“Diversity and coevolutionary dynamics in high-dimensional phenotype spaces”

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Michael Doebeli and Iaroslav Ispolatov

Complex evolutionary dynamics during macroevolutionary community assembly

Chaetanthera villosa in a new lava field in Chile: an example of the colonization of an empty niche.
(Credit: Iaroslav Ispolatov)

Understanding grand patterns of life is a central goal of biological research, and large-scale, macroevolutionary patterns, such as mass extinctions, bursts of new diversity during adaptive radiations, or long-term changes in the speed of evolution, have fascinated evolutionary biologists for decades. Ultimately, macroevolutionary patterns are consequences of births and deaths of individual organisms, which cause changes in the genetic makeup of populations. For example, adaptive radiations occur because new ecological types of individuals arise that can coexist with already existing types.

Generating links between microevolutionary processes such as competition and predation, which directly affect individual birth and death rates, and macroevolutionary patterns is a major problem in theoretical biology. In a new study in The American Naturalist, Michael Doebeli from the University of British Columbia in Vancouver and Iaroslav Ispolatov from the University of Santiago in Chile have used microevolutionary models based on competition for resources to study long-term dynamics of diversification and coevolution between species.

These two authors have a longstanding interest in the problem of speciation and the evolution of diversity, and their previous work has shown that gradual evolutionary change in phenotypes (evolutionary dynamics) can be nonstationary and never-ending, and even chaotic when the number of phenotypic features (phenotypic dimensions) that affect ecological interactions between individuals is high. They have now extended these models to include the emergence of new species over long time spans, and they then studied the long-term evolutionary dynamics of emerging lineages. They found that long-term evolutionary dynamics tend to be fast and nonstationary for an intermediate level of diversity, but tend to stabilize as the evolving communities reach a saturation level of diversity. They also found that the amount of diversity present at the saturation level increases rapidly with the number of phenotypic dimensions.

These results provide new perspectives on major macroevolutionary patterns such as adaptive radiation, long-term changes in the speed of evolution, and the evolution of diversity. For adaptive radiation, the results suggest that the rate of evolutionary change should decrease as the radiation unfolds, resulting in stasis once the saturation level is reached. If new phenotype dimensions evolve, e.g., through gene duplication, another bout of fast evolutionary dynamics followed by stasis can be expected, thus generating a pattern resembling punctuated equilibrium. Finally, diversity may saturate for a given dimension of phenotype space, but may not saturate over very long time scales as new phenotypic dimensions evolve, essentially resulting in open-ended evolution of diversity. Hopefully, these theoretical insights can help guide empirical research trying to understand large-scale patterns in the evolutionary tree of life. Read the Article