PosterPDF Available

Soldier-biased gene expression in a termite implies indirect selection for defensiveness

May 2018

DOI:10.13140/RG.2.2.18970.95683

Conference: Biology and Genomics of Social Insects, Cold Spring Harbor, New York, 5-9 May 2018. p 42

Authors:

Anna M Chernyshova

Western University

Western University

Graham J Thompson

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Caste-biased genes in a subterranean termite are taxonomically restricted: implications for novel gene recruitment during termite caste evolution

Article

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Jul 2018

The caste system of social insects presents a classic polyphenism in which widely divergent reproductive and non-reproductive phenotypes are expressed from the same genome. In termites, the sterile soldier caste is particularly divergent in phenotype and presumably evolved under selection for defensiveness. In this study, we use genomic phylostratigraphy to show that genes with soldier- and other caste-biased expression from the Eastern subterranean termite Reticulitermes flavipes are more taxonomically restricted on the tree of life than genes with no caste-biased expression. This pattern suggests that caste-biased genes are relatively young and implies past selection for novel gene recruitment during termite caste evolution. Moreover, a soldier-biased set of 74 genes contains a higher proportion of orphan genes with no known homology than does a nymph-biased set or any null gene sets. This again suggests that the termite caste—and soldiers in particular—makes disproportionate use of evolutionarily novel genes that are potentially recruited from non-coding regions of the genome. Given that Reticulitermes and most termite soldiers are sterile, any past selection for genetic novelty of this caste must have been indirect and mediated through reproducing relatives.

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Additional file 5

September 2010

Index of gene expression level. Example of calculation of gene expression index. Three steps were used for the calculation of the preformed defense index. 1 - For each gene, the mean is calculated for the 23 cultivars. 2 - the expression value for each gene in each cultivar is then divided by the mean expression level. 3 - for each cultivar, the mean for the 21 genes selected is calculated

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Caste Differentiation: Genetic and Epigenetic Factors

January 2021

The process of caste differentiation is central to understanding insect sociality, because it is task specialization that enables division of labor within eusocial colonies. Selection presumably favors colonies that can adjust their division of labor in response to changing environmental demands, and for many taxa genetic and epigenetic factors are an important part of this equation. In this ... [Show full abstract] entry, we provide a framework for understanding genetic and epigenetic effects on caste. From mostly ant, bee, and termite examples discovered so far, we make clear that genotype-caste associations can evolve in different and sometimes complex ways and can involve additive or nonadditive genetic effects that, in turn, may arise directly from focal individuals or indirectly via their social partners. Epigenetic effects, by contrast, provide an interface between environmental experience and gene expression. For the most part, both genetic and epigenetic effects on caste appear to be highly conditional upon socio-environmental context.

Article

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Caste-biased genes in a subterranean termite are taxonomically restricted: implications for novel ge...

July 2018 · Insectes Sociaux

The caste system of social insects presents a classic polyphenism in which widely divergent reproductive and non-reproductive phenotypes are expressed from the same genome. In termites, the sterile soldier caste is particularly divergent in phenotype and presumably evolved under selection for defensiveness. In this study, we use genomic phylostratigraphy to show that genes with soldier- and other ... [Show full abstract] caste-biased expression from the Eastern subterranean termite Reticulitermes flavipes are more taxonomically restricted on the tree of life than genes with no caste-biased expression. This pattern suggests that caste-biased genes are relatively young and implies past selection for novel gene recruitment during termite caste evolution. Moreover, a soldier-biased set of 74 genes contains a higher proportion of orphan genes with no known homology than does a nymph-biased set or any null gene sets. This again suggests that the termite caste—and soldiers in particular—makes disproportionate use of evolutionarily novel genes that are potentially recruited from non-coding regions of the genome. Given that Reticulitermes and most termite soldiers are sterile, any past selection for genetic novelty of this caste must have been indirect and mediated through reproducing relatives.

Poster

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Molecular signatures of kin selection are difficult to detect: Lessons from termites

March 2021

Abstracts of papers presented at the 2021 virtual meeting on Biology & Genomics of Social Insects, Cold Spring Harbor Laboratory

Article

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No obvious transcriptome‐wide signature of indirect selection in termites

December 2020 · Journal of Evolutionary Biology

The evolution of sterile helper castes in social insects implies selection on genes that underlie variation in this nonreproductive phenotype. These focal genes confer no direct fitness and are presumed to evolve through indirect fitness effects on the helper's reproducing relatives. This separation of a gene's phenotypic effect on one caste and its fitness effect on another suggests that genes ... [Show full abstract] for this and other forms of reproductive altruism are buffered from selection and will thus evolve closer to the neutral rate than genes directly selected for selfish reproduction. We test this hypothesis by comparing the strength of selection at loci associated in their expression with reproductive versus sterile castes in termites. Specifically, we gather caste‐biased gene expression data from four termite transcriptomes and measure the global dN/dS ratio across gene sets and phylogenetic lineages. We find that the majority of examined orthologous gene groups show patterns of nucleotide substitution that are consistent with strong purifying selection and display little evidence for distinct signatures of direct versus indirect selection in reproductive and sterile castes. For one particular species (Reticulitermes flavipes), the strength of purifying selection is relaxed in a reproductive nymph‐biased gene set, which opposes the nearly neutral idea. In other species, the synonymous rate (dS) alone was often found to be the highest in the sterile worker caste, suggesting a more subtle signature of indirect selection or an altogether different relationship between caste‐biased expression and rates of molecular evolution.