Seed Dormancy Variability in Lonicera etrusca and Its Relationship with Environmental Heterogeneity Across Localities

Seed dormancy is a key ecological attribute influencing germination timing and the ability of species to establish in variable environments. This study investigated whether inter-population variability in seed dormancy expression exists in Lonicera etrusca, a Mediterranean shrub known for producing seeds with underdeveloped embryos and multiple dormancy types. Seeds were collected from four geographically and ecologically distinct populations in central Iberia and subjected to a series of germination experiments simulating natural seasonal temperature regimes, stratification treatments, and gibberellic acid application. Across all populations, seeds exhibited morphological dormancy (MD) and varying degrees of morphophysiological dormancy (MPD), including non-deep simple and deep complex types. Despite high intra-specific variability in dormancy expression, no significant differences were found among populations for germination patterns or embryo growth responses. This indicates that dormancy variability is an intrinsic, conserved feature of the species rather than a locally adaptive trait. The homogenization of germination strategies across populations may be facilitated by bird-mediated seed dispersal, promoting gene flow and limiting local selection. These findings support the hypothesis that dormancy polymorphism in L. etrusca reflects a flexible germination strategy that enhances colonization potential across heterogeneous Mediterranean environments, rather than an environmentally induced plastic response.