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First published online November 17, 2006
Journal of Experimental Biology 209, 4690-4700 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02563

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Photoperiod-induced plasticity of thermosensitivity and acquired thermotolerance in Locusta migratoria

Corinne I. Rodgers^*, Kelly L. Shoemaker and R. Meldrum Robertson

Department of Biology, Queen's University, Biosciences Complex, Kingston, ON, K7L 3N6, Canada

View larger version (13K): [in a new window]   Fig. 1. Recording of the ventilatory rhythm at room temperature, at hyperthermic failure, and at recovery of ventilatory motor pattern generation in the locust. (A) Simultaneous recording of the temperature of the superfusing saline at the MTG (Temp) and the ventilatory motor pattern recorded from muscle 161 in the second abdominal segment (M161). Areas marked B-E are shown in expanded form below. (B) A section of the ventilatory rhythm during the first 20 min while the preparation was allowed to stabilize at room temperature. (C) Heat-induced failure of motor pattern generation. The arrow indicates where failure of motor patterning was determined. The burst of electrical activity following hyperthermic failure of the rhythm is typical and usually marks the cessation of all electrical activity. (D) Post-stress recovery of the ventilatory rhythm. The arrow indicates where recovery of the rhythm was determined. (E) The rhythm returns to normal shortly following recovery. (F) Expansion of bursts displaying intraburst activity. Mean ventilatory frequencies were obtained by calculating the inverse of the cycle period (1/P) for all bursts and calculating the average of these values.

View larger version (15K): [in a new window]   Fig. 2. Locusts reared under 16 h:8 h L:D and 12 h:12 h L:D regimes differed in morphology and lifetime survival probability. (A) 12:12 females (N=24) weighed significantly more than 16:8 females (N=24). (B) 12:12 males (N=24) had a significantly greater F/C ratio than 16:8 males (N=24). (C) 12:12 locusts had a significantly higher survival probability over time than 16:8 locusts (starting sample sizes: N12:12=111, N16:8=113). Significant differences are denoted by asterisks.

View larger version (19K): [in a new window]   Fig. 3. Thermosensitivity to increasing heat stress, time-to-failure and time-to-recovery of the ventilatory motor pattern in control and HS locusts. There was a main effect of photoperiod on ventilatory rate during a temperature ramp in control locusts (Control: N16:8=19, N12:12=16) (A), but not in HS locusts (HS: N16:8=17, N12:12=17) (B). The ventilatory motor pattern of 16:8 and 12:12 locusts responded differently to increasing temperature in the control condition (A) and after a HS (B). 12:12 control males and females (N=12) ventilated significantly longer than 16:8 control males and females (N=19) when temperature was increased to and held at 45°C (C), and a similar difference was found between 12:12 HS males and females (N=13) and 16:8 HS males and females (N=17) (D). 12:12 control males and females (N=9) had a significantly shorter time-to-recovery following hyperthermic failure than 16:8 control males and females (N=17) (E), and a similar difference was found between 12:12 HS males and females (N=13) and 16:8 HS males and females (N=17) (F). Asterisks indicate a significant difference between 16:8 and 12:12 locusts. Error bars indicate s.e.m.; some in A,B may be hidden behind symbols.

View larger version (14K): [in a new window]   Fig. 4. Mean ventilatory frequency at 20°C and 40°C, and the average change in frequency from 20°C to 40°C in each group. (A) There was a significant interaction between the effects of pre-treatment and sex on ventilatory rate at 20°C, which was driven by a significant difference between control and HS females. 16:8 control females had a significantly lower ventilatory rate at 20°C than 16:8 control males, 16:8 HS males, 16:8 HS females, and 12:12 HS females. (B) There were main effects of photoperiod and sex on ventilatory rate at 40°C. 16:8 control females had a significantly lower ventilatory rate at 40°C than 16:8 HS males, 12:12 control males, 12:12 HS males, and 12:12 control females. 16:8 HS females had a significantly lower ventilatory rate at 40°C than 12:12 HS males. (C) There was a main effect of photoperiod on the change in ventilatory frequency from 20 to 40°C, and there was a significant interaction between the effect of sex and pre-treatment, which was driven by a significant difference between HS males and females. 12:12 HS males had a significantly higher change in ventilatory rate from 20 to 40°C than 16:8 control males, 16:8 control females, 16:8 HS females, and 12:12 HS females. 12:12 control males and 12:12 control females had a significantly higher change in ventilatory rate from 20 to 40°C than 16:8 control females and 16:8 HS females. Error bars may be hidden behind symbols.

View larger version (11K): [in a new window]   Fig. 5. Time-to-failure during increasing and maintained high-temperature stress, and time-to-recovery following hyperthermic failure of motor patterning, in each group. (A) There was a main effect of photoperiod on time-to-failure. 12:12 locusts had a significantly longer time-to-failure than 16:8 locusts. (B) There was a significant interaction between the effects of photoperiod, pre-treatment and sex on time-to-recovery. In general, 16:8 animals had a longer time-to-recovery than 12:12 animals, but this difference was mainly driven by the 16:8 control females, whose time-to-recovery was significantly longer than all other groups. 16:8 HS males had a significantly longer time-to-recovery than 12:12 HS males.

View larger version (9K): [in a new window]   Fig. 6. Frequency of ventilatory bursts during high temperature stress was positively correlated to time-to-failure (A) and negatively correlated to time-to-recovery (B). Animals that ventilated more rapidly at 40°C could tolerate a greater duration of heat stress, and recovered more quickly following failure. All animals pooled: (A), N=51; (B), N=48.