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Hanna Kokko - One of the best experts on this subject based on the ideXlab platform.
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Parthenogenesis and the Evolution of Anisogamy
'MDPI AG', 2021Co-Authors: George W. A. Constable, Hanna KokkoAbstract:Recently, it was pointed out that classic models for the evolution of Anisogamy do not take into account the possibility of parthenogenetic reproduction, even though sex is facultative in many relevant taxa (e.g., algae) that harbour both anisogamous and isogamous species. Here, we complement this recent analysis with an approach where we assume that the relationship between progeny size and its survival may differ between parthenogenetically and sexually produced progeny, favouring either the former or the latter. We show that previous findings that parthenogenesis can stabilise isogamy relative to the obligate sex case, extend to our scenarios. We additionally investigate two different ways for one mating type to take over the entire population. First, parthenogenesis can lead to biased sex ratios that are sufficiently extreme that one type can displace the other, leading to de facto asexuality for the remaining type that now lacks partners to fuse with. This process involves positive feedback: microgametes, being numerous, lack opportunities for syngamy, and should they proliferate parthenogenetically, the next generation makes this asexual route even more prominent for microgametes. Second, we consider mutations to strict asexuality in producers of micro- or macrogametes, and show that the prospects of asexual invasion depend strongly on the mating type in which the mutation arises. Perhaps most interestingly, we also find scenarios in which parthenogens have an intrinsic survival advantage yet facultatively sexual isogamous populations are robust to the invasion of asexuals, despite us assuming no genetic benefits of recombination. Here, equal contribution from both mating types to zygotes that are sufficiently well provisioned can outweigh the additional costs associated with syngamy
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|Research Focus It takes two to tango
2016Co-Authors: Hanna Kokko, Michael JennionsAbstract:In most taxa, females are more likely than males to care for offspring. Why? Ever since Trivers ’ landmark work, the answer has been traced back to sexual differences in pre-mating reproductive investment (unequal gamete size or Anisogamy). However, recent work shows that parental investment theory has inadvertently ignored a profoundly simple fact of life: every offspring has a mother and father. Taking this into account completely changes how we should think about sex differences in parental care. In one of the best-known evolutionary game theory models to explain sex differences in parental care [1], both males and females have the option to desert rather than care for offspring, but the benefits of desertion differ between the sexes. A deserting femal
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doi:10.1111/j.1420-9101.2008.01540.x REVIEW Parental investment, sexual selection and sex ratios
2013Co-Authors: Hanna Kokko, Michael D JennionsAbstract:mating success; parental care; parental investment; sex ratio; sex roles; sexual selection. Conventional sex roles imply caring females and competitive males. The evolution of sex role divergence is widely attributed to Anisogamy initiating a self-reinforcing process. The initial asymmetry in pre-mating parental investment (eggs vs. sperm) is assumed to promote even greater divergence in postmating parental investment (parental care). But do we really understand the process? Trivers [Sexual Selection and the Descent of Man 1871–1971 (1972), Aldine Press, Chicago] introduced two arguments with a female and male perspective on whether to care for offspring that try to link pre-mating and post-matin
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Two roads to two sexes: unifying gamete competition and gamete limitation in a single model of Anisogamy evolution
Behavioral Ecology and Sociobiology, 2011Co-Authors: Jussi Lehtonen, Hanna KokkoAbstract:Recent studies have revealed the importance of self-consistency in evolutionary models, particularly in the context of male–female interactions. This has been largely ignored in models of the ancestral divergence of the sexes, i.e., the evolution of Anisogamy. Here, we model the evolution of Anisogamy in a Fisher-consistent context, explicitly taking into account the number of interacting individuals in a typical reproductive group. We reveal an interaction between the number of adult individuals in the local mating group and the selection pressures responsible for the divergence of the sexes. The same underlying model can produce Anisogamy in two different ways. Gamete competition can lead to Anisogamy when it is relatively easy for gametes to find each other, but when this is more difficult and gamete competition is absent, gamete limitation can provide another route for Anisogamy to evolve. In line with earlier models, organismal complexity favors Anisogamy. We argue that the early contributions of Kalmus and Scudo, largely dismissed as group selectionist, are valid under certain conditions. Linking their work with the contributions of Parker helps to explain why precisely males keep producing more sperm than can ever lead to offspring: sperm could evolve to provision zygotes but this brings little profit for the effort required, because sperm would have to be equipped with provisioning ability before it is known which sperm will make it to the fertilization stage. This insight creates a logical link between paternal care under uncertain paternity (where again investment is selected against when some investment never brings about genetic benefits) and gamete size evolution.
