A new study on Malawian mbuna has shown incipient speciation by sexual selection.
Professor George Turner and Dr Mairi Knight of the University of Hull undertook a laboratory experiment which monitored the mate choice of five different geographical races of the mbuna Metriaclima (Pseudotropheus) zebra which differ in male courtship colouration.
Once the fish had spawned, the offspring were removed from the buccal cavities of the mouthbrooding females and their paternity was examined using a technique which looks at microsatellite DNA. Microsatellites are short sections of DNA in which certain bases (G, A, T or C) are repeated - a trait which can vary among individuals, populations and species.
Of the 1955 fry produced in the experiment, 1296 of them (66.3%) were sired by the corresponding male from their own geographical race.
Turner and Knight say: "This result indicates that mate preferences of geographical races are strongly differentiated, consistent with the races representing incipient geographical species diverging under sexual selection exerted by female preferences for different male courtship colours."
You can read more about their research in: Knight, ME and Turner GF (2004) - Laboratory mating trials indicate incipient speciation by sexual selection among populations of the cichlid fish Pseudotropheus zebra from Lake Malawi. Proc R Soc Lond B Biol Sci. 2004 Apr 7; 271(1540): 675-80.