RESUMEN
Soil seedbanks are particularly important for the resiliency of species living in habitats threatened by climate change, such as alpine meadows. We investigated the germination rate and seedbank potential for the endemic species Dianthus pavonius, a carnation native to the Maritime Alps that is used as model system for disease in natural populations due to its frequent infections by a sterilizing anther-smut pathogen. We aimed to ascertain whether this species can create a persistent reserve of viable seeds in the soil which could impact coevolutionary dynamics. Over three years, we collected data from seeds sown in natural soil and analyzed their germination and viability. We found that D. pavonius seeds are not physiologically dormant and they are able to create a persistent soil seed bank that can store seeds in the soil for up to three years, but lower than the estimated plant lifespan. We conclude that while the seedbank may provide some demographic stability to the host population, its short duration is unlikely to strongly affect the host's ability to respond to selection from disease. Our findings have implications for the conservation of this alpine species and for understanding the evolutionary dynamics between the host and its pathogen.
RESUMEN
Comparative studies of seed germination of closely related taxa can help increase our understanding of the ecological limitations of cold-adapted plants and forecast how they might respond to global warming. No studies exist on the relationship between thermoclimatic belts that classify mountain life zones according to bioclimatic criteria and the germination strategy of alpine plants. The aim of this study was to assess this relationship using two closely related species growing in different thermotypes and to test whether their germination responses were related to the climate at natural sites. Fresh Rhaponticum bicknellii and R. scariosum seeds were cold stratified for 0, 30, 60 and 90 days and tested for germination at 10, 15 and 20 °C. At the same time, seed burial experiments were run in the field and in the plant nursery. A GLM analysis showed that the length of cold stratification affected significantly only the germination of R. bicknellii seeds, while increasing temperatures prompted germination in both species. We found that R. bicknellii adopts a drought-avoiding germination strategy, while R. scariosum germination is favoured by warm temperatures. Our findings support the general view that alpine plants do not share common germination requirements and that any conclusions should be interpreted from a biogeographical and bioclimatic perspective. Therefore, seed germination and seedling establishment of endemic alpine species can also be predicted by looking at the bioclimate of the species' range.
RESUMEN
In flowering plants, the evolution of females is widely hypothesized to be the first step in the evolutionary pathway to separate male and female sexes, or dioecy. Natural enemies have the potential to drive this evolution if they preferentially attack hermaphrodites over females. We studied sex-based differences in exposure to anther-smut (Microbotryum), a sterilizing pollinator-transmitted disease, in Dianthus pavonius, a gynodioecious perennial herb. We found that within a heavily diseased population, females consistently had lower levels of Microbotryum spore deposition relative to hermaphrodites and that this difference was driven by rapid floral closing in females following successful pollination. We further show that this protective closing behavior is frequency dependent; females close faster when they are rare. These results indicate that anther-smut disease is an important source of selection for females, especially since we found in a common garden experiment no evidence that females have any inherent fecundity advantages over hermaphrodites. Finally, we show that among populations, those where anther-smut is present have a significantly higher frequency of females than those where the disease is absent. Taken together our results indicate that anther-smut disease is likely an important biotic factor driving the evolution and maintenance of females in this gynodioecious species.