Rhododendron meddianum
is a critically endangered species with important ornamental value and is also a plant species with extremely small populations. In this study, we used double digest restriction-site-associated DNA sequencing (ddRAD) technology to assess the genetic diversity, genetic structure and demographic history of the three extant populations of
R. meddianum
. Analysis of SNPs indicated that
R. meddianum
populations have a high genetic diversity (π = 0.0772 ± 0.0024,
H
E
= 0.0742 ± 0.002). Both
F
ST
values (0.1582–0.2388) and AMOVA showed a moderate genetic differentiation among the
R. meddianum
populations. Meanwhile, STRUCTURE, PCoA and NJ trees indicated that the
R. meddianum
samples were clustered into three distinct genetic groups. Using the stairway plot, we found that
R. meddianum
underwent a population bottleneck about 70,000 years ago. Furthermore, demographic models of
R. meddianum
and its relative,
Rhododendron cyanocarpum
, revealed that these species diverged about 3.05 (2.21–5.03) million years ago. This divergence may have been caused by environmental changes that occurred after the late Pliocene, e.g., the Asian winter monsoon intensified, leading to a drier climate. Based on these findings, we recommend that
R. meddianum
be conserved through
in situ
,
ex situ
approaches and that its seeds be collected for germplasm.
A mixture Markov regression model is proposed to analyze heterogeneous time series data. Mixture quasi-likelihood is formulated to model time series with mixture components and exogenous variables. The parameters are estimated by quasi-likelihood estimating equations. A modified EM algorithm is developed for the mixture time series model. The model and proposed algorithm are tested on simulated data and applied to mosquito surveillance data in Peel Region, Canada.
Rhododendron longipedicellatum is an endangered species endemic to southeastern Yunnan, China. Assessment of genetic variation is critical for protecting endangered species. Therefore, we used EST-SSR markers to analyze the genetic characteristics of R. longipedicellatum. The results revealed high genetic diversity at the species level ( He = 0.559, NA = 9.529) and within populations ( He = 0.507, NA = 5.910) and moderate genetic differentiation between populations ( FST = 0.083). In addition, more genetic variation existed within populations (91.25%) compared with variation among populations (8.75%). The STRUCTURE analysis showed that 150 individuals from five existing populations could best be divided into two genetic groups. At the population level, the neighbor-joining (NJ) tree and principal coordinates analysis (PCoA) analyses also divided them into two groups. In addition, Bottleneck analyses using the Two-Phase Model (TPM) and Stepwise Mutation Model (SMM) as well as the Garza-Williamson Index revealed widespread signatures of bottleneck events. These results provide vital information for scientifically formulating conservation strategies for the endangered R. longipedicellatum.
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