Genetic structure of the critically endangered plant Tricyrtis ishiiana (Convallariaceae) in relict populations of Japan

Abstract

Tricyrtis ishiiana is a relic endemic plant taxon of the Convallariaceae that inhabits two nearby gorges in Kanagawa Prefecture, Japan. The distribution range and number of populations are thought to have been reduced to the present refugial populations during the Quaternary climatic oscillations. Because of its showy flowers, this plant has faced illegal removal from its natural habitats for horticultural use and has been designated a critically endangered species (class IA). In this study, we analyzed the genetic structure of the relict populations of T. ishiiana in order to contribute to the conservation strategies of the prefectural government. Our analyses of nine nuclear microsatellite loci detected high genetic diversity (H E = 0.704 and H O = 0.541) for the two populations. The two populations were slightly differentiated (R ST = 0.032), accompanied by faint substructure across the populations (K = 3). In addition, each population exhibited spatial genetic structuring. The relatively low inbreeding coefficient for both populations together (F IS = 0.233) and each population separately (F IS = 0.217-0.246) may be attributable to crossing among descendants within a population along with occasional gene flow between the populations. These results suggested that the extant populations have not experienced a severe bottleneck. The two extant populations were genetically differentiated at a very low level, accompanied by occasional pollen flow via pollinators and/ or seed dispersal by gravity in the mountainous environment. Occasional gene exchange between the populations has allowed T. ishiiana to harbor high genetic diversity despite being a relic plant confined to two small refugial populations.

Temperate origin and diversification via southward colonization in Fatsia (Araliaceae), an insular endemic genus of the West Pacific Rim

“…The levels of nucleotide diversity of the cpDNA spacer and nrITS assessed within Fatsia (θ=0.00070-0.00417, Table 1) were lower than other angiosperms Conti et al 1999). For microsatellite loci, all Fatsia species also had lower allele number, and observed and expected heterozygosities (Table 3) (Setoguchi et al 2011), altogether seemingly agreeing with the expectations for island species. However, F. oligocarpella of oceanic islands with a narrow distribution possessed much higher levels of nucleotide diversity for all loci than other Fatsia species distributed in continental islands (Table 1).…”

Population fragmentation causes randomly fixed genotypes in populations of Arabidopsis kamchatica in the Japanese Archipelago

“…kawasakiana is self-compatible (Sugisaka and Kudoh 2008) and its life cycle is accomplished within one year, which would facilitate strong genetic drift. In contrast, plant species with very limited habitats may harbour high genetic diversities (e.g., Maki et al 1999;Takahashi et al 2011;Setoguchi et al 2011). Thus, detecting low or high genetic diversity of A. kamchatica in these limited habitats is plausible.…”

Genetic diversity and population structure of the endangered endemic speciesPaeonia decompositafrom China and implications for its conservation

“…This result was obtained for three potential reasons. Firstly, P. decomposita is a long-lived shrub that may exhibit genetic diversity from ancestral populations (Luan et al ., 2006; Setoguchi et al ., 2011). Secondly, the mating system is often viewed as a principal factor influencing the genetic diversity of species.…”

“…Gene flow is a basic micro-evolutionary phenomenon that destroys genetic differentiation among populations and affects maintenance of genetic diversity (Slatkin, 1994; Yao et al ., 2007). Many endangered plants currently occur only as highly isolated and narrowly distributed within a few small populations, possibly leftovers of a formerly widespread species, which had large and continuous populations (Yao et al ., 2007; Setoguchi et al ., 2011). In the present research study, gene flow (mean Nm value) among P. decomposita populations was >1 and did not exhibit genetic differentiation, resulting from genetic drift (Hamrick et al ., 1992).…”