Anther Evolution: Pollen Presentation Strategies When Pollinators Differ

Abstract

Male-male competition in plants is thought to exert selection on flower morphology and on the temporal presentation of pollen. Theory suggests that a plant's pollen dosing strategy should evolve to match the abundance and pollen transfer efficiency of its pollinators. Simultaneous pollen presentation should be favored when pollinators are infrequent or efficient at delivering the pollen they remove, whereas gradual dosing should optimize delivery by frequent and wasteful pollinators. Among Penstemon and Keckiella species, anthers vary in ways that affect pollen release, and the morphology of dried anthers reliably indicates how they dispense pollen. In these genera, hummingbird pollination has evolved repeatedly from hymenopteran pollination. Pollen production does not change with evolutionary shifts between pollinators. We show that after we control for phylogeny, hymenopteran-adapted species present their pollen more gradually than hummingbird-adapted relatives. In a species pair that seemed to defy the pattern, the rhythm of anther maturation produced an equivalent dosing effect. These results accord with previous findings that hummingbirds can be more efficient than bees at delivering pollen.

Sequential stamen maturation and movement in a protandrous herb: mechanisms increasing pollination efficiency and reducing sexual interference

“…Pollen presentation theory suggests that selection to maintain staggered pollen presentation should be high in cases involving pollinators that are abundant and inefficient at pollen transfer (Thomson 2003; Castellanos et al 2006; Li et al 2014). In our study, halictid bees were both frequent and relatively inefficient pollinators compared with honey bees, as they made 60 % of the total visits and subsequently deposited only 0.36 % of the removed pollen onto a stigma.…”

“…Pollen presentation theory (PPT) suggests that plants with frequent and inefficient pollinators tend to present pollen gradually in doses, whereas simultaneous pollen presentation should be preferred when plants are pollinated by infrequent but efficient visitors (Harder and Thomson 1989; Harder and Wilson 1994; Li et al 2014). Through either pollen packaging or dispensing mechanisms, plants can vary their pollen presentation schedules using various floral strategies, such as staggering the opening of anthers, flowers, or inflorescences or opening them simultaneously (Thomson and Barrett 1981; Harder and Wilson 1994; Castellanos et al 2006). …”

Is There ‘Anther-Anther Interference’ within a Flower? Evidences from One-by-One Stamen Movement in an Insect-Pollinated Plant

“…Despite having several stamens, pollen loss during the pollination process is very high, with less than 1% of the pollen removed reaching conspecific stigmas [6], [7]. Because of this significant waste, many flowers have evolved to present their pollen separately rather than all at once, to maximize the amount of pollen donated to stigmas [7], [8], [9]. Staggered dehiscence of anthers in the same flower is one of the most widespread mechanisms to present pollen sequentially to pollinators, which is known as one type of pollen ‘packaging’ and ‘dispensing’ mechanisms [8], [9], [10].…”

“…Because of this significant waste, many flowers have evolved to present their pollen separately rather than all at once, to maximize the amount of pollen donated to stigmas [7], [8], [9]. Staggered dehiscence of anthers in the same flower is one of the most widespread mechanisms to present pollen sequentially to pollinators, which is known as one type of pollen ‘packaging’ and ‘dispensing’ mechanisms [8], [9], [10]. However, the advantage of such separated dehiscence of anthers may be accompanied with a cost.…”

Floral biology of Senecio macrophyllus M. BIEB. (Asteraceae), a rare Central European steppe plant

“…Another visual attractant for insect visitors to S. macrophyllus is the changeable color of anthers in disc florets, which acts as an indicator of flower reward availability. The visual signaling of flower reward shortage is widespread and the mechanism could involve different parts of flowers [28,47]. The anthers of different Asteraceae taxa are known to change color after pollen presentation [26,29].…”