Quoll male die-off doesn't fit pattern.

A study of the short but enthusiastic lives of the male quoll--a ferretlike marsupial--may demand new theories of male die-offs after mating, say Australian biologists.

Many plants put all their reproductive effort into one big season. That strategy, called, semelparity, has been found in only a few terrestrial vertebrates, all smaller than the quoll, explains Meri Oakwood, now at the University of New England in Armidale, Australia.

In such species, including the teacup-scale antechinus, groups of females become fertile simultaneously only once a year. Then, males "commit themselves totally to obtaining mates," Oakwood and her colleagues say in the Feb. 22 PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON B. Usually before females give birth, males die.

Theorists suggested that high concentrations of corticosteroid hormones keep the tiny males, without much fat, on the go during the food-poor winter mating season. However, this boost, in theory, eventually inhibits the immune system and triggers fatal gastrointestinal bleeding.

Some larger marsupials like quolls follow a male die-off pattern, too, Oakwood and her colleagues contend. The researchers monitored quolls in Kakadu National Park. During the austral winter breeding time, males lost weight and fur, and most disappeared by season's end.

Unlike their tiny cousins, however, quolls weigh several pounds and store fat in their tails, and females register higher corticosteroid concentrations than males do. Such traits suggest that the biology of marsupial die-offs needs rethinking, Oakwood and her colleagues conclude.

--S.M.