Sex Change By the Numbers: a tax season reflection

Getting the arithmetic right matters more than you may think for fish...

Getting the arithmetic right matters more than you may think for fish…

While we’ve all been busy crunching numbers for tax time, the female bucktooth parrotfish has been doing a little math, too—except instead of calculating taxes, she’s deciding whether or not to change sex.  In the world of fish, getting the arithmetic right can make or break your sex life.

Fish are some of the few vertebrates that have the ability to regularly change sex (other verts, such as some frogs, may do it under extreme circumstances). And while this is a pretty nifty party trick, changing sex takes a lot of energy- transforming one’s genitals and gonads (external and internal sex parts) is no simple task. So why do fish bother? The answer is: reproductive success. It all comes down to how many offspring an individual can produce. Here’s how it works:

The most common way fish change sex is from female to male. This is called (take a breath) sequential (one gender after another) protogynous (first female, then male) hermaphroditism (one individual, two sexes in a lifetime). In general, for species where big males can control access to females (think harem), it pays to be female when small (you get to reproduce with the dominant male) and then turn into a male when you are big enough to duke it out with a competing male to win access to a group of females.  There are also protandrous hermaphrodites, who start male and turn to female (brace yourselves, Finding Nemo fans, the folks at The Fisheries Blog don’t mince fins on this one)—more on that strategy later.

Back to why switching to male can make sense: sperm are less expensive to manufacture than eggs, so one male will be able to make lots more sperm than a similar sized female can produce eggs—as long as there are enough females churning out enough eggs for the male to fertilize, he’ll make more offspring. The female-to-male sex switching strategy allows for maximum reproduction during all stages of life, when small and when larger…if the conditions are right.

Bucktooth parrotfish. Photo credit: Kevin Bryant.

Bucktooth parrotfish. Photo credit: Kevin Bryant.

And here’s where a little math goes a long way.

Unlike us, the bigger the fish, the more eggs or sperm they can produce. For our species, every woman is born with a set number of eggs, no matter if she grows to be a towering 5’11″ or petite 5’0″. And a man’s sperm count has little to do with body size.  Not so for fish. The bigger the female, the larger the number of eggs she produces (and often, the higher quality).  A fish that doubles in size may gain over 10x as many eggs. This fact alone has major implications for management: catching one large female fish can reduce the reproductive output of a school by the same amount as several smaller females. Accounting for that in setting quotas and size limits can be really complicated, but it is critical to effective management. Saving these Big Old Fat Fertile Female Fish (BOFFFS) has become a focused effort of some conservation initiatives, including design of marine protected areas.

Which takes us back to the arithmetic those bucktooth parrotfish females are constantly conducting.  As they grow larger, they have to weigh which choice will bring more babies: changing to male and gaining access to multiple females or staying female, and having your eggs fertilized by the dominant male.  If the sum total of all the eggs produced by all the other females is more than your total number of eggs, it pays to switch and be the male. But, if as a large female you make more eggs than all the other females combined, than you should stay female.


Photo credit: Flickr Creative Commons

Photo credit: Flickr Creative Commons

If (female 1 + female 2 + female 3) < eggs than female 4, female 4 stays female.

If (female 1 + female 2 + female 3) > eggs than female 4, female 4 will likely switch to male and take over the harem (and thus begin fertilizing all those eggs).

A large female is especially likely to skip sex change if there are other males around crashing the love nest. In some species, the dominant male is not as dominant as he looks: “sneaker” males that hide nearby can dash in and add their own sperm to the mix (remember, fish have external fertilization, casting sperm and eggs into the water) right when the dominant male spawns. These “sneakers” create high levels of sperm competition that dilute the dominant male’s success rates.  This is good for females, whose eggs are bathed by plenty o’sperm (and a greater diversity of genes), but it is bad news for the male. Studies have shown that in species where this happens, large females often choose not to turn into males. Such is the case with bucktooth parrotfish.

