Night life on the beach

Evolution of autonomous selfing may be advantageous because it allows for reproductive assurance. Buide et al. analyse sympatric populations of Silene niceensis and S. ramosissima, two closely related species that overlap in space and time and which have the same night-pollinator syndrome. They find high levels of autonomous selfing in S. ramosissima, which shows low levels of pollinator visitation, whereas S. niceensis has low levels of autonomous selfing and is visited by moths, hawkmoths and syrphids. These finding suggest that the different strategies are important for avoiding pollinator competition and interspecific pollen flow, allowing both species to co-flower in the restricted dune habitat in which they exist.

Buide, M.L., del Valle, J.C., Pissatto, M., & Narbona, E. (2015) Night life on the beach: selfing to avoid pollinator competition between two sympatric Silene species. Annals of Botany, 116(2), 201-211
Evolution of autonomous selfing may be advantageous because it allows for reproductive assurance. In co-flowering plants competing for pollinators, the least common and/or attractive could suffer pollen limitations. Silene niceensis and S. ramosissima are taxonomically related species sharing the same habitat, although S. ramosissima is less abundant and has a more restricted distribution. They also have the same a priori nocturnal pollinator syndrome, and show an overlapping flowering phenology. The aim of this study was to investigate whether a selfing strategy in S. ramosissima allows it to avoid pollinator competition and/or interspecific pollen transfer with S. niceensis, which would thus enable both species to reach high levels of fruit and seed set.
The breeding system, petal colour, flower life span and degree of overlap between male and female phases, floral visitor abundance and visitation rates were analysed in two sympatric populations of S. niceensis and S. ramosissima in southern Spain.
Autonomous selfing in S. ramosissima produced very high fruit and seed set, which was also similar to open-pollinated plants. S. niceensis showed minimum levels of autonomous selfing, and pollen/ovule ratios were within the range expected for the breeding system. In contrast to S. niceensis, flower life span was much shorter in S. ramosissima, and male and female organs completely overlapped in space and time. Upper surface petals of both species showed differing brightness, chroma and hue. Flowers of S. niceensis were actively visited by moths, hawkmoths and syrphids, whereas those of S. ramosissima were almost never visited.
The findings show that different breeding strategies exist between the sympatric co-flowering S. niceensis and S. ramosissima, the former specializing in crepuscular–nocturnal pollination and the latter mainly based on autonomous selfing. These two strategies allow both species to share the restricted dune habitat in which they exist, with a high female reproductive success due to the absence of pollinator competition and/or interspecific pollen flow.