Meeting Abstract

P3.8  Friday, Jan. 6  Change in thermal refuge seeking behavior during development of Battus philenor larvae. NIELSEN, M.E.*; PAPAJ, D.R.; University of Arizona; University of Arizona

Temperature is an often highly variable component of any organism’s environment, and such variation can strongly impact an organism's physiology and thereby its fitness. Because of this, organisms have evolved a wide range of mechanisms for coping with temperature change. Effective thermoregulation is particularly crucial for larvae of the Pipevine Swallowtail, Battus philenor, in the Southwestern US because their host plant grows close to the ground and thus reaches extremely high temperatures on summer days. One way B. philenor deals with these high temperature extremes is by leaving their procumbent host and seeking a thermal refuge higher up in the vegetation. Although size and developmental stage have been found to influence thermoregulation in other lepidopterous species, previous studies of thermal refuge-seeking in B. philenor have only examined large, late instars. Here, we investigated how refuge-seeking behavior changed over the course of larval development, specifically assessing the temperature at which caterpillars of different instars would leave the host plant and seek a thermal refuge. Since the cost of leaving a host plant is likely greater for earlier instars due to their smaller size and more limited dispersal abilities, we reasoned that earlier instars would leave the plant at higher temperatures than later ones. Such instar-dependent responses would have implications for the evolution of other traits, such as heat tolerance. It would also have implications for how caterpillar body coloration, a temperature-dependent, phenotypically plastic trait in this species, varies during development under different temperature regimes.