19 November 2007

Females Finessed By Fishy Fellatio

by Kate Melville

Researchers from Konstanz University in Germany have identified a gene in male cichlid fish that evolved to lure female fish into close proximity so that the male can deposit sperm in the female's mouth. The study, in BMC Biology, reveals that the gene is responsible for egg-like markings on the fin which are central to the success of the fishes' exotic oral mating behavior.

Researchers Walter Salzburger, Ingo Braasch and Axel Meyer identified the gene involved in producing the yellow spots on the fishes' fins. These markings, known as "egg-dummies," are found on the anal fins of the male fish. The fish are known as maternal mouth-brooders, because once the female has laid her eggs, she picks them up in her mouth.

Attracted by what she takes to be eggs - actually the egg-dummy markings - the female then approaches the male. When the female is close enough, the male discharges his sperm into the female's mouth to fertilize the real eggs.

The study notes that there are more than 1,800 cichlid species and more than 80 percent of these belong to a grouping known as the haplochromines, which exhibit the characteristic egg dummies.

The gene that is involved in producing the fake egg markings is called the colony-stimulating factor 1 receptor a (or csf1ra). The researchers also showed that the gene was expressed in the egg-dummies of a distantly related species, in which the spots developed on the pectoral fins rather than the anal fins. "The two kinds of independently evolved egg-dummies serve as a model system to test whether the same genetic pathways are involved in the morphogenesis of both types of dummies," say the authors.

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Promiscuous Females Make For Competitive Sperm

Source: BioMed Central
Pic courtesy Erwin Schraml