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Caren B Cooper - One of the best experts on this subject based on the ideXlab platform.
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solar noon and tactile cues synergistically regulate clutch size a new approach to investigations of avian Life History Theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-History Theory is central to our understanding of the evolutionary processes that drive adaptation. According to Life-History Theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in Life-History Theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian LifeHistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately solar noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before solar noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of Life-History Theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives Life-History trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common Life-History variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
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Solar noon and tactile cues synergistically regulate clutch size: a new approach to investigations of avian Life‐History Theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-History Theory is central to our understanding of the evolutionary processes that drive adaptation. According to Life-History Theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in Life-History Theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian LifeHistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately solar noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before solar noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of Life-History Theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives Life-History trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common Life-History variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
Margaret A Voss - One of the best experts on this subject based on the ideXlab platform.
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solar noon and tactile cues synergistically regulate clutch size a new approach to investigations of avian Life History Theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-History Theory is central to our understanding of the evolutionary processes that drive adaptation. According to Life-History Theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in Life-History Theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian LifeHistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately solar noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before solar noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of Life-History Theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives Life-History trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common Life-History variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
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Solar noon and tactile cues synergistically regulate clutch size: a new approach to investigations of avian Life‐History Theory
Ibis, 2013Co-Authors: Margaret A Voss, Caren B CooperAbstract:Life-History Theory is central to our understanding of the evolutionary processes that drive adaptation. According to Life-History Theory, a trade-off between reproduction and survival means that organisms cannot maximize both at the same time (Gadgil & Bossert 1970, Charnov & Krebs 1974, Stearns 1976, 1989, Reznick 1985, Morris 1986). As Reznick (1985) stated while reviewing the costs of reproduction, ‘To be the best in all possible worlds is not biologically possible; to be well adapted to even one world requires compromise.’ Throughout the progression of thought in Life-History Theory, clutch size has been a trait of primary interest. For over half a century, it has been argued that diverse selection pressures operate on clutch size in birds (Ricklefs 2000) so as to optimize it, although the relative importance of each pressure remains unclear. A few examples of competing selection pressures on clutch size include the trade-offs between clutch size and number of clutches in a given year, clutch size and parental care, clutch size and access to food resources, clutch size and parental age, and the list goes on. A vast body of literature demonstrates the extent of these trade-offs and their importance in understanding emergent avian LifeHistory patterns, yet we still do not understand how birds regulate or determine clutch size. Although avian clutch size often varies systematically and in predictable ways, we cannot adequately explain the emergent patterns. While investigations have explored possible roles of predation, food availability and seasonality (e.g. Beukeboom et al. 1988, Hochachka 1990, Crick et al. 1993) on variation in clutch size, additional insights may be found by asking how (mechanistically) clutch size is determined, rather than why (evolutionarily). Such a shift in question might change our perception of which traits selection might be acting upon to optimize clutch size. A paper by Sacha Haywood in this issue of Ibis brings us closer to resolving a fundamental problem in identifying the proximate selection pressures regulating clutch size. Haywood’s egg removal experiments with Common Swifts Apus apus nicely demonstrate that the trait (or suite of traits) under selection is not the number of eggs in a clutch, an ordinal trait measured quantitatively, but rather the physiological mechanisms controlling the endpoint of the laying sequence. Haywood presents evidence that there is a specific point in time, approximately solar noon on the day the first egg is laid, that plays a decisive role in determining how many subsequent eggs will be produced (Haywood 2013). Haywood builds his argument in two parts. First he explores the possibility that the tactile cue that stops the production of yolky follicles is invariant in its timing. In other words, the production of yolky follicles is halted by the stimulus of the brood patch coming in contact with the first egg laid. Invariance in the timing of this tactile cue means that a second mechanism must come into play to account for the observed variability in egg production. Second, he postulates a role for an internal circadian clock that might govern the ability of ovarian tissue to receive and respond to hormone fluxes, thereby allowing for temporal plasticity in follicular development and eventual disruption. In the case of the Common Swift, this competency to receive the hormonal signal develops over a period of 3–6 h before solar noon on the day the first egg is laid, at which point it becomes fully functional. With these two mechanisms, Haywood’s model accounts for variability in clutch size in a species that would otherwise seem to be physiologically constrained to a predetermined number of eggs. A key implication of Haywood’s findings is that the focal point of Life-History Theory with regard to clutch size might actually be a set of physiological processes and their underlying gene regulation, rather than a single quantitative characteristic (i.e. number of eggs produced). A strong argument for considering physiological processes as the target of selection that subsequently drives Life-History trade-offs was outlined by Sinervo and Svensson (1998). Haywood’s study fits this paradigm shift in that it forces us to view clutch size, a common Life-History variable, not as a single quantitative trait under selection pressure but rather as the product of several intersecting endocrine feedback loops. Furthermore, his experimental results set the stage for clarification of the differentiation between determinate layers with invariant clutch size and indeterminate layers (variable clutch size). *Corresponding author. Email: mav11@psu.edu
Vladas Griskevicius - One of the best experts on this subject based on the ideXlab platform.