Instead of the standard large size/status-triggered sex change of most protogynous hermaphrodites, large female bucktooth parrotfish are constantly sizing up the other females in the harem, noting the sneakers streaking in, and doing a little mental math to figure out whether its worth it to change sex. And you thought figuring out your taxes was hard.






Lolita of the Sea(weed)

Seaweed by the shore. Photo by Nick Ellis.

Seaweed by the shore. Photo by Nick Ellis.

Swaying gently with the surge, seaweeds appear remarkably passive. But don’t be fooled—there’s a wild sex engine hidden within those seemingly limp fronds that’s been driving eons of sexual experimentation. And the results are kind of mind-blowing: just trying to read the life-cycle diagrams sent me reaching for some kelp cocktails.

Luckily, I met seaweed guru, Dr. Thierry Chopin, professor at the University of New Brunswick.  I was interviewing him about his interesting work on Integrated Multitrophic Aquaculture (IMTA), for a project I was working on at Future of Fish. After our conversation, Dr. Chopin was kind enough to whip out a fantastic summary of the remarkable diversity of seaweed sex lives on his website. You can read his detailed S.S.S. article here.  From the completely illogical lumping of seaweeds as a group (many are more distantly related to each other than we are to a tree) to the remarkable stories of the discovery of some of these sexual exploits, he weaves a wonderful tale.

And the take home message is clear: there is no one “sex life” of seaweeds. Instead, there is an endless fractal-like sexscape with every imaginable permutation: male-female couplings? They got that. Hermaphrodites? Sure. Asexual inter-generational phases? Check. Dwarf females? Yup. Self-perpetuating gametes alternating with parthenogenetic spore-replication…they got that too (go ahead, grab that second kelp cocktail, now).

Amidst all this crazy kinkiness, there is one story that I found particularly intriguing, and it’s about a rather well-known and popular edible seaweed called dulse (Palmaria palmata). Though it has been used for food and medicine for centuries, the ability to cultivate it remains a challenge—in part because its sex life was unknown until 1980.  The greatest puzzle was the absence of mature females: nomatter where we looked, we couldn’t find them. The male dulse certainly knew where they were; the species grows all over the intertidal on both sides of the Atlantic. But we remained in the dark.


Shoreline covered in dulse and irish moss. Photo by Akuppa John Wigham

Shoreline covered in dulse and irish moss. Photo by Akuppa John Wigham

A little luck, and a lot of detective work, finally lifted the veil on this mysterious species about 30 years ago. I’ll leave it to Chopin’s blog to tell the tale of discovery. I’ll focus here on translating what they discovered. It goes something like this:

Every dulse has three “siblings.”

So, when Dad meets Mom, her twin sister and two younger twin brothers are hanging around too. Her sister we will ignore, but let’s call the brothers Dave and Don.

Dad releases his tail-less sperm, called spermatia, into the water and they bob their way over to Mom’s egg-holding fronds. Mind you, Mom is really, really tiny, a stunted version of Dad. It’s one of the reasons we kept missing her (but not the only one-read on!) If even one lucky spermatia makes contact, fertilization can happen.

Meanwhile, brothers Dave and Don are slowly starting to grow-up.

Back on Mom’s frond, the fertilized egg does not develop into a mini Dad or Mom; instead, it is a kind of asexual other that starts to sprout from Mom’s frond. Let’s call it Pat.

At the same time that Pat starts to grow up and mature, Mom’s brothers Dave and Don are also entering into manhood.

Pat, Dave, and Don all continue to grow bigger and bigger. Pat eventually overgrows Mom entirely, swallowing her up as if she never existed. Once Mom is squashed, Pat then produces four spores. These spores then develop to become 2 boys and 2 girls. And they can reproduce.

And here’s where things get all Nabokov. These girls grow up really fast—we are talking only 4-5 days and they are mature and ready for action.  Meanwhile, their “sibling” brothers take 8-12 months to mature. So, within the same generation, there is no way for one of these nubile females—which Dr. Chopin refers to as “Lolitas”—to mate with a guy her own age (of course, this also means she can’t mate with her brothers, which may be why the dulse does it this way).

