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Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila
Published on: October 1, 2011
Can clade age alone explain the relationship between body size and diversity?
Rampal S Etienne1, Sara N de Visser, Thijs Janzen
1Community and Conservation Ecology, Centre for Ecological and Evolutionary Studies, University of Groningen, PO Box 11103, 9700 Groningen, The Netherlands.
Interface Focus
|March 16, 2012
Summary
Smaller animals are more diverse due to older evolutionary origins and faster "evolutionary clocks." This study reveals that body size influences speciation and extinction rates, contributing to diversity patterns in Metazoan taxa.
Area of Science:
- Evolutionary Biology
- Ecology
- Biodiversity Science
Background:
- A well-documented pattern in nature is that smaller-bodied animal taxa exhibit higher diversity than larger-bodied taxa.
- Previous studies, often using the birth-death model, attributed this to older evolutionary origins of smaller taxa, suggesting body size does not impact diversification rates.
Purpose of the Study:
- To investigate the relationship between body size and diversification rates in Metazoa.
- To apply a refined statistical method accounting for allometric scaling of speciation and extinction rates.
Main Methods:
- Developed a statistical approach to maximize the likelihood of a birth-death model with allometric scaling.
- Analyzed a comprehensive dataset of Metazoan taxa, including diversity, clade age, and average body size.
- Incorporated a wide range of taxa from midges to elephants.
Main Results:
- Higher diversity in smaller taxa is partly explained by older clade age, but also significantly by body-size-dependent speciation and extinction rates.
- Both speciation and extinction rates decrease with increasing body size, resulting in a net diversification rate near zero.
- An allometric scaling exponent of approximately -0.25 suggests per-generation rates are body-size independent.
Conclusions:
- The observed diversity-body size pattern is a complex interplay of clade age and body-size-dependent diversification rates.
- A faster evolutionary clock (per generation rates) in smaller-bodied taxa provides a parsimonious explanation for their higher diversity.
- This highlights the importance of considering body size in models of macroevolutionary diversification.
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