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First published online November 10, 2003
Inside JEB |
'ROACHES SUFFER RAVAGES OF TIME
kathryn{at}biologists.com
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Getting old isn't easy, and it seems that cockroaches have it just as hard as humans. Angela Ridgel explains that Paul Schaefer was already looking at the aged insects' problems when she joined R. Ritzmann's lab. Schaeffer realised that when the elderly cockroaches needed to escape from a tight corner, they just didn't seem up to it! But it wasn't clear whether they'd just lost the ability to flee, or were facing other problems. Ridgel decided to focus on the aging problem from an insect's perspective. Setting the seniors a series of tasks, she tested how much of their youthful agility had been lost, and was astonished when she realised how closely the insect's decline mirrored that of elderly mammals.
But before Ridgel could put the ancient insects through their paces, she needed a group of cockroaches that were well past their prime. Fortunately, Ritzmann had been collecting cockroaches and letting them grow old gracefully for some time, so when she arrived in Cleveland, there were already plenty of elderly insects for her to test out.
Watching the insect's behaviour in an enclosure, it was clear that time had taken its toll. While the youngsters tore around at a frantic rate in search of cover, the elderly insects just stayed put for a while, before taking a short gentle walk and stopping again; they were far more sedate.
But how well could they walk? Ridgel set them on a treadmill and filmed the both young and old walking. Sure enough the youngster's pace was twice the older insect's, and when Ridgel took a closer look, it was clear that the aged cockroaches had a serious problem. Once in while, one of their prothoracic legs got tangled up with the leg behind, bringing the insect to a complete stand still before it unlocked the limbs and set off again. Ridgel wondered what caused the elderly insects to `trip up'? Were they controlling their limbs in a different way, or had their legs deteriorated?
Examining the insect's foreleg, Ridgel noticed that the leg which caught the one behind was much more bent than the freely moving limbs. Looking closely at the leg the tarsal pads were shrivelled and dry, and the retractor unguis tendon appeared to have vanished. It was clearly in bad shape, which probably accounted for the insect's mobility problem.
Ridgel also tested the insect's mobility under a variety of other circumstances, and found other problems too. The older insects couldn't climb as well as the youngsters, or right themselves when turned on their backs. And they never managed to mount a steep incline that the youngsters scuttled up without effort; not only did they lose their footing, but their ascent was uncoordinated too. And when she tested the elderly insect's escape behaviour, they seemed better at fleeing without their heads! Something in the insect's deteriorating central nervous system was blocking their flight.
The aging process had hit the insects hard. Not only were the insect's limbs deteriorating, but their nervous system seemed to have been affected by their lengthy lifespan too. Ridgel admits that she is surprised that the insects deteriorate to the extent that they do. She had expected that they'd die before the ravages of time became apparent, but it seems as if cockroach old age is as fraught as our own.
References
Ridgel, A. L. Ritzmann, R. E. and Schaefer, P. L.
(2003). Effects of aging on behavior and leg kinematics during
locomotion in two species of cockroach. J. Exp. Biol.
206,4453
-4465.
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