BONN, Germany -- For the first time, biologists have described the evolution of the size of a female trait which males use to choose a partner. The research, published in the open access journal BMC Evolutionary Biology, shows that male cichlid fish prefer females with a larger pelvic fin and that this drives females to grow fins out of proportion with their body size.
Sebastian Baldauf from the University of Bonn, Germany, worked with a team of researchers to study the effects of female ornamentation in the African cichlid fish Pelvicachromis taeniatus. He said, "In contrast to the well-known phenomenon of sexual selection influencing male traits, the expression of female ornaments in relation to body size is almost completely unexplored".
Female P. taeniatus develop exceedingly large pelvic fins, which differ from male fins in shape and color. During courtship, females fan out their violet pelvic fin, suggesting that the fin is actively used during mate choice. The researchers found that males clearly preferred females with a larger pelvic fin and that pelvic fins grew in a more disproportionate way than other fins on female fish.
According to Baldauf, "Our study is, to our knowledge, the first to show that male choice might scale the proportions of a female sexual trait, and therefore has implications for the understanding of the relationship of female traits with body size".
Reference: Baldauf, Sebastian A. & Theo CM Bakker, Fabian Herder, Harald Kullmann & Timo Thunken, 2010, Male mate choice scales female ornament allometry in a cichlid fish., BMC Evolutionary Biology, v. 10, 10:301; 26 p..
http://www.biomedcentral.com/content/pd ... 10-301.pdf
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, still 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.
We show that allometry of the female pelvic fin is scaled more positively in comparison to other fins. The pelvic fin exhibits isometry, whereas the other fins (except the caudal fin) show negative allometry. The size of the pelvic fin might be exaggerated by male choice because males prefer female stimuli that show a larger extension of the trait. Female pelvic fin size is correlated with individual condition, suggesting that males can assess direct and indirect benefits.
The absence of positive ornament allometry might be a result of sexual selection constricted by natural selection: fins are related to locomotion and thus may be subject to viability selection. Our study provides evidence that male mate choice might scale the expression of a female sexual ornament, and therefore has implications for the understanding of the relationship of female sexual traits with body size in species with conventional sex-roles.
Discussions on cichlid behaviour in nature & captivity.
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Change in habit, producing change of function, is the main cause of the production of change in living structure. F. Wood Jones (1953) Trends of life