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Immune systems pose fascinating puzzles for evolutionary biologists. They feature some of the most polymorphic genes and reflect the strongest natural selection known. Evolution of immune systems plays a key role in host–parasite interactions, speciation, and eco-evolutionary dynamics that have community- and ecosystem-wide consequences. Conversely, evolutionary perspectives enrich our understanding of immunology, revealing macroevolutionary origins of key immune traits, their function in wild populations as opposed to sterile lab settings, and trade-offs that constrain immune adaptation. Here, we review key themes in the fast-growing interdisciplinary field of evolutionary immunology, focusing on multicellular animals. We describe macroevolution of immune functions, evidence of contemporary selection on immune genes, and the underlying theory seeking to explain this selection at multiple biological scales. We identify major open questions and opportunities in the field today. Foremost among these is the challenge of accurately and appropriately measuring relevant immune traits in wild and nonmodel organisms, which is necessary to understand their evolution in natural settings. A second challenge is to describe how diverse communities of symbionts impose selection on the highly multivariate and pleiotropic immune system.
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Trade-offs, Pleiotropy, and Shared Molecular Pathways: A Unified View of Constraints on Adaptation
Synopsis The concept of trade-offs permeates our thinking about adaptive evolution because they are exhibited at every level of biological organization, from molecular and cellular processes to organismal and ecological functions. Trade-offs inevitably arise because different traits do not occur in isolation, but instead are imbedded within complex, integrated systems that make up whole organisms. The genetic and mechanistic underpinning of trade-offs can be found in the pleiotropic nodes that occur in the biological pathways shared between traits. Yet, often trade-offs are only understood as statistical correlations, limiting the ability to evaluate the interplay between how selection and constraint interact during adaptive evolution. Here, we first review the classic paradigms in which physiologists and evolutionary biologists have studied trade-offs and highlight the ways in which network and molecular pathway approaches unify these paradigms. We discuss how these approaches allow researchers to evaluate why trade-offs arise and how selection can act to overcome trait correlations and evolutionary constraints. We argue that understanding how the conserved molecular pathways are shared between different traits and functions provides a conceptual framework for evolutionary biologists, physiologists, and molecular biologists to meaningfully work together toward the goal of understanding why correlations and trade-offs occur between traits. We briefly highlight the melanocortin system and the hormonal control of osmoregulation as two case studies where an understanding of shared molecular pathways reveals why trade-offs occur between seemingly unrelated traits. While we recognize that applying such approaches poses challenges and limitations particularly in the context of natural populations, we advocate for the view that focusing on the biological pathways responsible for trade-offs provides a unified conceptual context accessible to a broad range of integrative biologists.
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- Award ID(s):
- 1927470
- PAR ID:
- 10196258
- Date Published:
- Journal Name:
- Integrative and Comparative Biology
- Volume:
- 60
- Issue:
- 2
- ISSN:
- 1540-7063
- Page Range / eLocation ID:
- 332 to 347
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/icb/icaa056
