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Adaptation, Exaptation, and Constraint: A Hormonal Perspective
The American Naturalist
|March 28, 2018
Summary
Evolutionary biology can be understood through endocrinology. Hormones mediate traits; distinguishing adaptations from exaptations depends on whether selection acted on hormone levels or tissue sensitivity.
Area of Science:
- Evolutionary Biology
- Endocrinology
- Phenotypic Plasticity
Background:
- Single hormones influence multiple traits, creating correlated suites of phenotypic traits.
- Evolutionary questions arise regarding whether these traits are adaptations or exaptations.
- Distinguishing between adaptations and exaptations depends on the evolutionary pressures acting on hormone levels versus target tissue sensitivity.
Purpose of the Study:
- To explore conceptual issues in evolutionary biology using an endocrinological perspective.
- To investigate how hormonal mechanisms influence the evolution of correlated traits.
- To differentiate between adaptations and exaptations within hormone-mediated trait suites.
Main Methods:
- Analyzing the relationship between systemic hormone levels, target tissue responsiveness, and trait evolution.
- Employing experimental hormonal manipulations (phenotypic engineering) to study endocrine constraints.
- Measuring interdependent responses of beneficial and detrimental traits to selection under hormonal alteration.
Main Results:
- Selection on systemic hormone levels may lead to exaptations for indirectly affected traits.
- Independent changes in target tissue sensitivity to invariant hormone levels can result in multiple adaptations.
- Hormonal manipulations in dark-eyed juncos provide insights into endocrine constraints on evolution.
Conclusions:
- Understanding hormonal mechanisms and historical selective regimes is crucial for distinguishing adaptations from exaptations.
- Endocrine systems can impose constraints on evolution, as evidenced by cases where hormonal alteration depresses fitness.
- Experimental endocrinology offers a powerful approach to studying evolutionary constraints and trait evolution.
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