Instead, Uncle Dave and Uncle Don swoop in. They’ve been growing up on the sidelines and are now full of spermatia of their own to share.  With no females their own age around (they’ve all been overgrown by their Pat offspring around the same time Pat’s mom was swallowed up), their only option is to go for the fully developed Lolitas.

Trying to decipher the daughter-smothers-mother-mates-with-her-brother strategy of dulse.

Trying to decipher the daughter-smothers-mother-mates-with-her-brother strategy of dulse.

Thus, as Dr. Chopin puts it: Precocious sexuality of little Palmaria females with their mother’s male siblings, who have finally reached maturity, condemns them to being buried by their offspring’s overgrowing holdfast on the same rocky spot they occupy, hence leading people to believe for a very long time that they never existed!

It’s a daughter-smother-mother-mate-with-her-brother world out their for dulse. If you’re waiting to hear what all this means for long-term conservation or ecological impacts… I haven’t yet wrapped my nori around it. What we do know, is that seaweeds confer a great deal of benefits, to the planet and to people—including our own sexual health and sex drive.  Evidently, the same stuff that makes sex fun and adventuresome for seaweeds, also works on us.

It’s Official!!!!

Book contract in the mail...

Book contract in the mail…

It is with great excitement that I can announce that Sex in the Sea has been picked up by the fantastic folks at Palgrave MacMillan. We entered discussions a few weeks ago and today I received the signed contract. With an official book deal to light a fire under me, this blog is set to house some exciting, entertaining, and far more frequent tales of wondrous ways life begets life beneath the waves—and why that matters.  Thanks for reading, be sure to subscribe, and please spread the word!

Hordes of horny horseshoe crabs likely saved you, but can you save them?

Mating Season, Lewes, Delaware  Jacqueline Bedell WOD submission

Forget the teenagers making out under the boardwalk, the real love fest at the Jersey Shore each summer happens at the water’s edge. That’s where hundreds of horny horseshoe crabs plow their helmeted heads into the shallow wedge between the surface and the sloping bottom. More closely related to scorpions and trilobites than crabs, these ancient arthropods look the same today as their ancestors did over 400 million years ago, and likely get it on much the same way their relatives did too: in gigantic orgies. Talk about a family tradition.

The males arrive first and begin patrolling the water’s edge looking for females. When spotted, they scuttle over and climb onto her back, using special hooked claws to latch on. For days or even weeks he may hang there just waiting for her to lay a batch of her 80,000 eggs. By the time she does, 5 or 6 males may have attached themselves to her (or often, to the other males gripping her shell, forming a love chain).  She’s got to drag them all over the beach as she gets ready to dig her nest and lay those eggs.  But, since she cannot choose who clings on, having multiple mates helps increase the chance of a few fit fathers getting into the mix.

Besides providing for provocative beachside entertainment, horseshoe crabs play another critical role for us humans: their blue blood provides the only defense we have against bacterial contamination in drugs and medical implants.

You read that right. It’s their remarkable fluid make-up that ensures our vaccinations are safe. And for anyone out there with a heart valve, prosthetic, or other intravenous device—horseshoe crabs have your back, too.  Compounds in their blood (and so far, only their blood seems to have it) can detect even the slightest traces of bacterial contaminant, providing the ultimate safety screening.

Their blood is so important, there are now horseshoe crab phlebotomists, experts at draining their blood and (ideally) releasing the animals back into the wild, woozy but hopefully unharmed (some studies show 10-15% mortality rates—not great for a blood bank, but the total deaths from medicinal use are still far below those from the fishery, the primary source of their demise).

Horseshoe crab blood bank.

Trouble is, there are fewer and fewer horseshoe crabs around these days. In Delaware Bay, numbers have dropped 90% in 150 years. Overfishing, mostly for their use as bait for the eel and whelk fishery, has caused dramatic declines in recent years.  But, as the demand for their blood has increased, the occasional clandestine pillage of the mating masses for their sacred sangre adds insult to injury.  Like grunion in the previous post, they also suffer from threats to their shallow love nests such as sea level rise.