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parental investment sexual selection and sex ratios
Journal of Evolutionary Biology, 2008Co-Authors: Hanna Kokko, Michael D JennionsAbstract:Conventional sex roles imply caring females and competitive males. The evolution of sex role divergence is widely attributed to Anisogamy initiating a self-reinforcing process. The initial asymmetry in pre-mating parental invest- ment (eggs vs. sperm) is assumed to promote even greater divergence in post- mating parental investment (parental care). But do we really understand the process? Trivers (Sexual Selection and the Descent of Man 1871-1971 (1972), Aldine Press, Chicago) introduced two arguments with a female and male perspective on whether to care for offspring that try to link pre-mating and post-mating investment. Here we review their merits and subsequent theoretical develop- ments. The first argument is that females are more committed than males to providing care because they stand to lose a greater initial investment. This, however, commits the 'Concorde Fallacy' as optimal decisions should depend on future pay-offs not past costs. Although the argument can be rephrased in terms of residual reproductive value when past investment affects future pay-offs, it remains weak. The factors likely to change future pay-offs seem to work against females providing more care than males. The second argument takes the reasonable premise that Anisogamy produces a male-biased operational sex ratio (OSR) leading to males competing for mates. Male care is then predicted to be less likely to evolve as it consumes resources that could otherwise be used to increase competitiveness. However, given each offspring has precisely two genetic parents (the Fisher condition), a biased OSR generates frequency- dependent selection, analogous to Fisherian sex ratio selection, that favours increased parental investment by whichever sex faces more intense competi- tion. Sex role divergence is therefore still an evolutionary conundrum. Here we review some possible solutions. Factors that promote conventional sex roles are sexual selection on males (but non-random variance in male mating success must be high to override the Fisher condition), loss of paternity because of female multiple mating or group spawning and patterns of mortality that generate female-biased adult sex ratios (ASR). We present an integrative model that shows how these factors interact to generate sex roles. We emphasize the need to distinguish between the ASR and the operational sex ratio (OSR). If mortality is higher when caring than competing this diminishes the likelihood of sex role divergence because this strongly limits the mating success of the earlier deserting sex. We illustrate this in a model where a change in relative mortality rates while caring and competing generates a shift from a mammalian type breeding system (female-only care, male-biased OSR and female-biased ASR) to an avian type system (biparental care and a male-biased OSR and ASR).
Michael D Jennions - One of the best experts on this subject based on the ideXlab platform.
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coevolution of parental investment and sexually selected traits drives sex role divergence
Nature Communications, 2016Co-Authors: Lutz Fromhage, Michael D JennionsAbstract:Sex-role evolution theory attempts to explain the origin and direction of male-female differences. A fundamental question is why Anisogamy, the difference in gamete size that defines the sexes, has repeatedly led to large differences in subsequent parental care. Here we construct models to confirm predictions that individuals benefit less from caring when they face stronger sexual selection and/or lower certainty of parentage. However, we overturn the widely cited claim that a negative feedback between the operational sex ratio and the opportunity cost of care selects for egalitarian sex roles. We further argue that our model does not predict any effect of the adult sex ratio (ASR) that is independent of the source of ASR variation. Finally, to increase realism and unify earlier models, we allow for coevolution between parental investment and investment in sexually selected traits. Our model confirms that small initial differences in parental investment tend to increase due to positive evolutionary feedback, formally supporting long-standing, but unsubstantiated, verbal arguments.
