Phylogenetic Separation of Holotrichia Species (Insecta, Coleoptera, Scarabaeidae) Exhibiting Circadian Rhythm and Circa'bi'dian Rhythm.

ABSTRACT

A unique two-day rhythm, circabidian rhythm, has been reported in the black chafer, Holotrichia parallela. However, it remains unknown how widely the circabidian rhythm appears in related species. We examined the activity rhythm and phylogeny of congeneric species inhabiting Japan to investigate the appearance of circabidian rhythms in a few subgenera of the genus Holotrichia. We found that Holotrichia picea also exhibited circabidian rhythm. In addition to the regular circabidian pattern, circabidian rhythms with day-switching or with a circadian activity component were also observed. In the day-switching pattern, H. picea switched appearance from odd to even days, or vice versa. In the circadian-like activity patterns, a major night activity and a minor dusk activity appeared alternately. Holotrichia kiotonensis, Holotrichia convexopyga, and Holotrichia loochooana loochooana exhibited a circadian rhythm. Two distinct clades, A and B, were recognized in the histone H3, cytochrome c oxidase subunit 1, and 16S ribosomal RNA phylogenetic trees. This phylogenetic separation was in accordance with the subgeneric classification based on external morphology in a previous study and with behavioral rhythm in the present study clade A included Nigrotrichia group members, H. kiotonensis, H. convexopyga, H. loochooana loochooana, and H. loochooana okinawana, while clade B included Pedinotrichia group members, H. paralella and H. picea. We suggest that after separation into Nigrotrichia and Pedinotrichia, the behavioral trait of circabidian rhythm probably appeared once in an ancestral species of the Pedinotrichia group, including H. parallela and H. picea.