Declining populations of horseshoe crabs isn’t only bad news for them and us. It’s also disastrous for migrating shorebirds, such as the endangered Red Knot. The eastern seaboard is a perfect pit stop on their 9000 mile journey from the tip of South America to their breeding grounds in the Arctic.  They rely on the millions of horseshoe crab eggs covering the beach to refuel themselves.  As horseshoe crabs plummet, so do the seabirds. It’s a system where success hinges on huge numbers of horseshoe crabs getting in on.

In other words, we all need those orgies—the horseshoe crabs, the seabirds, and us. Without successful mass mating, we’re all sunk.

Good news is, there are efforts to design new bait sources and techniques to reduce the number of horseshoe crabs tossed into traps. And efforts to make catching gravid females illegal (evidently the females with the eggs make for the choicest bait—but you can’t make more horseshoe crabs if you keep serving up the adults and their eggs to eels and snails).

So, the next time you get that flu shot and walk away feeling fine, give a nod to those ancient helmeted warriors and their bright blue blood.  And then, see if you can help bring them back. If you live on the eastern seaboard, search for “volunteer horseshoe crab” and your state to find out more.

50 Shades of Grunion Run

Grunion run along the CA coast. Photo credit: Haris Lakisic, Pepperdine.

Her skin shone silver in the moonlight, a flash against the dark beach. She knew he wanted her. She could see him struggling, desperately fighting his way toward her. She positioned herself perfectly, knowing the site of her bound body, restrained and prostrate in the sand would make him—would make of all them—quiver with excitement.  The first to reach her, he feverishly curled himself around her as the others closed in, forming their own half-circle embraces.  She strained with the effort, with the closeness of all those bodies squeezing against her, and yet, her arousal only climbed with the number of strong, sleek forms wrapping around her. 

But just when she thought she couldn’t take any more, just as the lack of oxygen began to make her head spin, she could feel their grips relax and the slow, sweet slide of their pleasure slipping down her body. Their desire to hold her vanished the moment their burden was unleashed. 

How quickly they relinquished their hold of her, turning tail and heading back into the night.  Alone, she struggled to free herself from her binds, now more treacherous than alluring.  She gasped for breath and with her last bit of energy tore free of the hold. Quickly, she too turned toward the water’s edge, catching the next wave back out to sea.  Her suitors long gone, she would never know their names, never recognize them, masked as they were by the shadow of night.  But back there on the beach, somewhere safely tucked down beneath a thousand grains of sand, their DNA mingled and mixed with her own.  Knowing this, she could swim at peace…until next month’s full moon cast it’s spell, luring her ashore once again.

And that, dear reader, is the cleaned up version.

It’s of one of the most heroic and extreme acts of sex the sea provides.  And it happens by the thousands, every year, along the southern coast of California all the way to Baja.  If you live there, right now, you may be able to catch the tail end of this event (and likely be one of the only tourists to recognize how friggin’ masochistic this behavior actually is). These sexual extremists are grunion, Spanish for “grunters”—their onomatopoeic namesake reflecting the raucous they make in their effort to reproduce on shore. Their mass beachings are  called the “grunion runs” and they happen a few days after the full moon in spring and summer.

Grunions are not alone in the category of marine life that comes ashore for sex.  Female sea turtles have to heave their heft up sandy slopes to lay their eggs and elephant seals haul out to hump it up. But as I’ve been purusing the literature about group sex in fish, thus far, these guys are the only fish I’ve found that seal the deal in the sand.  Please let me know if I am missing others.

