Heteromorphic stamen: a strategy in nectarless entomophilous plants to increase pollination efficiency? An investigation
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ORIGINAL ARTICLE
Heteromorphic stamen: a strategy in nectarless entomophilous plants to increase pollination efficiency? An investigation with regard to three species of Commelinaceae Viswanathan Veena1 · Santhosh Nampy1 Received: 24 January 2020 / Accepted: 31 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Entomophilous plants produce flowers with bright colours, patterns, and rewards like nectar, pollen, etc. for self-advertising. Many such plants only have pollen as a reward, so they deceive pollinators by appearing to offer more reward than is actually present. This is accomplished by hairy filaments, broad anther connectives, variously modified staminodes, etc. More than 20 angiosperm families have heteromorphic stamens, the significance of which has not been adequately studied. Their role with regard to Commelina diffusa, Dictyospermum montanum and Rhopalephora scaberrima of Commelinaceae is investigated here. These plants, apart from being nectarless, produce short-lived flowers and are an excellent system for studying the relevance of morphological adaptations in reproductive success. It has been suggested that the dimorphic anthers address the conflict of using pollen, the carriers of male gametes, as a reward to lure pollinators, thereby reducing the available gametes for fertilization. This is accomplished by functionally separating the anthers for ‘feeding’ and ‘pollinating’ purposes. Our study showed that while the feeding anthers infatuate the insects and are manipulated by them, the pollinating anthers succeed in maximizing pollen exports by using specific un-groomed ‘safe sites’ on the body of the insect to solve the conflict by using pollen as a reward. Keywords Division of labour · Heteranthery · Nectarless · Reciprocal enantiostyly · Reward · Safe sites
Introduction Entomophilous plants depend entirely or partly on the aid of insects to proliferate, by establishing either a mutual or deceptive relationship with them. The extent of their reproductive success is thus dependent upon how well they manage to attract these pollinators to visit their flowers. Plants are well known to accomplish this task by offering a variety of rewards such as pollen, nectar (Simpson and Neff 1981), and fatty oils (Buchmann 1987). Although nectar is regarded as the primary reward sought by most pollinators (Woodcock et al. 2014; Simpson and Neff 1981), many entomophilous Handling Editor: Louis P. Ronse De Craene. * Santhosh Nampy [email protected] Viswanathan Veena [email protected] 1
Department of Botany, University of Calicut, Malappuram District, Kerala 673635, India
plants lack nectar (members of Pontederiaceae, Solanaceae, Commelinaceae, etc.), which places them at a disadvantage in the competition for pollinators. Such plants have known to evolve floral adaptations, which help them in attracting pollinators (Dafni 1984; Peter and Johnson 2008). The Commelinaceae family consisting of about 41 genera and 734 species (Govaerts and Faden 2015) is a typical example
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