Nectar Sugar Production across Floral Phases in the Gynodioecious Protandrous Plant Geranium sylvaticum

Abstract

Many zoophilous plants attract their pollinators by offering nectar as a reward. In gynodioecious plants (i.e. populations are composed of female and hermaphrodite individuals) nectar production has been repeatedly reported to be larger in hermaphrodite compared to female flowers even though nectar production across the different floral phases in dichogamous plants (i.e. plants with time separation of pollen dispersal and stigma receptivity) has rarely been examined. In this study, sugar production in nectar standing crop and secretion rate were investigated in Geranium sylvaticum, a gynodioecious plant species with protandry (i.e. with hermaphrodite flowers releasing their pollen before the stigma is receptive). We found that flowers from hermaphrodites produced more nectar than female flowers in terms of total nectar sugar content. In addition, differences in nectar production among floral phases were found in hermaphrodite flowers but not in female flowers. In hermaphrodite flowers, maximum sugar content coincided with pollen presentation and declined slightly towards the female phase, indicating nectar reabsorption, whereas in female flowers sugar content did not differ between the floral phases. These differences in floral reward are discussed in relation to visitation patterns by pollinators and seed production in this species.

Sexually-trimorphic interactions with colour polymorphism determine nectar quality in a herbaceous perennial

“…Our results confirm the previously reported patterns of sexual dimorphism in sugar production in gynodioecious plants, where female flowers have lower nectar quality than hermaphrodites514. Moreover, we show for the first time that intermediate flowers have different patterns of nectar sugar content from the other two genders, but patterns of production that are similar to hermaphrodites and not to females.…”

“…Full experimental details can be found in5. Briefly, during summer 2008, we measured sugar quantity (referred as sugar content hereafter) in nectar samples randomly collected from 103 female, 157 intermediate and 313 hermaphrodite flowers ( N  = 573) within a wild population growing at Oulu University Botanical Gardens, Finland (65°03’N, 25°27’E).…”

“…1). We noted the floral stage for each flower (see5). Air temperature and humidity at the time of the samplings were obtained from the Finnish Meteorological Institute (http://en.ilmatieteenlaitos.fi).…”

“…At the same time, there are several secondary extrinsic and intrinsic factors that drive nectar quality. Some well-known ones include abiotic factors such as humidity3 and temperature4, as well as floral specific ones such as sexual phase of flowers5 or flower age4. However, the innumerable sources of variation may mask potentially key patterns of variation within populations.…”

Mesurer la sécrétion nectarifère : exemple d'une lignée hybride F1 et de son parent mâle stérile chez le colza d'hiver (Brassica napusL.)

“…4.4.1 Âge de la fleur et pollinisation D'autres facteurs sont encore à prendre en compte pour expliquer la variabilité de la sécrétion nectarifère, avec en premier lieu l'âge de la fleur, la sécrétion se réalisant en continu jusqu'au moment de sa sénescence où le nectar est peu à peu réabsorbé (Nepi et Stpiczyńska, 2008). C'est un facteur particulièrement important pour les espèces protogynes ou protandres, comme le tournesol ou la carotte, où la sécrétion peut varier selon la phase sexuelle qui évolue avec l'âge (Langenberger et Davis, 2002 ;Wist et Davis, 2006, 2008Varga et al, 2013). Il faut également tenir compte de l'effet de la pollinisation, qui peut déclencher précocement le processus de sénescence de la fleur et du coup interrompre la sécrétion (Stead, 1992 ;van Doorn, 1997 ;Rogers, 2006 Thom et al (2016).…”