'Mum' communicates through the egg

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Female sticklebacks are able to influence the development, growth and behaviour of their offspring by altering the amount of chemicals in the eggs.

According to a paper published in the most recent issue of the Proceedings of the Royal Society B: Biological Sciences, the study by Eric Giesing and coauthors revealed that female sticklebacks that were frequently exposed to a predator produced eggs and fry significantly different in physical attributes and behaviour compared to those that were not.

The authors regularly exposed 30 gravid female Threespine sticklebacks (Gasterosteus aculeatus) housed individually in tanks to a model predator. This was done by chasing the fish for approximately 30 seconds once a day at a randomly chosen time with a painted model of a natural predator, the Northern pike (Esox lucius) in an experimental setup prior to and during egg formation.  

Another 15 females were left undisturbed in an identical setup acting as a control experiment.  

After an average of 25 days, the females were removed from their tanks and stripped of their eggs. The eggs were then artificially fertilised and the authors then compared the resulting offspring from the two treatments for egg characteristics (egg size, egg number, egg cortisol concentration, metabolic rate) and post-hatching characteristics (growth and shoaling behaviour).

The authors found that the females that were exposed to the predator produced larger eggs (although the number of eggs they produced was not significantly different from those produced by the control group).

The eggs produced by the females that had been exposed to the predator also had a higher concentration of cortisol in them, with the developing fry consuming more oxygen shortly after fertilisation (as a result of the elevated cortisol) compared with the control group.  

The young of the predator-exposed fish schooled more tightly (evidenced by a smaller average distance between neighbouring fish) compared to those of the control group.

The authors hypothesise that the increased egg size of the predator-exposed fish may provide the fry with an additional advantage, since previous studies have shown that fry hatched from larger eggs feed, swim, and in general survive better.  

The difference in the shoaling behavour of the fry suggested that maternal experience might cause intergenerational transmission of information about predation risk. However, the authors are unsure if the changes in fry behaviour observed are due to the cortisol level, the size, or some other modification (e.g. to the fats or the egg protein) of the eggs, nor do they know for how long maternal effects on offspring behaviour will persist or whether the effects extend to other behaviours (or are just limited to antipredator behaviour).

For more information, see the paper: Giesing, ER, CD Suski, RE Warner and AM Bell (2011) Female sticklebacks transfer information via eggs: effects of maternal experience with predators on offspring. Proceedings of the Royal Society B: Biological Sciences 278, pp. 1753–1759.