TARPLEY, S. L.; HAYES, T. J.; DAHLHOFF, E. P.; RANK, N. E.; Santa Clara Univ.; Sonoma State Univ.; Santa Clara Univ.; Sonoma State Univ.: Is color pattern variation in California willow beetles the result of temperature adaptation?

We examined effects of environmental and rearing temperature on color pattern variation in the California leaf beetles Chrysomela schaefferi and C. confluens. Melanic (darkly pigmented) and light-colored forms are found in both species. Melanic forms occur in higher frequency at sites near the coast than for inland localities, and melanics are more frequent at shady than sunny sites. To test the prediction that higher frequency of non-melanics at inland sites were due to elevated air temperature, early-stage larvae were collected from multiple sites in Sonoma, Santa Clara and Santa Cruz counties in April 2004 and reared in the laboratory to adulthood at either a moderate (20�C) or elevated (28�C) temperature. Larval growth rate was also measured. For both species, frequency of melanic color forms was highly correlated with the frequency of the melanics at the site where larvae were collected. Larval rearing temperature did not affect frequency of melanic forms in adults of either species. However, for C. schaefferi, significantly more males were melanic than females, regardless of rearing temperature. We also found that for C. schaefferi, larval families collected from sites with a high frequency of melanics grew more slowly than those from sites where light forms are common. These data suggest both potential advantages and costs of melanism, at least for C. schaefferi. Dark males have higher body temperatures at a given air temperature in nature, which may lead to higher activity levels and greater mating success. However, dark individuals may grow slower in nature, leaving them in the larval stage longer, and thus more vulnerable to predators.