thought to exhibit this general pattern throughout its wide range in Central America and the Caribbean Islands. Workers of P. punctata from the Caribbean produce diploid female offspring from unfertilized eggs by thelytokous parthenogenesis, and mated females and males are rare. In contrast, workers in one colony from Costa Rica were incapable of thelytoky; instead mated workers produced all female offspring. Because sample sizes were very low in former studies, we here use microsatellite markers and explicit tests of thelytoky to examine the population genetic structure of ancestral and derived populations of P. punctata throughout the Caribbean and Central America. Populations from the Caribbean islands were fully capable of parthenogenesis and population genetic signatures indicate that this is the predominant mode of reproduction, although males are occasionally produced. In contrast, the northernmost population on the mainland (Texas) showed signatures of sexual reproduction and individuals were incapable of reproduction by thelytoky. Contrary to expectations from a geographic parthenogenesis distribution pattern, most parts of the mainland populations were found to be facultatively thelytokous, with population genetic signatures of both sexual and parthenogenetic reproduction.
Data from: Outstanding intraindividual genetic diversity in fissiparous planarians (Dugesia, Platyhelminthes) with facultative sex
Background: Predicted genetic consequences of asexuality include high intraindividual genetic diversity (i.e., the Meselson effect) and accumulation of deleterious mutations (i.e., Muller's Ratchet), among others. These consequences have been largely studied in parthenogenetic organisms, but studies on fissiparous species are scarce. Differing from parthenogens, fissiparous organisms inherit part of the soma of the progenitor, including somatic mutations. Thus, in the long term, fissiparous reproduction may also result in genetic mosaicism, besides the presence of the Meselson effect and Muller's Ratchet. Dugesiidae planarians show outstanding regeneration capabilities, allowing them to naturally reproduce by fission, either strictly or combined with sex (facultative). Therefore, they are an ideal model to analyze the genetic footprint of fissiparous reproduction, both when it is alternated with sex and when it is the only mode of reproduction. Results: In the present study, we generate and analyze intraindividual cloned data of a nuclear and a mitochondrial gene of sexual, fissiparous and facultative wild populations of the species Dugesia subtentaculata. We find that most individuals, independently of their reproductive strategy, are mosaics. However, the intraindividual haplotype and nucleotide diversity of fissiparous and facultative individuals is significantly higher than in sexual individuals, with no signs of Muller's Ratchet. Finally, we also find that this high intraindividual genetic diversity of fissiparous and facultative individuals is composed by different combinations of ancestral and derived haplotypes of the species. Conclusions: The intraindividual analyses of genetic diversity point out that fissiparous reproduction leaves a very special genetic footprint in individuals, characterized by mosaicism combined with the Meselson effect (named in the present study as the mosaic Meselson effect). Interestingly, the different intraindividual combinations of ancestral and derivate genetic diversity indicate that haplotypes generated during periods of fissiparous reproduction can be also transmitted to the progeny through sexual events, resulting in offspring showing a wide range of genetic diversity and putatively allowing purifying selection to act at both intraindividual and individual level. Further investigations, using Dugesia planarians as model organisms, would be of great value to delve into this new model of genetic evolution by the combination of fission and sex.
