Pricey Eggs

One of the defining differences between the sexes is in the size of their gametes. Males make many tiny sperm while females make only a few large eggs. This suggests that sperm are cheap while eggs are expensive.

Yet sperms can be very long lived, while eggs degenerate quickly after they are made if they are not fertilized. Why don't females take better care of their expensive eggs? After all, if the females don't use their eggs, they have fewer offspring, whereas males make more sperm then they will use anyway.

Researchers examined why females don't keep their eggs fresh in a cockroach when they mate only once during a reproductive cycle, give live birth, and therefore are choosy about the male with which they will mate.

Females can't be too choosy, however. If they wait too long to mate they lose good quality germ cells through programmed cell death. But the scientists found that some females have genes that allow them to maintain eggs even if they delay mating. So why aren't all females delaying cell death and holding onto their eggs?

Researchers speculate that perhaps these genes play a dual role and while they may be beneficial under one environment, when females don't mate, they might be harmful under another, such as when food is limiting.

"When females are starving, hanging on to yolky eggs full of nutrients is bad," said Trish Moore from the University of Exeter.  "Instead a female could recycle those nutrients into her survival. So females face a decision between keeping eggs fresh for producing offspring now, or using those nutrients herself and taking the chance she can reproduce later."

---LiveScience Staff

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Credit: Allen Moore