Species distribution modeling and population genetics of <i>Nannophya pygmaea</i> (Odonata: Libellulidae)

Abstract The Scarlet Pygmy Nannophya pygmaea Rambur, 1842 (Odonata: Libellulidae), the smallest described dragonfly species, is found across the Pacific coast and along the island chains of eastern Asia. Previous research has questioned whether N. pygmaea is potentially a complex of multiple species. Past studies have proposed a new species, N. koreana, based on mitochondrial genetic data, but the N. pygmaea complex remains unresolved. Using increased taxon sampling, we assessed genetic differentiation across populations and reconstructed evolutionary relationships of the N. pygmaea complex. From 141 COI-5P sequences, we calculated genetic structure through estimation of pairwise FST values among 10 populations and constructed a haplotype network to determine genetic differentiation, which revealed extremely high differentiation between northern populations (Japan, South Korea, China, and Laos) and southern peninsula/island chain populations (Malaysia, Singapore, Indonesia, and Vietnam). Species distribution models (SDMs) showed large stretches of less suitable habitat between regions populated by N. pygmaea. A lack of gene flow and geographical isolation between the clades supports these highly differentiated populations being described as separate species. Additionally, our SDMs explored the prevalence of present suitable habitats and how habitat suitability may shift between now and 2070. Our paleodistribution modeling provides insight into possible land migration routes that would allow N. pygmaea, as a weak flyer, to have dispersed to its present-day distribution. Ordination analysis of niche divergence between the northern and southern clades found no significant levels of niche differentiation or similarity between the 2 clades.