Genetic Diversity and Population Structure in Camellia Japonica L. (Theaceae)

Abstract

Camellia japonica is a widespread and morphologically diverse tree native to parts of Japan and adjacent islands. Starch gel electrophoresis was used to score allelic variation at 20 loci in seeds collected from 60 populations distributed throughout the species range. In comparison with other plant species, the level of genetic diversity within C. japonica populations is very high: 66.2% of loci were polymorphic on average per population, with a mean number of 2.16 alleles per locus; the mean observed and panmictic heterozygosities were 0.230 and 0.265, respectively. Genotypic proportions at most loci in most populations fit Hardy‐Weinberg expectations. However, small heterozygote deficiencies were commonly observed (mean population fixation index = 0.129). It is suggested that the most likely cause of the observed deficiencies is population subdivision into genetically divergent subpopulations. The overall level of population differentiation is greater than is typically observed in out‐breeders: The mean genetic distance and identity (Nei's D and I) between pairs of populations were 0.073 and 0.930, respectively, and Wright's Fst was 0.144. Differences among populations appeared to be manifested as variation in gene frequencies at many loci rather than variation in allelic composition per se. However, the patterns of variation were not random. Reciprocal clinal variation of gene frequencies was observed for allele pairs at six loci. In addition, principal components analysis revealed that populations tended to genetically cluster into four regions representing the geographic areas Kyushu, Shikoku, western Honshu, and eastern Honshu. There was a significant relationship between genetic and geographic distance (r = 0.61; P < 0.01). Analysis of variance on allozyme frequencies showed that there was approximately four times as much differentiation among populations within regions, as among regions. It is likely that the observed patterns of population relationships result from the balance between genetic drift in small subpopulations and gene flow between them.

Genetic Structure of Age Classes in Camellia Japonica (Theaceae)

“…All C. japonica isozymes expressed phenotypes that were consistent in subunit structure and genetic interpretation with other isozyme studies in plants, as documented by Weeden and Wendel (1989). In addition, the genetic inference and description of enzyme systems employed here were reported in Wendel and Parks (1982).…”

“…This inference conflicts somewhat with the significant F-values on age classes I, III, IV, and VII (see the next section, below). Because insect food is scarce in winter and early spring, the birds (Zosterops palpebrosa insularis) in warm temperate broad-leaved evergreen forests in northeastern Asia collect nectar from the flowers of C. japonica (Wendel and Parks 1985;Yumoto 1987;M. Y. Chung and M. G. Chung, pers.…”

“…Camellia japonica is, however, almost self-incompatible, and highly outcrossing (t ϭ 0.98) under garden conditions (C. R. Parks, unpubl. data, cited in Wendel and Parks 1985). Assuming that the population is at equilibrium and the estimated fixation index in adults (F ϭ 0.005-0.173; Table 3) is entirely due to mating system, crude estimates of outcrossing rate suggest some levels of selfing (t ϭ 0.827-0.995).…”

Temporal aspects of the fine-scale genetic structure in a population of Cinnamomum insularimontanum (Lauraceae)

“…Some of these species are also important members of coastal forest vegetation in Japan and Korea, and through a series of studies of population dynamics (eg, Yamamoto, 1992), pollination ecology (eg, Yumoto, 1987), allozyme variation in local populations (eg, Wendel and Parks, 1985;Chung and Kang, 1994), and population genetic structure (eg, Chung et al, 2000;Ueno et al, 2000;Chung et al, 2003), the dynamics of these populations are beginning to become elucidated. As mentioned in the Introduction, parts of this study were undertaken to address how the relationships between trees and birds affect the internal spatial genetic structure of newly founded plant populations.…”

Effects of canopy gaps on the genetic structure of Camellia japonica saplings in a Japanese old-growth evergreen forest

“…japonica L. is one of the most widely spread subcanopy tree species in evergreen forests, with a distribution ranging from the south and western coasts of the Korean Peninsula through Taiwan, Kyushu and Shikoku to Honshu of Japan (Kitamura and Murata, 1979). Allozyme studies have shown that high levels of genetic diversity are maintained in the species (Wendel and Parks, 1985;Chung and Kang, 1996). We have already studied the fine-scale genetic structure of C. japonica trees with a diameter at breast height (d.b.h.)…”