Self-fertilization is likely in plants with hermaphrodite flowers like Rosmarinus officinalis that simultaneously expose many flowers to pollinators. However, despite favoring high levels of self-fertilization and mating among relatives, this species holds very high levels of genetic diversity within populations. To understand how this species maintain such high levels of genetic variation, we performed pollination experiments and observation in wild populations living at the extremes of its altitudinal range along two reproductive seasons. Seeds from cross-pollination experiments germinated four times more than those from self-pollination, largely as the consequence of reduced seed viability. Wild populations consistently showed low seed germination and high allogamy rates during the two seasons. Germination rates were positively influenced mostly by flowering synchrony, the number of days that plants flowered and plant density within populations, but their relative importance depended on the altitude and the reproductive season. Allogamy was positively related to the ratio of male-sterile flowers of individuals but was negatively related to the number of simultaneously open flowers. Seedlings of wild rosemary plants are mostly outcrossed because plants purge most of the inbreeding produced by self-fertilization prior to germination. Male sterility, length of the flowering season and flowering synchrony within populations all favor allogamy and high seed viability. However, they cannot be considered as adaptations to reduce self-fertilization because they varied with local environmental conditions. This plasticity combined with high levels of gene flow among populations contribute to maintain the high levels of genetic variation in populations.

Trabajo presentado en la XIV MEDECOS (Mediterranean Ecological Society) & XII AEET Meeting (Asociación Española de Ecología Terrestre). Human driven scenarios for evolutionary and ecological changes, celebrado en Sevilla (España) del 31 de enero al 4 de febrero de 2017

Peer reviewed