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Ticking Biological Clock Drives Female Cockroaches to Lower Standards

When it comes to reproduction, human females aren't the only ones to hear the tick-tock of their biological clocks. According to a report published today in the Proceedings of the National Academy of Sciences, aging female cockroaches face similar pressure. In response, the study shows, female roaches beyond optimal mating age lower their standards, demanding far less courtship from suitors than younger counterparts.

A popular model of mate choice holds that females should choose mates based on their own reproductive quality. In other words, dishy females in their prime should hold out for the most desirable males, whereas females of low reproductive quality must be less discriminating. This theory, study authors Patricia J. Moore and Allen J. Moore of the University of Manchester note, considers reproductive quality as an intrinsic value of the female. But what happens when a female's reproductive quality changes over time?

To address the question, the Moores studied Nauphoeta cinerea, a cockroach that, like humans, has reproductive cycles and gives live birth. The scientists measured female choosiness by the amount of wooing required from males before mating. Their findings fit neatly with predictions: older females, which have decreased reproductive potential owing to age-related changes in their reproductive systems, were less selective than younger females. "As females age past an optimal breeding period, the cost of mating preferences increased rapidly if preferences delayed mating," the authors conclude.

Males, in contrast, did not exhibit changes in their courtship and mating behavior as a function of female age. "Under our experimental conditions, perhaps males were unable to assess female age and reproductive quality," the researchers write, "or that the cost of passing up even a poor mating opportunity was greater than the investment in time and sperm production." Or they just weren't that picky.

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