Comparative studies on the Silene mollissima aggregate (Caryophyllaceae)

In this PhD thesis, a multidisciplinary approach was adopted to contribute to the knowledge of some taxa of the Silene mollissima aggregate and to provide useful information and data to support conservation measures. In Chapter I, a statistical classifier for the Tyrrhenian taxa of the S. mollissima aggregate (Silene badaroi, Silene ichnusae, Silene velutina, Silene oenotriae, Silene hicesiae), based on 132 morpho-colorimetric variables describing seed size, shape and color of seed, was tested at inter- and intra-specific levels. The performed analysis confirmed the systematic treatment at section and species level. At the population level both the presence of connections and high differentiation rates among populations were identified. In particular, the most differentiated populations, both for S. velutina and S. badaroi, were those at the edge of the species’ distribution area; indeed, seeds from populations of the core areas of distribution ranges were less different among each other. In Chapters II and III, relevant information was reported about phenology and ecological requirements of some Tyrrhenian (S. velutina, S. ichnusae and S. badaroi) and Ibero-Levantine species (Silene mollissima and Silene hifacensis) of the S. mollissima aggregate, providing germination and seedling growth protocols useful for their ex situ propagation and conservation. Seeds germination of the three Tyrrhenian species was improved by light and occurred with high percentages at the lowest tested temperatures (5-15°C) and under the alternating temperature regime (25/10 °C). Silene velutina and S. ichnusae seeds germinated until 300 mM NaCl, while S. badaroi up to 100 mM. Except for S. badaroi, salt did not affect seed viability and recovery. The addiction of KNO3 did not affect germination of the three species and their recovery under saline conditions. Seeds germination of the two Ibero-Levantine species was not affected by photoperiod. For both studied species seeds germination rates were higher at the lowest tested temperatures (10 and 15°C). The two species were able to germinate up to 250 mM NaCl, but inter-population differences were detected in the tolerance limit. The highest germination occurred in the non-saline control and decreased with increasing salinity. Silene mollissima and S. hifacensis seeds totally recovered their germination after the NaCl exposure. For both S. mollissima populations the increasing temperature promoted the seedling dry weight and the growth rate, while this pattern was observed only for one S. hifacensis population. In Chapter IV, by taking into account several environmental and population parameters, the microniche variation and the niche breadth dynamics, at local and regional scales, were investigated in Mediterranean islands of different size (large and small islands; LI and SI, respectively) for the Sardinian-Corsican endemic S. velutina. As regards SI populations, a realized niche characterized by harsh and homogeneous environments, with low disturbance levels and potentially low competition was detected, where the life-history strategy of populations was based more on the persistence of adult individuals than on recruitment of juveniles. In contrast, LI populations showed a highly heterogeneous ecological niche, characterized by higher levels of biodiversity, plant cover and the presence of woody vegetation. Such a realized niche on LI appeared to be even more diversified because of the presence of several disturbances to which populations seem to respond by the increase of juveniles and showing a more reliance on the regeneration niche. Concerning the niche breadth, at the regional scale wider niche were observed on LI, probably for the high spatial heterogeneity, which was positively correlated to island size. In contrast, at the local scale, SI showed a wider niche breadth which appears to be due to a release from competition.