And, true to the title of this post, the act of flinging oneself on shore isn’t all these fish do to get laid. The females take the whole suffocation fetish (fish can’t breathe while out of the water, remember) and throw a little beach-sand bondage into the mix.  Once on shore, she digs her tail into the soft sand, sinking herself deep down, up to her armpits (sometimes, a females whole head will go under).  With her head sticking straight out of the sand, she presents herself as one sexy beast. The males flap their way up slope (she is holding her breath this whole time, remember, and the girl did some digging!), circle themselves around her, and then use her side as a slide for their sperm.  Oozing all over her body, the slippery stuff makes it way down to the eggs she has deposited below.  The males then turn tail and head back to the water, leaving her to dig herself out (still holding her breath) and catch the next wave out to sea.

Why go through such effort? Why risk beach stranding? I’m still getting to the heart of the matter, but thus far, it seems as though the benefits are associated with higher fertilization rates—the result of 1) the eggs being contained in the sand and not dispersed into the big blue sea and 2) nearly direct deposit of sperm onto the eggs, something more difficult to achieve in water.

Why the group sex? Well, first, the conditions have to be right for the fish to get far enough ashore to lay the eggs and not have them washed right back out to sea, but have the eggs in the right spot to be carried back out to see once they are hatched.  The grunion have adapted to local tidal cycles exactly in order to perfect this timing. The moon cues this timing, so the whole population takes advantage at once.  Second, from the female’s perspective, by having multiple males wrap around her and deposit sperm all together, she increases the diversity of DNA that reaches her eggs. This ups the odds that among that mix of dads, there will be some really fit dudes to make up for any duds.

So, why do we need to know this? Well, for some, watching the grunion runs is quite the experience. It is a pretty spectacular visual, seeing thousands of silver shards flapping in the moonlight.  It also brings up the importance of protecting prime mating habitat. These fish depend on these beaches to support their sexual endeavors. As extreme as they are, they cannot overcome massive beach erosion due to poor land management, or disappearing beaches due to rising sea levels. For these fish, life literally is bound to beach.  To protect these kinky little silversides, and continue to watch them flaunt their stuff, requires we take action to protect the coastline they depend upon.

Check out this cool new documentary, Surf, Sand, and Silversides: The California Grunion for more info.

Stay tuned for more on oceanic orgies as I continue to research this chapter for my book! As always, comments welcomed!

The Sex Appeal of High Heels

Jessica Rabbit from Disney's Who Framed Roger Rabbit

Jessica Rabbit from Disney’s Who Framed Roger Rabbit

There is no doubt about it. High heels are sexy. But why?

It likely has nothing to do with feet and everything to do with the up-turned ass that wearing these shoes creates (see dramatic Disney renditioning of the effect to the right).  Called “lordosis”, the posture is a universal signal of sexual readiness (probably something those 17th C. aristocratic dudes didn’t realize when they first adopted the fashion of wearing heels).

Cats do it, rats do it, even elephant seals do it.  It’s just that in the animal kingdom, such a stance comes as a spontaneous, hormon-driven response to the touch of a male, as opposed to a wardrobe selection.

According to the authors of the fabulous book, Zoobiquity, here is how it works: a nerve signal triggered by a mounting (or in some cases, gently touching) male sends a message to the female brain. Depending on where the female is in her cycle, levels of sex hormones relay the message to say “assume the position” if the female is receptive or “Clock him one and get the hell outta there” if the female is not so ready.

In cats, the response is really extreme and obvious. So too in rats and horses—a female may even lift her tail out of the way to expose herself.  It’s slightly more subtle in cows and primates. And in elephant seals, it takes a keen eye to spot.

Mating Northern Elephant Seal near San Simeon, CA

Mating Northern Elephant Seal near San Simeon, CA by Mike Baird

In this species, the female rarely outwardly solicits sex from the harem master (and who can blame her? Would you want 5000 lbs of hulking seal bubbler pressing you into the shifting sands?). But closer scrutiny shows she may subtly cue that she is ready by spreading her flippers and raising her rear when he lays a flipper across her back.  It’s slight, but it is definitely lordosis.

So, gentlemen attracted to the hot brunette in the six-inch red stilettos can feel in good company with a host of other mammalian males: it is a deep-rooted, primitive evolutionary response.


