Interacting Effects of Eyespot Number and Ultraviolet Reflectivity on Predation Risk in Bicyclus anynana (Lepidoptera: Nymphalidae)

Abstract

Small marginal eyespots on lepidopteran wings are conspicuous elements that attract a predator’s attention to deflect attacks away from the body, but the role of ultraviolet (UV) reflectivity at the center of these patterns and variation in eyespot number in altering the function of eyespots remains unclear. Here, we performed a field-based predation experiment with artificial prey items based on the appearance of squinting bush brown butterflies Bicyclus anynana (Butler, 1879). We tested how two visual properties of the wing pattern affect predation risk: i) the number of eyespots on the ventral forewing surface—two or four; and ii) the UV reflectivity of eyespot centers—normal (where the UV reflectivity of the centers contrasts strongly with that of the darker surrounding ring) or blocked (where this contrast is reduced). In total, 807 prey items were deployed at two sites. We found a significant interaction between the number of ventral forewing eyespots and UV reflectivity in the eyespot centers: in items with fewer eyespots, blocking UV resulted in increased predation risk whereas in items with more eyespots, blocking UV resulted in decreased predation risk. If higher predation of paper models can be equated with higher levels of wing margin/eyespot conspicuity, these results demonstrate that UV reflectivity is an important factor in making eyespots more conspicuous to predators and suggest that the fitness of particular butterfly eyespot number variants may depend on the presence or absence of UV in their centers and on the ability of local predator guilds to detect UV.

Predation favours Bicyclus anynana butterflies with fewer forewing eyespots

“…However, this would not affect the conspicuity of the white eyespot centres. They should therefore still draw attacks to themselves in a manner similar to isolated eyespots [ 12 ]. Nevertheless, future research should ensure that eyespot shape remains consistent.…”

“…Both constant and non-constant hazard functions were fitted and the model with the lowest Akaike information criterion value was chosen. Because mantid gender, which we expect to be important in experimental trials (those with mantids) [ 12 ], cannot be run in the same model as control trials (without a mantid), three separate models were run: (i) analysing all trials (control and experimental) with mantid presence/absence as the main effect to assess the effects of predation; (ii) analysing only control trials with butterfly form as the main effect to investigate the difference between forms in the absence of predation; and (iii) analysing only experimental trials with butterfly form and mantid gender as interacting main effects to assess differences between the two forms under predation. Where appropriate, cage number was included as a random effect to account for among-cage differences.…”

“…More directly, ventral eyespots in Melanitis leda and Bicyclus anynana deflect attacks from reptiles [ 11 ] and mantids [ 7 ], respectively. Furthermore, butterfly paper models with more conspicuous small ventral marginal eyespots are more readily attacked [ 6 , 12 ]. This increased conspicuousness, however, can confer fitness benefits because the eyespots draw attacks to less important body parts, as demonstrated in studies using live prey items [ 7 ].…”

Warmer temperatures result in maladaptive learning of sexual preferences

“…1), leading to lush, green vegetation and an abundance of resources [35][36][37][38]. High temperatures (> 23ºC; [35]) lead to the development of a typical wet season male butterfly morph that is characterized by conspicuous eyespots to avoid predation [39][40][41]. Several successive generations of wet season butterflies appear during the wet season.…”

“…1) and there is an abundance of resources (Brakefield & Mazzotta, 1995; Brakefield, Pijpe, & Zwaan, 2007; Brakefield & Reitsma, 1991; Windig, Brakefield, Reitsma, & Wilson, 1994). High temperatures (> 23ºC; (Brakefield & Mazzotta, 1995)) lead to the development of a typical wet season male morph that is characterized by conspicuous eyespots to avoid predation (Chan, Rafi, & Monteiro, 2019; Kooi & Brakefield, 1999; Lyytinen, Brakefield, Lindstrfom, & Mappes, 2004). Several successive generations of wet season butterflies appear during the wet season.…”