A mouse diced with death when it stole some food from under the nose of a leopard at the Santago Rare Leopard Project in Hertfordshire.
Instead of pouncing on the mouse, the 12-year-old African leopard, called Sheena, simply watched as it fed on scraps of meat thrown into its enclosure.
At one stage she tried to nudge the mouse away with her nose, but the mouse carried on eating regardless.
Imagine an infection that made you enthusiastically seek out the presence of grizzly bears, essentially offering yourself up as a tasty snack. Sounds ridiculous or even impossible, right? Oddly enough, it is entirely plausible. The parasite Toxoplasma gondii - a mere single-celled organism - is able to manipulate the brain responses of rodents to the odour of cat urine. The usual fear response is replaced by sexual attraction, so causing individuals to actively seek out areas where they are likely to run into their predators. Toxoplasma gondii requires the feline digestive system in order to sexually reproduce, so by modifying the rodent’s behaviour to cause it to spend more time around cats, it increases the likelihood of the individual ending up exactly where they need it to be - in its stomach.
Ref: House, Vyas & Sapolsky (2011) Predator Cat Odors Activate Sexual Arousal Pathways in Brains of Toxoplasma gondii Infected Rats. PLoS ONE 6(8): e23277.
Compared with our lowly 350 olfactory receptors in humans, rats and mice have over 1200, essential in their mostly scent-guided world. As such, the social behaviour of rats and mice is influenced by pheromones - chemical factors that elicit a response in the same species. Less well studied are the effects of kairomones, chemical factors that elicit behavioural response across different species. An example of this complex interspecific communication has recently been discovered between rats and mice and their predators: a compound found in high concentrations in the urine of carnivorous mammals produces an instinctive avoidance response in rats and mice.
The kairomone 2-phenylethylamine, a product of protein metabolism, is found at a concentration over 3000 times greater in carnivorous mammals than in herbivorous mammals. Due to its volatility (particles are easily suspended in the air), these high levels of 2-phenylethylamine can de detected from great distances. When it reaches the nose of a rat or mouse, the kairomone activates trace amine-associated olfactory receptor TAAR4, causing an innate avoidance response. While this is a key aid in survival for rats and mice, meanwhile, we would walk on by oblivious, as we completely lack the gene for TAAR4. The mechanism by which chemical receptors are translated via neural circuits to behaviours is a fascinating subject, as yet unresolved.
Ref: D. M. Ferrero et al. (2011) Detection and avoidance of a carnivore odor by prey. Proceedings of the National Academy of Sciences 108(27) 11235-11240 [link]