Are males more scared of predators? Differential increase in metabolic rate between males and females under risk of predation. (#254)
The risk of predation is known to negatively affect many aspects of prey. They may kill or seriously injure them, reducing survival. The risk of predation also restricts the habitats animals use, both in size and quality. Moreover, it has physiological costs, such as increased oxidative damage and increase in stress hormone. It has also been proposed that predation has an energetic cost for the prey, which is represented by an instantaneous increase in the metabolic rate. The evidence supporting this hypothesis comes mostly from fishes, but little is known about the energetic cost of predation on invertebrates in general. Here, we present our experiments measuring the effect of a chemical predatory cue on the standard metabolic rate (SMR) of the Black Field Cricket (Teleogryllus commodus ). We predict that metabolic rate should increase when crickets are presented with chemical predatory cues. We also predict that this effect should be higher on females than males, since females are the ones looking for mates, while males only wait and call, making females more susceptible to predation. Â Finally, we predict that the increase of SRM will be preceded by an increase in the levels of octopamine, the stress hormone in insects. Our results confirm our first hypothesis. In fact, a significant increment of metabolic rate was found when predatory cues were added. However, this effect was stronger in males than in females. Also, octopamine does not seem to be causing the increase in metabolic rate, since the increase in this hormone does not temporally correlates with the increase in the CO2 produced by the crickets.