Competition drives evolution of 'super sperm'
A yellow cichlid swimming in the southern shores of Lake Tanganyika. (Image: Sigal Balshine)
When females shop around, sperm evolve to be faster and fitter in just about every way.
It's known, for example, that sperm from promiscuous chimps move faster than those from relatively monogamous gorillas
, but no-one knew if this pattern was common among animals. Studies in other species have produced conflicting results.
To settle the issue, Sigal Balshine of McMaster University in Hamilton, Ontario, Canada, and colleagues studied a variety of species of cichlid fish living in Lake Tanganyika in central Africa.
Cichlids form a major family of fish, with species employing the full range of mating behaviours – from monogamy to "sperm shopping", in which a female gets several males to ejaculate into her mouth, which is where she carries her eggs.