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Sense of control under uncertainty depends on people's childhood environment: a Life History Theory approach
Journal of personality and social psychology, 2014Co-Authors: Chiraag Mittal, Vladas GriskeviciusAbstract:Past research found that environmental uncertainty leads people to behave differently depending on their childhood environment. For example, economic uncertainty leads people from poor childhoods to become more impulsive while leading people from wealthy childhoods to become less impulsive. Drawing on Life History Theory, we examine the psychological mechanism driving such diverging responses to uncertainty. Five experiments show that uncertainty alters people’s sense of control over the environment. Exposure to uncertainty led people from poorer childhoods to have a significantly lower sense of control than those from wealthier childhoods. In addition, perceptions of control statistically mediated the effect of uncertainty on impulsive behavior. These studies contribute by demonstrating that sense of control is a psychological driver of behaviors associated with fast and slow Life History strategies. We discuss the implications of this for Theory and future research, including that environmental uncertainty might lead people who grew up poor to quit challenging tasks sooner than people who grew up wealthy.
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the influence of mortality and socioeconomic status on risk and delayed rewards a Life History Theory approach
Journal of Personality and Social Psychology, 2011Co-Authors: Vladas Griskevicius, Joshua M Tybur, Andrew W Delton, Theresa E RobertsonAbstract:Why do some people take risks and live for the present, whereas others avoid risks and save for the future? The evolutionary framework of Life History Theory predicts that preferences for risk and delay in gratification should be influenced by mortality and resource scarcity. A series of experiments examined how mortality cues influenced decisions involving risk preference (e.g., $10 for sure vs. 50% chance of $20) and temporal discounting (e.g., $5 now vs. $10 later). The effect of mortality depended critically on whether people grew up in a relatively resource-scarce or resource-plentiful environment. For individuals who grew up relatively poor, mortality cues led them to value the present and gamble for big immediate rewards. Conversely, for individuals who grew up relatively wealthy, mortality cues led them to value the future and avoid risky gambles. Overall, mortality cues appear to propel individuals toward diverging Life History strategies as a function of childhood socioeconomic status, suggesting important implications for how environmental factors influence economic decisions and risky behaviors.
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The influence of mortality and socioeconomic status on preferences for risk and delayed rewards: A Life History Theory approach
Journal of personality and social psychology, 2011Co-Authors: Vladas Griskevicius, Joshua M Tybur, Andrew W Delton, Theresa E RobertsonAbstract:Why do some people take risks and live for the present, whereas others avoid risks and save for the future? The evolutionary framework of Life History Theory predicts that preferences for risk and delay in gratification should be influenced by mortality and resource scarcity. A series of experiments examined how mortality cues influenced decisions involving risk preference (e.g., $10 for sure vs. 50% chance of $20) and temporal discounting (e.g., $5 now vs. $10 later). The effect of mortality depended critically on whether people grew up in a relatively resource-scarce or resource-plentiful environment. For individuals who grew up relatively poor, mortality cues led them to value the present and gamble for big immediate rewards. Conversely, for individuals who grew up relatively wealthy, mortality cues led them to value the future and avoid risky gambles. Overall, mortality cues appear to propel individuals toward diverging Life History strategies as a function of childhood socioeconomic status, suggesting important implications for how environmental factors influence economic decisions and risky behaviors.
Theresa E Robertson - One of the best experts on this subject based on the ideXlab platform.
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the influence of mortality and socioeconomic status on risk and delayed rewards a Life History Theory approach
Journal of Personality and Social Psychology, 2011Co-Authors: Vladas Griskevicius, Joshua M Tybur, Andrew W Delton, Theresa E RobertsonAbstract:Why do some people take risks and live for the present, whereas others avoid risks and save for the future? The evolutionary framework of Life History Theory predicts that preferences for risk and delay in gratification should be influenced by mortality and resource scarcity. A series of experiments examined how mortality cues influenced decisions involving risk preference (e.g., $10 for sure vs. 50% chance of $20) and temporal discounting (e.g., $5 now vs. $10 later). The effect of mortality depended critically on whether people grew up in a relatively resource-scarce or resource-plentiful environment. For individuals who grew up relatively poor, mortality cues led them to value the present and gamble for big immediate rewards. Conversely, for individuals who grew up relatively wealthy, mortality cues led them to value the future and avoid risky gambles. Overall, mortality cues appear to propel individuals toward diverging Life History strategies as a function of childhood socioeconomic status, suggesting important implications for how environmental factors influence economic decisions and risky behaviors.
