Abstract

Many plants can produce seeds via multiple reproductive modes, such as selfing and outcrossing. Having multiple reproductive modes can be advantageous if it assures seed production when outcrossing fails, which is important for species inhabiting environments where pollinators are scarce or variable. However, it can also be disadvantageous due to the fitness costs associated to selfing. Consequently, plants have mechanisms to reduce the incidence of selfing. Here we examined the breeding system of Myrcianthes coquimbensis; this threatened Atacama Desert shrub is the last species to bloom in the community and exhibits low visitation rates per flower because pollinators are less abundant. Our aim was to determine whether this plant can produce fruits by modes other than outcrossing, and whether it possesses floral traits to prevent sexual interference. We conducted experimental flower treatments in two localities to determine whether fruits were produced by outcrossing, selfing, autonomous selfing and agamospermy. We also evaluated stigma receptivity and pollen viability during a flower's lifespan. M. coquimbensis developed fruits and seeds by all the reproductive modes assessed, including selfing and agamospermy. Flowers presented partial segregation of sexual functions, with the peak of pollen viability occurring before the peak of stigma receptivity. Selfing is unavoidable in M. coquimbensis and likely interferes with outcrossing. Coupled with possible early inbreeding depression, it probably results in a cost for seed production. Our results suggest that this species may be vulnerable in scenarios where pollinators are scarce; however, agamospermy may provide an alternative route of seed production in these scenarios.