Natural and sexual selection in satyrine wing patterns: a complex story
Key words: behavior, evolution, eye spots, wing pattern
A recent article by Oliver et al. (2009) suggests that evolution of different wing pattern elements in Satyrinae happens at different rates and under different selective pressures. Using a model group of Bicyclus satyrines, the authors test the hypothesis that dorsal and ventral sides are subjected to different selective pressures and hence evolve at different rates. This research group has also previously shown that male dorsal eyespots play a vital role in mate choice by females (Robertson and Monteiro, 2005). In the new study, using a phylogeny of Bicyclus, they showed that dorsal wing characters evolve faster than those on the ventral wing surface, and that forewing characters evolve faster than those on the hindwing. The ventral pattern, the authors suggest, serves mostly as cryptic coloration and therefore is more conserved compared to the dorsal one.
It might be tempting to extrapolate the above results to other groups of butterflies. In Junoniini, however, another group which is also very rich with eye-spot patterns that are frequently variable within a species, the eye-spots are apparently an antipredatory device. Their evolution has been shown to be non-linear, with the appearance and disappearance of individual spots having happened several times, and inheritance of individual spots may be linked (Kodandaramaiah, 2009). Even when it comes to other satyrine genera, different mechanisms might be employed by different species in nature for communication.
Here, I report behavioral observations on Archeuptychia cluena (Drury, 1782) and Chloreuptychia arnaca (Fabricius, 1776),
which illustrate that the dorsal eyespots as well as shiny coloration in two of
the neotropical satyrines function for signaling territoriality. I also would like to share observations on Pseudochazara pelopea (Klug, 1832) in
In June, 2009, in
In Cosmosatyrus leptoneuroides (Fig. E), Auca barrosi (Fig. F), Pseudochazara pelopea (Fig. G), and many other satyrines, while the ventral hindwing pattern serves as cryptic coloration, the exposure of the bright coloration of the ventral forewings by protruding the latter forward, rather than by the opening of the wings, is used for communication (Fig. G). This might be due to the need to conserve water and minimize exposure to direct sunlight, and hence overheating and dehydration, which are common problems in their habitats. It is therefore the ventral forewing pattern that is actively involved in mate signaling, while the dorsal surface in these species is rarely exposed and possesses no, or very limited, wing pattern elements.
To view a video clip of Chloreuptychia arnaca; Archeuptychia cluenarival signaling behavior, visit
Oliver, J. C.Robertson, K. A.Monteiro, A.2009Accommodating natural and sexual selection in butterfly wing pattern evolutionProc. R. Soc. B: Biol. Sci
Robertson, K. A. and Monteiro, A. 2005. Female Bicyclus anynana butterflies choose males on the basis of their dorsal UV-reflective eyespot pupils. Proc. R. Soc. B 272: 1541-1546.
Silberglied R. E., 1984. Visual communication and sexual selection among butterflies. In: R. I. Vane-Wright and P. R. Ackery, Editors, The Biology of Butterflies (Symposium of the Royal Entomological Society of London, number 11), Academic Press, London.
Fig. Competitor and mate signaling in satyrines (see text for details): (A-B) male Chloreuptychia arnaca; (C-D) male Archeuptychia cluena; (E) female Cosmosatyrus leptoneuroides; (F) Auca barrosi; (G) Pseudochazara pelopea