In a review article just published in the Proceedings of the Royal Society B, Gabriel Jamie, a PhD student in the Department of Zoology, examines the logic by which mimicry in nature can be conceptually organised and analysed.
While many examples of mimicry represent textbook examples of natural selection’s power to produce stunning adaptations, Jamie argues that “there remains a lack of clarity over how mimetic resemblances are related to each other. The result is that categories denoting the traditional subdivisions of mimicry are applied inconsistently across studies, hindering attempts at conceptual unification”.
Jamie lays out a framework by which to categorise and compare examples of mimicry across sensory modalities and taxonomic groups, drawing attention to the commonalities and differences in the processes underpinning the evolution of mimicry. The framework highlights the following key distinctions: i) Are the model’s traits being mimicked signals or cues? (ii) Does the mimic signal a fitness benefit or fitness cost in order to manipulate the receiver’s behaviour? (iii) Is the mimic’s signal deceptive?
The first distinction divides mimicry into two broad categories: ‘signal mimicry’ and ‘cue mimicry’. Jamie shows that ‘signal mimicry’ occurs when mimic and model share the same receiver, and ‘cue mimicry’ when mimic and model have different receivers or when there is no receiver for the model’s trait, illustrating this distinction with empirical studies.
The second and third distinctions divide both signal and cue mimicry into four types each. These are the three traditional mimicry categories (aggressive, Batesian and Müllerian) and a fourth, often overlooked category for which the term ‘rewarding mimicry’ is suggested. Rewarding mimicry occurs when the mimic’s signal is non-deceptive (as in Müllerian mimicry) but where the mimic signals a fitness benefit to the receiver (as in aggressive mimicry). The existence of rewarding mimicry is a logical extension of the criteria used to differentiate the three well-recognized forms of mimicry. The best examples of rewarding mimicry come from flowering plants in which groups of nectar-producing species evolve similar flowers to more effectively signal their rewarding nature to pollinators.
As an example of the framework’s application, the image above shows the mimetic egg of a brood-parasitic cuckoo finch (right) alongside the egg of the host species it is mimicking (a tawny-flanked prinia). This constitutes “aggressive signal mimicry”. It is “signal mimicry” because mimic and model share the same receiver (the host parent) and the mimic is therefore copying signals rather than cues of its model. It is aggressive mimicry because the mimic is deceptively signaling a fitness benefit to manipulate receiver behaviour.
Importantly, these forms of mimicry are not discrete, immutable types, but rather help to define important axes along which mimicry can vary. Jamie outlines processes by which these various forms of mimicry can transition from one to another.
Signals, cues and the nature of mimicry, in Proceedings of the Royal Society B.