Phylogeographic Investigation of an Endangered Longhorn Beetle, Callipogon relictus (Coleoptera: Cerambycidae), in Northeast Asia: Implications for Future Restoration in Korea

SIMPLE SUMMARY: The critically endangered Callipogon relictus is one of the largest longhorn beetle species and also the only remnant species of the genus Callipogon found in the Palearctic region. Knowledge of the phylogeographic history and current conservational status is essential to understand its unique distribution and to establish efficient conservation strategies. We studied the phylogeographical pattern and genetic diversity of C. relictus from almost its entire geographical range. The level of genetic diversity and divergence of C. relictus from the known distributions in four regions in Russia, China, North Korea, and South Korea using two mitochondrial markers (COI and COII) revealed that genetic diversity lies within the range of intraspecific levels. Relatively high genetic diversity with no distinct phylogeographic structures indicates that the wide range of current fragmented populations might be the remnant of genetically diverse populations in the past. The results of our phylogenetic and population genetic analyses suggest that C. relictus populations surveyed in the present study can be used as a “source” for a future restoration and conservation program. The findings of the genetic characteristics and phylogeographic history of C. relictus will help to establish effective conservation strategies for this endangered longhorn beetle species in Northeast Asia. ABSTRACT: The longhorn beetle, Callipogon (Eoxenus) relictus Semenov, is the only remnant species found in the Palearctic region, while all other Callipogon species are distributed mainly in Central America and partly in South America. This species has been placed in the first category (as ‘critically endangered’) of the Red Data Book in Russia and designated as one of the top-priority target species among all endangered invertebrate species for restoration in South Korea since 2006. Although its restricted distribution in Northeast Asia with a high conservational value has been highlighted, genetic features of C. relictus from different geographic regions remain unexplored. We first investigated the level of genetic diversity and phylogeographic patterns of C. relictus to evaluate the current conservational status and the feasibility of the implementation of a restoration program. The average genetic divergence of mitochondrial gene COI based on Kimura-2-parameter distance among the four regions in Russia, China, North Korea, and South Korea was 2.2%, which lies within the range of intraspecific levels. However, two separate clades with 3.8% divergence were identified, despite no geographical clustering of haplotypes. The linear pattern of the haplotype network with a high level of haplotype and nucleotide diversities suggests that the wide range of currently fragmented populations might be the remnant of genetically diverse populations in the past. This study will provide crucial information on the genetic characteristics and phylogeographic history of C. relictus, which will help to establish conservation strategies for this cherished insect species in Northeast Asia.