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Related Experiment Videos

Cope's Rule in a modular organism: Directional evolution without an overarching macroevolutionary trend.

Lee Hsiang Liow1,2, Paul D Taylor3

  • 1Natural History Museum, University of Oslo, Oslo, Norway.

Evolution; International Journal of Organic Evolution
|July 14, 2019
PubMed
Summary

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Cope's Rule, which predicts increasing body size over evolutionary time, does not apply to module size in colonial bryozoans. While some lineages show size increases, the overall pattern reveals no significant change in zooid size.

Area of Science:

  • Evolutionary Biology
  • Paleontology
  • Marine Biology

Background:

  • Cope's Rule posits that body size increases in evolutionary lineages over geological time.
  • This rule is well-documented in unitary organisms but its applicability to colonial organisms remains unclear.
  • Colonial organisms, like bryozoans, exhibit modular growth, raising questions about module size evolution.

Purpose of the Study:

  • To investigate whether Cope's Rule applies to module (zooid) size in colonial cheilostome bryozoans.
  • To analyze evolutionary trends in zooid size across the entire 150-million-year history of cheilostomes.
  • To test alternative hypotheses, such as latitudinal effects (Bergmann's Rule), for observed size changes.

Main Methods:

  • Analysis of a dataset comprising 1169 cheilostome bryozoan species.
Keywords:
Bergmann's Rulecheilostome bryozoansfossilsmacroevolutionmodule size

Related Experiment Videos

  • Examination of temporal trends in zooid size across geological time.
  • Statistical analysis of (paleo)latitudinal distribution to account for environmental factors.

    • Main Results:

    • The overall evolutionary pattern for cheilostome bryozoans shows no significant change in zooid size.
    • Individual subclades within genera exhibit increases in zooid size over time.
    • Latitudinal effects, including Bergmann's Rule and "out of the tropics" hypotheses, do not explain the observed size trends.

    Conclusions:

    • Cope's Rule, as applied to body size, is not a universal pattern for module size in colonial organisms.
    • Observed size increases within specific bryozoan lineages may be linked to feeding or competition, but require further investigation.
    • Evolutionary patterns in colonial organisms may differ significantly from those in unitary organisms and cannot be directly extrapolated.