Spatial and temporal determinants of genetic structure in Gentianella bohemica

Abstract

The biennial plant Gentianella bohemica is a subendemic of the Bohemian Massif, where it occurs in seminatural grasslands. It has become rare in recent decades as a result of profound changes in land use. Using amplified fragment length polymorphisms (AFLP) fingerprint data, we investigated the genetic structure within and among populations of G. bohemica in Bavaria, the Czech Republic, and the Austrian border region. The aim of our study was (1) to analyze the genetic structure among populations and to discuss these findings in the context of present and historical patterns of connectivity and isolation of populations, (2) to analyze genetic structure among consecutive generations (cohorts of two consecutive years), and (3) to investigate relationships between intrapopulational diversity and effective population size (Ne) as well as plant traits. (1) The German populations were strongly isolated from each other (pairwise FST= 0.29–0.60) and from all other populations (FST= 0.24–0.49). We found a pattern of near panmixis among the latter (FST= 0.15–0.35) with geographical distance explaining only 8% of the genetic variance. These results were congruent with a principal coordinate analysis (PCoA) and analysis using STRUCTURE to identify genetically coherent groups. These findings are in line with the strong physical barrier and historical constraints, resulting in separation of the German populations from the others. (2) We found pronounced genetic differences between consecutive cohorts of the German populations (pairwise FST= 0.23 and 0.31), which can be explained by local population history (land use, disturbance). (3) Genetic diversity within populations (Shannon index, HSh) was significantly correlated with Ne (RS= 0.733) and reflected a loss of diversity due to several demographic bottlenecks. Overall, we found that the genetic structure in G. bohemica is strongly influenced by historical periods of high connectivity and isolation as well as by marked demographic fluctuations in declining populations.

Genetic and reproductive characterisation of seasonal flowering morphs ofGentianella bohemicarevealed strong reproductive isolation and possible single origin

“…Königer et al . ). The proceeding spatial isolation, through abandonment of traditional grassland management or intensification of land use, further aggravates inter‐population pollination, since plant–pollinator mutualisms might be disturbed and pollinators often are not able to overcome large geographic distances and/or specific barriers, such as forests (cf.…”

“…between Bohemia (today Czech Republic) and Austria, where several trails for salt trade existed (Hajná ; see also Königer et al . ). For our study region, at least the population at ASB is adjacent to a historically important post station (personal communication with tenant).…”

“…Königer et al . () also discussed the harvest and transport of hay together with cattle drives as possible dispersal vectors in former times. They found low genetic differentiation between Austrian and Czech populations, which they mainly explain by earlier periods of connectivity between these trading regions.…”

Inter-annual maintenance of the fine-scale genetic structure in a biennial plant

“…Several factors may promote between-cohort gene flow via different pathways in E. mediohispanicum (Figure S4). Seed dormancy can be activated by unfavourable weather conditions45 and leads to mating between the descendants of different cohorts25. In addition, the arrival of inter-annual migrants can take other different paths.…”

“…Several processes promote variation in biennial life span, permitting the existence of inter-annual migrants that bridge years (‘facultative biennials’)2324. These inter-annual migrants favour gene flow between cohorts, leading to homogenisation of their allelic frequencies25. However, little is known regarding how inter-annual migrants affect the similarities in SGS among cohorts of a biennial, particularly for small plant populations where temporal changes in population size could dramatically vary their genetic composition26.…”