Thermoperiodic involvement in antifreeze protein production in the cold hardy beetle Dendroides canadensis: Implications for photoperiodic time measurement

Abstract

This study considers a possible role for thermoperiods (i.e. the duration of thermophase (T) and cryophase (C) during a 24-h period) in the regulation of antifreeze protein production in Dendroides canadensis. Larvae were exposed to thermocycles consisting of long (16 h) and short (8 h) thermophases in the form T C , 25° 17°C , while maintained in a background of either constant darkness, or constant light. Short-day thermoperiods stimulated, while long-day thermoperiods prevented, antifreeze protein production under both aperiodic lighting conditions. If the cryophase temperature was allowed to reach 13°C ( T C , 25° 17°C ), significant differences ( P < 0.001) between long and short-day thermoperiodic responses persisted in both constant light and constant darkness, while the overall levels of antifreeze protein production increased under constant light conditions independent of the thermoperiod. Studies incorporating conflicting photothermal regimes in the form short photoperiod with a long thermoperiod, and vice versa, triggered intermediate antifreeze protein activity. These results indicate that D. canadensis are capable of distinguishing long from short-day thermoperiods, over the cycling temperature from 25 to 13°C, and will initiate antifreeze protein production under the appropriate conditions. Furthermore, the expression of this thermoperiodic response under both constant darkness and constant light holds important implications for photoperiodic time measurement in this species by suggesting that the circadian clock involved with daylength measurement is of an internal coincidence type. The observed interaction of the light-cycle and thermocycle in the regulation of antifreeze protein production is discussed from the perspective of entrainment of the D. canadensis circadian system.