Long-term survival and successful conservation? Low genetic diversity but no evidence for reduced reproductive success at the north-westernmost range edge of Poa badensis (Poaceae) in Central Europe

Kristina Plenk,Maria Höhn,Matthias Kropf,Katharina Bardy

doi:10.1007/s10531-019-01722-x

Abstract

Many steppe species reach their (north)westernmost distribution limit in western Central Europe. This also applies to Poa badensis, a rare steppe plant of calcareous rock/sand vegetation. To explore potential differences in reproductive success and genetic composition of peripheral populations, we analysed the absolute (north)westernmost occurrences in Western Germany and populations at the western margin (Eastern Austria) and the centre (Central Hungary) of the Pannonicum, representing a part of the continuous range. Specifically, we discuss the genetic and reproductive constitution of the (north)westernmost exclave and draw conclusions on the species’ biogeographical and conservation history in this region. Therefore, we used two independent molecular marker systems (AFLPs, cpDNA sequences) and a set of performance parameters. Overall, lowest regional genetic diversity was found in Western Germany, which is mainly a result of the specific history of two populations. However, this low genetic diversity was not accompanied by reduced reproductive success. The Eastern Austrian populations showed reduced genetic diversity and predominantly reduced performance, interpreted as a consequence of small population sizes. Central Hungarian populations showed the overall highest genetic diversity and comparatively high performance values. We observed high admixture and haplotype sharing between Austrian and Hungarian populations, indicating gene flow among these regions. In contrast, we interpreted the increased population differentiation within, and the clear distinctiveness of the German exclave as a long-term isolation of these (north)westernmost occurrences. Our results, overall, prove the good constitution of these populations and, together with their particular biogeographical history, highlight their conservation value.

Highlights

Investigating the constitution of species at their absolute distributional periphery, we can test commonly and controversially discussed biogeographical hypotheses, e.g. the ‘abundant centre’ distribution (Sagarin and Gaines 2002) or the ‘central-marginal hypothesis’ (Eckert et al 2008; see Sexton et al 2009; Abeli et al 2014; Pironon et al 2016)
1874 seeds from 223 mother plants were included in the germination experiment
Results of the post hoc test demonstrated that the number of seeds differed significantly due to the low values observed in the Austrian region

Summary

Introduction

Investigating the constitution of (rare) species at their absolute distributional periphery, we can test commonly and controversially discussed biogeographical hypotheses, e.g. the ‘abundant centre’ distribution (Sagarin and Gaines 2002) or the ‘central-marginal hypothesis’ (Eckert et al 2008; see Sexton et al 2009; Abeli et al 2014; Pironon et al 2016). Genetic bottlenecks, genetic drift and inbreeding may reduce genetic diversity and influence species’ fitness and potential for adaptation to local conditions. These predictions on the genetic composition were partially detected in several studies on steppe plant species (cf Pérez-Collazos et al 2009; Wagner et al 2011a; but see Kajtoch et al 2016). Few studies have analysed the influence on species’ performance and the expected patterns of reduced reproductive success were mostly not observed (cf Wagner et al 2011b; but see Pironon et al 2016)

Methods

Results

Conclusion