High-throughput DNA barcoding provides insight into the factors shaping spider diversity in the biodiversity hotspot of Wallacea

Biodiversity hotspots, housing an immense portion of Earth's terrestrial biodiversity, are under severe threat due to anthropogenic change. The prevalence of undescribed taxa in these locations poses a significant challenge to community-level biodiversity monitoring and protection. In this study, we use a DNA mini-barcode to test predictions of biodiversity patterns in Sulawesi, Indonesia, part of the Wallacean biodiversity hotspot. We tested the elevational diversity gradient, the presence of areas of endemism (AOEs), and patterns of diversification in a diverse taxonomic group, the spiders (order Araneae). Our approach utilized individually sequenced adult specimens paired with juvenile specimens sequenced using a metabarcoding approach to assess diversity patterns within and between three mountains. 2,357spiders were sequenced and produced 926 amplicon sequence variants, clustered into 508 operational taxonomic units. Alpha diversity was significantly associated with elevation, peaking at the 1,000-1,500m elevation band, which supports the elevational diversity gradient. Distinct OTUs were found on each mountain, indicating areas of endemism for Sulawesi spider biodiversity. Additionally, communities between neighboring elevation bands within a mountain shared few OTUs; this high elevational turnover demonstrates how mountains act as biodiversity hotspots in and of themselves. Using a coarser sequence clustering approach, we found evidence for extensive in-situ diversification, reflected by a high number of 97% clusters that collapse into a low number of 95% clusters. Patterns of shared clusters between communities showed elevational structuring in line with niche conservatism with limited local diversification occurring between sites within a narrower elevational range. The approach we adopted greatly expanded our knowledge of Sulawesi spider biodiversity while also providing insights into the relative roles of pre-adapted lineages and local diversification in shaping overall diversity patterns across the island.