Behaviour of pollinator insects within inflorescences of Scrophularia species from Iberian Peninsula

Abstract

Several hypotheses have been proposed to explain the pattern of pollinator visits to vertical inflorescences. These range from a response to a pattern of resources to merely instinctive behaviour. In dichogamous plants, such behaviour has been associated with promoting outcrossing and avoiding geitonogamy. We here analyse behaviour of the principal pollinator groups in five protogynous species of Scrophularia with different flower sizes (S. sambucifolia, S. grandiflora, S. lyrata, S. scorodonia and S. canina), and the distribution of sexual phases along the inflorescences. The results in all cases show that pollinators follow a pattern of ascending visits accompanied by movements between flowers of the same whorl (horizontal movements). The relative frequency of these horizontal movements depends on the flower size, with a higher frequency in species with large flowers. In vertical movements of the three more common pollinator groups to several plant species (bumblebees, wasps and small bees), the behaviour was essentially independent of flower size, with bumblebees having the highest ratio of ascents to descents. Behaviour of the pollinators, together with the absence of a definite pattern of distribution of the sexual phases along the inflorescence, implies that geitonogamy is not avoided in any of the Scrophularia species studied.

Strategies of the honeybee Apis mellifera during visual search for vertical targets presented at various heights: a role for spatial attention?

“…However, when bees are foraging in a meadow with flowers at various heights, flowers can also appear in the upper part of the visual field and information received from the dorsal part of the eyes become important. For example, bees which visit raceme inflorescences tend to begin collecting nectar at the bottom of the inflorescence and ascend vertically step by step ( Fisogni et al , 2011; Ishii et al , 2008; Pyke, 1978; Valtueña et al , 2013; Waddington & Heinrich, 1979). In this situation the flowers below the just probed ones, which are perceived by the ventral visual field, typically contain no nectar, because the bee had just visited them ( Heinrich, 1975; Ishii et al , 2008).…”

Change of Floral Orientation within an Inflorescence Affects Pollinator Behavior and Pollination Efficiency in a Bee-Pollinated Plant, Corydalis sheareri

“…The inflorescences with horizontal flowers are thought to receive more visits due to enhanced recognition. Secondly, consistency of pollinator movement on inflorescences: bees have a tendency to move upwards in vertical inflorescences [4], [19]–[22], and a horizontal orientation is thought to ensure consistency of pollinator movements on inflorescences [12]. Finally, pollination precision: A horizontal orientation may function to control the access of landing sites and ensure the contact between floral reproductive organ and pollinator body [17].…”

Evolution of the staminode in a representative sample of Scrophularia and its role as nectar safeguard in three widespread species

“…1b) have mediumsized corollas (6.5-10 mm). It preferentially lives in (Schremmer 1959;Valtueña et al 2013;Rodríguez-Riaño et al 2014). We studied two Spanish populations for each species during 2012 and 2013 (Table 2).…”

“…The bicarpellary gynoecium consists of a long style with a stigma that typically matures before the androecium, and, after pollination, it curves over the central lobe of the corolla lower lip, at the time when the stamens begin to unfold (Ortega-Olivencia and Devesa 1993a). The main pollinators are wasps (Sprengel 1793;Müller 1883;Shaw 1962;Faegri and van der Pijl 1979), honeybees, bumblebees, and/or hoverflies in some species (Schremmer 1959;de Vos 1983;Ortega-Olivencia and Devesa 1993b;Ortega-Olivencia et al 2012;Valtueña et al 2013), whereas other species have a mixed pollination system involving insects and vertebrates (passerine birds and lizards, Ortega-Olivencia et al 2012). Scrophularia macrantha, endemic to New Mexico (USA), possesses an ornithophily syndrome (Shaw 1962;Grant 1994).…”