Flower trade-offs derived from nectar investment in female reproduction of two Nicotiana species (Solanaceae)

Abstract

Animal-pollinated flowers may orient resources for competing activities, such as nectar production for attracting flower visitors but then saving nectar (through inhibiting nectar production or by final resorption) for the subsequent maturation of fruits and seeds. Nectar production is continuous in Nicotiana longiflora and N. alata after flower opening, but early nectar removal reduces total secreted nectar. Resource trade-off between nectar investment and seed production were experimentally assessed in manually pollinated flowers experiencing different numbers of repeated nectar removals, while controlling for maternal effects. We expected that flowers with less nectar secretion produce larger seed sets. The results showed that for both species the earlier the nectar removal during flower anthesis, the lower the total nectar secreted and the higher the mass of seeds produced. This general pattern was clearer for N. longiflora. The link between decreased nectar production and the subsequent increase in the seed set implies that resources are limited. Consequently, nectar savings during the pollination process through early nectar removal by pollinators can be interpreted as a trade-off between resources secreted by flowers for pollinator attraction and those utilized during fruit and seed maturation.

Floral nectar production: what cost to a plant?

“…Four additional studies (Ordano & Ornelas, 2005; Ornelas et al ., 2007; Dutton et al ., 2016; Galetto et al ., 2018) included direct experimental tests of possible nectar costs, but yielded equivocal results. In these studies, nectar was repeatedly removed from one group of flowers and sampled just once from a second group of flowers, while flowers from both groups were artificially pollinated.…”

Features of floral odor and nectar in the distylous Luculia pinceana (Rubiaceae) promote compatible pollination by hawkmoths

“…As another important floral attraction signal, nectar is derived from the phloem and is crucial for most pollinators, its sugars being simple to metabolize and thus to use as a readily available fuel for an animal's activities (de La Barrera & Nobel, 2004 ; Nicolson et al, 2007 ). Nectar properties, including nectar volume, sugar concentration, and sugar composition (Leiss & Klinkhamer, 2005 ; Mitchell, 2004 ), are subjected to pollinator‐mediated selection (Baker, 1975 ; Galetto et al, 2018 ; Potascheff et al, 2020 ; Vandelook et al, 2019 ). There was no significant difference in total sugar concentration between L‐ and S‐morphs of Fagopyrum esculentum , while the S‐morph secreted higher volumes of nectar than the L‐morph (Cawoy et al, 2008 ).…”

Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration

“…Increased reward quality or quantity can result in longer pollinator visits or in a higher likelihood that a pollinator will visit another flower of the same species in the near future, potentially increasing the flower's fitness by increasing the chances of pollination and reproduction (Faegri & Van Der Pijl 1979;Pappers et al 1999;Stout & Goulson 2002). Producing an enhanced reward can be expensive (Pleasants & Chaplin 1983;Southwick 1984;Pyke 1991;Ordano & Ornelas 2005;Ornelas & Lara 2009;Galetto et al 2018) and standing crop of nectar is subjected to degradation by microbes (Herrera et al 2008;Vannette et al, 2013) as well as to robbery (Irwin et al 2010), including silent robbers like ants (Galen 1999). Thus, a mechanism for timing the production of enhanced reward to a time when pollinators are likely to be present could be highly beneficial to the plant.…”