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The influence of mortality and socioeconomic status on preferences for risk and delayed rewards: A Life History Theory approach
Journal of personality and social psychology, 2011Co-Authors: Vladas Griskevicius, Joshua M Tybur, Andrew W Delton, Theresa E RobertsonAbstract:Why do some people take risks and live for the present, whereas others avoid risks and save for the future? The evolutionary framework of Life History Theory predicts that preferences for risk and delay in gratification should be influenced by mortality and resource scarcity. A series of experiments examined how mortality cues influenced decisions involving risk preference (e.g., $10 for sure vs. 50% chance of $20) and temporal discounting (e.g., $5 now vs. $10 later). The effect of mortality depended critically on whether people grew up in a relatively resource-scarce or resource-plentiful environment. For individuals who grew up relatively poor, mortality cues led them to value the present and gamble for big immediate rewards. Conversely, for individuals who grew up relatively wealthy, mortality cues led them to value the future and avoid risky gambles. Overall, mortality cues appear to propel individuals toward diverging Life History strategies as a function of childhood socioeconomic status, suggesting important implications for how environmental factors influence economic decisions and risky behaviors.
Brenda W Gillespie - One of the best experts on this subject based on the ideXlab platform.
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Life History Theory fertility and reproductive success in humans
Proceedings of The Royal Society B: Biological Sciences, 2002Co-Authors: Beverly I Strassmann, Brenda W GillespieAbstract:According to Life-History Theory, any organism that maximizes fitness will face a trade-off between female fertility and offspring survivorship. This trade-off has been demonstrated in a variety of species, but explicit tests in humans have found a positive linear relationship between fitness and fertility. The failure to demonstrate a maximum beyond which additional births cease to enhance fitness is potentially at odds with the view that human fertility behaviour is currently adaptive. Here we report, to our knowledge, the first clear evidence for the predicted nonlinear relationship between female fertility and reproductive success in a human population, the Dogon of Mali, West Africa. The predicted maximum reproductive success of 4.1+/-0.3 surviving offspring was attained at a fertility of 10.5 births. Eighty-three per cent of the women achieved a Lifetime fertility level (7-13 births) for which the predicted mean reproductive success was within the confidence limits (3.4 to 4.8) for reproductive success at the optimal fertility level. Child mortality, rather than fertility, was the primary determinant of fitness. Since the Dogon people are farmers, our results do not support the assumptions that: (i) contemporary foragers behave more adaptively than agriculturalists, and (ii) that adaptive fertility behaviour ceased with the Neolithic revolution some 9000 years ago. We also present a new method that avoids common biases in measures of reproductive success.
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Life–History Theory, fertility and reproductive success in humans
Proceedings of The Royal Society B: Biological Sciences, 2002Co-Authors: Beverly I Strassmann, Brenda W GillespieAbstract:According to Life-History Theory, any organism that maximizes fitness will face a trade-off between female fertility and offspring survivorship. This trade-off has been demonstrated in a variety of species, but explicit tests in humans have found a positive linear relationship between fitness and fertility. The failure to demonstrate a maximum beyond which additional births cease to enhance fitness is potentially at odds with the view that human fertility behaviour is currently adaptive. Here we report, to our knowledge, the first clear evidence for the predicted nonlinear relationship between female fertility and reproductive success in a human population, the Dogon of Mali, West Africa. The predicted maximum reproductive success of 4.1+/-0.3 surviving offspring was attained at a fertility of 10.5 births. Eighty-three per cent of the women achieved a Lifetime fertility level (7-13 births) for which the predicted mean reproductive success was within the confidence limits (3.4 to 4.8) for reproductive success at the optimal fertility level. Child mortality, rather than fertility, was the primary determinant of fitness. Since the Dogon people are farmers, our results do not support the assumptions that: (i) contemporary foragers behave more adaptively than agriculturalists, and (ii) that adaptive fertility behaviour ceased with the Neolithic revolution some 9000 years ago. We also present a new method that avoids common biases in measures of reproductive success.