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Recent and ancient asexuality in Timema walkingsticks
Jennifer H Law1, Bernard J Crespi
1Department of Biosciences, Simon Fraser University, Burnaby, British Columbia, Canada. jhlaw@canada.com
Evolution; International Journal of Organic Evolution
|October 2, 2002
Summary
Determining the evolutionary age of asexual lineages provides insights into the evolution of asexuality and sex. Younger asexual lineages in the Timema walkingstick species were found further north.
Area of Science:
- Evolutionary biology
- Genetics
- Phylogenetics
Background:
- Understanding the evolutionary age of asexual lineages is crucial for studying the evolution of asexuality and sex.
- Assessing selective factors involved in asexuality requires knowledge of lineage age.
Purpose of the Study:
- To infer the evolutionary age of asexual lineages within Timema walkingstick species.
- To investigate the relationship between geographic position and the age of asexual lineages.
Main Methods:
- Phylogenetic analysis using 416 bp of the mitochondrial COI gene.
- Intraspecific sampling across known asexual Timema species and their sexual relatives.
- Maximum-likelihood molecular-clock dating to estimate lineage ages.
Main Results:
- Two asexual lineages, T. douglasi and T. shepardii, are evolutionarily young (<0.5 million years old).
- T. monikensis and T. tahoe showed weak evidence for antiquity, with estimated ages ranging from 0.26 to 2.39 million years.
- T. genevieve was identified as an ancient asexual lineage (0.81–1.42 million years old).
- Younger asexual lineages were geographically located further north.
Conclusions:
- The evolutionary age of asexual Timema lineages varies significantly.
- Geographic position correlates with the age of asexual lineages, with northern populations being younger.
- This study provides insights into the tempo and mode of asexuality evolution.