Genetic structure and diversity in Juniperus communis populations in Saxony, Germany

Abstract

In recent years, land use changes led to a rapid decline and fragmentation of J. communis populations in Germany. Population isolation may lead to a restricted gene flow and, further, to negative effects on genetic variation. In this study, genetic diversity and population structure in seven fragmented J. communis populations in Saxony, Germany, were investigated using nuclear microsatellites (nSSR) and chloroplast single nucleotide polymorphism (cpSNP). In all Saxony J. communis populations, a high genetic diversity was determined but no population differentiation could be detected whatever method was applied (Bayesian cluster analysis, F-statistics, AMOVA). The same was true for three J. communis out-group samples originating from Italy, Slovakia and Norway, which also showed high genetic diversity and low genetic differences regarding other J. communis populations. Low genetic differentiation among the J. communis populations ascertained with nuclear and chloroplast markers indicated high levels of gene flow by pollen and also by seeds between the sampled locations. Low genetic differentiation may also provide an indicator of Juniper survival during the last glacial maximum (LGM) in Europe. The results of this study serve as a basis for the implementation of appropriate conservation measures in Saxony.

Using genetic evaluation to guide conservation of remnant Juniperus communis (Cupressaceae) populations

“…All populations exhibited significantly positive F IS and F ISnull inbreeding coefficients, indicating a deficit in heterozygotes. This pattern has also been reported in previous studies of J. communis (Oostermeijer & De Knegt 2004;Reim et al 2016) or other members of the Cupressaceae in general (Ritland et al 2001;Bettencourt et al 2015). The presence of null alleles affects the F IS values in our studied populations, but not the overall genetic structure.…”

“…The populations of juniper we studied exhibited high levels of genetic variation for both nuclear and plastid markers, despite their small size (usually fewer than 100 male and female trees together). Values of genetic variation are similar or even higher than the levels reported in Germany (Reim et al 2016) and Ireland (Provan et al 2008) based on the same markers. Hence, we conclude that these small populations are not genetically depauperate compared to large populations.…”

“…Hence, we conclude that these small populations are not genetically depauperate compared to large populations. Other studies of J. communis or J. brevifolia in Western Europe also reported high genetic diversity levels within small populations (Bettencourt et al 2015; Reim et al 2016). This is not surprising for a long‐lived species, as small population remnants may hold old individuals which reflect pre‐fragmentation genetic variation (Van Geert et al 2015; Reim et al 2016; Van Rossum & Raspé 2018).…”

“…Finally, given the geographic isolation of the remnant populations, connectivity between populations might be restored by creating so‐called ‘stepping stone’ populations in favourable open areas, such as the edges of fields or under power supply lines (Frankham et al 2004; Van Rossum & Triest 2012; Reim et al 2016; Broome et al 2017). Even isolated individuals could act as stepping stones for bridging large distances between groups of trees or populations.…”

“…Results from previous assessments of juniper population genetic structure have varied, with significant population differentiation within Ireland (Provan et al 2008) but low levels of differentiation in the Netherlands and Germany (Oostermeijer & De Knegt 2004; Reim et al 2016). Inbreeding, which is recognized as a long‐term threat for population viability (Keller & Waller 2002; Edmands 2007; Weeks et al 2011), has not been consistently investigated for this species (Michalczyk et al 2006; Provan et al 2008; Reim et al 2016). These data may be particularly important given that junipers span diverse ecological contexts ( e.g .…”