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-A- Black males -A- Yellow males

-•- Black females -o- Yellow females

Time period

Figure 6.10 Survival of artificially blackened male butterflies (Pontia occidentals) is less than for artificially yellowed butterflies (a), whereas for females paint colour has no effect (b).

Note: The four time periods are for different dates in July 1993. SEs for survival probablilities are indicated.

Source: American Naturalist, Kingsolver, 147, 296-306. © 1996 by The University of Chicago. All rights reserved. 0003-0147/96/4702-0008$02.00

differences other than colour which might have resulted from the rearing environment. Artificially blackened male Colias butterflies resembled the spring phenotype and showed lower survival probability under summer conditions than yellowed butterflies resembling summer phenotypes, but paint treatment had no effect on the less active and initially darker females (Fig. 6.10). Release of different cohorts of butterflies in different seasons showed that plasticity was sometimes, but not always, adaptive, providing partial support for the beneficial acclimation hypothesis. This is an important experimental study of natural selection. Short-term unpredictability in the weather probably prevents a more precise match between phenotype and environment (Kingsolver and Huey 1998). Watt (1991) has also stressed that habitat variability

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