Flux de pollen chez Astragalus tragacantha (Fabaceae) et réseaux d’interactions de pollinisation pour la conservation de ses populations au sein du Parc National des Calanques.

Abstract

The increase of habitat fragmentation impacts plant-pollinator interactions and threatens the sustainability of plant species. Astragalus tragacantha (Fabaceae), is a rare endangered plant endemic to the Mediterranean coastal habitats mainly located in the Calanques National Park (CNP, Marseille, France). Its fragmented populations present important regressive demographic dynamics. Using controlled pollination treatments, observations and captures of pollinators within six populations, we studied (1) the self- versus cross-reproduction, and within- versus between-populations crossings, (2) the presence of inbreeding and/or outbreeding depressions, and (3) the role of pollinators on the reproductive performance of A. tragacantha. Here we showed a dependence of this plant to pollinators for its reproduction and no pollen limitation. We showed a clear difference in pollinator guilds among populations and some populations presented a predominance of a single species (Bombus terrestris, Anthophora plumipes and Eucera caspica). These species are suspected to be especially efficient in the pollination of A. tragacantha because the populations with their predominance presented a good reproduction performance. Moreover, there was better reproductive success of A. tragacantha for within-population crossings than between-population crossings. Indeed, the population with the higher reproductive success seems to favor autogamy. However, this population presents evidences of inbreeding depression. So autogamy strategy seems to be not viable to a medium-term. To make A. tragacantha reproductive success viable in a longer-term, pollinators which realize preferentially cross-pollination within populations (like Anthophora and Eucera genus) have to be favored. Results from these studies were discussed in light of A. tragacantha populations’ restoration in the LIFE project context. Particularly, the conservation of A. tragacantha has to take into account the protection of its pollinator’s network integrity, including both A. tragacantha, wild pollinators, and Mediterranean coastal habitat conservation