In 2012, researchers found one of the Animal Kingdom's costliest parenting jobs belonged to snail dads

Snail dads: In 2012, researchers reported that male marine whelks, Solenosteira macrospira, take on one of the animal kingdom's most demanding parenting roles. The fathers carry hundreds of developing eggs on their shells for about a month until they hatch, even though most of the young they protect are not their own.

The study, published in Ecology Letters, described Solenosteira macrospira as part of a small group of reproductive outliers characterized by male-only child care.

Male snails raise young that often are not their own

The marine whelk, Solenosteira macrospira, lives in tidal mudflats off Baja California. When the snails mate, females glue capsules containing hundreds of eggs onto the male's shell.

Researchers from the University of California, Davis found that, on average, only about one in four of the eggs carried by a male actually belonged to him. Some males were found carrying offspring fathered by as many as 25 other males.

Stephanie Kamel, a postdoctoral researcher in Rick Grosberg's laboratory, used DNA analysis to determine the parentage of the eggs, as per a report by UCDavis. She also found that some female snails mate with as many as a dozen different males.

Carrying the eggs comes at a price

A male's shell can become covered with dozens of egg capsules, each holding up to 250 eggs. The eggs remain attached for about a month before hatching.

Researchers found that carrying the capsules is not without consequences. By tethering individual snails to posts in the sand and monitoring them over time, Rick Grosberg showed that the egg capsules imposed a significant burden, reflected in weight loss.

The researchers suggested that males may have little choice because females attach egg capsules during mating. Grosberg also said carrying the capsules could signal to females that a male is capable of providing parental care.

Grosberg said, "If he wants to get any action, he has to pay the price," as quoted in the UCDavis report.

Only a few hatchlings survive

The male's shell likely serves as a substitute for rocks, which are scarce in the snails' habitat. Carrying the egg capsules also protects them from heat and drying as the snails move in and out with the tides.

When the eggs hatch, however, not all of the young survive. Researchers reported that some baby snails eat their littermates inside the egg capsule, leaving only a handful of hatchlings to emerge and crawl away.

According to Grosberg, the species provides an opportunity to study conflicts between parents, siblings and offspring as they compete for resources and reproductive success. The research was funded by the National Science Foundation.