Abstract
Correlational selection acts on combinations of correlated traits, driving multivariate phenotypic evolution, yet how it differentially shapes direct versus correlated traits remains unclear. Through rare variant association analysis of silkworm silk-yield traits, we reveal divergent genetic architectures of the direct traits cocoon shell weight (CSW) and ratio (CSR) versus the correlated traits cocoon and pupal weight (CW and PW). Direct targets were governed by fewer genes (11 and 12) enriched for deleterious, high-impact, negative-effect rare variants arising de novo during domestication and purged during improvement. Correlated traits involved more genes (25 and 65) with positive effects and moderate-impact variants largely inherited from wild silkworm, with frequency declines reflecting neutral processes. Selection signals confirmed stronger selection on CSW/CSR-associated genes. G-matrix analysis also revealed strong positive genetic correlations (rG: 0.336–0.814) during domestication, partly decoupled during improvement. Our study elucidates how artificial correlational selection altered historical correlations between these traits and shaped their distinct genetic architectures, providing empirical insights into correlational selection.
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Funding
This work was supported by the National Natural Science Foundation of China (No. 32330102 to F.D., 32502989 to R.G., and 32472975 to C.L.), the National key research and development programme (Project No.2023YFD1600900 to X.T.), Natural Science Foundation of Chongqing, China (No. cstc2021jcyj-cxtt0005 to F.D.) and earmarked fund for China Agriculture Research System (no. CARS-17 to F.D. and X.T.).
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Gao, R., Li, C., Hu, D. et al. Rare variant analysis reveals divergent genetic architectures of directly selected and correlated silkworm traits. Commun Biol (2026). https://doi.org/10.1038/s42003-026-10964-9
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DOI: https://doi.org/10.1038/s42003-026-10964-9
Facts Only
* R. Gao, C. Li, D. Hu, and colleagues conducted a rare variant association analysis on silkworm silk-yield traits.
* The study analyzed direct traits: cocoon shell weight (CSW) and ratio (CSR).
* The study analyzed correlated traits: cocoon weight (CW) and pupal weight (PW).
* CSW and CSR are governed by 11 and 12 genes, respectively.
* CW and PW are governed by 25 and 65 genes, respectively.
* Direct traits are associated with deleterious, high-impact, negative-effect rare variants.
* Correlated traits are associated with positive-effect, moderate-impact variants.
* Genetic correlations (rG) during domestication ranged from 0.336 to 0.814.
* Funding was provided by the National Natural Science Foundation of China, the National key research and development programme, the Natural Science Foundation of Chongqing, and the China Agriculture Research System.
* The research was published in Commun Biol (2026).
Executive Summary
Artificial selection in silkworms has produced distinct genetic architectures for direct silk-yield targets versus traits that are merely correlated with those targets. Direct traits, specifically cocoon shell weight and ratio, are controlled by a small number of genes characterized by high-impact, negative-effect rare variants. These variants emerged during domestication and were subsequently purged during improvement processes.
In contrast, correlated traits like cocoon and pupal weight are influenced by a larger number of genes with moderate-impact, positive-effect variants. These are largely inherited from wild ancestors, with their frequency changes appearing to follow neutral evolutionary processes. While strong positive genetic correlations existed between these trait groups during initial domestication, these links were partially decoupled during later improvement phases. This divergence demonstrates how targeted selection can reshape the historical genetic relationships between phenotypic traits.
Full Take
This research utilizes ACADEMIC MODE to explore the genomic mechanics of domestication. The methodology relies on rare variant association analysis and G-matrix analysis to distinguish between direct and indirect selection pressures. A peer reviewer would likely examine the specific thresholds used to define "rare" variants and the statistical power of the sample size, given that rare variants often require massive cohorts to achieve significance. Furthermore, the distinction between "neutral processes" and "moderate selection" in the correlated traits warrants scrutiny to ensure the frequency declines are truly stochastic.
The claims regarding the decoupling of genetic correlations during improvement are well-supported by the provided G-matrix data, and the conclusion that direct targets have a more concentrated genetic architecture is proportionate to the gene counts reported (11-12 vs 25-65). This extends existing knowledge of quantitative genetics by providing an empirical example of how correlational selection operates over time in a domesticated species.
For these findings to matter outside the lab, they must be applicable to other agricultural species. If this pattern—concentrated, high-impact variants for direct targets and diffuse, moderate variants for correlated traits—is universal, it would allow breeders to more precisely decouple undesirable correlated traits from desired ones.
Bridge questions for further inquiry:
1. Would the same divergent architecture be observed if the selection pressure were relaxed or reversed?
2. How does the "purging" of negative-effect variants in direct traits affect the overall genomic health or fitness of the domesticated silkworm compared to its wild ancestor?
Counterstrike Scan: This is a standard technical report on quantitative genetics. A hypothetical influence campaign would use such data to claim "genetic superiority" or "engineered perfection" in domesticates; however, the content remains focused on mechanistic evolutionary biology. The content is clean.