A common mechanism explaining the evolution of female‐limited and both‐sex Batesian mimicry in butterflies

Abstract

Summary 1.Batesian mimicry describes the situation in which a palatable mimic resembles an unpalatable model. In some species of butterflies, both sexes mimic, but in others only females do. Two mechanisms have been proposed to generate female-limited mimicry: sexual selection via female choice, and sexual selection via male-male competition. Each is not satisfactory because of too many exceptions. 2. I hypothesized that reductions in physiological life span because of mimicry constituted the costs, while extensions of ecological life span because of mimicry constituted the benefits. Mimicry would result from the balance of a costs/benefits relationship; when balances are favourable, mimicry occurs. 3. Non-mimetic females of female-limited mimicry butterfly Papilio polytes lived longer than its mimetic females in a butterfly farm greenhouse. Therefore, reduction in physiological life span must be a cost of mimicry. 4. Male-biased sex ratios were found in 11 of the 14 non-mimetic and non-model species netted in the Kakamega tropical rainforest in west Kenya, in other one species almost equivalent, and in remaining two species female-biased. For each species, the sexes netted less frequently had more beak marks than those netted more frequently. That is, the biased sex ratios could be responsible for the higher predation rates of the opposite sex. 5. Predators may have selectively attacked females with wider thoraxes, which flew at higher levels and flew more quickly. However, attack rates on males of some species may be high or low regardless of thorax width. 6. As the benefits accrue largely to females with wider thorax due to female-biased predation, balances of costs/benefits relationships divide participating species into three theoretical groups: those in which the adaptation is favourable for both sexes; favourable only for females; and unfavourable for both sexes. 7. In female-limited mimics of five species, thorax widths varied, whereas thoraxes tended to be wider in both-sex mimics of four species.Key-words : cost and benefit, ecological life span, female-biased beak mark ratio, flight velocity, male-biased sex ratio, physiological life span, predation pressure.

Identifying the ecological conditions that select for intermediate levels of aposematic signalling

“…There is relatively little published work which demonstrates that conspicuous colouration may be costly either in proximate physiological terms, or in terms of direct fitness correlates. A good example, however, was recently reported by Ohsaki (2005) who demonstrated that the expression of bright mimicry patterns in the Batesian mimetic butterfly, Papilio polytes, is associated with decreased longevity in captive animals (Speed and Ruxton 2007, outline other studies which demonstrate or strongly imply that displays can be costly).…”

Chemical Ecology of Poisonous Butterflies: Model or Mimic? A Paradox of Sexual Dimorphisms in Müllerian Mimicry

“…Several Rutaceae-feeding black swallowtails such as Papilio macilentus and P. protenor (females of the former are highly mimetic to A. alcinous males) often share the same microhabitat spatiotemporally in the middle part of Japan. Potential higher predation on females due to behavioral vulnerability may underlie behind this mechanism (Ohsaki 1995(Ohsaki 2005. Thus, in addition to the chemistry, further studies are warranted especially on the geographical variations of wing color in both the butterflies and moths but also on the potential interspecific impacts from co-occurring Batesian mimics.…”

Mimetic butterflies support Wallace's model of sexual dimorphism

“…Many female-limited mimics also exhibit mimic/non-mimic female polymorphism in which at least one female form is non-mimetic (very often male-like), and at least one female form is mimetic ( Wallace 1865;Wickler 1968;Mallet & Joron 1999). Although female polymorphism also occurs outside of mimicry (Magnus 1963;Graham et al 1980), a combination of frequency-dependent advantages of Batesian mimicry ( Turner 1978;Ohsaki 1995), physiological trade-offs of being mimetic or non-mimetic (Ohsaki 2005) and the mating advantage of being nonmimetic (Burns 1966;Vane-Wright 1984;Lederhouse 1995; but also see Platt et al 1984 and references therein) raises the possibility that female-limited mimicry fosters the evolution of female polymorphism more than any other factors under which female polymorphism might evolve. Finally, some Papilio species are remarkably brilliantly coloured, undoubtedly due to sexual selective pressures.…”