Which makes me wonder: could we create this effect in other species, too?

Walk_a_thon by William Wegman.

In other words, if it were possible to give a little lift to the rear of a female, would an otherwise uninterested male swoop in? Could it help captive breeding programs struggling to get endangered species to mate?  What would that look like? Come on designers… chime in.



The world’s only disposable-re-growable penis-just in time for Valentine’s Day

Photo credit: xmatt

Photo credit: xmatt

Move over lizards. Re-growing a tail ain’t nothing compared to re-growing a penis—especially when it only takes 24 hours. And what strapping, brawny, stallion is man enough to un-man for a few moments and then regenerate an entirely new, functional member “all in a day’s work”?  None other than Chromodoris reticulata. It’s a sea slug, folks. And scientists yesterday just announced it is also the only known disposable-re-growable johnson on the planet.

Not only can they drop their penises, but, a back-up penis, ready for action, emerges within 24hrs.

Turns out, these slugs have a long, coiled structure that unfurls penis, after penis, after penis, for up to at least 3 mating bouts. All that is needed is a days rest in between.  That’s some serious sexual stamina.

But, why peel off the penis?

The sea slugs are hermaphrodites, and participate in reciprocal matings where each inserts a penis into the partners’ vagina.

Transparent penises of the hermaphroditic sea slug, S. quadrispinosum. From Lang et al. PLOS.doi:10.1371/journal.pone.0043234.g001

(This is a cool picture of a different species, showing the mutual mating tactic. p = penis. H= head of sea slug. s= stylet- a syringe like penis appendage that hypodermically stabs the other slug’s foot. More on this lovely mating duo to come).

It’s all quite civilized, really.  The thing is, though, this is likely not the only mating each slug has done recently.  Living in dense populations, they mate with each other ALOT. That means the female “side” of the slug may be storing sperm from several other suitors. So, as the male “side” retracts its penis after several minutes of mutual mating, tiny hooks along the penis head snag and ensnare sperm lining the vagina. This helps yank out the competition.

And, because a spiked penis is a bit difficult to retract (who wants to pull that sucker back inside their own body?), the slugs just ditch it, leaving their penis—and their competitor’s sperm—out to dry.  Having two more lengths of penis to unfurl means there is not too much to worry about in terms of lost mating opportunity.  Within 24hrs, they are ready to rock again.  Just goes to show how density of a population can select for some pretty crazy sexual strategies—where sperm competition isn’t so fierce, dudes tend to hang onto their dangles.

It must be tough for the guy to have to let go of his manly member. Even if he is also a she. Perhaps that’s why this strategy has only shown up in hermaphrodites: there’s enough female persuasion to get over any penis-attachement issues the male side may be holding on to…


Nudibranchs Help Undress Human Sexuality

Two Nudibranchs getting cozy. Photo credit: Stephen Childs

Two Nudibranchs getting cozy. Photo credit: Stephen Childs

While my book, Sex in the Sea, focuses on the consequences of animal sex on sustainability, these tales of wet and wild habits can lend insight into understanding human sexuality as well. The article by gender professor, Eva Hayward, lays out the links between hermaphroditic and sex changing snails and her own personal sex-change journey. She notes:

“In general, we pretend sex is obvious, as if our chromosomes calculate our entire physiology. But as we’ve slowly come to realize—with the help of feminism, “queer theory,” and biology—sex is many processes that include X and Y chromosomes, hormones, gonads, internal sex structures, and external genitalia, as well as history, culture, environment, and variables still to be named. Some marine inverts “know” that sex is a process; know it as part of their way of life…”

The more I delve into the tales of Sex in the Sea, the more malleable and mysterious sex (and gender) appear– the mammalian condition of girl OR boy seeming an outlier among the vast variability that exists beneath the waves. And, as Hayward writes, this black and white conceptualization doesn’t hold for us, either:

“There is no direct relationship between a nudibranch and me—not even when I, a woman who was a fag-identified male seduced a man who was a lesbian-identified female. We are now married “heterosexuals” living in a swing state. But the nudibranch’s particular sexuality emerges from the same fundament as mine: life proliferates difference. I’m a woman with a transsexual history, because transsexuality is part of my species’ potential—by which I mean the web of relationships that make us human, like culture, environment, imagination, communication, and physiology. Transsexuality is just one way of being human, of being a thread in the web.”

