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Seasonal Polyphenism in Butterfly Wings
Seasonal polyphenism is not uncommon in many butterfly species. Moreover, more than one environmental cue is often able to induce the polyphenism. As mentioned in Gilbert (1997), the cabbage white (Pontia) and the sulfur butterfly (Colias) have seasonal polyphenisms such that their ventral hindwings become darker when the temperature drops. This allows them to heat more quickly when they alight on leaves. Below are photos of these polyphenisms, courtesy of Tom Valente, Swarthmore College.
|Figure 2 Polyphenic variation of Colias eurytheme (Pieridae). Top row: Summer morph, male (left) and female (right); bottom row: Cold-season "ariadne" morph, male (left) and female (right).|
The buckeye butterfly (Precis coenia) also shifts color with the season. As the season progresses, the color pattern of the emerging butterflies shifts from a tan ("linea") ventral hindwing in the spring to a red ("rosa") ventral hindwing in the autumn. There are multiple ways to induce this "redshift" in the laboratory. Both low temperatures and shortened daylight periods will induce the larvae to eclose as rosa morphs. Moreover, these two factors (and perhaps others) interact. The inductive temperature works better with the shortened daylengths. The rosa pattern can also be assimilated genetically; by selecting individuals within the population, one can easily obtain a strain of buckeye butterfly that produces the red morph under all conditions (Smith 1993). Below is a photograph of the seasonal morphs of the buckeye butterfly.
|Figure 3 The seasonal morphs of the buckeye butterfly, Precis coenia (Nymphalidae). The ventral surfaces are shown. The Summer morph ("linea") is on the left; the Fall morph ("rosa") is on the right.|
Another example of a seasonally dimorphic butterfly is Polygonia c-aureum, a Japanese species akin to the North American comma butterfly, Polygonia comma. This dimorphism is environmentally controlled through the neuroendocrine system of the larvae. Day length and temperature are the major environmental determinants of the polyphenism. The reproductively active summer form can be induced experimentally by long day length and higher temperatures, and the diapausing autumn morph can be induced by shorter day length and lower temperatures (Hidaka and Aida 1963; Fukuda and Endo 1966; Matsuda 1979). Fukuda and Endo (1966) also found that long day length at higher temperatures activated the brain-corpus cardiacum system (which potentiates the production of ecdysone). Moreover, the hormones released from the corpus cardiacum could induce the summer pattern, while ablation of the corpora cardiaca prevented its formation. It appears, then, that the summer form of the butterfly is produced when brain registers the day length and temperature, and transmits this information into the activation of the corpora cardiaca. Presumably, the changes in ecdysone stimulate the morphogenetic and behavioral changes in the butterfly.
All specimens are courtesy of Tom Valente, Swarthmore College. Photographs were taken by George Flickinger.
Fukuda, S. and Endo, K. 1966. Hormonal control of the development of seasonal forms in the butterfly, Polygonia c-aureum L. Proc. Japan. Acad. 42: 1082-1087.
Gilbert, S. F. 1997. Developmental Biology. Fifth ed., Sinauer Associates, Inc., Sunderland, MA.
Hidaka, T. and Aida, S. 1963. Day length as the main factor of seasonal form determination in Polygonia c-aureum (Lepidoptera, Nymphalidae) [in Japanese]. Zool. Mag. 72: 77-83.
Matsuda, R. 1979. Abnormal metamorphosis and arthropod evolution. In Arthropod Phylogeny. A. P. Gupta, (ed.). Van Nostrand Reinhold Company, New York. pp. 137-256.
Smith, K. 1993. The effects of temperature and daylight on the rosa polyphenism in the buckeye butterfly, Precis coena (Lepidoptera: Nymphalidae). J. Res. Lepidopt. 30: 225-236.
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