Allozyme Diversity and Geographical Differentiation ofParasenecio adenostyloides(Asteraceae), an Endemic Forest Herb in Japan

Abstract

In this study, allozyme variation at 15 putative loci was analyzed in 11 populations of Parasenecio adenostyloides (Asteraceae), a perennial herb endemic to Shikoku and Honshu, Japan. This species occurs mainly in the understory of subalpine coniferous forests and shows an islandlike pattern of geographical distribution. Genetic variation at the species level (P ¼ 73:3, mean number of alleles per locus A ð Þ ¼ 4:00, expected heterozygosity H E ð Þ ¼ 0:237) and at the population level (percentage of polymorphic loci ½P ¼ 42:4, A ¼ 2:05, H E ¼ 0:173) was considerably higher than the means for other short-lived perennial herbs and endemic species. A moderate but significant genetic differentiation was observed among the populations (G ST ¼ 0:179). The distribution of genetic variation showed an evident geographical pattern. In addition to the pattern of isolation by distance, a genetic distance phenogram and a principal components analysis based on allele frequencies roughly supported three clusters of the populations in central Honshu, northern Honshu, and Shikoku. In particular, two isolated populations in Shikoku were also characterized by remarkably lower genetic variation than those in Honshu, possibly resulting from strong genetic drift associated with their isolated distribution. This geographical structure of genetic variation was not in accord with the predictions based on migration history of subalpine coniferous forest in Japan, and it exemplified the importance of geographical isolation in establishing the genetic structure of P. adenostyloides.

Phylogeographic patterns of highland and lowland plant species in Japan

“…However, the genetic structure of a component of sub-alpine coniferous forests, Parasenecio adenostyloides, was not in agreement with that of A. mariesii. Nakagawa (2008) reported that this species maintained extremely limited amounts of genetic variation in southwestern Japan, suggesting that this pattern of P. adenostyloides, seems to have been primarily shaped by current geographical isolation among populations, i.e., ecological factors, rather than by historical factors.…”

“…Alpine and sub-alpine: Parasenecio adenostyloides (Nakagawa 2008), Picea jezoensis (Aizawa et al 2007(Aizawa et al , 2009, Pinus parviflora (Tani et al 2003), and Pinus pumila (Tani et al 1996) Montane: Quercus crispula Chamaecyparis obtusa (Tsumura et al 2007b;Matsumoto et al 2010), Conocephalum conicum (Akiyama and Hiraoka 1994), Cryptomeria japonica (Takahashi et al 2005), and Fagus japonica (Hiraoka and Tomaru 2009a) Lowland: Raphanus sativus var. (Huh and Ohnishi 2001;Ohsako and Ohnishi 2007).…”