No reduction in genetic diversity of Swiss stone pine (Pinus cembra L.) in Tatra Mountains despite high fragmentation and small population size

Abstract

In Europe, most of the alpine timberline ecotone has been altered by human activities and climate change. Hence, mountain forests are of the highest conservation interest. Here, we screened 25 populations of Swiss stone pine (Pinus cembra L.) from the Carpathians and the Alps, using a set of ten microsatellite primers to assess the relative conservation value of populations sampled in Polish and Slovak Tatra National Parks, where potential extinction risk is the highest within the Carpathian range. Although endangered, with small and fragmented populations, P. cembra in the Tatra Mts. shows high levels of allelic richness (AR = 5.0) and observed heterozygosity (H o = 0.554). Our results suggest that anthropogenic habitat fragmentation has had little impact on DNA variation of Swiss stone pine in the Tatra Mts. However, the effects of changing conditions on the genetic structure may occur with a substantial time delay due to the long life span of P. cembra. Moreover, inbreeding depression may occur in the next generations, since we found inbreeding (F IS = 0.063) and elevated coancestry coefficient (h = 0.062) in all populations. Also a shallow pattern of genetic differentiation between populations was found, indicating recent fragmentation of a common gene pool that formerly occupied a larger range. Therefore, the Tatra Mts. can be considered as a single conservation unit. Based on our results, we suggest possible conservation activities for Swiss stone pine both in Poland and Slovakia.

Bayesian approach reveals confounding effects of population size and seasonality on outcrossing rates in a fragmented subalpine conifer

“…Our results show that gene flow through pollen should be generally sufficient to counterbalance genetic drift. In fact, studying genetic structure of P. cembra in the Tatras, we detected very weak genetic differentiation (Dzialuk et al 2014), suggesting that gene exchange between subpopulations is probably high. On the other hand, based on mating system parameters, we argued that small and isolated subpopulations of P. cembra both in the Alps and Carpathians can experience severe local pollen limitation, which can dramatically lower seed production (Salzer and Gugerli 2012) and fitness of individuals due to inbreeding.…”

“…Moreover, the latter is assumed to result entirely from pollen dispersal and not population genetic structure (Austerlitz and Smouse 2001). The absence of correlation between genetic and geographic distance found in the Tatras (Dzialuk et al 2014) suggests that the observed pollen structure was indeed a result of limited pollen dispersal. Nonetheless, due to discontinuous sampling (see Fig.…”

“…The results for P. cembra fully support this prediction (Salzer and Gugerli 2012) in respect to populations in the Swiss Alps. In the case of the Tatras, a related study revealed that the population of mature individuals is only slightly inbred, with the overall average F=0.051 (Dzialuk et al 2014). Using the equilibrium equation (Ritland 1990), we can estimate the relative fitness of selfed individuals to be as low as w = 2tF/((1-t)(1-F))= 0.283.…”

“…In particular, seed yield can be reduced (Salzer and Gugerli 2012), lowering (variance) effective population size. However, because tree species seem to be generally "resistant" to the impact of fragmentation on the genetic diversity (O'Connel et al Kramer et al 2008), the question of whether high adult genetic homogeneity in the Tatras (Dzialuk et al 2014) will be preserved in future generations remains open. To answer this, we need to know if potentially high pollen-mediated gene flow can preclude erosion of the gene pool in small populations.…”

“…This approach was chosen because, unlike TwoGener ), it does not require an effective density of pollen parents (D e ) to be known. We need to stress here that in our case, due to problematic delimitation of a mating population (see Dzialuk et al 2014), D e cannot be practically assessed. During the analysis, we focused particularly on the assessment of whether the dispersal kernel is thin-or fat-tailed or whether long-distance pollen dispersal (LDD) is a likely phenomenon in the study system.…”