Lonely flatworms inject sperm into their own heads

Consider the lengths that some hermaphroditic flatworms will go to in the name of reproduction. In the absence of mating opportunities, hermaphroditic flatworms such as Macrostomum hystrix self-fertilize by stabbing themselves in the head with their penile appendage and injecting sperm, report biologists from the University of Basel in Switzerland today in the Proceedings of the Royal Society B. 

The researchers suspect that the head penetration is necessary simply because the worms can’t fold tightly enough to get their penile appendage any closer to the ovaries. The sperm then presumably swim through the body cavity to the ovaries where development of a hatchling can begin.

Lukas Schaärer/Flickr/Creative Commons

Ladies first: The manners of the California sheephead

A young lady sheephead on the move in Monterey.

Like many fish in the wrasse family, California sheephead (Semicossyphus pulcher) change genders as they age. All begin life as females and tragically/luckily become males later in life—depending on your perspective.

There are many reasons to change genders in the fish world. For sheephead, it’s a matter of how many offspring you can have—and size matters.

A big girl cruising off of Santa Rosa Island in the Channel Islands National Park.

Eggs are energetically expensive to make, and they take up a lot of room. Eventually, you could fertilize more eggs as a male than you could make as female—giving females an evolutionary incentive to cut their losses and make the switch.

As a result, sheephead change genders between 5 and 8 years of age if there isn’t enough food to get very big. When there is a lot of food—giving egg-making a longer shelf-life—females grow larger and make the switch as teenagers. 

A large and in-charge male in the Channel Island—who is also a Giants fan, apparently.

Seeing large males is one of the great pleasures of diving in marine protected areas. By protecting their food, reserves help females—and the males they’ll become— grow larger. By protecting big males—which are the limited resource on the dating scene—sheephead are healthier genetically. 

And get this: you can help our work to protect our oceans and the fascinating animals that live there through a strong network of marine protected areas.

On your visit, you can find juvenile, adult female, and adult male sheephead in our kelp forest exhibits—and if you find our big boy, you can remember his life story with this little ditty:

There once was a little girl sheephead

Who recently her childhood completed

But one day on a date

She had outgrown her mate

So she became her own brother instead.