Cichlids produce bigger eggs in hazardous environments


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Mum can give you a helping hand when you are born into a rough neighbourhood, according to a paper to be published in a forthcoming issue of the Proceedings of the Royal Society B: Biological Sciences.

In this study, Francisca Segers and Barbara Taborsky report that female Tanganyika clowns (Eretmodus cyanostictus) can anticipate a hazardous environment for their offspring and increase offspring survival by producing larger eggs (which in turn lead to larger young).

The authors tested the hypothesis that a higher predation risk in their environments perceived by female mouthbrooding cichlids when young would induce them to produce larger eggs (that in turn produce larger young).  

The logic behind this hypothesis is relatively straightforward: in fish, the major predators are gape-size limited, so larger juveniles may outgrow these predators faster. Moreover, larger juveniles have a higher burst swim speed, which increases their chances of escaping from predators.

The mothers are expected to benefit, since they produce relatively few eggs (that make each offspring highly valuable) and increasing offspring survival heightens the chances of perpetuating their genetic material.

The authors hand-raised Tanganyikan clowns from eggs of known sizes and divided each clutch into two treatments. The fry were repeatedly exposed (using both visual and olfactory cues) to either to an empty tank or to an offspring predator (Ctenochromis horei) for a period of four months while growing up. A total of eight clutches were treated this way. After ten months, the female fish from both treatments were allowed to breed and the eggs they produced were harvested and weighed.

The authors found that the females that were exposed to visual and chemical predator cues as juveniles produced heavier eggs (that produced larger young) than those exposed to empty tanks. Their results thus suggested that the females used their experience when young to expect a high risk of offspring predation, and compensated for the reduced offspring survival chances by increasing their egg size.

For more information, see the paper: Segers, FHID and B Taborsky (2011) Juvenile exposure to predator cues induces a larger egg size in fish. Proceedings of the Royal Society B: Biological Sciences. doi:10.1098/rspb.2011.1290

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