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A test of ecologically dependent postmating isolation between sympatric sticklebacks
1Department of Zoology and Centre for Biodiversity Research, University of British Columbia, Vancouver, Canada. rundle@zoology.ubc.ca
Evolution; International Journal of Organic Evolution
|April 3, 2002
Summary
Ecological speciation drives reproductive isolation through natural selection in different environments. Studies on threespine sticklebacks show hybrid fitness depends on habitat, supporting divergent selection as a key speciation mechanism.
Area of Science:
- Evolutionary Biology
- Speciation Research
- Ecology and Behavior
Background:
- Ecological speciation is driven by divergent natural selection between populations in different environments.
- Two sympatric species of threespine sticklebacks, Benthic and Limnetic, exhibit ecological and morphological divergence.
- Benthic sticklebacks inhabit the littoral zone, feeding on invertebrates, while Limnetic sticklebacks occupy open water, feeding on zooplankton.
Purpose of the Study:
- To test the ecological speciation model by evaluating hybrid fitness between Benthic and Limnetic sticklebacks.
- To determine if hybrid fitness is dependent on the environment, as predicted by ecological speciation.
- To assess the role of divergent natural selection in the evolution of reproductive isolation.
Main Methods:
- Growth rates of Benthic, Limnetic, Benthic backcross, and Limnetic backcross sticklebacks were measured in controlled lake enclosures.
- Enclosures were situated in both the littoral zone and open water habitats, mimicking parental environments.
- Backcross hybrids were used to estimate ecologically dependent fitness components while controlling for genetic incompatibilities.
Main Results:
- Benthic backcross sticklebacks exhibited approximately twice the growth rate of Limnetic backcross sticklebacks in the littoral zone.
- Conversely, Limnetic backcross sticklebacks showed approximately twice the growth rate of Benthic backcross sticklebacks in the open water.
- This reversal in relative fitness of backcrosses between habitats strongly supports ecological dependence.
Conclusions:
- The observed pattern of fitness reversal provides strong evidence for divergent natural selection in ecological speciation between Benthic and Limnetic sticklebacks.
- Results suggest that ecological factors play a central role in the evolution of reproductive isolation in these species.
- Further research is needed to clarify open water results and potential introgressive hybridization.