Abstract
Pollination of deceptive orchids has enabled scientists to understand how these species avoid inbreeding depression by reducing the number of pollinator visits per inflorescence. In rewarding species, which receive a higher rate of visits per plant, geitonogamy is usually higher and therefore the risk of inbreeding increases. In this study, we assess the breeding system of the rewarding orchid A. coriophora, and the spatio-temporal changes in its fitness as well as variation in nectar content after pollination. We found that the species partially selects allogamous pollen if pollinia from the same stalk and other plants arrive to the stigma. Furthermore, when self-pollination occurs, despite successful fructification, seed viability is significantly lower than that of cross-pollinated plants. A. coriophora exhibits spatio-temporal variation in fitness that does not correlate with any plant feature. Moreover, nectar volume is reduced after pollination, but the sugar concentration is maintained. This study emphasizes how essential the pre-zygotic and post-zygotic reproductive barriers are for rewarding orchids to avoid inbreeding depression.
Highlights
The strategies used by orchids to attract pollinators are a key factor in their fitness, and the selective forces that have driven their evolution are a key topic in evolutionary biology
We studied Anacamptis coriophora, one of the few nectar-rewarding orchid species native to the Balearic Islands, to better understand the evolutionary advantage of offering nectar as a reward to pollinators compared to other deceptive species that live in the same habitats
Distance of the pollen origin showed higher fruit set in control than in assisted treatments but no differences were detected between intra-population and inter-population cross-pollination (t = - 0.49, p = 0.626) neither among treatments for seed viability
Summary
The strategies used by orchids to attract pollinators are a key factor in their fitness, and the selective forces that have driven their evolution are a key topic in evolutionary biology. The mechanisms by which orchids attract pollinators have been studied for a long time due to the extraordinary evolutionary success of deception. Almost one-third of all orchids are reported to be deceptive (Tremblay et al 2005; Renner 2006), with food deception [e.g. a wide range of species of Orchis and Anacamptis genera; 2009; Wong et al 2017)], sexual deception [e.g. Ophrys species (Schiestl et al 2000)] or oviposition deception [e.g. Gastrodia species (Martos et al 2015)] the most common strategies. How deceptive strategies evolved in the light of natural selection has been an intriguing topic since Darwin (Darwin 1887)
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