Morphology and Genetic Diversity of Golden Silk Orb-weaver (Nephila) Spiders in Thailand.

Spiders play a pivotal role in ecosystems, serving as predators to regulate populations of small organisms. They commonly exhibit body color polymorphism which could be due to a combination of environmental factors, adaptation, or genetic drift from population subdivision. This polymorphism, in turn, could affect their behavior and prey capture efficiency. Certain morphological traits may be unique to specific subregions, suggesting possible subspecies classification. In this study, we examined morphological polymorphism in the giant wood spider, Nephila pilipes, in Thailand, particularly focusing on leg variation and genetic variation at the cytochrome c oxidase I (COI) gene. We used partial sequence of the COI gene for our samples and constructed a phylogenetic tree by including other species. We explored the relationship between morphological polymorphism, COI genotype, and geographic distribution. Our findings categorized female N. pilipes into seven types based on legs I and IV, with no correlation to geographic region. The N. pilipes specimens formed two clades, each containing all leg types and collection regions, consistent with low genetic differentiation within the species. Trichonephila antipodiana specimens formed three clades while all Argyrodes flavescens specimens were grouped into a monophyletic clade. Additionally, Nephila kuhli, previously suggested to be a melanic morph of N. pilipes, was also included in the N. pilipes cluster, with a low genetic distance. Our results suggest that the leg variants in N. pilipes represent polymorphism within the species rather than distinct biospecies.