Pollination ecology and breeding system of Ecbolium Ligustrinum (Acanthaceae): a transition from autogamy to xenogamy through specialised plant-pollinator interactions

Abstract

In view of the ongoing rarity of Ecbolium ligustrinum there is an urgent need for conservation of the species. For this, a detailed work was carried out regarding the untold story of its reproductive ecology. The work was done for three consecutive years (2015–2017) at Midnapore, West Bengal over three different populations collected from three different areas of West Bengal. Field data were also recorded from these three wild populations. The species produces gullet flowers with bi-labiate corolla having long slender tubes. The flowers exhibit one day of longevity. The flowers are visited by 10 species of insects. Among those, four species viz. Eristalis tenax, a Dipteran member and three ant species of Hymenoptera such as Camponotus sp., Formica sp. and Monomorium sp. are the effective pollinators. As per pollination efficiency, Eristalis tenax (PE i = 0.76) is the most successful one. The flowers are shortly protandrous (dichogamous) and passed by three distinct reproductive (male, bisexual and female) phases. The breeding system clearly depicts that the species is facultatively xenogamous supported by myophilous mode of pollination. However, geitonogamous type of pollination is also observed through myrmecophily, an atypical instance found in plants. Lastly, the plant retained some sort of autogamy through ‘fail-safe’ mechanism of pollination, an adaptation which might be developed in absence of pollinators. Therefore, undoubtedly it can be concluded that E. ligustrinum is a partially self-incompatible (ISI = 0.27) species having a mixed mating system, adapted for xenogamy through specialised mode of plant-pollinator interactions.