July 7, 2009

Male seahorses prefer large mates

Swiss scientists say they've found male seahorses have a strong preference for large females so as to have more and bigger eggs, as well as larger offspring.

Beat Mattle and Tony Wilson of the Zoological Museum at the University of Zurich, Switzerland, said seahorses have an unusual mode of reproduction: male pregnancy. And male seahorses provide all post-fertilization parental care, yet despite the high levels of paternal investment, they have long been thought to have conventional sex roles, with females choosing mating partners and males competing for their attention.

But Mattle and Wilson said clutch, egg and offspring size all increase with female body size in seahorses, suggesting males can obtain fecundity benefits by mating with large-bodied females.

They also discovered differences in courtship behavior between male and female seahorses, with males highly active and showing a clear preference for larger partners. In contrast, females were significantly less active and showed ambiguous mating preferences.

The findings appear in the journal Behavioral Ecology and Sociobiology.