Floral biology, pollinator guilds, and male fitness of Aconitum spicatum (Bruhl) stapf in central Nepal

Abstract

Floral biology includes several studies on reproductive and pollination biology, such as biology of various floral parts, floral rewards (nectar and pollen), and pollination by various pollen vectors. Plant-pollinator interactions are greatly influenced by floral traits, which also determine the group of specific floral visitors of a particular plant. This study aims to document different floral traits as well as their potential floral visitors and male fitness of Aconitum spicatum (Brühl) Stapf. Flower (bud and mature flower) samples were collected from 3043-4197m altitude while pollinator samples were collected from 3315-4265m altitude along the Annapurna trekking route of Annapurna Conservation Area, Kaski, Central Nepal. Floral traits like tepals length, anther number, anther and stamen length, pollen and ovule number were measured in the laboratory under microscope and few floral traits were measured in the field. The result showed that all floral traits varied significantly among the populations except for the pollen-ovule ratio. The variation in floral traits of A. spicatum among different populations might be due to pollinator mediated selection. It was observed that, the bumblebee (Bombus miniatus) actively visited flower of A. spicatum during day time among all population while nocturnal visitors were not observed. B. miniatus actively visited the flower after 9 a.m. till 6 p.m. and total 1916 visits were recorded within three days for total 23 hours at an elevation of 3901m while only 5 visits were recorded at an elevation of 4265m for 2 hours of observation period when weather was extremely cold. The visitation rates vary across the different timing of the day and also among the various days. The visitation rate of B. miniatus was maximum when the weather was clear and sunny and least visitation rate was recorded during cloudy and windy weather. The male fitness of A. spicatum was found to be 14.08% and very high male fitness of A. spicatum linked with B. miniatus; the bumblebee transports 2416.65±652.85 pollen grains out of total 17169±1125 (mean ± SE) pollen grains of A. spicatum during a single foraging bout. These facts thus indicate that B. miniatus could be the prime pollinator of A. spicatum. Keywords: Floral traits, potential floral visitors, Annapurna trekking route, medicinal plant