Genetic and Demographic Patterns in Naturally Fragmented Mountain Endemics: Insights from Degenia velebitica

Isolated mountain ecosystems provide an opportunity to study how long-term natural fragmentation shapes population persistence. Unlike species fragmented by human activities, many mountain endemics have evolved under naturally discontinuous conditions over long timescales, allowing historical and contemporary processes to be disentangled. Degenia velebitica (Brassicaceae) represents a suitable model for such studies. We analysed nuclear microsatellites, chloroplast DNA, fine-scale spatial genetic structure, effective population size, and demographic characteristics across all currently known populations. Despite pronounced genetic differentiation, restricted contemporary gene flow, small effective population sizes, and marked demographic differences, populations maintained moderate nuclear genetic diversity. Chloroplast DNA revealed low haplotype variation and strong spatial structuring of maternal lineages, consistent with limited historical seed-mediated dispersal. Importantly, demographic and genetic indicators were not always concordant: in one population, an apparent recent decline in census size and low effective population size were accompanied by relatively well-preserved nuclear genetic diversity. These findings demonstrate that neutral genetic diversity alone may provide an incomplete picture of population status and evolutionary potential, highlighting the importance of integrating genetic, demographic, and ecological information and maintaining existing population structure and habitat integrity in conservation planning.