Exploring the diversity of sexual strategies of marine life—and the consequences it has for ocean conservation—is the focus of my work. But, if sharing this information in an accessible, if not slightly kinky way, can help bring sustainability to oceans and foster greater appreciation for our own sexual diversity as a species (and its inherent “naturalness”), well then, that will be a great bonus, indeed.

Your Salty Sex Stories Here

Thanks to those of you who have started to share your own experiences witnessing the wet and wild world of sea life sex. Blog posts of your tales will be coming up soon.. teasers include a shark sex cave, grouper sex as seen from a sub, and the time when sex looked like a sea monster… Thanks for sharing and keep ‘em coming

Sea Urchin Eggs Play Hard to Get


Photo credit: jkirkhart35

There is a battle of the sexes raging beneath the waves and the outcome could lead to breakthroughs in our own sexual success. But this war is not waged between two fully matured, sexually primed adults. Instead, it is a match of molecules, a deft dance between the two most fundamental aspects of male and female: the sperm and the egg. And although it all plays out among the strange sex life of sea urchins, the scenario is all too familiar: guy (sperm) chases gal (egg), while she plays hard to get.

In the cold dark waters of the deep, a male sea urchin starts to spawn. His 10 to 100 billion sperm erupt forth in a milky cloud and begin their impossible race to find a tiny egg floating somewhere in the abyss. (Compared to the mere 280 million sperm per ejaculation of a human, sea urchin males seem pretty studly. Of course, they have to compete with dozens to hundreds of other males also releasing sperm into a very, very large ocean. Most men don’t tend to have that kind of intense competition, nor the relatively infinite space in which to find an egg, so no need for the enormous sperm count. So cheer up, chaps, it’s simply a situational thing). Of course, such spawning only occurs when other sea urchins are also close by (yes, in the sea, sex can be triggered by the proximity of your nearest neighbors. More on that phenomena, later). Female sea urchins sense the sperm and release about a million eggs each into the black waters.

When sperm bump into the egg, Viola! Fertilization occurs…sometimes.


Close up of sea urchin spines and tube feet. Photo credit: julia_koefender

The trick is, the sperm has to match the egg perfectly, and she is mighty selective. These eggs are manufactured with some serious partner-scrutiny proteins that would make any over-protective father proud. When a sperm meets an egg it must match her protein configuration exactly, or it can’t get in.  Just like a lock and key.

If it is a good match, the sperm penetrates the egg and then the egg immediately constructs a defensive coating to prevent any other intruders. The door of opportunity slams shut.

However, if there are too many sperm around, more than one may sneak in before the barrier is up, and that is bad news for the egg. One sperm is all she can take—more than one and she dies.  So, eggs are constantly evolving to be highly selective, to keep down the number of sperm that could possibly match and enter her delicate sphere. Sperm on the other hand, are constantly evolving to fit the latest lock eggs configures—kind of like trying to keep up with never-ending software updates.  But this is a battle of the sexes at the most fundamental level.

And from this tantalizing tango comes our most thorough understanding of how fertilization actually works—from proteins to the influence of sperm number on egg health, sea urchins have provided the peep show into the minute and marvelous world of egg-sperm coupling. Because the same proteins are found on human and other mammal eggs, understanding egg-sperm compatibility in sea urchins may pave the way to better understanding of human fertilization down the road.

Uni sushi. Photo credit: coolinsights

Uni sushi. Photo credit: coolinsights

So the next time you are glomming down some uni (sea urchin roe) in your favorite sushi joint, take a minute to thank those little eggs not only for their taste, but for what they’ve taught us about sex.