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Honeybees host a specialised gut microbiota composed of five ever-present bacteria, which undergo seasonal variation in their proportions. The objective of this study was to investigate how host genetics can affect the microbial composition of the honeybee gut over a 5-month sampling period. Seventy-seven colonies from eight maternal genetic lines were sampled from a breeding population located in Lombardy, Italy. The colonies have been selected since 2015 for three different traits, using isolated mating stations for reproduction. Worker bees were sampled three times: June, July and October 2021. From each colony, gut from ten worker bees were pooled, and the V3-V4 region of the 16S rRNA gene was amplified and sequenced. Statistical analyses were conducted in the R environment to assess the impact of genetic lines, timepoints, and their interaction on α-diversity and β-diversity. Results for α-diversity showed a significant effect of genetic line on the Simpson index, as well as a consistent effect of the timepoint. Specifically, genetic line H showed a lower Simpson index, and this line also produced less honey in the same years, suggesting a genetic influence on both microbiota richness and honey yield. For β-diversity, results revealed that the month of sampling had the strongest effect, while no significant differences were identified for the genetic line or their interaction. [ABSTRACT FROM AUTHOR]

• Natural and artificial selection apply selective pressure to specific genomic regions. • Heterozygous-Rich Regions help to understand the relationship between genetic diversity and fitness. • More than ten thousand cattle belonging to four breeds were included in the study. • Heterozygosity patterns of Local and cosmopolitan cattle breeds were compared. • Genes linked to fertility, survival, immune response and growth were identified. The analysis of livestock heterozygosity is less common compared to the study of homozygous patterns. Heterozygous-Rich Regions (HRR s) may harbor significant loci for functional traits such as immune response, survival rate, and fertility. For this reason, this study was conducted to investigate and characterize the heterozygosity patterns of four beef cattle breeds, which included two cosmopolitan breeds (Limousine and Charolaise) and two local breeds (Sarda and Sardo Bruna). Our analysis identified regions with a high degree of heterozygosity using a consecutive runs approach, the Tajima D test, nucleotide diversity estimation, and Hardy Weinberg equilibrium test. These regions exhibited recurrent heterozygosity peaks and were consistently found on specific chromosomes across all breeds, specifically autosomes 15, 16, 20, and 23. The cosmopolitan and Sardo Bruna breeds also displayed peaks on autosomes 2 and 21, respectively. Thirty-five top runs shared by more than 25% of the populations were identified. These genomic fragments encompassed 18 genes, two of which are directly linked to male fertility, while four are associated with lactation. Two other genes play roles in survival and immune response. Our study also detected a region related to growth and carcass traits in Limousine breed. Our analysis of heterozygosity-rich regions revealed particular segments of the cattle genome linked to various functional traits. It appears that balancing selection is occurring in specific regions within the four examined breeds, and unexpectedly, they are common across cosmopolitan and local breeds. The genes identified hold potential for applications in breeding programs and conservation studies to investigate the phenotypes associated with these heterozygous genotypes. In addition, Tajima D test, Nucleotide diversity, and Hardy Weinberg equilibrium test confirmed the presence of heterozygous fragments found with Heterozygous-Rich Regions analysis. [ABSTRACT FROM AUTHOR]