Abstract:

Aims: Baotianman National Nature Reserve is located in the southern Funiu Mountain range in the eastern Qinling Mountains. It is one of the hotspots of biodiversity research. However, the current understanding of earthworm diversity is limited in the literature. Our study aims to investigate the earthworm diversity and their geographical distribution in Baotianman National Nature Reserve, and to discuss the potential factors impacting the formation of earthworm diversity at a local scale.

Method: Earthworm specimens were collected from nine sampling sites at different altitudes in Baotianman National Nature Reserve during the rainy season using digging and hand-sorting method. Subsequently, five mitochondrial genes (COI, COII, ND1, 12S rRNA and 16S rRNA) were extracted from the tail of the earthworms, and then sequenced. The phylogenetic tree was constructed using the Bayesian method based on the five mitochondrial genes. The standardized effect size-phylogenetic diversity (SES-PD), net relatedness index (NRI), net nearest taxa index (NTI) and α diversity index were calculated using R. Additionally, structural equation modeling (SEM) was used to assess the potential environmental factors influencing the formation of earthworm diversity. The combination of morphological and molecular methods facilitated the identification of the collected earthworms.

Results: A total of 14 earthworm species belonging to 5 genera and 3 families. The majority of these species were widely distributed across China with Megascolecidae as the dominant family. Earthworm species richness in the Baotianman National Nature Reserve increased with the altitude. However, the species diversity of earthworm at the altitude of 500-1,000 m was particularly abundant with a more uniform species distribution, which was consistent with the middle height expansion pattern. At the local scale, altitude exerted the greatest influence on both the species and phylogenetic diversity of earthworms, followed by soil properties and litter quality.

Conclusions: Baotianman National Nature Reserve stands out as a significant hotspot for earthworm diversity. The α diversity at the altitude of 500-1,000 m conforms to the middle height expansion pattern. The altitude, soil properties and litter quality play important roles in the formation of species diversity and phylogenetic diversity of earthworms, respectively. The study of earthworm species composition and diversity in Baotianman National Nature Reserve has enriched the species and gene bank of earthworms in China.

Key words: earthworm, biodiversity, altitude, Baotianman National Nature Reserve