Rodent Defense: Rat daubs fur with poison-arrow plant toxins

The deadly secret of a rat that kills lions and jackals has at last been revealed. 

Unlike some mammals that produce their own toxins, the African crested rat is the first known to protect itself by daubing its fur with poisons from plants. 

The same lethal toxins are used by African tribal hunters to coat their arrow-tips.

Suspecting that Lophiomys imhausi may obtain toxins from chewing on the bark of the poison-arrow plant, acokanthera, Fritz Vollrath of the University of Oxford and his team offered some to a captive animal. 

Over the course of a week, it periodically chewed the bark then smeared its saliva over a section of short hairs that lies along its flank, hidden inside its fur.

Placing the hairs under a microscope revealed that their surface is perforated. Each also contains fibres at its core, allowing it to soak up the toxins and store them.

Vollrath says the findings tally with reports that when attacked, the rat stands its ground, parts its fur to reveal the stripe of poisonous hair, and invites the aggressor to bite its flank. 

Aggressors who do go in for the kill have been seen to shrink back, froth at the mouth and often collapse and die, apparently from heart failure.

The rats are also known to have abnormally thick skins and skulls, which probably evolved so that they could survive attacks until the poison kicks in. They have also – clearly – evolved immunity to the toxins.

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2011.1169

Men and women respond to stress in different ways

Men and women respond differently to stress ScienceBlog.com

Defensiveness is a trait characterised by avoidance, denial or repression of information perceived as threatening. In women, a strong defensive reaction to judgment from others or a threat to self-esteem will result in high blood pressure and heart rate. Contrarily, older men with low defensive reactions have a higher cardiovascular rates.

A study was conducted on 81 healthy working men and 118 women. According to Dr. Jean-Claude Tardif a Université de Montréal professor and Montreal Heart Institute researcher, the physiological response to stress in women and older men is linked to this desire of maintaining self-esteem and securing social bonds.

"The sense of belonging is a basic human need," says D'Antono. "Our findings suggest that socialising is innate and that belonging to a group contributed to the survival of our ancestors. Today, it is possible that most people view social exclusion as a threat to their existence. A strong defensive reaction is useful to maintain one's self-esteem faced with this potential threat."

As part of the experiment, participants completed four tasks of varying stress levels.

• The first task involved reading a neutral text on Antarctica's geography before a person of the same sex.
• The second and third tasks involved role-playing in which participants followed a script where they were sometimes agreeable and sometimes aggressive.
• The final task involved a non-scripted debate on abortion.

Heart rate and blood pressure were measured during each of these tasks as was the level of cortisol in saliva. Results showed that women and older men had elevated cardiovascular, autonomic and endocrine responses to stress, all potentially damaging to their health.

However. the research team cautions that more studies are needed to evaluate the long-term effects of defensiveness and its association to stress response patterns in disease development.