“… natural selection will ensure that modifications consequent on other modifications at a different period of life shall not be in the least degree injurious: for if they became so, they would cause the extinction of the species.”
- Charles Darwin. 1859. On the Origin of Species
- Charles Darwin. 1859. On the Origin of Species
Plants, animals, and fungi face a basic problem as they proceed through their life cycles: the demands on juveniles differ from, and frequently oppose, those on adults. For some taxa, like frogs or salmon, this problem manifests because each life-cycle stage occurs in a radically different habitat from the others. For many more taxa, however, this problem arises simply from the fact that juveniles must maximize growth and survival whereas adults must maximize reproduction. Although each life-cycle stage’s demands are often at odds with one another, organisms nevertheless must adapt to them all. This raises two long-standing questions in biology that our research aims to address. First, what conditions allow life-cycle stages to evolve independently from each other? Second, what are the consequences when life-cycle stages do not decouple?
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Development, physiology, & the decoupling of
life-cycle stages
Our work in dragonflies is unraveling when juveniles and adults can evolve freely from each other
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Biologists have long assumed that organisms possess mechanisms that prevent adaptation in one stage from affecting adaptation in others. Though theory and natural history made this notion the conventional wisdom for >150 years, a growing body of evidence reveals that life-cycle stages are actually independent from one another in only some circumstances. A major problem in biology therefore concerns the situations in which life-cycle stages are able to evolve freely.
Our research seeks to understand the developmental and physiological conditions wherein life-cycle stages can (or cannot) adapt independently from one another. Using data from insects, amphibians, and fish, this work harnesses comparative, meta-analytic, and experimental approaches to address questions such as: 1) What kinds of life-history transitions permit juveniles and adults to evolve independently from each other? 2) What features of development allow some traits to evolve more independently between stages than others? 3) What parts of organisms' life cycles evolve most independently from the influence of parental effects? 4) How does developmental plasticity minimize conflict between life-cycle stages? |
Adaptation, diversification, & the costs of life-cycle stages that do not evolve independently from each other
Since the earliest days of evolutionary thinking, biologists realized that organisms could incur extreme costs if adaptation in one life-cycle stage was hindered by adaptation in other stages. Although they assumed this meant that life cycles would ultimately evolve mechanisms that minimize correlations between the stages, the last 20 years has shown that stages are far less decoupled than previously anticipated. This opens up the possibility that evolutionary changes in one life-cycle stage could be an overlooked constraint on adaptation and ecological diversification in other stages. Alternatively, as Darwin suggested, life-cycle stages may not evolve independently, but correlations between stages do not ultimately restrict an organism’s performance in its current habitat and/or its ability to adapt to new ones.
Our research aims to characterize the extent to which natural selection in one life-cycle stage constrains adaptation and diversification in other stages. By blending meta-analytic, experimental, and comparative approaches, our work in this area tackles questions such as: 1) How much is juvenile fitness reduced by producing the optimal adult phenotype (and vice versa)? 2) Do parents have a larger influence on the juvenile or adult fitness of offspring? 3) Does evolution in one stage limit the ecological niches to which other stages can adapt? |
Our work in dragonflies is also uncovering the costs when life-cycle stages cannot evolve freely from each other
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The planet is undergoing unprecedented rates of environmental change, and organisms must respond or face extinction. For the many plants, animals, and fungi that use different habitats during different life-cycle stages, there is the added complexity that they must acclimate and/or adapt to very different kinds of environmental change across ontogeny. While researchers have made tremendous strides illuminating how organisms are responding to individual threats posed by the Anthropocene, we are only just beginning to evaluate these responses across multiple life-cycle stages.
Our research is now expanding to address how organisms optimize their performance across life-cycle stages as they respond to global change. Such work not only offers critical insight for conservation and management, but it also provides unique opportunities to study how organisms resolve trade-offs between life-cycle stages at the very onset of adaptation to new environments. In some earlier work, we studied dragonfly responses to global warming. This work revealed some exciting physiological and morphological adaptations that adult dragonflies consistently employ over historical and contemporary timescales. It remains unclear, however, what these predictable patterns of adult evolution entail for the ecology and evolution of the larvae. Moving forward, we will leverage the phylogenetically replicated patterns of adult evolution to study questions such as:
1) How does adaptation to environmental change in the adult stage affect local adaptation in the larval stage?
2) What evolutionary changes must larvae undergo so that adults can adapt to novel selective pressures?
3) How does evolution in one stage affect ecological dynamics in other stages?
Our research is now expanding to address how organisms optimize their performance across life-cycle stages as they respond to global change. Such work not only offers critical insight for conservation and management, but it also provides unique opportunities to study how organisms resolve trade-offs between life-cycle stages at the very onset of adaptation to new environments. In some earlier work, we studied dragonfly responses to global warming. This work revealed some exciting physiological and morphological adaptations that adult dragonflies consistently employ over historical and contemporary timescales. It remains unclear, however, what these predictable patterns of adult evolution entail for the ecology and evolution of the larvae. Moving forward, we will leverage the phylogenetically replicated patterns of adult evolution to study questions such as:
1) How does adaptation to environmental change in the adult stage affect local adaptation in the larval stage?
2) What evolutionary changes must larvae undergo so that adults can adapt to novel selective pressures?
3) How does evolution in one stage affect ecological dynamics in other stages?