Understanding Genetic Diversity For Silk

Jim Crocker
12th August, 2025

Understanding Genetic Diversity For Silk

The geographical location of the "El Pílamo" experimental station and the representative Pílamo II hybrid illustrate the source and nature of the Colombian silkworm (Bombyx mori) germplasm, which was evaluated to establish a baseline for future genetic improvement and conservation programs.

Image adapted from: González-Muñoz et al. / CC BY (Source)

Key Findings

  • The study in Colombia found that silkworm lines possess significant genetic diversity, with most variation occurring within individual populations
  • While commercial silkworm lines are genetically similar, those from the ICA and unknown origins are more diverse and stable, making them valuable for future breeding
  • Combining physical traits and genetic markers helps classify silkworms, identifying promising lines for improving silk production and conservation efforts
Silkworms, specifically Bombyx mori, have been domesticated for thousands of years, becoming a cornerstone of silk production. Over centuries, this domestication has led to the development of more than 4000 distinct varieties, or 'ecotypes'. While this vast diversity is a resource, it also presents a significant challenge: many of these lines share similar physical and reproductive traits, making it difficult to differentiate them and select the most promising ones for genetic improvement programs. In countries like Colombia, where 67 silkworm lines are maintained, their industrial potential remains largely unfulfilled due to a lack of detailed genetic and observable trait data. This knowledge gap prevents breeders from effectively enhancing desirable characteristics such as silk quality, cocoon weight, and disease resistance. To address this, a recent study conducted by researchers from UTP and the University of Waterloo[1] embarked on a comprehensive evaluation of the genetic and morphological, or physical, variability within Colombia's Bombyx mori germplasm. Their goal was to provide a foundational understanding of these silkworm lines, enabling more informed decisions for conservation and breeding efforts. The study employed a dual approach, analyzing both observable physical traits and molecular genetic markers. They assessed 13 different morphological characteristics, such as the silkworm's voltinism (how many generations it produces per year), larval markings, and cocoon color. These physical traits proved to be highly informative, with patterns in voltinism, larval markings, and cocoon color being particularly useful in distinguishing between different silkworm breeds. For the genetic analysis, the researchers utilized 23 simple sequence repeat (SSR) markers. SSRs, also known as microsatellites, are short, repeating DNA sequences found throughout an organism's genome. These sequences are highly variable in length among individuals, making them excellent "molecular fingerprints" for genetic analysis. Earlier research on Bombyx mori[2] has shown that while these microsatellites are somewhat rare and have specific characteristics like a high adenine and thymine (A/T) content, their high level of polymorphism – meaning they show many variations – makes them very effective for determining genetic profiles and analyzing diversity. This versatility allows them to be useful for advancing genetic and molecular knowledge, even if their scarcity has historically limited their use in detailed genetic mapping[2]. In the Colombian study, 17 of the 23 SSR markers used were found to be polymorphic, confirming their utility. These markers revealed a significant range of genetic variation, with each marker showing between 2 and 11 different versions, or 'alleles', indicating substantial genetic diversity within the silkworm lines. The genetic analysis, specifically using a method called Analysis of Molecular Variance (AMOVA), revealed that the vast majority of genetic variation—a striking 96%—occurred within the individual silkworm populations or lines, with only 4% of the variation found among them. This finding is consistent with earlier comprehensive genomic studies[3] which constructed a single-base pair resolution genetic variation map of silkworms. That research indicated that despite centuries of domestication, domesticated silkworms have maintained large levels of genetic variability, suggesting that the initial domestication event likely involved a large number of individuals[3]. The current Colombian study's results further support this, highlighting the rich genetic diversity still present within domesticated lines. The study also provided insights into the genetic stability of different silkworm groups. Commercial lines, which have likely undergone intensive selective breeding for specific traits, showed greater molecular homogeneity, meaning they were more genetically similar. In contrast, lines from the ICA (Colombian Agricultural Institute) collection and those of unknown origin (NC lines) showed no significant deviation from Hardy-Weinberg equilibrium. This indicates greater genetic stability and suggests these lines could be valuable resources for improving inbred breeds, as they possess a broader genetic foundation. The molecular markers also proved effective in classifying the silkworm lines according to categories defined by breeders. Interestingly, while some lines retained ancestral morphological characteristics, certain Japanese and Chinese lines exhibited low heterozygosity. Heterozygosity refers to the presence of different versions of a gene (alleles) at a particular location on a chromosome. Low heterozygosity can be a sign of a 'bottleneck event' – a sharp reduction in population size, or in this case, a reduction in genetic diversity, often associated with intensive breeding programs, such as those aimed at developing specific hybrid silkworms. This observation aligns with the broader understanding that different silkworm strains, often grouped by geographical origin like Japanese or Chinese types, have distinct genetic backgrounds that influence various traits[4]. For example, earlier research has shown how these distinct genetic backgrounds lead to different strategies for counteracting bacterial infections, with specific strains exhibiting varying susceptibility based on their unique genetic makeup related to immune responses[4]. The selective pressures during hybrid development could lead to the reduced genetic diversity observed in these lines. Furthermore, the morphological markers offered clues about the origins of unclassified strains based on their physical patterns. Crucially, a few lines showed similar clustering patterns in both the morphological and molecular analyses, indicating that their observable traits are well-conserved and directly reflect their underlying genetic makeup. By combining the insights from both morphological and molecular markers, the study provided a more comprehensive classification of the Colombian silkworm germplasm. This integrated approach allowed the researchers to identify candidate lines with promising genetic and physical characteristics for future breeding efforts. These findings offer new and valuable insights into the genetic diversity of Bombyx mori in Colombia, establishing a crucial baseline for conservation programs and for developing new hybrid silkworms with enhanced vigor and productivity, ultimately benefiting the sericulture industry.

BiotechGeneticsAnimal Science

References

Main Study

1) Genetic and morphological variation in the Colombian Bombyx mori germplasm: A first SSR-based assessment

Published 11th August, 2025

https://doi.org/10.1371/journal.pone.0330183

Related Studies

2) Role of microsatellites in genetic analysis of Bombyx mori silkworm: a review.

https://doi.org/10.12688/f1000research.20052.1

3) Complete resequencing of 40 genomes reveals domestication events and genes in silkworm (Bombyx).

https://doi.org/10.1126/science.1176620

4) Differential sensitivity to infections and antimicrobial peptide-mediated immune response in four silkworm strains with different geographical origin.

https://doi.org/10.1038/s41598-017-01162-z


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