The evolution of imperfect mimicry.

Abstract

This paper discusses the basic ideas of mimicry theory, and illustrates how they fail to account for the commonly imperfectly mimetic patterns of the main taxonomic group in the Holarctic that contains mimics, the hoverflies (Diptera, Syrphidae). New theories, i.e. multiple model theory [see Behavioral Ecology (2002) 13(6), 821-826], of imperfect mimicry that have been put forward largely to account for the evolution of the colour patterns are also discussed.

The Relationship between Morphological and Behavioral Mimicry in Hover Flies (Diptera: Syrphidae)

“…Our work also confirms, to human eyes at least, that bee mimics are among the highest fidelity mimics (Gilbert 2005). This close mimicry of bee mimics may well have arisen as a consequence of the models' lack of averseness which requires close similarity before a reasonable high degree of protection from predators is achieved (Sherratt 2002;Gilbert 2005).…”

“…Hymenopteran models clearly vary in appearance, but a simple reason for the absence of leg waving in bee mimics may be that many of the common bee models lack the long antennae of wasps, so there may be less value in portraying long antennae. In addition, many bees do not wag their wings in quite the same manner as wasps, and there is little evidence that birds find the sting of a bee a significant deterrent (Gilbert 2005). Collectively therefore, there may have been little additional selection pressure to adopt behavioral mimicry in this group of mimics, because their models do not exhibit sufficiently characteristic behaviors and/or because the behaviors themselves do not evoke aversive responses in observers.…”

“…Our approach employed a simple human ranking system which correlates well both with an avian assessment of hover fly mimetic similarity and a multidimensional measure of morphological similarity of hover flies to their hymenopteran models (Penney et al 2012). While humans and birds have different visual systems, there is no evidence of a widespread UV component to either wasp or hover fly mimetic patterns (Gilbert 2005), which may explain why quantifications of mimetic similarity by pigeons were broadly consistent when pigeons were presented with naturally lit specimens of hover flies (Green et al 1999) compared to their projected images (Dittrich et al 1993). …”

“…Nevertheless, it has been proposed repeatedly that poor mimics can use behavior to compensate for their ease of visual discriminability (Howarth et al 2004;Gilbert 2005;Pekár et al 2011). By contrast, behavioral mimicry might provide little selective benefit if imperfect mimics are readily visually discriminated.…”

Frequency-dependent variation in mimetic fidelity in an intraspecific mimicry system

“…However, variation in the degree of resemblance is common in nature, with the maintenance of imperfect mimicry now thought to arise through a variety of evolutionary mechanisms, including selective trade-offs (e.g. [2,3]) and mutation -selection balance [4] (see [5] for review). Signal detection theory predicts that once the mimic achieves a certain degree of resemblance to its model, sufficient to reduce the motivation of the signal receiver to respond, then further selection to improve similarity may not be present [4].…”