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The Cost Of Keeping Eggs Fresh For Mother Cockroaches

Date:
March 16, 2007
Source:
University of Chicago Press Journals
Summary:
Tiny multiple sperm can be long lived, while large "expensive" eggs degenerate quickly if they are not fertilized. This conundrum -- there should be selection for females to keep their eggs fresh until they are used -- has recently been studied in a cockroach where some choosy females have genes that allow them to maintain eggs while looking for the best mate. Perhaps, however, these genes are limited because they are harmful in some environments.

A cockroach mom shelters her newborn babies.
Credit: Allen Moore

Tiny multiple sperm can be long lived, while large "expensive" eggs degenerate quickly if they are not fertilized. This conundrum -- there should be selection for females to keep their eggs fresh until they are used -- has recently been studied in a cockroach where some choosy females have genes that allow them to maintain eggs while looking for the best mate. Perhaps, however, these genes are limited because they are harmful in some environments.

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 sperm 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. This evolutionary conundrum -- there should be selection for females to keep their eggs fresh until they are used -- has recently been studied by Dr. Trish Moore and her colleagues at the Cornwall Campus of the University of Exeter, with support from NERC, and is published in the March issue of The American Naturalist.

Moore and colleagues examined why females don't keep their eggs fresh in a cockroach where females 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 oocytes through programmed cell death. But Moore's team finds that some females have genes that would allow them to maintain eggs even if they delay mating. So why aren't all females delaying cell death and holding onto their eggs? Moore speculates 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.

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." The group is currently investigating this trade-off arising from a conflict over food or sex. Although this is a new twist in the conflict over food or sex, the result is a familiar one in evolutionary biology; it is hard to be best at everything.


Story Source:

The above story is based on materials provided by University of Chicago Press Journals. Note: Materials may be edited for content and length.


Cite This Page:

University of Chicago Press Journals. "The Cost Of Keeping Eggs Fresh For Mother Cockroaches." ScienceDaily. ScienceDaily, 16 March 2007. <www.sciencedaily.com/releases/2007/02/070227105430.htm>.
University of Chicago Press Journals. (2007, March 16). The Cost Of Keeping Eggs Fresh For Mother Cockroaches. ScienceDaily. Retrieved October 22, 2014 from www.sciencedaily.com/releases/2007/02/070227105430.htm
University of Chicago Press Journals. "The Cost Of Keeping Eggs Fresh For Mother Cockroaches." ScienceDaily. www.sciencedaily.com/releases/2007/02/070227105430.htm (accessed October 22, 2014).

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