Too Much Sex Lowers Sperm Quality in Bats

May 10, 2016 | Erica Tennenhouse

A bat roosting at the Ueno Zoo in Tokyo
Photo credit: tomosuke214/flickr (CC BY-NC-SA 2.0)

Some bats seem to have it all — but appearances can be deceiving.

Harem males are the studs of the bat world, maintaining exclusive groups of fertile females and beating up any intruder males that wander too close to the roost.

In Seba’s short-tailed bats, harem males have essentially unlimited sexual access to the females they defend — an ideal situation for a bat looking to spread his seed. But this apparent good fortune might actually be a bit of a curse, according to a study published in the Journal of Experimental Biology.

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Though harem males aggressively remove intruders from the roost when they can, sometimes it can take just a moment for a male to sneak in and mate with a female or two. Previous research has shown that sneaker males who frequently use this strategy produce faster, longer-lived sperm than harem males. It was at first thought that this super sperm was an adaptation that compensated for the sneaker males’ rare access to females.

However, the researchers have now found that there is no super sperm in the mix. Rather, less frequent sex gives the sneaker male sperm time to get into better shape.

The researchers forced harem males to be abstinent by separating them from females for a few days, and then collected sperm samples. They found that sperm quality vastly improved in speed and motility by the end of that period. A quick break from all of that sex was all that harem males needed to bring their sperm up to par.

Longer storage time may help sperm accumulate important proteins and improve their structure, according to the researchers.

Despite these new findings, harem male short-tailed bats are unlikely to adopt abstinence as a strategy for improving their sperm any time soon because, luckily for the sneaker males, bats cannot read scientific papers.

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