London, July 8 - Male sea-horses prefer bigger females for sex and for bigger offspring, a recent study has revealed. This finding is consistent with predictions on the importance of female body size for reproduction in this species.

Sea-horses have a unique mode of reproduction: male pregnancy. Male sea-horses 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.

However, clutch, egg and offspring size all increase with female body size in sea-horses, suggesting that males may obtain fecundity benefits by mating with large-bodied females.

Beat Mattle and Tony Wilson from the Zoological Museum at the University of Zurich, Switzerland, probed the mating behaviour of the pot-bellied sea-horse, concentrating on the importance of partner body size in mate selection.

Ten female and 16 male sexually mature sea-horses, obtained from a captive breeding facility in Tasmania, took part in the experiment.