Q34 — Cichlid Fish — Anal Fin Egg-Spot Signalling

Theoretical 1 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license

Lake Malawi in Africa is home to the cichlid Labidochromis caeruleus, whose females carry their eggs and larvae in their mouths for several weeks before the juveniles become independent. Each adult male individually tries to protect its territory from other males, showing them its mouth and opening its gills. Males also have yellow, round dots on the anal fin that resemble the species’ eggs.

Female (top) and male (bottom) Labidochromis caeruleus, showing the male’s yellow anal-fin egg-spots. Labidochromis caeruleus female.

Male Labidochromis caeruleus with yellow egg-mimicking dots on the anal fin. Labidochromis caeruleus male.

Using the information and images, determine whether the following statements are true or false:

A. The yellow dots on the male anal fins attract females because they signify strength in the male.

B. Yellow dots are selected for through intersexual selection, i.e. female preference rather than intrasexual selection, i.e. male-to-male competition.

C. The male of Labidochromis caeruleus shows the dots on its anal fin during the breeding season to other males, disrupting their mating behaviour, and thus getting a higher chance to fertilize the eggs of a female.

D. Females of Labidochromis caeruleus can re-enter the reproductive process after the embryo and larvae, which are kept in their mouths for a week, become independent.

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Question reproduced from IBO 2022, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)