Pollination ecology of the rare desert species Eremosparton songoricum (Fabaceae)

Abstract

The pollination ecology of Eremosparton songoricum (Litv.) Vass., a rare desert species endemic to central Asia, was examined by a series of observational studies and manipulative experiments in two natural populations during 2007–2008. Results showed that the duration of flowering lasted 21 and 23 days, respectively, in Populations A and B from late May to late June in 2008. Anthesis of a single flower often lasted for 3 days. However, if pollinators were excluded, both the anthesis and stigma receptivity lasted 2 days longer. Mating-system experiment showed that E. songoricum was self-compatible and pollination success relied on pollinators. Fruit set after bagging without emasculation was 0.02 ± 0.01%. This suggested that spontaneous autogamy rarely happened. E. songoricum primarily relies on a combination of large floral display, secretion of nectar and a yellow ‘nectar guide’ on the standard to further attract pollinators, which may be the result of adaptation to a habitat with unreliable access to pollinators. A single flower produced ~0.18 μL and 0.50 μL of nectar during 2 days in Populations A and B, respectively. The peak secretion occurred at 1300–1500 hours, which overlapped with the climax of visitation of the effective pollinators at 1300–1400 hours. There were four effective pollinators in both populations, namely Colletes popovi Nosk., Megachile terminate Morawitz, Coelioxys sp. and Bembix planifrons F.Mor. The most frequent one, Colletes popovi Nosk., was observed pollinating many flowers of the same individual plant (65.8 ± 1.1%) in Population A, suggesting that geitonogamous self-pollination is unavoidable. Inbreeding depression played a role during the period from fertilisation to fruit maturation.