Studies addressing the adaptive significance of female ornamentation have gained ground recently. However, the expression of female ornaments in relation to body size, known as trait allometry, remains unexplored. Here, we investigated the allometry of a conspicuous female ornament in Pelvicachromis taeniatus, a biparental
cichlid that shows mutual mate choice and ornamentation. Females feature an eye-catching pelvic fin greatly differing from that of males.
This is a nice paper that offers a neat explanation for the large pelvic fins found in female kribs. Anyone who has kept and bred P. taeniatus will agree entirely with the arguments made in this paper. The female uses her pelvic fins to exaggerate the colour and size of her belly to the male. Males are attracted to gravid females – the more gravid the higher the attraction. It follows that females with bigger, more colourful pelvic fins will be more likely to attract males and thus be more likely to pass on the genes for bigger more colourful pelvic fins. Thus over the generations the female pelvic fins will tend to get larger and more colourful.
Of course if the pelvic fins are too large they will interfere with the females ability to swim, catch food and avoid predators. A balance will therefore occur between the forces of sexual selection – bigger and more colourful and natural selection – correct size for efficient swimming.
Read the whole paper here.