Invasive Spiders and Their Microbiomes: Patterns of Microbial Variation in Native and Invasive Species in Hawai'i

Invasive species can have detrimental impacts on the community structure and native species persistence, causing cascading impacts on ecosystem function. These effects are amplified in remote island ecosystems that are characterized by non-representative and often diverse biota. The mechanisms behind successful invasions, particularly of arthropods, are varied, but growing evidence suggests that invasive species escape from their native predators and competitors. Recent research has suggested that gut microbiota can play an important role in arthropod fitness, with vertically transmitted endosymbionts and horizontally acquired microbes performing different functions. Here, we explored the extent to which the microbiome may facilitate the ability of spiders to exploit and ultimately adapt to novel environments. We examined co-occurring pairs of native and invasive spiders across three locations in the Hawaiian Islands and compared them with mainland counterparts to test two core predictions: (1) gut microbiota would be shaped primarily by local environmental filters rather than invasion status, and (2) vertically transmitted endosymbionts would show stronger host-specificity and reduced diversity in invasives. Using 16S rRNA amplicon sequencing, we found that the site explained 11.7% of gut-microbial compositional variance compared to 6.5% for host species. These results suggest that each spider maintains a species-specific level of α-diversity but reassembles taxonomic composition according to local microbial pools, thus indicating high context dependence in environmental filtering. Invasive species were found to have a lower relative abundance of gut endosymbiont taxa, with one species, <i>Badumna longinqua</i>, showing little to no endosymbiont presence across sites, and the other, <i>Steatoda grossa</i>, exhibiting low but site-specific abundance. We observed a strong localization effect, suggesting that these endosymbionts are also being acquired from local environments, not carried from ancestral ranges. These results suggest host-symbiont interactions have differential impacts on native and invasive species and that microbiota may facilitate the success of spiders in novel environments.