Population Structure and Genetic Diversity Within the Endangered Species Pityopsis ruthii (Asteraceae).

E Anne Hatmaker,Ðenita Hadziabdic,Edward E Schilling,Margaret E Staton,Timothy A Rinehart,Phillip A Wadl,Adam J Dattilo,Robert N Trigiano

doi:10.3389/fpls.2018.00943

Abstract

Pityopsis ruthii (Ruth’s golden aster) is a federally endangered herbaceous perennial endemic to the Hiwassee and Ocoee Rivers in southeastern Tennessee, United States. Comprehensive genetic studies providing novel information to conservationists for preservation of the species are lacking. Genetic variation and gene flow were evaluated for 814 individuals from 33 discrete locations using polymorphic microsatellites: seven chloroplast and twelve nuclear. A total of 198 alleles were detected with the nuclear loci and 79 alleles with the chloroplast loci. Gene flow was estimated, with the Hiwassee River (Nm = 2.16; FST = 0.15) showing higher levels of gene flow and lower levels of population differentiation than the Ocoee River (Nm = 1.28; FST = 0.19). Population structure was examined using Bayesian cluster analyses. Nuclear and chloroplast analyses were incongruent. From the chloroplast microsatellites, three clusters were identified; all were present in sampling sites at both rivers, indicating a lack of allele fixation along rivers. Nuclear markers revealed two clusters and separated by river. When the Hiwassee River locations were analyzed, four clusters were identified for both the chloroplast and nuclear microsatellites, though the individuals clustered differently. Analysis of the Ocoee River revealed two clusters for the chloroplast microsatellites and three for the nuclear microsatellites. We recommend P. ruthii be managed as four populations for the Hiwassee River and three populations for the Ocoee River. Our results provide critical genetic information for P. ruthii that can be used for species management decisions to drive future population augmentation/reintroduction and ex situ conservation efforts.

Highlights

Endangered species generally have small or declining populations, and often these populations suffer from inbreeding and erosion of genetic diversity resulting in elevated extinction risks (Frankham, 2003)
This study enables discourse on broader issues such as the role of damming on the genetic diversity of riparian species, which can be monitored over time using molecular means outlined
Pityopsis ruthii is characterized by high levels of variation at nuclear microsatellite loci and moderate levels of variation for chloroplast microsatellite loci

Summary

Introduction

Endangered species generally have small or declining populations, and often these populations suffer from inbreeding and erosion of genetic diversity resulting in elevated extinction risks (Frankham, 2003). Pityopsis ruthii Genetic Diversity slopes of the Hiwassee and Ocoee Rivers (Bowers, 1972). The two geographically separated rivers are the only populations of P. ruthii (2n = 2x = 18) that remain in the wild, one containing approximately 1,000 individuals along ∼3 km of the Ocoee River and a larger population of around 12,000 individuals along ∼6.5 km of the Hiwassee River (Moore et al, 2016). Thomson and Schwartz (2006) noted that altered river flow due to damming has led to higher competition rates and lower seed dispersal, which has put P. ruthii at risk for short-term extinction The riparian habitat of P. ruthii is highly dynamic and is typified by seasonally high temperatures, frequent drought, and regular inundating flood flows. Thomson and Schwartz (2006) noted that altered river flow due to damming has led to higher competition rates and lower seed dispersal, which has put P. ruthii at risk for short-term extinction

Methods

Results

Conclusion