Study: Water bugs with wider paternal care get more mates

Asahi Shimbun

2 days ago

A male giant water bug with eggs on its back and a female bug (Provided by Shinya Oba, an associate professor of biology at Nagasaki University)
Men desperate for affection from females could learn a lesson from the mating habits of giant water bugs.
According to a study by researchers from Hiroshima Shudo University, Nagasaki University and Shinshu University, male giant water bugs that show tenderness and care for a wider number of potential offspring--even those of other fathers--are particularly popular among female bugs.
Giant water bugs are about 2 centimeters long and found primarily in rice paddies and reservoirs.
Females of the aquatic species lay their eggs on males' backs during breeding season from spring to summer.
The variant, closely related to the shield bug, is called 'kooimushi' (baby-carrying insect) in Japanese.
It takes about 10 days to two weeks for the eggs to hatch. Males are occasionally loaded with more than 100 eggs during the process.
This heavy burden makes it impossible for males to fly. Despite the escalated risk of predation, the males regularly rise to the water surface to provide oxygen to the eggs.
The devoted insect fathers also stretch their legs over their backs to brush dirt off the eggs and keep them in good condition.
The study to determine bug popularity was started in 2012 by Tomoya Suzuki, an assistant professor of biology at Hiroshima Shudo University. Suzuki belonged to the graduate school of Shinshu University at the time.
Twenty male and 20 female giant water bugs were collected in Matsumoto, Nagano Prefecture, and placed in a breeding cage for voluntary mating.
The team of scientists determined the parentage of 390 of the 2,640 hatched larvae through DNA data.
The genetic analysis found that males that carried more eggs tended to produce more descendants in their lifetimes.
The scientists also found that an average of 35 percent of the eggs carried by the males were offspring of other males.
The results confirmed the hypothesis in previous research by Shinya Oba, an associate professor of biology at Nagasaki University and a member of the team.
Oba theorized that 'males who closely care for eggs are more often chosen by females for mating partners.'
'It has been confirmed that even if the eggs come from other males, bearing more of them on their backs increases the likelihood that they will further propagate,' Suzuki said.
PATERNAL BUG CARE
According to the research team, male insects rarely care for eggs or larvae on their own. This behavioral pattern, called paternal care, has also been observed in bird and fish species.
As paternal care naturally takes a heavy toll on males, such behavior was believed limited to circumstances in which the biological relationship between fathers and children was certain.
The water bug research has cast doubt on this conventional notion.
The team's findings were published in the international academic journal Ecology and Evolution in late April.
The researchers plan to examine paternal care styles in the Japanese giant salamander and millipede species.