Geographical structure of morphological characters in Semanotus japonicus (Coleoptera: Cerambycidae) in Japan

Abstract

The sugi bark borer, Semanotus japonicus, occurs naturally in Honshu, Shikoku, Sado Is., Oki Is., and Yaku Is. in Japan, and its main host tree is the Japanese cedar, Cryptomeria japonica. Because of a correspondence between the present distribution of geographical variation in the borer and the refugia of the Japanese cedar during the last fullglacial period, isolation of the cedar is thought to have caused differentiation in the borer between local populations. In this study, we used morphological information to elucidate the geographical differentiation of S. japonicus populations. Multivariate analyses were performed based on ten morphological characters for ten populations. Populations between the Pacific coast side and the Wakasa Bay area showed remarkable variation in morphological characters. Because the distribution of the refugia of the cedar coincided with the patterns of morphological variations in S. japonicus, it is suggested that the geographical structure of the present S. japonicus population was caused by isolation during the last glacial period. While vicariance is no longer a factor with the expansion of C. japonica's distribution, its past effects may have been important enough to influence the present genetic structure of S. japonicus.

Geographical structuring of mitochondrial DNA in Semanotus japonicus (Coleoptera: Cerambycidae)

“…We deduced that these two lineages corresponded to morphological divergence between populations on the Pacific Ocean side and the Japan Sea side. The Ehime population had typical morphological characters of the Pacific coastal lineage, and the Fukui population showed the opposite trend (Shoda et al, 2003). Thus, the clade, including haplotypes A and B, is thought to correspond to the Pacific coastal lineage and the other clade, which includes haplotypes from Fukui, is thought to be a lineage from the Japan Sea side.…”

“…The Fukui and Shimane populations may thus include two finely divergent clades which had mutually introgressed. The Shimane population showed differences from the Fukui population in its morphology, and its origin was hypothesized to be endemic of the Chugoku area or hybrids between the Pacific Ocean side and the Japan Sea side populations (Shoda et al, 2003). According to the molecular data, endemic morphologies of the population distributed offshore of Chugoku area in the last glaciation are supposed to be sustained in Shimane population.…”

“…1 from Tsukada, 1982). Previously, the morphologies of Semanotus japonicus that were thought to be descendants of borers living in 1) and 3) during the last glacial maximum were shown to indicate reverse trends in multivariate statistics (Shoda et al, 2003). Key historical events (e.g.…”

“…With the retreat of Haplotypes B and C, which belonged to the Pacific coastal and Japan Sea side lineages respectively, were detected in the Iwate population. From multivariate statistics of morphology and history of the dispersal of the cedar into the Tohoku area, the population in Iwate was thought to be a hybrid of Pacific and Japan sea lineages (Shoda et al, 2003). The haplotypic distribution possibly showed incidence of secondary contact.…”