“EvoHeritage," goes beyond a one-dimensional view of phylogenetics


Biodiversity, the breathtaking tapestry of life on Earth, extends far beyond a simple headcount of species. Phylogenetic metrics, which delve into the evolutionary relationships between species, paint a richer picture by considering the historical branches on the tree of life. However, a recent article in Systematic Biology by FitzJohn et al. (2022) argues that current metrics have a blind spot: the erosion of evolutionary history over time.

The article, titled "Phylogenetic Biodiversity Metrics Should Account for Both Accumulation and Attrition of Evolutionary Heritage," sheds light on the limitations of prominent metrics like phylogenetic diversity (PD). PD focuses on the total length of branches in a phylogenetic tree, reflecting the cumulative evolutionary history within a community. While valuable, it overlooks a critical process – attrition.

Attrition refers to the gradual loss of evolutionary features over time, independent of extinction events. Traits can be lost due to various mechanisms, such as gene silencing or convergent evolution, where unrelated species develop similar adaptations. These lost features still represent a significant chunk of evolutionary history, yet PD fails to capture them.

The authors propose a groundbreaking metric, "EvoHeritage," that goes beyond a one-dimensional view. EvoHeritage incorporates both accumulation (represented by PD) and attrition. It considers the total branch length on the phylogenetic tree but adjusts it based on the estimated amount of evolutionary features lost within each lineage. This provides a more nuanced picture of biodiversity, reflecting not just the total evolutionary history but also the functional and potentially unique aspects preserved within a community.

The power of EvoHeritage lies in its ability to bridge several key gaps:

  • Connecting the Dots Between Metrics: At one extreme, with no attrition, EvoHeritage seamlessly recovers PD. Conversely, with complete loss of features, it aligns with species richness, the simplest measure of biodiversity. This positions EvoHeritage on a spectrum, offering a bridge between established metrics.

  • A Stronger Predictor of Ecosystem Function: The authors compared EvoHeritage to PD and species richness in predicting ecosystem productivity (the rate at which organic matter is produced). Remarkably, EvoHeritage emerged as the strongest predictor, suggesting a closer link between preserved evolutionary history and the functional capacity of ecosystems.

The implications of EvoHeritage extend far beyond theoretical considerations:

  • Guiding Conservation Efforts: Conservation biology prioritizes the protection of irreplaceable biodiversity. EvoHeritage can be a powerful tool for identifying areas harboring unique evolutionary lineages, even if those lineages have lost some features through attrition. This can help optimize conservation strategies to maximize the preservation of evolutionary heritage.

  • Unlocking Ecological Mysteries: Understanding how evolutionary history shapes the assembly and functioning of ecological communities is a central question in ecology. EvoHeritage can provide valuable insights into how past evolutionary processes influence present-day ecological dynamics, shedding light on complex ecological relationships.

  • A Window into Deep Time: Studying large-scale evolutionary patterns often involves analyzing biodiversity loss through deep time. EvoHeritage's ability to account for attrition might offer a more comprehensive understanding of historical biodiversity trends, enriching our understanding of the evolutionary journey of life on Earth.

While EvoHeritage presents a promising paradigm shift, the article acknowledges some limitations. Accurately estimating the rate of attrition across diverse lineages is a complex challenge. Further research is needed to develop robust methods for quantifying this loss. Additionally, the authors call for further exploration of how EvoHeritage integrates with other biodiversity metrics to provide an even more comprehensive picture of life.

In conclusion, FitzJohn et al. (2022) offer a compelling argument for incorporating attrition into the equation of biodiversity. Their proposed EvoHeritage metric has the potential to revolutionize how we measure and understand biodiversity, providing invaluable insights for conservation, ecology, and evolutionary biology. As research into quantifying attrition progresses, EvoHeritage could become a cornerstone metric, enabling us to unveil the full depths of the evolutionary heritage preserved within our planet's biosphere.


Rethinking Biodiversity Metrics: A Challenge to Neo-Darwinism? 

The article "Phylogenetic Biodiversity Metrics Should Account for Both Accumulation and Attrition of Evolutionary Heritage" critiques current methods for measuring biodiversity. It argues that existing metrics, like phylogenetic diversity (PD), focus solely on the accumulation of evolutionary history, neglecting a crucial aspect: the loss of features over time. This concept, termed "attrition," presents a challenge to the neo-Darwinian view of evolution.

Neo-Darwinism emphasizes the gradual accumulation of advantageous traits through natural selection. Phylogenetic diversity reflects this idea by summing the branch lengths of a phylogenetic tree, essentially quantifying the total evolutionary history present in a community. However, the authors argue that PD fails to consider features lost through processes other than extinction.

For example, imagine two closely related species with similar branch lengths on a phylogenetic tree. According to PD, they would contribute equally to biodiversity. But what if one species has lost a unique adaptation due to environmental change? The current PD metric wouldn't capture this loss of evolutionary heritage.

The article proposes a new metric, "EvoHeritage," which incorporates both accumulation and attrition. EvoHeritage goes beyond the total branch length and considers the specific features retained by each species. This shift acknowledges that not all evolutionary history is equally valuable for understanding biodiversity or ecosystem function. Traits that have successfully persisted through time might hold greater significance for ecological processes.

This focus on retained features challenges the neo-Darwinian narrative in a subtle but important way. While neo-Darwinism emphasizes the power of selection in shaping advantageous traits, EvoHeritage highlights the potential for features to be lost even without extinction. This highlights the complex and dynamic nature of external pressures that play a role in shaping biodiversity.

The impact of this article extends beyond theoretical debates. By offering a more nuanced measure of biodiversity, EvoHeritage could have practical applications in conservation biology. It could help prioritize areas for protection based on the irreplaceable evolutionary history they harbor, not just species richness.

In conclusion, the introduction of EvoHeritage compels us to reconsider how we measure biodiversity and its connection to evolutionary processes. This, in turn, challenges the neo-Darwinian framework towards a more comprehensive understanding of evolution, one that acknowledges the interplay of attrition and the persistence of unique evolutionary heritage.



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