The roles of positive and negative selection in the molecular evolution of insect endosymbionts

Fry, Adam J.; Wernegreen, Jennifer J.

doi:10.1016/j.gene.2005.05.021

Cited by 29 publications

(18 citation statements)

References 59 publications

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“…The proportion of genes affected by diversifying selection in Wolbachia was higher than reports from other screens in bacteria [26] and may reflect the well-documented phenomenon of rapid evolution in endosymbionts [30-32]. The small effective population sizes of these bacteria would predict more rapid fixation of nonsynonymous mutations due to drift and hence generate higher average ratios of d N to d S [33].…”

Section: Resultsmentioning

confidence: 98%

Diversifying selection and host adaptation in two endosymbiont genomes

et al. 2007

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Background: The endosymbiont Wolbachia pipientis infects a broad range of arthropod and filarial nematode hosts. These diverse associations form an attractive model for understanding host:symbiont coevolution. Wolbachia's ubiquity and ability to dramatically alter host reproductive biology also form the foundation of research strategies aimed at controlling insect pests and vectorborne disease. The Wolbachia strains that infect nematodes are phylogenetically distinct, strictly vertically transmitted, and required by their hosts for growth and reproduction. Insects in contrast form more fluid associations with Wolbachia. In these taxa, host populations are most often polymorphic for infection, horizontal transmission occurs between distantly related hosts, and direct fitness effects on hosts are mild. Despite extensive interest in the Wolbachia system for many years, relatively little is known about the molecular mechanisms that mediate its varied interactions with different hosts. We have compared the genomes of the Wolbachia that infect Drosophila melanogaster, wMel and the nematode Brugia malayi, wBm to that of an outgroup Anaplasma marginale to identify genes that have experienced diversifying selection in the Wolbachia lineages. The goal of the study was to identify likely molecular mechanisms of the symbiosis and to understand the nature of the diverse association across different hosts.

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Section: Resultsmentioning

confidence: 98%

Diversifying selection and host adaptation in two endosymbiont genomes

et al. 2007

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“…www.genome.org B. pennsylvanicus lineage) showed no consistent increase in dN/dS in B. floridanus or its close relatives (Fry and Wernegreen 2005) that would be predicted under relaxed selection or drift hypotheses. Evidence supporting the mutation hypothesis includes a lower genomic GC content for B. floridanus than B. pennsylvanicus (Table 1).…”

Section: Genome Research 1029mentioning

confidence: 86%

Genome sequence of Blochmannia pennsylvanicus indicates parallel evolutionary trends among bacterial mutualists of insects

Degnan¹,

Lazarus²,

Wernegreen³

2005

Genome Res.

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171

156

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The distinct lifestyle of obligately intracellular bacteria can alter fundamental forces that drive and constrain genome change. In this study, sequencing the 792-kb genome of Blochmannia pennsylvanicus, an obligate endosymbiont of Camponotus pennsylvanicus, enabled us to trace evolutionary changes that occurred in the context of a bacterial–ant association. Comparison to the genome of Blochmannia floridanus reveals differential loss of genes involved in cofactor biosynthesis, the composition and structure of the cell wall and membrane, gene regulation, and DNA replication. However, the two Blochmannia species show complete conservation in the order and strand orientation of shared genes. This finding of extreme stasis in genome architecture, also reported previously for the aphid endosymbiont Buchnera, suggests that genome stability characterizes long-term bacterial mutualists of insects and constrains their evolutionary potential. Genome-wide analyses of protein divergences reveal 10- to 50-fold faster amino acid substitution rates in Blochmannia compared to related bacteria. Despite these varying features of genome evolution, a striking correlation in the relative divergences of proteins indicates parallel functional constraints on gene functions across ecologically distinct bacterial groups. Furthermore, the increased rates of amino acid substitution and gene loss in Blochmannia have occurred in a lineage-specific fashion, which may reflect life history differences of their ant hosts.

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“…The Buchnera clade of aphid endosymbionts is a classic example: Buchnera experience population bottlenecks in each transmission cycle, reducing the efficacy of purifying selection, and allowing frequent fixation of deleterious mutations (Itoh et al, 2002;Herbeck et al, 2003;Fry and Wernegreen, 2005). This is recapitulated in the genome-wide S:F distributions for Buchnera, as well as the Wigglesworthia and Candidatus Blochmannia species of insect endosymbionts, which are all biased toward high S:F ratios (Figure 3b).…”

Section: Wigglesworthiamentioning

confidence: 91%

The slow:fast substitution ratio reveals changing patterns of natural selection in γ-proteobacterial genomes

Shapiro

Alm

2009

The ISME Journal

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Different microbial species are thought to occupy distinct ecological niches, subjecting each species to unique selective constraints, which may leave a recognizable signal in their genomes. Thus, it may be possible to extract insight into the genetic basis of ecological differences among lineages by identifying unusual patterns of substitutions in orthologous gene or protein sequences. We used the ratio of substitutions in slow-versus fast-evolving sites (nucleotides in DNA, or amino acids in protein sequence) to quantify deviations from the typical pattern of selective constraint observed across bacterial lineages. We propose that elevated S:F in one branch (an excess of slowsite substitutions) can indicate a functionally relevant change, due to either positive selection or relaxed evolutionary constraint. In a genome-wide comparative study of c-proteobacterial proteins, we find that cell-surface proteins involved with motility and secretion functions often have high S:F ratios, whereas information-processing genes do not. Change in evolutionary constraints in some species is evidenced by increased S:F ratios within functionally related sets of genes (for example, energy production in Pseudomonas fluorescens), whereas other species apparently evolve mostly by drift (for example, uniformly elevated S:F across most genes in Buchnera spp.). Overall, S:F reveals several species-specific, protein-level changes with potential functional/ecological importance. As microbial genome projects yield more species-rich gene trees, the S:F ratio will become an increasingly powerful tool for uncovering functional genetic differences among species.

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The roles of positive and negative selection in the molecular evolution of insect endosymbionts

Cited by 29 publications

References 59 publications

Diversifying selection and host adaptation in two endosymbiont genomes

Diversifying selection and host adaptation in two endosymbiont genomes

Genome sequence of Blochmannia pennsylvanicus indicates parallel evolutionary trends among bacterial mutualists of insects

The slow:fast substitution ratio reveals changing patterns of natural selection in γ-proteobacterial genomes

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