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Published on: February 20, 2012
Ribosomal RNA-encoding DNA introgression across a narrow hybrid zone between two subspecies of grasshopper
M L Arnold1, D D Shaw, N Contreras
1Population Genetics Group, Research School of Biological Sciences, The Australian National University, Canberra, ACT 2601 Australia.
Summary
Genetic analysis of the grasshopper Caledia captiva reveals asymmetrical gene flow of ribosomal RNA (rRNA) genes from the Moreton to the Torresian subspecies, despite reproductive barriers. This finding highlights nonrandom genetic processes shaping subspecies evolution.
Area of Science:
- Genetics
- Evolutionary Biology
- Molecular Biology
Background:
- Ribosomal RNA-encoding DNA (rDNA) plays a crucial role in cellular function and is subject to evolutionary pressures.
- Distinguishing between closely related subspecies often requires detailed genetic markers.
Purpose of the Study:
- To identify diagnostic DNA fragments for differentiating Caledia captiva subspecies.
- To investigate patterns of rDNA variation and gene flow within a hybrid zone.
- To understand the mechanisms driving asymmetrical introgression of genetic material.
Main Methods:
- Cloning of a 0.8-kilobase fragment from the 26S/nontranscribed spacer region of rDNA.
- Restriction fragment analysis to identify diagnostic markers.
- Analysis of over 250 individuals from a narrow geographical hybrid zone.
Main Results:
- Diagnostic restriction fragments successfully distinguished between Moreton and Torresian subspecies.
- Asymmetrical introgression of Moreton ribosomal RNA genes into the Torresian subspecies was clearly demonstrated.
- This introgression occurred despite significant postmating inviability between the subspecies.
Conclusions:
- Nonrandom genetic processes, such as biased gene conversion and/or natural selection, likely contribute to the observed asymmetrical introgression.
- The distinct chromosomal locations of rDNA loci in each subspecies offer opportunities to further elucidate the roles of these processes.
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