Xyleborine ambrosia beetles began their dispersal from Asia to the New World soon after their origin approximately 23 Ma.Tolerance for extreme inbreeding and fungus farming have made them successful colonizers.These ancient globetrotters have radiated throughout the tropics, including the Hawaiian archipelago. Twenty-one endemic Xyleborus Eichhoff species are recorded from the current islands, but this radiation is poorly known. We used a multigene phylogeny for half of the endemic species and outgroups from the worldwide xyleborine fauna to test the monophyly of the endemic species, to hypothesize their sister group, and to estimate their age of diversification. Bayesian analysis found the endemic Hawaiian Xyleborus species monophyletic and sister to X. glabratus Eichhoff, an Asian species. Individuals of two endemic species demonstrate long phylogenetic branches, suggesting cryptic diversity. Based on the BEAST estimates of age, the Hawaiian endemics originated at least 9.8 Ma (95% HPD bound of 6.0–13.4 Ma) before the emergence of the current islands.The species radiation does not follow the progression rule whereby species age is positively correlated with island age. This discordance between species and island ages is likely due to the movement of species between older and younger islands without subsequent speciation; gaps in sampling caused by extinction may also be obscuring the original distributions of species. Both scenarios are plausible given the vagility of xyleborines and the destruction of the native Hawaiian forests. Further surveys for endemic species and conservation planning are needed to improve our understanding of their evolution and to save them from continued extinction.
Insect Systematics and Diversity
Vol. 2 • No. 3
Vol. 2 • No. 3