Evolution of Mimicry in the Bio-semiosphere
I have described different dimensions of scaffolding processes as ontogenetic, evolutionary, physiological and cognitive scaffolding with reference to mimicry systems. It would be more correct, however, to consider these as aspects or dimensions and not as types, due to the fact that ontogenetic, evolutionary, physiological and cognitive scaffolds can combine in different ways in the actual mimicry systems. The understanding of this connecting faculty of scaffolds is also evident in Hoffmeyer’s writings: “semiotic scaffolding systems painlessly bridge the mind- body gap, being in their function as controllers, essentially somatic and social in one and the same process” (Hoffmeyer 2014b: 95-96). Let us return for a moment to the example of the eyespots on butterfly wings. We saw how ontogenetic scaffolds have an important role in the development of eyespots on butterfly wings. However, eye- spots also depend on evolutionary scaffolds. From an evolutionary perspective, the eyespots co-opt earlier use of the eyes that have vivid colouration and sign value in the intraspecific communication of many animals and birds (for discussion, see Kleisner 2011; Kleisner and Maran 2014). There has been a recent discussion about whether it is resemblance to the eye or conspicuousness in general that makes eye- spots effective as a deterring device (Stevens et al. 2009; Stevens and Ruxton 2014). Here we should note that eyespots may well be involved in both functions simultaneously, but it is very difficult to consider eyespots without any reference to the interpretative act (the signification) on the part of many vertebrates, which gives the meaning of “eye” to the visual perception organs. In other words, with their reference to an active animal, eyes function as biological archetypes, and any later similar structure tends to become grounded on the meaning that vividly coloured irises have.
In regard to physiological scaffolding, it needs to be mentioned that in many cases, the development of eyespots is based on the general structure of the butterfly wing-plan and the way in which homological serial development in different segments contributes to the creation of the overall image. The segmented wing-plan creates conditions for the genes to be expressed in a similar way in multiple neighbouring compartments, which, being influenced by local regulatory forces, create the eyespot or eyespots as a complete visual structure (Hombria 2011; Oliver et al. 2014). Also, the development of eyespots appears to make use of some preexisting network of developmental genes/programme: for instance, ventral appendage development, wound healing or wing margin development have been co-opted to function in eyespot development (Monteiro 2014).
Stepwise change as described by the concept of scaffolding is an important mechanism for the regulation and development of mimicry systems. Unlike the communication system of a single species, mimicry often includes several species through ecological and semiotic relations. Due to the interrelations between these aspects and the recursiveness of the mimicry system, as well as the fact that there are several participants involved, it seems plausible to regard mimicry as a system that scaffolds itself. This means that at least in principle, scaffolding in mimicry may cross the boundaries of species in such a way that a genetic, developmental or ecological property of one species becomes a scaffolding device for another species and so on. The example of brood parasitism of indigobirds on weaver finches, given above, fulfils this criterion. While such examples might not be very common, they demonstrate how effective mimicry is in influencing the open-ended nature of evolution. Let us consider another example of brood parasitism — that of the common cuckoo and small passerine birds (see Fig. 8.3, left). Whereas the primary mimicry relation takes place between the eggs and nestlings of the cuckoo (mimic) and those of the host (model, receiver), there is a secondary resemblance present between the body shapes and plumage of adult cuckoos (mimic) and a local hawk species (model) (Welbergen and Davies 2011). Secondary resemblance has been described, for instance, between the common cuckoo and the sparrow hawk Accipiter nisus. It is believed to reduce the mobbing behaviour of the host species, as they appear to be less aggressive toward hawks than they are toward cuckoos (Davies and Welbergen 2008). Due to the local diversity in both the cuckoos’ host species and the hawks, cuckoos are the subjects of different selection pressures through semiotic means that increase the local variety of the cuckoos (Thorogood and Davies 2013). It also shapes the conditions of their own intraspecific recognition and communication.
Mimicry has been shown, at least in some cases, to catalyse the emergence of new species (Mallet et al. 1998). Mimicry can increase the local diversity of communication patterns in mimetic species and create similarities between different species in the region (as in the case of so-called mimicry rings). This kind of local variation and constrained change (partly due to semiotic scaffolds) inevitably brings along changes in species. Chris D. Jiggins (2008: 542) describes the importance of local variation for the speciation of Heliconius butterflies: “It appears that color pattern and color based assortative mating are the first traits to diverge between adjacent populations. [...] Selection for phenotypic convergence due to mimicry is undoubtedly an important force in the evolution of Heliconius patterns.” In addition to Heliconius butterflies, this connection between mimicry resemblance and specia- tion has been described for instance in poison frogs (Twomey et al. 2014), parasitic indigobirds (Sorenson et al. 2003) and fly orchids (Ayasse et al. 2010).
From a semiotic viewpoint, it also needs to be emphasised that mimicry systems are not closed systems, but exist in the rich and open environment of signs. The semiotic understanding of the systems of mimicry, usually described with the triadic representation of the mimic, the model and the receiver, is heuristically useful but still an idealisation. In the actual environment, mimicry systems are open; that is, they can occasionally include individuals of many species beyond the fixed model of the mimicry triad. Interpretations of these individuals are to a certain extent underdetermined, as they can perceive and interpret the resemblances between mimics and models in many ways. As a most primitive distinction, the receiver can recognise: (a) the mimic to be the model (erroneous recognition); (b) the mimic to be different from the model (correct recognition); (c) the mimic to be something resembling the model (recognition based on analogous interpretation); (d) the mimic to correspond simultaneously to the mimic and the model (recognising two sign sets simultaneously). Receivers may also make interpretive connections between signs in the mimicry systems and other semiotic structures in the biosemio- sphere as principally new analogy-based sign relations. In cases where mimicry is underdetermined and a space of different interpretations becomes existent, the subjective properties of individuals as interpreters start influencing the future of the mimicry system.
The notions of semiotic selection and semiotic scaffolding fit well with and support the understanding of mimicry as a two-layered structure. In addition to the ecological composition of the species in predation, symbiosis, and parasitism, mimicry also includes the layer of semiotic processes. Whereas the first layer is composed of specific species and individuals, the second layer consists of characteristic cues or signals of the species, properties of the environment, or more abstract signs. In semiotic relations, different organisms are bound together through perception, recognition, communication and action, and it is in this layer that the organism’s interpretation starts shaping the future stages of the mimicry system. The interplay between the ecological and semiotic layers is important for the dynamics of mimicry as an open system. The combinations of species situate mimicry in an ecosystem but also open it up to new ecological relations in the surrounding ecological network, whereas the sign processes enable mimicry to relate with existing meaning complexes, generalised images and conventions of communication.