Müllerian and Batesian mimicry out, Darwinian and Wallacian mimicry in, for rewarding/rewardless flowers

ABSTRACT

Müllerian and Batesian mimicry were originally defined in defensive (anti-predetory) animal systems. Later these terms were adopted by botanists studying pollination that defined rewarding flowers as Müllerian mimics and rewardless flowers as Batesian mimics. The use of these terms concerning pollination predated our recent understanding of how common plant aposematism is and the related defensive Müllerian and Batesian mimicry types. Being non-defensive, using the terms Müllerian and Batesian mimicry for rewarding/rewardless flowers is, however, confusing if not misleading, and is also logically inappropriate. I suggest to first stop using the terms Batesian and Müllerian mimicry concerning rewarding/rewardless flowers and pollination, and second, to define the guild of flowers that reward pollinatiors as Darwinian mimics and those that do not reward pollinators as Wallacian mimics.

Müllerian and Batesian mimicry belong to the biological phenomenon known as aposematism. Aposematic (warning) signaling is a common defensive phenomenon in which poisonous, dangerous or otherwise unpalatable or unprofitable organisms advertise these qualities to other organisms, usually to animals, as defense from predation.^1–3 Aposematic signalling may be conveyed visually by color, movement and morphology, chemically by odor and taste, and even by sound; all these are from a lower trophic level to a higher one.³ The evolution of aposematic signaling is based on the ability of target enemies to associate the visual, chemical or acoustic signal with risk, damage, or non-profitable handling, and later to avoid such organisms as prey.^2,3 In certain cases there is even an innate tendency to avoid potential food objects with certain colors or color patterns.^3–5

Like in animals, aposematic coloration in plants is commonly yellow, orange, red, brown, black, white, or combinations of these colors. Aposematic coloration is expressed by many thorny, spiny, prickly and poisonous plants, and in plants unpalatable or of low nutritive value for various other reasons, as well as by plants that are unsuitable habitats for small herbivores because of their color or texture.^6–8 Many types of plant aposematic coloration may simultaneously serve other functions, such as physiological, communicative and even other defensive functions.⁸ It is therefore difficult in many cases to evaluate the relative functional share of visual and chemical aposematism in various plant color or odor patterns versus the relative share of other functions of these characters. Moreover, the specific selective agents that were involved in the evolution of plant aposematism are usually unknown.⁸

The common defense achieved by aposematic signaling has resulted in the evolution of many mimicking animals.^3,9,10 The mimics usually belong to one out of two general categories, Müllerian mimicry and Batesian mimicry. Müllerian mimicry is a phenomenon in which two or more species with effective defenses share a similar appearance or signaling, and by this sharing reduce the cost of associative learning, and even promote the evolution of refraining from attack by their enemies.^3,9–11 Batesian mimicry is a phenomenon in which members of a palatable species or a group of such species, gain protection from predation by resembling or mimicking the defensive signaling of an unpalatable or defended species or of a group of defended species.^{2,3,9,10,12,13} However, there are intermediate situations known as quasi-Batesian mimicry, i.e., defended and signaling species that differ in their strength of defense or signaling,¹⁴ and there are also various other less studied classes of mimicry.^9,15,16 An innovative and elegant attempt to overcome the problematic, complicated and not fully satisfying definitions of mimicry by defining them as “adaptive resemblance” ¹⁷ did not convince many and was not cited sufficiently to be used instead of the imperfect but commonly used term “mimicry”.

The evolution of mimicry requires a model or models, a mimic, and a predator/herbivore or predators/herbivores (an operator) that select for the mimicking phenotype. The model should be another species or a group of species, or their actions (e.g., release of chemicals or causing physical damage to other organisms)⁹ but the model can belong to the same species and in various cases of automimicry even parts of the same individual.^18,19 Organisms may also mimic a biological or non-biological substrate on which they grow as a camouflage against enemies or to hide from potential prey.^{2,3,9,10,20,21}

In plants there are additional, non-defensive recognized types of Müllerian and Batesian mimicry that may cause confusion. Accordingly, flowers that attract their pollinators with rewards are called Müllerian mimics and rewardless flowers are called Batesian.^22–24 Being non-defensive, I think that borrowing the terms Müllerian and Batesian mimicry for rewarding and rewardless flowers is inappropriate and has an inherited logical discrepancy, because defensive Müllerian and Batesian mimicry is aimed at repelling animals, and in pollination they are aimed at attracting them.⁸

I propose to stop using the terms Batesian and Müllerian mimicry concerning pollination, and to honor two other scientists and define the guild of flowers that reward pollinatiors as Darwinian mimics and those that do not reward pollinators as Wallacian mimics. The many contributions of Charles Darwin in the area of reproductive plant biology stand as a cornerstone for my suggestion.