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18S rDNA sequences and the holometabolous insects
D Carmean1, L S Kimsey, M L Berbee
1Department of Entomology, University of California, Davis 95616-8584.
Molecular Phylogenetics and Evolution
|December 1, 1992
Summary
Investigating insect evolution, this study used 18S ribosomal RNA gene sequences to clarify relationships among holometabolous insect orders. Results suggest beetles may be basal, but interordinal relationships remain largely unresolved.
Area of Science:
- * Entomology
- * Molecular Phylogenetics
- * Evolutionary Biology
Background:
- * Holometabola, insects with complete metamorphosis, represent most animal species but interordinal relationships are unclear.
- * Morphological characters define holometabolous orders, yet DNA sequencing is needed to resolve evolutionary connections.
- * The 18S ribosomal RNA gene is a target for phylogenetic analysis in insects.
Purpose of the Study:
- * To clarify interordinal relationships within Holometabola using DNA sequence data.
- * To identify a suitable DNA region for resolving evolutionary links among insect orders.
- * To investigate the phylogenetic position of Hymenoptera, Neuroptera, Siphonaptera, and Mecoptera.
Main Methods:
- * Sequencing of approximately 1080 nucleotides from the 5' end of the 18S ribosomal RNA gene.
- * Analysis of representatives from Hymenoptera, Neuroptera, Siphonaptera, and Mecoptera.
- * Sequence alignment with Coleoptera, Diptera, and outgroups (aphid, shrimp, spider) followed by phylogenetic analyses (parsimony, maximum likelihood).
Main Results:
- * Neuropterans exhibit unique A-T rich insertions in the 18S rDNA.
- * Diptera (mosquito, Drosophila) show rapid 18S rDNA evolution with significant unalignable regions.
- * Excluding long-branched taxa, parsimony analysis placed Coleoptera as basal and supported a monophyletic Fleas+Scorpionflies clade (96% bootstrap).
- * Most interordinal relationships lacked statistical support and were sensitive to taxon inclusion.
- * Coleoptera and Neuroptera were separated in parsimony and maximum likelihood trees, but without statistical significance.
Conclusions:
- * The 18S ribosomal RNA gene presents challenges for resolving deep holometabolous relationships due to rapid evolution and insertions in some taxa.
- * Phylogenetic analyses suggest beetles may be basal within Holometabola, and fleas+scorpionflies form a monophyletic group.
- * Further molecular data and analytical approaches are required to definitively resolve interordinal relationships within Holometabola.