From cold mountains to warm coastal cliffs: insights for the future of a Primula species

Primula palinuri Petagna is the only species in the genus growing on maritime cliffs, the only from a Mediterranean habitat, and the most southerly in the whole Auricola section. It is an endemic species and has a small and severely fragmented geographical range confined to vertical cliffs of a narrow Tyrrhenian coastal area of southern Italy. Genetic and molecular analyses allowed to hypothesise its origin from an ancestor which moved from the western Alps by long-distance dispersal or, more likely, colonising the Apennines during a cold period of the Pleistocene (50,000 ± 40,000 yrs b.p.) (1).Given that P. palinuri might have endured all past changes, from mountain to coastal cliffs, from alpine to Mediterranean environment, we considered this species a suitable comparative study system to predict possible consequences of global warming also on other Primula species, now surviving in mountain habitats. Specific aim of our work on P. palinuri was to disclose any morphological and physiological traits adaptive to a warmer environment.Altogether, biological and ecological data suggested that local survival of this species relies on both phenotypic plasticity and selective pressure phenomena. P. palinuri is a fully distylous species with high reproductive success: each plant develops numerous viable seeds as a result of inter-morph pollination. Nevertheless, generation turnover is unlikely to occur because seedling establishment is rare (2). Plants of P.palinuri are long living due to the slow growth of rhizomes which accumulate water and starch. Most vegetative and reproductive stages occur in winter. Plants are summer deciduous: the large leaves, that develop from the beginning of autumn throughout the winter, have no anatomical traits of xeromorphy and dry up in summer (3). Reproductive features such as winter flowering, the presence of pendulous flowers avoiding rain damage and the best pollen performances at low temperatures, associate P. palinuri more to cold mountain habitats than to Mediterranean maritime cliffs. These features might be considered as evolving in a cooler past and persisting in the existing populations (4). At present, the remarkable longevity of the single flowers can be a result of the interactions with a) the environmental factors affecting flower biology and b) flower pollinators. More specifically, given that flower induction and gametophyte development are under control of low winter temperatures, within a scenario of global warming, phenotypic plasticity might bring forward flowering to provide the right temperature for reproductive functions. Moreover, since the species is dependent on insect pollination, selective pressure toward late (spring) flowering can avoid pollination limitation due pollinator inactivity at winter temperatures (4). P. palinuri has evolved no specific adaptations to Mediterranean environment. Under the pressure of a warming climate, it is unlikely that populations of P. palinuri will move towards northern latitudes and higher altitudes due to geographical limits. Phenotypic plasticity anticipating flowering and selective pressure by pollinators extending flowering could be possible strategies for local survival of this and its relative species now living in mountain habitats.