Natural and sexual selection in satyrine wing patterns: a complex story

 

Download pdf of the reference: Sourakov, A. 2010. Natural and sexual selection in satyrine wing patterns: a complex story. News of Lepidopteristsf Society. 52(1): 6-7, 15.

 

 

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 Armenia and other satyrines of xeric habitats, such as Auca barrosi (Silva, 1917) and Cosmosatyrus leptoneuroides (Felder&Felder, 1867) in Patagonia, genus Calisto in the West Indies and many others, in which the signaling is restricted to the ventral rather than dorsal wing surface.

 

Observations

In June, 2009, in Bahia, Brazil, I observed Archeuptychia cluena and Chloreuptychia arnaca in the field.  Males of both species normally perched in sunlight with their wings closed, orienting to the sun in such a manner that they would project a minimal shadow (Fig. A, C) – perhaps one of the defensive strategies they employ. They perched thus for many minutes. Abrupt opening of the wings occurred only when a conspecific male entered their territory at the distance of approximately 10 feet (Fig. B, D).  Repeated observation confirmed that the opening/closing of the wings was caused by the potential rivalsf entry or departure from the perching malefs territory. The bright dorsal surface in this case was directed not at the attraction of females, but for repelling a competitor, which coincides with the traditional explanation for the bright wing pattern coloration (e. g., Silberglied, 1984).  Unlike Bicyclus, it is the hindwings, not the forewings, that carry most of the signaling elements in the above two species.

 

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

 

http://www.lepidopterist.org/butterflies-fighting.htm

 

 

Literature cited

 

Kodandaramaiah U., 2009. Eyespot evolution: phylogenetic insights from Junonia and related butterfly genera (Nymphalidae: Junoniini). Evolution and Development. 11(5): 489-497.

 

Oliver, J. C., Robertson, K. A., and Monteiro, A. 2009. Accommodating natural and sexual selection in butterfly wing pattern evolution. Proc. R. Soc. B: Biol. Sci. 2369-2375.

 

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