Marine worms prefer experienced fathers
6 November 2009, by Sara Coelho
Forget about manliness or dominant status - for Neanthes marine worm females, nothing is more attractive than a male reeking of babies. The smell of fatherhood is crucial when choosing a partner because the female dies after laying her eggs and the survival of her offspring depends entirely on the male's parenting skills.
In many species of animals, discerning females decide who to mate with by watching dominance fights between males or screening their potential partners for signs of health or strength. That is why stags fight for harems and why male peacocks evolved their glamorous tails for show-off purposes.
For the females of the Neanthes acuminata marine worm choosing the right partner is the most important and last decision of their lives. They die shortly after laying eggs and the survival of their larvae depends on the care provided by the male.
'The females have only one chance of success, so they have to choose a good mate,' says Dr Jörg Hardege. His lab at the University of Hull focuses on how animals use odour and chemical compounds to choose mates and communicate.
After the female's death, 'the male takes care of the eggs and produces white mucous to feed the larvae,' he adds. 'If the females pick a bad father the larvae will perish and the dying mother loses the opportunity to pass on her genes to the next generation.'
Hardege and PhD students Nichola Fletcher and Ellen Storey ran a series of experiments to find out what lies behind the females' decision making. The results, published this week in the journal PLoS One, show that they choose males not for their size or fighting prowess, but for their parental care credentials.
'The females really go for the most experienced fathers,' says Hardege.
When the female marine worms were allowed to witness a fight between two inexperienced males, they chose to mate with the winner. But when they were given a choice between a rookie and an experienced father, they always went for the latter, even if they had just lost a fight.
It's not clear how females tell experienced parents from clueless males, but Hardege suspects some sort of baby smell in the water. In his experiments, females had second thoughts about previously rejected males after they were bathed in a small tank with larvae. 'There is some chemical in the water that makes them more attractive,' he says.
Hardege doesn't know which compound is responsible for the smell of parenting experience. 'It might be a steroid as in fish, or a protein hormone like in mammals - we just opened the door and there is a lot more to discover.'
Whatever the chemical involved, it's powerful. The smell of experience is such a strong preference that males are known to develop parenting skills caring for broods which are not their own.
'It's an investment,' explains Hardege. 'They are not wasting time raising unrelated larvae, they need to do it to become more attractive and have a reasonable chance to sire their own offspring.'
Fletcher N, Storey EJ, Johnson M, Reish DJ, Hardege JD (2009) Experience Matters: Females Use Smell to Select Experienced Males for Paternal Care. PLoS ONE 4(11): e7672. doi:10.1371/journal.pone.0007672
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