Abstract:

Aims: Urbanization, the rapid expansion of urban areas and the transformation of natural landscapes into manmade environments, has significantly altered the habitat of many organisms. This process has not only reshaped landscapes but also impacted ecological balance. Soil fauna are integral components of the food chain and play a crucial role in nutrient cycling, soil formation, and overall ecosystem health. Investigating the impact of urban landscape patterns on the genetic diversity and population structure of soil fauna can lead to new knowledge that can be used to protect the biodiversity within urban ecosystems.

Methods: A total of 133 samples of Thereuopoda clunifera from seven populations in Nanjing, China were collected for this study. The mitochondrial Cytbgene and six microsatellite loci were used as molecular markers to analyze the genetic diversity and genetic structure of T. clunifera. To investigate the impact of urban landscape patterns on soil fauna genetic diversity and genetic structure, correlation analysis was used to understand the association between genetic diversity and habitat or urbanization levels. We then evaluated potential corridors that could enable gene flow between local T. cluniferapopulations by calculating the Euclidean distance, least-cost path, and effective resistance between these populations. Finally, we explored the effect of geographical and resistance distance on genetic differentiation among local populations using the Mantel test for each local population based on their genetic distance.

Results: We identified six haplotypes and 14 mutation sites, from the Cytb dataset. Nucleotide diversity indices were below 0.005 for all populations, signifying low genetic diversity. The microsatellite markers revealed an average number of alleles ranging from 4.167 to 5.167 and observed heterozygosity from 0.470 to 0.603, indicating high microsatellite diversity across populations. No correlation was found between habitat area, degree of urbanization near the habitat, and population genetic diversity. The fixation index between populations ranged from 0.020 to 0.106, with gene flow ranging from 2.108 to 12.266, suggesting low levels of genetic differentiation and frequent gene exchange between populations. Cluster analysis based on individual classifications was performed on the seven populations. The results indicated that the highest value of Delta K was observed when K = 2, indicating that all individuals could be divided into two genetic groups. Among the seven populations, Tang Mountain and Fang Mountain (TS and FS) exhibited similar genetic structures, which were significantly different from the other five populations. The level of genetic differentiation between populations was significantly positively correlated with the predicted physical barriers between them, suggesting that the genetic structure of T. clunifera populations may be influenced by urbanization. Effective connectivity between patches facilitates gene flow among populations, with dispersed urban green spaces acting as corridors that offer opportunities for gene flow.

Conclusion: The overall genetic diversity of mitochondrial genes in the population of T. clunifera is relatively low, but the microsatellite diversity across all populations is high. Urbanization and habitat area are not correlated with the level of population genetic diversity in T. clunifera. There is moderate genetic differentiation among T. clunifera populations within the city of Nanjing, indicating a certain level of gene flow between them. Compared to geographical distance, diffusion resistance better reflects the diffusion patterns of T. clunifera within the city. Insights from this work establish a foundational framework for the preservation of urban biodiversity and the strategic design of ecological spaces, such as preserving green spaces to encourage gene flow between soil fauna populations.

Key words: soil fauna, Thereuopoda clunifera, genetic diversity, genetic structure, landscape connectivity