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Population density drives the local evolution of a threshold dimorphism
Joseph L Tomkins1, Gordon S Brown
1Division of Environmental and Evolutionary Biology, Sir Harold Mitchell Building, University of St Andrews, St Andrews, Fife KY16 9TH, UK. jlt1@st-andrews.ac.uk
Nature
|October 29, 2004
Summary
Male earwigs evolve different reproductive tactics based on their size and status. Population density drives this evolution, leading to distinct male dimorphisms within short distances.
Area of Science:
- Evolutionary biology
- Behavioral ecology
- Animal behavior
Background:
- Evolution can favor multiple reproductive tactics within a single sex.
- Conditional evolutionarily stable strategies link tactics to individual status and fitness returns.
- A 'switchpoint' threshold often underlies divergent male morphologies.
Purpose of the Study:
- To investigate threshold evolution in the forceps dimorphism of the European earwig (Forficula auricularia).
- To document the transition between monomorphic and dimorphic earwig populations.
- To determine the role of population density in driving male dimorphism.
Main Methods:
- Studied forceps dimorphism in European earwigs (Forficula auricularia).
- Documented population structure and morphology over a 40 km range.
- Correlated population density with the observed threshold evolution.
Main Results:
- Observed threshold evolution in earwig forceps dimorphism.
- Documented a rapid transition from monomorphic to dimorphic populations.
- Found a strong correlation between population density and the evolution of the male dimorphism switchpoint.
Conclusions:
- Population density is a key factor driving the local evolution of male dimorphism.
- Phenotypic diversity can originate within populations via switchpoint evolution in conditional strategies.
- Earwig dimorphism provides a model for understanding the origin of phenotypic diversity.
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