Indirect and Direct Mate Choice in diversification of Lake Malawi Bower-Building Cichlid Fish

Sand-dwelling cichlids from Lake Malawi exhibit fascinating breeding behavior: seasonally mature males congregate on leks where they defend territories consisting of an elaborate sand-castle ("bower") maintained for a period of several weeks with the sole purpose of atracting females. Receptive females visit the leks to spawn, tipically with multiple males , before leaving with the fertilized eggs in their mouth, and release free-swimming fry aproximately 3 weeks later. Multiple species can coexist on the same lek, and bowers are always species specific. Sand bowers appear to be used both by females to access their potential mates (direct sexual selection) and also in male-male comptetion for territories and females (indirect sexual selection).

This project was divided in two parts, one of them based on experiments conducted in 2 large tropical pools set up in the botanic gardens where I studied their behaviour in a controlled environment. The objectives of this research were: (1) to understand the importance of substrate heterogeneity in the formation of differently shaped bowers in bower diversity (each pond has a different type of sand); and (2) to comprehend the importance of building and holding a bower for the mating success of these fish, by analysing numbers of offspring fathered by fish that hold bowers versus fish that did not.

The second part consisted of a field experiment at the Lake Malawi National Park, where we tested the idea that reduced male aggression towards males with less common bowers can maintain polymorphisms in populations. We found that males with altered bower shape (manipulation group) were involved in significantly fewer aggressive interactions with conspecific males than males of other treatment groups. This part of the work has now been published and mentioned in the national press (see publication list and national press).