Evolutionary Ecology Research, 2006, 8: 703–715
Thermal reaction norms for caterpillar
growth depend on diet
Joel G. Kingsolver,* J. Gwen Shlichta,‡ Gregory J. Ragland
and Katie R. Massie§
Department of Biology, University of North Carolina, Chapel Hill, NC 27599, USA
ABSTRACT
Hypothesis: Interactions between diet and temperature affect reaction norms for growth rate
in ectotherms.
Organisms: Full-sib families of the small cabbage white butterfly, Pieris rapae, derived from
field populations near Seattle, WA, USA.
Methods: We used a split sib-family experimental design with two food treatments (collard
leaves and artificial diet) and four test temperatures (11, 23, 35 and 40⬚C), and measured
short-term growth rate (mass increase) of fourth-instar caterpillars. The data were analysed
using mixed-model analysis of variance.
Results: Temperature, food type, family, and two- and three-way interactions all had
significant effects on growth rate. The thermal sensitivity of growth rate was greater on collards
than on the artificial diet; mean growth rate was greater on collards than on the artificial diet for
temperatures from 11 to 35⬚C, but this effect was reversed at 40⬚C. Estimated broad-sense
genetic variances were greater on collards than on the artificial diet; the genetic covariance
of growth rate at 35 and 40⬚C was strongly positive on the artificial diet, but weak or negative
on collard leaves.
Conclusions: Both the mean and genetic variation in thermal reaction norms for insect
growth rate were influenced by food type in this system. Studies of the thermal sensitivity
of growth and feeding that utilize artificial diets may not accurately reflect genetic variation or
constraints on thermal reaction norms that may occur on natural food resources.
Keywords: diet, insect growth, phenotypic plasticity, Pieris rapae, reaction norm, temperature.
INTRODUCTION
Temperature impacts many aspects of the physiology, growth, performance, and fitness of
ectothermic animals (Huey and Berrigan, 2001). Temperature effects may be considered as a form
of phenotypic plasticity in which the phenotypic trait (e.g. body size, growth or locomotory
rate, fitness) expressed by an individual organism or genotype varies as a function of
* Author to whom all correspondence should be addressed. e-mail: [email protected]
‡ Present address: Department of Entomology, University of Maryland, College Park, MD 20740, USA.
§ Present address: Department of Ecology and Evolution, University of Arizona, Tucson, AZ 85721, USA.
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© 2006 Joel G. Kingsolver
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