Predation is a driving force in the evolution of anti-predator defences, and death faking, or immobility in reaction to dangers, is a widespread defensive strategy shared by many animal species.
While this behaviour can improve an individual's chances of survival by diminishing a predator's interest, it also has drawbacks, such as less possibilities for eating and reproduction. Okayama University in Japan has explored how pheromones, crucial chemical cues that impact feeding and reproduction, can influence death-feigning behaviour in the red flour beetle, Tribolium castaneum.
These findings were published in the Journal of Ethnology.
“Male beetles release an aggregation pheromone called 4,8-dimethyldecanal (DMD), which attracts both males and females, aiding in successful foraging and mating. However, it remained unclear whether this pheromone could affect the duration of death feigning in these beetles,” said Professor Takahisa Miyatake from the Graduate School of Environmental, Life, Natural Science and Technology, Okayama University, Japan, who led the study. Prof. Miyatake collaborated with colleagues Motoya Ishikawa and Kentarou Matsumura from the same department on this study.
The team used a population of T. castaneum that had undergone artificial selection for death-feigning duration for more than 40 generations. The study encompassed two distinct experimental schedules. In the first, beetles were initially exposed to the pheromone, following which their death-feigning duration was measured.
In the second schedule, beetles were first evaluated for their death-feigning duration without the presence of the pheromone, and subsequently, the duration was measured with the pheromone introduced. In both scenarios, the researchers meticulously compared the death-feigning durations between the treatments.
The team found that T. castaneum beetles exposed to the DMD pheromone exhibited significantly shorter durations of death feigning compared to their counterparts that were not exposed to the pheromone.
This discovery suggests that the mere presence of the aggregation pheromone played a pivotal role in shaping the behaviour of these beetles, causing them to curtail their protracted death feigning.
Interestingly, while previous research has primarily focused on the triggers for initiating death feigning, little has been known so far about what cues awaken individuals from this state. The study suggests that aggregation pheromones, like DMD, may serve as one of these awakening factors. This adaptive response allows individuals to save precious time and increase their chances of survival when predators lose interest.
Furthermore, the study brought to light the potential sex-related differences in death-feigning behaviour. Previous studies have already indicated that both male and female adult red flour beetles exhibit a strong attraction to DMD, with males even intensifying DMD release upon sensing it.
Remarkably, during this investigation, researchers noted that males tended to have a longer duration of death feigning when compared to females. This observation raises intriguing questions about how the sexes allocate their time and energy, particularly in the context of dispersal and reproductive activities.
"Our study suggests that T. castaneum possesses the capacity to adapt its death-feigning duration when it detects the presence of an aggregation pheromone. This represents a remarkable example of behavioural plasticity in response to external chemical cues, as shown by previous studies. This may offer valuable insights into the intricate world of animal instincts, potentially paving the way for further exploration in the future," concluded Prof. Miyatake.
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