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doi:10.1111/j.1420-9101.2008.01540.x REVIEW Parental investment, sexual selection and sex ratios
2013Co-Authors: Hanna Kokko, Michael D JennionsAbstract:mating success; parental care; parental investment; sex ratio; sex roles; sexual selection. Conventional sex roles imply caring females and competitive males. The evolution of sex role divergence is widely attributed to Anisogamy initiating a self-reinforcing process. The initial asymmetry in pre-mating parental investment (eggs vs. sperm) is assumed to promote even greater divergence in postmating parental investment (parental care). But do we really understand the process? Trivers [Sexual Selection and the Descent of Man 1871–1971 (1972), Aldine Press, Chicago] introduced two arguments with a female and male perspective on whether to care for offspring that try to link pre-mating and post-matin
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parental investment sexual selection and sex ratios
Journal of Evolutionary Biology, 2008Co-Authors: Hanna Kokko, Michael D JennionsAbstract:Conventional sex roles imply caring females and competitive males. The evolution of sex role divergence is widely attributed to Anisogamy initiating a self-reinforcing process. The initial asymmetry in pre-mating parental invest- ment (eggs vs. sperm) is assumed to promote even greater divergence in post- mating parental investment (parental care). But do we really understand the process? Trivers (Sexual Selection and the Descent of Man 1871-1971 (1972), Aldine Press, Chicago) introduced two arguments with a female and male perspective on whether to care for offspring that try to link pre-mating and post-mating investment. Here we review their merits and subsequent theoretical develop- ments. The first argument is that females are more committed than males to providing care because they stand to lose a greater initial investment. This, however, commits the 'Concorde Fallacy' as optimal decisions should depend on future pay-offs not past costs. Although the argument can be rephrased in terms of residual reproductive value when past investment affects future pay-offs, it remains weak. The factors likely to change future pay-offs seem to work against females providing more care than males. The second argument takes the reasonable premise that Anisogamy produces a male-biased operational sex ratio (OSR) leading to males competing for mates. Male care is then predicted to be less likely to evolve as it consumes resources that could otherwise be used to increase competitiveness. However, given each offspring has precisely two genetic parents (the Fisher condition), a biased OSR generates frequency- dependent selection, analogous to Fisherian sex ratio selection, that favours increased parental investment by whichever sex faces more intense competi- tion. Sex role divergence is therefore still an evolutionary conundrum. Here we review some possible solutions. Factors that promote conventional sex roles are sexual selection on males (but non-random variance in male mating success must be high to override the Fisher condition), loss of paternity because of female multiple mating or group spawning and patterns of mortality that generate female-biased adult sex ratios (ASR). We present an integrative model that shows how these factors interact to generate sex roles. We emphasize the need to distinguish between the ASR and the operational sex ratio (OSR). If mortality is higher when caring than competing this diminishes the likelihood of sex role divergence because this strongly limits the mating success of the earlier deserting sex. We illustrate this in a model where a change in relative mortality rates while caring and competing generates a shift from a mammalian type breeding system (female-only care, male-biased OSR and female-biased ASR) to an avian type system (biparental care and a male-biased OSR and ASR).
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Review: Parental investment, sexual selection and sex ratios
2008Co-Authors: Hanna Kokko, Michael D JennionsAbstract:mating success; parental care; parental investment; sex ratio; sex roles; sexual selection. Conventional sex roles imply caring females and competitive males. The evolution of sex role divergence is widely attributed to Anisogamy initiating a self-reinforcing process. The initial asymmetry in pre-mating parental invest-ment (eggs vs. sperm) is assumed to promote even greater divergence in post-mating parental investment (parental care). But do we really understand the process? Trivers [Sexual Selection and the Descent of Man 1871–1971 (1972), Aldine Press, Chicago] introduced two arguments with a female and male perspective on whether to care for offspring that try to link pre-mating and post-matin
Tatsuya Togashi - One of the best experts on this subject based on the ideXlab platform.
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Evidence for equal size cell divisions during gametogenesis in a marine green alga Monostroma angicava
Scientific Reports, 2015Co-Authors: Tatsuya Togashi, Hironobu Sasaki, Yusuke Horinouchi, Jin YoshimuraAbstract:In cell divisions, relative size of daughter cells should play fundamental roles in gametogenesis and embryogenesis. Differences in gamete size between the two mating types underlie sexual selection. Size of daughter cells is a key factor to regulate cell divisions during cleavage. In cleavage, the form of cell divisions (equal/unequal in size) determines the developmental fate of each blastomere. However, strict validation of the form of cell divisions is rarely demonstrated. We cannot distinguish between equal and unequal cell divisions by analysing only the mean size of daughter cells, because their means can be the same. In contrast, the dispersion of daughter cell size depends on the forms of cell divisions. Based on this, we show that gametogenesis in the marine green alga, Monostroma angicava , exhibits equal size cell divisions. The variance and the mean of gamete size (volume) of each mating type measured agree closely with the prediction from synchronized equal size cell divisions. Gamete size actually takes only discrete values here. This is a key theoretical assumption made to explain the diversified evolution of isogamy and Anisogamy in marine green algae. Our results suggest that germ cells adopt equal size cell divisions during gametogenesis.
