West meets East: How do rainforest beetles become circum-Pacific? Evolutionary origin of Callipogon relictus and allied species (Cerambycidae: Prioninae) in the New and Old Worlds.

ABSTRACT

The longhorn beetle genus Callipogon Audinet-Serville represents a small group of large wood-boring beetles whose distribution pattern exhibits a unique trans-Pacific disjunction between the East Asian temperate rainforest and the tropical rainforest of the Neotropics. To understand the biogeographic history underlying this circum-Pacific disjunct distribution, we reconstructed a molecular phylogeny of the subfamily Prioninae with extensive sampling of Callipogon using multilocus sequence data of 99 prionine and four parandrine samples (ingroups), together with two distant outgroup species. Our sampling of Callipogon includes 18 of the 24 currently accepted species, with complete representation of all species in our focal subgenera. Our phylogenetic analyses confirmed the purported affinity between the Palearctic Callipogon relictus and its Neotropical congeners. Furthermore, based on molecular dating under the fossilized birth-death (FBD) model with comprehensive fossil records and probabilistic ancestral range reconstructions, we estimated the crown group Callipogon to have originated in the Paleocene circa 60 million years ago (Ma) across the Neotropics and Eastern Palearctics. The divergence between the Palearctic C. relictus and its Neotropical congeners is explained as the result of a vicariance event following the demise of boreotropical forest across Beringia at the Eocene-Oligocene boundary. As C. relictus represents the unique relictual species that evidentiates the lineage's expansive ancient distribution, we evaluated its conservation importance through species distribution modelling. Though we estimated a range expansion for C. relictus by 2050, we emphasize a careful implementation of conservation programs towards the protection of primary forest across its current habitats, as the species remains highly vulnerable to habitat disturbance.