How caterpillars avoid overheating: behavioral and phenotypic plasticity of pipevine swallowtail larvae |
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Authors: | Chris C Nice James A Fordyce |
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Institution: | (1) Department of Biology, Population and Conservation Biology Program, Texas State University, San Marcos, TX 78666, USA;(2) Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996, USA |
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Abstract: | We tested the hypothesis that larvae of the pipevine swallowtail butterfly, Battus philenor, employ behavioral and phenotypic plasticity as thermoregulatory strategies. These larvae are phenotypically varied across
their range with predominantly black larvae (southeastern USA and California) and red larvae (western Texas, Arizona) occurring
in different regions. Two years of field observations in south Texas indicate that the proportion of red larvae increases
with increasing daily temperatures as the growing season progresses. Larvae were also observed to shift their microhabitats
by climbing on non-host vegetation and avoided excessive heat in their feeding microhabitat. Larvae of ten half-sib families
from populations in south Texas and California, reared under different temperature regimes in common garden experiments, exhibited
plasticity in larval phenotype, with larvae from both populations producing the red phenotype at temperatures greater than
30°C and maintaining the black phenotype at cooler temperatures. However, larvae from Texas were more tolerant of higher temperatures,
showing no decrease in growth rate in the highest temperature (maximum seasonal temperature) treatment, compared to the California
population. In a field experiment, black larvae were found to have higher body temperatures when exposed to sunlight compared
to red larvae. These results suggest that microhabitat shifts and the color polyphenism observed in pipevine swallowtail larvae
may be the adaptive strategies that enable larvae to avoid critical thermal maximum temperatures. |
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Keywords: | Battus philenor Larval color Microhabitat shifts Polyphenism Thermoregulation |
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