Marine Whelk Dads Babysit for Other Dads

Posted on August 30, 2012

Solenoptera Macrospira Babysitting

A male marine whelk, Solenosteira macrospira, will do all the work of raising the young, from egg-laying to hatching. He does this even though few of the baby snails are his own. The surprising new finding was made by researchers at the University of California, Davis. The snails live in tidal mudflats off Baja California. A male marine whelk is pictured in the photo above on the left with egg capsules on its back. A female free of capsules is on the right.

In the study, UC Davis researchers report that, on average, only 25% of the eggs a male S. macrospira carries around on his back belong to him. Some carry the offspring of as many as 25 other males. The snails were first described in an amateur shell-collectors newsletter, The Festivus, in 1973. Rick Grosberg, a professor of evolution and ecology at UC Davis, started studying the animals in 1994, when he brought some back from a collecting trip and realized that only male snails had egg capsules on their shells.

When the snails mate, the female glues capsules containing hundreds of eggs each to the male's shell. A male's shell may become covered in dozens of capsules, each containing up to 250 eggs. As the eggs hatch, a process that takes about a month, some of the baby snails devour the rest of their littermates. Typically only a few hatchlings survive the fratricide to emerge from a capsule and crawl away.

Stephanie Kamel, a postdoctoral researcher in Grosberg's lab, says, "The promiscuity in the female snails is extraordinary."

Grosberg says that it may be that carrying the egg capsules simply represents the best of limited options for the males, since it's impossible for them to mate without the female attaching an egg capsule to their backs. Carrying the egg capsules may be a way for a male to show a female that he's good parent material.

Grosberg says, "If he wants to get any action, he has to pay the price."

The research was published here in the journal Ecology Letters.

Photo: Peter Marko

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