Evidence for the Deflective Function of Eyespots in Wild Junonia evarete Cramer (Lepidoptera, Nymphalidae)

Wing pattern diversity in Eunica butterflies (Nymphalidae: Biblidinae): phylogenetic analysis implies decoupled adaptive trends in dorsal sexual dimorphism and ventral eyespot evolution

Butterfly eyespots are wing patterns reminiscent of vertebrate eyes, formed by concentric rings of contrastingly coloured scales. Eyespots are usually located close to the wing margin and often regarded as the single most conspicuous pattern element of butterfly wing colour displays. Recent efforts to understand the processes involved in the formation of eyespots have been driven mainly by evo-devo approaches focused on model species. However, patterns of change implied by phylogenetic relationships can also inform hypotheses about the underlying developmental mechanisms associated with the formation or disappearance of eyespots, and the limits of phenotypic diversity occurring in nature. Here we present a combined evidence phylogenetic hypothesis for the genus Eunica, a prominent member of diverse Neotropical butterfly communities, that features notable variation among species in eyespot patterns on the ventral hind wing surface. The data matrix consists of one mitochondrial gene region (COI), four nuclear gene regions (GAPDH, RPS5, EF1a and Wingless) and 68 morphological characters. A combined cladistic analysis with all the characters concatenated produced a single most parsimonious tree that, although fully resolved, includes many nodes with modest branch support. The phylogenetic hypothesis presented corroborates a previously proposed morphological trend leading to the loss of eyespots, together with an increase in the size of the conserved eyespots, relative to outgroup taxa. Furthermore, wing colour pattern dimorphism and the presence of androconia suggest that the most remarkable instances of sexual dimorphism are present in the species of Eunica with the most derived eyespot patterns, and are in most cases accompanied by autapomorphic combinations of scent scales and "hair pencils". We discuss natural and sexual selection as potential adaptive explanations for dorsal and ventral wing patterns.

Artificial eyespots on cattle reduce predation by large carnivores

Eyespots evolved independently in many taxa as anti-predator signals. There remains debate regarding whether eyespots function as diversion targets, predator mimics, conspicuous startling signals, deceptive detection, or a combination. Although eye patterns and gaze modify human behaviour, anti-predator eyespots do not occur naturally in contemporary mammals. Here we show that eyespots painted on cattle rumps were associated with reduced attacks by ambush carnivores (lions and leopards). Cattle painted with eyespots were significantly more likely to survive than were cross-marked and unmarked cattle, despite all treatment groups being similarly exposed to predation risk. While higher survival of eyespot-painted cattle supports the detection hypothesis, increased survival of cross-marked cattle suggests an effect of novel and conspicuous marks more generally. To our knowledge, this is the first time eyespots have been shown to deter large mammalian predators. Applying artificial marks to high-value livestock may therefore represent a cost-effective tool to reduce livestock predation.

Both Palatable and Unpalatable Butterflies Use Bright Colors to Signal Difficulty of Capture to Predators

Birds are able to recognize and learn to avoid attacking unpalatable, chemically defended butterflies after unpleasant experiences with them. It has also been suggested that birds learn to avoid prey that are efficient at escaping. This, however, remains poorly documented. Here, we argue that butterflies may utilize a variety of escape tactics against insectivorous birds and review evidence that birds avoid attacking butterflies that are hard to catch. We suggest that signaling difficulty of capture to predators is a widespread phenomenon in butterflies, and this ability may not be limited to palatable butterflies. The possibility that both palatable and unpalatable species signal difficulty of capture has not been fully explored, but helps explain the existence of aposematic coloration and escape mimicry in butterflies lacking defensive chemicals. This possibility may also change the role that putative Müllerian and Batesian mimics play in a variety of classical mimicry rings, thus opening new perspectives in the evolution of mimicry in butterflies.

Eyespots deflect predator attack increasing fitness and promoting the evolution of phenotypic plasticity

Some eyespots are thought to deflect attack away from the vulnerable body, yet there is limited empirical evidence for this function and its adaptive advantage. Here, we demonstrate the conspicuous ventral hindwing eyespots found on Bicyclus anynana butterflies protect against invertebrate predators, specifically praying mantids. Wet season (WS) butterflies with larger, brighter eyespots were easier for mantids to detect, but more difficult to capture compared to dry season (DS) butterflies with small, dull eyespots. Mantids attacked the wing eyespots of WS butterflies more frequently resulting in greater butterfly survival and reproductive success. With a reciprocal eyespot transplant, we demonstrated the fitness benefits of eyespots were independent of butterfly behaviour. Regardless of whether the butterfly was WS or DS, large marginal eyespots pasted on the hindwings increased butterfly survival and successful oviposition during predation encounters. In previous studies, DS B. anynana experienced delayed detection by vertebrate predators, but both forms suffered low survival once detected. Our results suggest predator abundance, identity and phenology may all be important selective forces for B. anynana. Thus, reciprocal selection between invertebrate and vertebrate predators across seasons may contribute to the evolution of the B. anynana polyphenism.

Origin, development, and evolution of butterfly eyespots

This article reviews the latest developments in our understanding of the origin, development, and evolution of nymphalid butterfly eyespots. Recent contributions to this field include insights into the evolutionary and developmental origin of eyespots and their ancestral deployment on the wing, the evolution of eyespot number and eyespot sexual dimorphism, and the identification of genes affecting eyespot development and black pigmentation. I also compare features of old and more recently proposed models of eyespot development and propose a schematic for the genetic regulatory architecture of eyespots. Using this schematic I propose two hypotheses for why we observe limits to morphological diversity across these serially homologous traits.

Some Possible Cases of Escape Mimicry in Neotropical Butterflies

The possibility that escape or evasive mimicry evolved in butterflies and other prey insects in a similar fashion to classical Batesian and Müllerian mimicry has long been advanced in the literature. However, there is a general disagreement among lepidopterists and evolutionary biologists on whether or not escape mimicry exists, as well as in which mimicry rings this form of mimicry has evolved. Here, we review some purported cases of escape mimicry in Neotropical butterflies and suggest new mimicry rings involving several species of Archaeoprepona, Prepona, and Doxocopa (the "bright blue bands" ring) and species of Colobura and Hypna (the "creamy bands" ring) where the palatability of butterflies, their ability to escape predator attacks, geographic distribution, relative abundance, and co-occurrence in the same habitats strongly suggest that escape mimicry is involved. In addition, we also indicate other butterfly taxa whose similarities of coloration patterns could be due to escape mimicry and would constitute important case studies for future investigation.