Queen-worker conflict can drive the evolution of social polymorphism and split sex ratios in facultatively eusocial life-cycles
<p>Hamilton's idea that haplodiploidy favors the evolution of altruism – the haplodiploidy hypothesis -- relies on the relatedness asymmetry between the sexes, caused by the sex-specific ploidies. Theoretical work on the consequences of relatedness asymmetries has significantly improved our understanding of sex-allocation and intra-colony conflicts, but the importance of haplodiploidy for the evolution of altruism came to be seen as minor. However, recently it was shown that haplodiploidy can strongly favor the evolution of eusociality, provided additional "preadaptations" are also present, such as the production of multiple broods per season and maternal ability to bias offspring sex ratios. These results were obtained assuming no influence of workers on the sex ratio, even though worker control of the sex ratio is known to occur. Here we model the evolution of sex-specific fratricide as a mechanism of worker control over the sex ratio. We show that fratricide can facilitate the initial evolution of helping. However, fratricide can also hamper the evolution of unconditional help. Instead, social polymorphism evolves, a mixture of helping and dispersing offspring. Finally, we show that the co-evolution of sex-allocation strategies of workers (fratricide) and queens leads to a split production of the sexes, with some colonies specializing in males and others in females. Thus, the model predicts that fratricide spawns a diversity of co-existing life cycles that strongly vary in degree of sociality and sex ratios.</p>
Data from: Sex ratio variations among years and breeding systems in a facultatively parthenogenetic termite
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Data from: A split sex ratio in solitary and social nests of a facultatively social bee
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Data from: Sex at the margins: parthenogenesis vs. facultative and obligate sex in a Neotropical ant
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Data from: Outstanding intraindividual genetic diversity in fissiparous planarians (Dugesia, Platyhelminthes) with facultative sex
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Queen-worker conflict can drive the evolution of social polymorphism and split sex ratios in facultatively eusocial life-cycles
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Data from: The consequences of facultative sex in a prey adapting to predation
A species reproductive mode, along with its associated costs and benefits, can play a significant role in its evolution and survival. Facultative sexuality, being able to reproduce both sexually and asexually, has been deemed evolutionary favourable as the benefits of either mode may be fully realized. In fact, many studies have focused on identifying the benefits of sex and/or the forces selecting for increased rates of sex using facultative sexual species. The costs of either mode however can also have a profound impact on a population's evolutionary trajectory. Here we used experimental evolution and fitness assays to investigate the consequences of facultative sexuality in prey adapting to predation. Specifically, we compared the adaptive response of algal prey populations exposed to constant rotifer predation and which had alternating cycles of asexual and sexual reproduction where sexual episodes were either facultative (sexual and asexual progeny simultaneously propagated) or obligate (only sexual progeny propagated). We found that prey populations with facultative sexual episodes reached a lower final relative fitness and suffered a greater trade-off in traits under selection, i.e. defense and competitive ability, as compared to prey populations with obligate sexual episodes. Our results suggest that costs associated with sexual reproduction (germination time) and asexual reproduction (selection interference) were amplified in the facultative sexual prey populations, leading to a reduction in the net advantage of sexuality. Additionally, we found evidence that the cost of sex was reduced in the obligate sexual prey populations because increased selection for sex was observed via the spontaneous production of sexual cells. These results show that certain costs associated with facultative sexuality can affect an organism's evolutionary trajectory.
Data from: The 'male escape hypothesis': sex-biased metamorphosis in response to climatic drivers in a facultatively paedomorphic amphibian
Paedomorphosis is a major evolutionary process that bypasses metamorphosis and allows reproduction in larvae. In newts and salamanders, it can be facultative with paedomorphs retaining gills and metamorphs dispersing. The evolution of these developmental processes is thought to have been driven by the costs and benefits of inhabiting aquatic versus terrestrial habitats. In this context, we aimed at testing the hypothesis that climatic drivers affect phenotypic transition and the difference across sexes because sex-ratio is biased in natural populations. Through a replicated laboratory experiment, we showed that paedomorphic palmate newts (Lissotriton helveticus) metamorphosed at a higher frequency when water availability decreased and metamorphosed earlier when temperature increased in these conditions. All responses were sex-biased, and males were more prone to change phenotype than females. Our work shows how climatic variables can affect facultative paedomorphosis and support theoretical models predicting life on land instead of in water. Moreover, because males metamorphose and leave water more often and earlier than females, these results, for the first time, give an experimental explanation for the rarity of male paedomorphosis (the 'male escape hypothesis') and suggest the importance of sex in the evolution of paedomorphosis versus metamorphosis.
Data from: The ‘male escape hypothesis’: sex-biased metamorphosis in response to climatic drivers in a facultatively paedomorphic amphibian
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Data from: Sex allocation theory for facultatively sexual organisms inhabiting seasonal environments: the importance of bet-hedging
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Data from: The paradox of obligate sex: the roles of sexual conflict and mate scarcity in transitions to facultative and obligate asexuality
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Data from: Evolutionary stable sex ratios with non-facultative male-eggs first sex allocation in fig wasps
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Data from: Local adaptation of sex-induction in a facultative sexual crustacean: insights from QTL mapping and natural population of Daphnia magna
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