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evolutionary trajectories explain the diversified evolution of isogamy and Anisogamy in marine green algae
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Tatsuya Togashi, John L Bartelt, Jin Yoshimura, Kei-ichi TainakaAbstract:The evolution of Anisogamy (the production of gametes of different size) is the first step in the establishment of sexual dimorphism, and it is a fundamental phenomenon underlying sexual selection. It is believed that Anisogamy originated from isogamy (production of gametes of equal size), which is considered by most theorists to be the ancestral condition. Although nearly all plant and animal species are anisogamous, extant species of marine green algae exhibit a diversity of mating systems including both isogamy and Anisogamy. Isogamy in marine green algae is of two forms: isogamy with extremely small gametes and isogamy with larger gametes. Based on disruptive selection for fertilization success and zygote survival (theory of Parker, Baker, and Smith), we explored how environmental changes can contribute to the evolution of such complex mating systems by analyzing the stochastic process in the invasion simulations of populations of differing gamete sizes. We find that both forms of isogamy can evolve from other isogamous ancestors through Anisogamy. The resulting dimensionless analysis accounts for the evolutionary stability of all types of mating systems in marine green algae, even in the same environment. These results imply that evolutionary trajectories as well as the optimality of gametes/zygotes played an important role in the evolution of gamete size.
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phototaxis and the evolution of isogamy and slight Anisogamy in marine green algae insights from laboratory observations and numerical experiments
Botanical Journal of the Linnean Society, 2004Co-Authors: Tatsuya TogashiAbstract:The evolution of Anisogamy in marine algae was studied through numerical simulations of gamete mating behaviour in three dimensions, using observed traits of marine green algae as input parameters. The importance of phototaxis became apparent from the numerical experiments: all gametes with phototactic systems are favoured over those without, but this advantage is reduced with increasing tank depth or shorter search times. Phototactic gametes were advantaged over non-phototactic gametes if the water was shallower than about 30–40 mm when the time available for gamete encounter was 1000 time steps (5.55 min). If gametes of both sexes are positively phototactic, slightly anisogamous species are at a disadvantage to isogamous species, which invalidates the sperm-limitation theory as a driver for the evolution of slight Anisogamy. Conflicting selection forces of search efficiency and zygote fitness may be needed. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 144, 321–327.
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production of anisogametes and gamete motility dimorphism in monostroma angicava
Sexual Plant Reproduction, 1997Co-Authors: Tatsuya Togashi, Terunobu IchimuraAbstract:The reproductive strategy of a marine alga with a heteromorphic biphasic life cycle was studied by analyzing various sexual reproductive characters in light of the evolution of Anisogamy. Gametophytes of Monostroma angicava were dioecious and their gametes were slightly anisogamous. Volume of gametangium, density of gametangia and area of mature gametangial parts on each gametophyte did not differ from male to female. Therefore, the reproductive biomass investment for gamete production was considered to be the same for each sex. Anisogamy in this alga appeared to be derived from the difference in the number of cell divisions during gametogenesis, because the majority of male gametangia each produced 64 (26) gametes and the female produced 32 (25) gametes. This corresponded with measurements of cell size in male and female gametes. Further, the sex ratio was 1:1 for sexually mature plants sampled at Charatsunai. Therefore, it was suggested that in the field twice as many male gametes are released as female gametes. Liberated gametes of both sexes showed positive phototaxis. The swimming velocity of freshly liberated male gametes was a little higher than that of female gametes. Male gametes had the potential to swim for ca. 72 h and female gametes for ca. 84 h. The difference in gamete motility between the two sexes seemed to be related to cell size. Planozygotes were negatively phototactic and swam more rapidly than gametes of either sex.
Jin Yoshimura - One of the best experts on this subject based on the ideXlab platform.
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Evidence for equal size cell divisions during gametogenesis in a marine green alga Monostroma angicava
Scientific Reports, 2015Co-Authors: Tatsuya Togashi, Hironobu Sasaki, Yusuke Horinouchi, Jin YoshimuraAbstract:In cell divisions, relative size of daughter cells should play fundamental roles in gametogenesis and embryogenesis. Differences in gamete size between the two mating types underlie sexual selection. Size of daughter cells is a key factor to regulate cell divisions during cleavage. In cleavage, the form of cell divisions (equal/unequal in size) determines the developmental fate of each blastomere. However, strict validation of the form of cell divisions is rarely demonstrated. We cannot distinguish between equal and unequal cell divisions by analysing only the mean size of daughter cells, because their means can be the same. In contrast, the dispersion of daughter cell size depends on the forms of cell divisions. Based on this, we show that gametogenesis in the marine green alga, Monostroma angicava , exhibits equal size cell divisions. The variance and the mean of gamete size (volume) of each mating type measured agree closely with the prediction from synchronized equal size cell divisions. Gamete size actually takes only discrete values here. This is a key theoretical assumption made to explain the diversified evolution of isogamy and Anisogamy in marine green algae. Our results suggest that germ cells adopt equal size cell divisions during gametogenesis.
