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Coupled evolutionary rates shape a Hawaiian insect-symbiont system.
Patrick H Degnan1, Diana M Percy2, Allison K Hansen3
1Department of Microbiology and Plant Pathology, University of California, Riverside, CA, USA. patrickd@ucr.edu.
BMC Genomics
|April 4, 2025
Summary
Hawaiian psyllids and their symbionts show correlated genome evolution, unlike other insect systems. Free-living psyllids with multiple symbionts exhibit higher mutation rates, impacting nuclear and endosymbiont genomes.
Area of Science:
- Evolutionary Biology
- Genomics
- Symbiosis
Background:
- The Hawaiian Pariaconus psyllid radiation offers a unique model for studying the co-evolution of nuclear, mitochondrial, and endosymbiont genomes.
- These psyllids diversified across Hawaiian Islands in the last 3-3.5 million years, occupying distinct ecological niches on their host plant, 'Ōhi'a lehua.
- Psyllids harbor one to three beneficial bacterial endosymbionts, and prior studies on similar systems indicated decoupled evolutionary rates between mitochondria and endosymbionts.
Purpose of the Study:
- To investigate the evolutionary trends in Pariaconus psyllids, their mitochondria, and their endosymbionts.
- To determine if Pariaconus psyllids fit the paradigm of decoupled sequence evolution rates observed in other multi-endosymbiont insect systems.
- To examine the interplay between ecological diversification and genomic evolution in this psyllid radiation.
Main Methods:
- Sequencing of a new Carsonella genome from the ohialoha species group.
- Comparative analysis of mitochondrial genomes from six Pariaconus species.
- Phylogenetic analyses of nuclear, mitochondrial, and endosymbiont genomes.
Main Results:
- High gene conservation was observed in the Carsonella genome among divergent species.
- Complete synteny was found in mitochondrial genomes across all studied Pariaconus species, indicating strong purifying selection.
- Phylogenetic analyses revealed correlated rates of substitution across nuclear, mitochondrial, and endosymbiont genomes, contradicting previous findings of decoupling.
- Free-living psyllids with three symbionts showed elevated mutation rates (1.2–1.6x) and increased fixation of nonsynonymous substitutions in nuclear and one endosymbiont genome.
Conclusions:
- Ecological diversification and genomic evolution are intricately linked in Pariaconus psyllids.
- The presence of multiple endosymbiont partners alone does not necessitate decoupled rates of sequence evolution.
- Further research on basal psyllid lineages will enhance understanding of the mechanisms driving insect-symbiont genome evolution.
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