World Oceans Day 2019 Part 2: Female Parrotfish Do Math for Better Reproductive Odds

Illustration by Missy Chimovitz

Illustration by Missy Chimovitz

This is part 2 of a three-part series honoring World Ocean Day 2019’s Theme of Gender and Oceans. See Part 1 here

Like many fish species, parrotfish form harems.  Because sperm is cheap to make, one male can produce plenty of it—enough to fertilize all the eggs of many females.  And like many harem-forming fish species, parrotfish sex changers, starting life as a female and then transitioning to male.  This strategy allows an individual to reproduce when small (as a female), and then when big enough to fight for and win a harem of females, they can transition to male and boost their reproductive output.

That’s usually what happens. But in bucktooth parrotfish, the largest female doesn’t always change to male when given the opportunity. Why?  Because sometimes, the transition just doesn’t add up when it comes to potential offspring output.

Bucktooth parrotfish, S. radians.

Bucktooth parrotfish, S. radians.

For fish, the bigger you are the more eggs you make. A very large female may produce ten times more eggs than a female half her size (we mammals are very different in this sense—all females have roughly the same number of eggs to start with, and that number goes down as we age). And somehow, female bucktooth parrotfish get this math…and act on it.

 If the largest female is so big that she produces more eggs than all the other females combined, she won’t transition to male.  A smaller female then takes up the male role, willing and able to fertilize all the eggs of the biggest female, plus the other females in the bunch.  

 Just how the big female conducts this calculation remains a mystery. But for this species, a little math goes a long way towards successful sex in the sea.For more details on this amazing strategy, see here.

Stay tuned for Part 3 of Sex in the Sea’s World Ocean Day: Gender and Oceans series.

World Oceans Day (WOD) 2019: Gender and Oceans Part 1

This June 8th, the UN’s theme for World Ocean’s Day is Gender and Oceans—a fitting subject as research highlights the importance of women in the long-term health of fisheries, the oceans, and communities worldwide. To honor this important theme, I’ve got a three-part series highlighting just some of the more fascinating female-driven strategies for successful sex from beneath the waves.  Here’s to celebrating the critical and awesome role of females in securing a sustainable future for the oceans—above and below the surface. Happy World Ocean Day!

WOD Part 1: Personal Sperm Banks Are Oh So Convenient

Finding a mate across the seven seas can be a right pain in the ass. It’s a lot of water to cover, and in three dimensions, don’t forget.  Instead of having to constantly search for and secure a mate, many females have instead  found ways to gather sperm and keep it—for when the timing’s right for reproduction.  Whether it is simply storing sperm in her uterus, or harboring the whole male inside her, these females have mastered the art of sperm-on-demand.

Ordering Sperm-to-Go

In sharks, females are known for their ability to store sperm for over three years after their last known mating and then use that sperm to successfully reproduce.  First observed in aquaria, this phenomena is seen across multiple species likely far more common than we had realized.  

In some squid, males place sperm packets onto females, often around her head.  Somehow, these sperm make their way through her body to a sperm storage receptacle.  When she’s ready, she releases her eggs, which pass by this holding tank and become fertilized in the process. 

The brownbanded bamboo catshark can  store sperm for over 3.5 years . Photo credit: Timothy Wong.

The brownbanded bamboo catshark can store sperm for over 3.5 years. Photo credit: Timothy Wong.

 

Keeping Him Close…Very Close

In the deep sea, we see a different twist on the personal sperm bank strategy.  There, Ceratioidei anglerfish females attract tiny dwarf males to them via chemical signals and then fuse their bodies with these parasitic mates.  The permanently attached male receives nutrients from the female and in return, provides her with sperm on demand.  In fact, that is his sole role in the relationship, given that most of his other internal organs dissolve in the fusing process.  Check out this awesome comic by the fantastic Oatmeal for a great summary of this strategy and see this amazing footage of a live female and male pair, caught on video for the first time.

An inside job

Spawning female Osedax worm. Photo credit: G. Rouse.

Spawning female Osedax worm. Photo credit: G. Rouse.

Female osedax worms take the personal sperm banks even farther—storing not just sperm but the entire male inside her body.In fact, it is likely that the female “makes” her own males by releasing a chemical that stunts the growth of nearby larvae swimming by and triggers them to develop testes. Microscopic and stuck in this pre-pubescent state, the tiny males swim down the female’s tube and gather around her ovaries. There, they spend their days pumping sperm out of holes in the tops of their head.A single female may have hundreds of these males working away in side her. Perhaps “sperm factory” is a better term than sperm bank, but, well, you get the idea. For more on this wild strategy, check out this episode on Stuff To Blow your Mind Podcast.

Check out Part 2 and Part 3 of the series, celebrating female-driven strategies for sexual success in the sea as part of World Ocean Day 2019: Gender and Oceans!