Climate change simulated temperature variability affects respiration and behaviour of insects

A wasp parasitoid and its prey, an aphid. Image source: https://www6.inra.fr/encyclopedie-pucerons/Especes/Parasitoides/Braconidae-Aphidiinae/Aphidius-rhopalosiphi . / INRA

A wasp parasitoid and its prey, an aphid. Image source: https://www6.inra.fr/encyclopedie-pucerons/Especes/Parasitoides/Braconidae-Aphidiinae/Aphidius-rhopalosiphi . / INRA

The Resting Metabolic Rate (RMR) is a physiological measure of the rate of heat release from an animal’s body. A common method to measure RMR is by measuring animal respiration or oxygen consumption. The rate of oxygen consumption in animals is positively correlated with the rate of heat production.

Oxygen consumption, and the metabolic rate, scale with animal size with larger animals of greater body mass having a higher RMR than smaller animals. RMR also scales with temperature with an increased temperature leading to a higher RMR on an animal with the same body mass. Ectotherms, such as insects, in particular, exhibit increased oxygen consumption with increased temperature.

Climate change theory suggests that not only will temperatures increase with increase greenhouse gases but there will also be greater day-to-day variability in temperature swings. Ectotherms may respond to variability in temperature, and their RMR, through behavioural changes. These changes may leave ectotherms more vulnerable or better able to respond to predators.

Le Lann et al (2014) tested the hypothesis that a prey species will have a greater RMR response to a 5°C temperature increase than one of its predators. The greater RMR response will enable the prey species to avoid the predator under the simulated higher temperature scenario. The prey species in their experiment was the grain aphid Sitobion
avenae and its predator was the habitat-specialist parasitoid wasp, Aphidius rhopalosiphi. The researchers employed the MicroRespiration system from Unisense to measure oxygen consumption and the RMR of the aphid and the wasp and observed a number of behavioural traits of the species.

 

instrumentation

 

Aphids and wasps were reared in growth cabinets with a constant temperature of 20°C. A sample of the aphids and wasps were then transferred to one growth cabinet with a temperature of 15°C or a second growth cabinet with a temperature of 25°C. After 24 hours of being allowed to acclimate to the change in temperature, the respiration rates of the aphids and wasps were measured with the Unisense MicroRespiration System:

Resting Metabolic Rate (RMR) Animal Physiology

 

Individual aphids and wasps were transferred to a microrespiration chamber. These are small, cylindrical chambers specifically designed for the MicroRespiration system. Le Lann et al used chambers 109–169 μl in volume:

Oxygen Consumption Chambers

 

Chambers are placed in a rack that is also designed to securely support the oxygen microsensor. The oxygen microsensor sensing tip fits exactly into a opening at the top of the chamber causing an air tight seal:

Magnetic Stirrer Rack

 

The aphids and wasps were left for 10 minutes to acclimate following the transfer to the chamber and insertion of oxygen microsensor. Oxygen was then measured periodically in the chamber for a period of 20 minutes. Oxygen consumption shows a strong negative linear relationship with time and the slope of the linear curve is used by the SensorTrace software to calculate respiration rates and oxygen concentration:

SensorTrace Software

 

results

The researchers confirmed their hypotheses and found that Resting Metabolic Rate (RMR) was positively correlated with temperature. The researchers also found that RMR for the aphid (prey/host) species was significantly higher than the wasp (predator/parasitoid) species at the +5°C temperature experimental treatment (see Figure 1, Le Lann et al 2014).

The researchers also found that the increase in respiration rates of the aphid changed the behaviour of both the aphid and the wasp. At increased temperature, the prey defence rate increased and the predator attack rate decreased (see Figure 2b and 2c, Le Lann et al 2014).

 

conclusion

The Unisense MicroRespiration System can successfully measure the Resting Metabolic Rate (RMR) of insects. These measurements can then be used to determine how species will respond to environmental changes.

 

further reading

 

reference

LE LANN,C.E.C.I. et al (2014), Thermal change alters the outcome of behavioural interactions between antagonistic partners, Ecological Entomology vol. 39, 578 – 588. Link