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evolutionary trajectories explain the diversified evolution of isogamy and Anisogamy in marine green algae
Proceedings of the National Academy of Sciences of the United States of America, 2012Co-Authors: Tatsuya Togashi, John L Bartelt, Jin Yoshimura, Kei-ichi TainakaAbstract:The evolution of Anisogamy (the production of gametes of different size) is the first step in the establishment of sexual dimorphism, and it is a fundamental phenomenon underlying sexual selection. It is believed that Anisogamy originated from isogamy (production of gametes of equal size), which is considered by most theorists to be the ancestral condition. Although nearly all plant and animal species are anisogamous, extant species of marine green algae exhibit a diversity of mating systems including both isogamy and Anisogamy. Isogamy in marine green algae is of two forms: isogamy with extremely small gametes and isogamy with larger gametes. Based on disruptive selection for fertilization success and zygote survival (theory of Parker, Baker, and Smith), we explored how environmental changes can contribute to the evolution of such complex mating systems by analyzing the stochastic process in the invasion simulations of populations of differing gamete sizes. We find that both forms of isogamy can evolve from other isogamous ancestors through Anisogamy. The resulting dimensionless analysis accounts for the evolutionary stability of all types of mating systems in marine green algae, even in the same environment. These results imply that evolutionary trajectories as well as the optimality of gametes/zygotes played an important role in the evolution of gamete size.
Scott Pitnick - One of the best experts on this subject based on the ideXlab platform.
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Intensity of sexual selection along the Anisogamy–isogamy continuum
Nature, 2006Co-Authors: Adam Bjork, Scott PitnickAbstract:Research into the evolution of giant sperm has uncovered a paradox within the foundations of sexual selection theory. Postcopulatory sexual selection on males (that is, sperm competition and cryptic female choice) can lead to decreased sperm numbers by favouring the production of larger sperm^ 1 . However, a decline in sperm numbers is predicted to weaken selection on males and increase selection on females^ 2 , 3 . As isogamy is approached (that is, as investment per gamete by males approaches that by females), sperm become less abundant, ova become relatively less rare, and competition between males for fertilization success is predicted to weaken. Sexual selection for longer sperm, therefore, is expected to be self limiting. Here we examine this paradox in Drosophila along the Anisogamy–isogamy continuum using intraspecific experimental evolution techniques and interspecific comparative techniques. Our results confirm the big-sperm paradox by showing that the sex difference in sexual selection gradients^ 4 decreases as sperm size increases. However, a resolution to the paradox is provided when this finding is interpreted in concert with the ‘opportunity for selection’ and the ‘opportunity for sexual selection’^ 5 , 6 . Furthermore, we show that most of the variation in measures of selection intensity is explained by sperm length and relative investment in sperm production.
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intensity of sexual selection along the Anisogamy isogamy continuum
Nature, 2006Co-Authors: Adam Bjork, Scott PitnickAbstract:Research into the evolution of giant sperm has uncovered a paradox within the foundations of sexual selection theory. Postcopulatory sexual selection on males (that is, sperm competition and cryptic female choice) can lead to decreased sperm numbers by favouring the production of larger sperm1. However, a decline in sperm numbers is predicted to weaken selection on males and increase selection on females2,3. As isogamy is approached (that is, as investment per gamete by males approaches that by females), sperm become less abundant, ova become relatively less rare, and competition between males for fertilization success is predicted to weaken. Sexual selection for longer sperm, therefore, is expected to be self limiting. Here we examine this paradox in Drosophila along the Anisogamy–isogamy continuum using intraspecific experimental evolution techniques and interspecific comparative techniques. Our results confirm the big-sperm paradox by showing that the sex difference in sexual selection gradients4 decreases as sperm size increases. However, a resolution to the paradox is provided when this finding is interpreted in concert with the ‘opportunity for selection’ and the ‘opportunity for sexual selection’5,6. Furthermore, we show that most of the variation in measures of selection intensity is explained by sperm length and relative investment in sperm production.