Female cockroach 'also driven by biological clock'

Women of a certain age are not the only ones affected by a ticking biological clock - female cockroaches feel it too, scientists revealed today.

Researchers found that as time runs out, older female cockroaches become less choosy about their mates.

They tend to throw themselves at available males, whereas younger bugs are far more picky.

Declining reproductive ability is behind the desperate behaviour of female cockroaches which are a little long in the mandible, according to the Manchester University scientists.

They believe the same principle applies to a wide range of creatures whose reproductive capacity declines with age including humans.

The findings were reported today in the American journal Proceedings of the National Academy of Sciences.

Patricia Moore and colleagues from the university’s School of Biological Sciences tested the choosiness of female cockroaches of different ages by placing them in a box with an eligible male.

Males had to work harder to woo the younger females, which sometimes rejected them altogether.

Females older than six days into their adult phase - their prime mating age - required far less courtship and mated more readily.

There was a clear correlation with reproductive ability.

Female cockroaches that mated at 15 or 18 days of adult age took much longer to produce a first clutch of young than younger insects.

The cockroach studied, Nauphoeta cinerea, does not lay eggs but develops its young in a brood pouch, and gives birth to live nymphs.

The researchers said in an article in the PNAS: ‘‘We have shown that female N. cinerea became less choosy as they age; that is, older females mated more quickly than younger females.’’

Male cockroaches were not affected in the same way. They remained just as eager to mate, whatever the female’s age.

This may have been because males were unable to assess female age and reproductive quality, or because the cost of passing up even a poor mating opportunity was greater than the investment in time and sperm production.

The scientists added: ‘‘Researchers are beginning to look for and identify variation among females in patterns of mate choice. As we show here, variation may occur within a female as well as between females if female condition changes.

‘‘Such changes may be common, because a similar pattern of reduced reproductive capacity with age is seen in organisms taxonomically distinct from cockroaches, such as humans.’’