Speciation, pattern recognition and the maximization of pollination: general questions and answers given by the reproductive biology of the orchid genus Ophrys

Abstract

Pollination syndromes evolved under the reciprocal selection of pollinators and plants (coevolution). Here, the two main methods are reviewed which are applied to prove such selection. (i) The indirect method is a cross-lineage approach using phylogenetical trees to understand the phylogeny. Thus, features of single origin can be distinguished from those with multiple origins. Nearly all pollination modes originate in multiple evolutionary ways. (ii) The most frequent pollinators cause the strongest selection because they are responsible for the plant’s most successful reproduction. The European sexually deceptive orchid genus Ophrys provides an example of a more direct way to prove selection because the attraction of a pollinator is species specific. Most members of the genus have remarkably variable flowers. The variability of the signals given off by the flowers enables the deceived pollinator males to learn individual flower patterns. They thus avoid already visited Ophrys flowers, interpreting them as females rejecting them. As the males will not return to these individually recognizable flowers, the pollinators´ learning behavior causes cross-pollination and prevents the orchid’s self-pollination.

Why Variation in Flower Color May Help Reproductive Success in the Endangered Australian Orchid Caladenia fulva

“…Such signal variability has previously been shown to promote fitness benefits for orchids with non-rewarding flowers ( Wong and Schiestl, 2002 ; Wong et al, 2004 ; Gaskett, 2011 ; Dyer et al, 2019 ; Jiménez-López et al, 2020 ). For example, sexually deceptive orchid Ophrys species display different spatial patterns in conspecific flowers ( Stejskal et al, 2015 ; Paulus, 2019 ). This avoids pollinators habituating to non-rewarding signals and so increases the probability of multiple flower visits by an individual pollinator ( Schiestl, 2005 ; Jersáková et al, 2006 ; Delle-Vedove et al, 2017 ; Dyer et al, 2019 ).…”

“…Field experiments suggest that bees prefer visiting similar but discriminable flowers rather than distinctly different colors, a perceptual magnet-type effect that may benefit rarer colored flowers in non-rewarding flower species ( Peter and Johnson, 2008 ; Dyer and Murphy, 2009 ). Thus species with non-rewarding flowers appear to benefit from having dissimilar colors ( Gaskett, 2011 ; Rakosy et al, 2012 ) and scents ( Delle-Vedove et al, 2017 ) that potentially confuse the decision-making of pollinators and encourage outcrossing in the orchid ( Streinzer et al, 2010 ; Paulus, 2019 ). Our observations from C. fulva using several lines of inquiry are consistent with this model, and explain the presence of the color variations previously reported for human observers.…”

The Size of it: Scant Evidence That Flower Size Variation Affects Deception in Intersexual Floral Mimicry

“…Signal detection theory predicts that receivers perceive signals as more similar when the signal distribution is broader, which can be a result of phenotypic variation among models and mimics (Figure 1; Lynn et al, 2005). Thus variation in model and mimic appearance should promote generalization (Amézquita et al, 2013;Gamberale-Stille et al, 2018;Arias et al, 2020), making it more difficult for bees to learn to avoid mimics (e.g., Gaskett, 2012;Paulus, 2019). We were therefore surprised that when we manipulated variation in model and mimic phenotype in an intersexual floral mimicry system, we found only modest evidence that bumble bees generalized learned responses among model and mimic flowers.…”

Interaction between Cymbidium aloifolium and Apis cerana: Incidence of an outlier in modular pollination network of oil flowers

“…The enormous variability and rate of speciation known among orchids are strongly attributed to their interaction with pollinators (Kiester et al, 1984; Paulus, 2019). However, information on the mechanistic basis for how such interactions are established among orchids is either limited or yet to be demonstrated.…”