Having lots of offspring is linked to a shorter lifespan for both males and females in the colourful strawberry poison frog, a study has shown.

Scientists confirmed that raising large numbers of young reduced longevity in female frogs, but were surprised to discover that males may also pay a high price for having many offspring.

The findings suggest male frogs might work harder to look after their young than previously thought.

“This study confirmed that [reproductive] care is costly to females, but surprisingly revealed that reproduction is similarly costly to males,” said Dr Matthew Dugas, a research associate at Case Western Reserve University in Cleveland, US, who worked on the study.

“In both sexes, frogs that bred more didn’t survive as long.”

Dr Dugas and researchers from Tulane University in New Orleans, US studied the lifespans of 120 frogs in captivity and have published their findings in the Biological Journal of the Linnean Society.

Relatively few studies have investigated the cost of reproductive care in father animals, compared with research about mothers.

Male strawberry poison frogs (Oophaga pumilio) had been assumed to invest relatively little in their young: males only tend to the clutches, while females – after having laid the eggs – transport tadpoles to water and spend a month looking after them and feeding them with unfertilised eggs.

But males’ investment in their eggs appears to take its toll on the frogs more than expected.

"It's presumably not a conscious decision but males that care for clutches probably produce more offspring than males that don't, even if they don't live quite as long," said Dr Dugas, explaining the reason for the frogs’ sacrifice.

The team now want to find out what aspect of reproductive care is so costly to male frogs.

Reproductive duties for strawberry frog fathers include moistening the clutches and consuming eggs that have been spoiled by fungal growth to stop fungus spreading to the rest of the clutch. While this might sound beneficial to the males, Dr Dugas speculates that perhaps consuming spoiled eggs presents some immune problems to males.

Another costly activity might be the males’ increased time courting females.

Strawberry poison frogs are native to Costa Rica, Nicaragua and Panama, and although some populations are strawberry coloured, they can also be blue, green, yellow, black, orange or white. The frogs tend to be relatively long-lived, surviving up to four years.

Dr Dugas told BBC Earth: “I just think it’s neat, and probably underappreciated, that all sort of tiny animals are living pretty complicated lives.”

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