******So complex and utterly alien are the sex lives of seaweeds that my original blog post on the subject from April required some updating. With much thanks to Dr. Chopin for editing assistance, here’s a revisit to the scandalous sex life of a seaweed. ******
Vladimir Nabokov’s Lolita
Lo-lee-ta: the tip of the tongue taking a trip of three steps down the palate to tap, at three, on the teeth. Lo. Lee. Ta.
One of the greatest opening lines of all time, this is the introduction to Vladimir Nabokov’s brilliant and disturbing Lolita. A long-held favorite of mine, I was utterly thrilled when seaweed guru Dr. Thierry Chopin referred to this modern classic as a model for understanding the complex and rather shocking sex life of a common edible seaweed.
I know what you may be thinking: seaweeds have sex lives?
The red seaweed called dulse and sugar kelp, a brown seaweed, seen in abundance at low tide along the rocky shore of the Bay of Fundy, New Brunswick, Canada (photo credit: Thierry Chopin)
Yes. Don’t let those passively swaying fronds fool you. Despite their rather limp appearance, seaweeds (also commonly known as marine macroalgae) are raging sex machines, with some of the strangest and most creative forms of sexual reproduction on the planet. A catch-all group that lumps together remarkably diverse species (green seaweeds are more closely related to trees than they are to brown seaweeds, for example, which are more closely related to fungi), it is no surprise that they display an enormous range of reproductive strategies. Chopin wrote a debrief here
on seaweed sex after our interview for Sex in the Sea
; he’s insisting that I must include a chapter (or two!) on seaweed reproduction, and I heartily agree. Here’s why: seaweed cultivation is big
. Globally, seaweed farmers grow 23.8 million tonnes a year—nearly 50% of all the world’s ocean farming worth $US 6.4 billion.
Large scale seaweed (kelp) cultivation in Sungo Bay, China. Note seaweeds grown integrated with the cultivation of several invertebrate species (oysters, scallops, abalones and sea cucumbers) (photo credit: Thierry Chopin).
Long recognized as a healthy and delicious food in Asia, seaweed farming is gaining traction in the west, including in Canada, Chile, Europe, and the USA. And it’s not just food that seaweed bestows; this video provides a great overview of the varied and everyday uses for seaweed.
Fast growing and photosynthetic, seaweeds don’t need to be fed like fish or shrimp; they just need sunlight and nutrient rich waters (which they help keep clean) to grow. They are being tested as natural ways to clean up effluent from fish farms (a key focus of Chopin’s work on Integrated Multi-Trophic Aquaculture), mitigate climate change, and produce healthy and abundant food. But in order for us to grow more seaweeds, we’ve got to know how they reproduce. We need to understand in intimate detail, the intimate acts of seaweed.
Talking with Chopin, it is clear that 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 parthenogenetic gametes alternating with asexual spore germination…they’ve got that too. And, they can also claim, according to Chopin, “old male perverts” and temptress nymphets. Which brings us back to Lolita.
Deciphering the wild life cycles of these remarkable food factories has challenged many a phycologist (note: that’s not a typo for a shrink, but a scientist who studies algae). But, with the help of Chopin’s expertise and anything-but-prude French perspective (and a few kelp cocktails), I’m slowly wrapping my nori around it all. Here, for your summer reading pleasure, is the tantalizing tale of a seaweed named dulse (Palmaria palmata) though “Dolores” would be more appropriate. May your innocent strolls along the seaside never be quite the same again.
An innocent stroll along the seaside (photo credit: windydress via Flickr)
It all starts with the females, who, according to Chopin, are all young and extremely sexually precocious (seaweeds, like many plants, can have separate sexes, with individuals maturing as males or females). At just a few weeks old, female dulse have fully mature sexual organs called trichogynes which are slender tubes that reach out to receive the male gametes.
Microscopic mature female gametophyte (left) of the red seaweed Palmaria palmata (dulse) with trichogyne filament visible on the left. On the upper right, a young male gametophyte just starting to elongate. The scale bar at the bottom right represents 0.1 mm (photo credit: Constanza Chianale).
But, these blossoming beauties (what Chopin refers to as the “Lolitas”) are also microscopic in size, a tiny disc less than a millimeter in diameter. For decades scientists searched for the mature females in vain, only discovering them through some accidental lab experiments in the 1980s. The much larger mature males were more easily spotted in the field (but specialists in the lab still had to confirm identification), while the females remained a mystery, their small size but one contributing factor…
…the other reason was that they were rapidly buried alive by their own offspring. But, we’ll get to that.
First, it’s important to note that male dulse, like in some other species we know, don’t grow-up quite as quickly as their female counterparts. In fact, males the same age as mature females are but young, pre-pubescent boys, incapable of satisfying the females’ desires. Males of the previous generation, however, don’t have this problem. Having weathered a winter, so to speak, these older males are more than capable of giving the females what they want: a shower of seed. These older males readily release their tail-less, sperm-like spermatia into the water, relying on the currents to whisk them atop the thin crust of the female. If just one lucky spermatium makes contact with a female’s trichogyne, fertilization can progress.
A general life cycle of dulse, adapted from van der Meer J.P. and Todd E.R. 1980. The life history of Palmaria palmata in culture. A new type for the Rhodophyta. Canadian Journal of Botany 58:1250-1256
But the product of this union is rather unusual. As Chopin explained it in Lolita terms: “So, say a female dulse, Dolores, receives a spermatium from an older male dulse, Humbert. When this happens, the fertilized egg develops into what looks like a mini Humbert, but is actually an asexual sporophyte that starts to sprout from Dolores’ thin surface.”
Let’s call that sporophyte, Pat. Unlike Dolores and Humbert, which are gametophytes—the gamete-producing part of the seaweed’s life cycle—Pat produces asexual spores. As it develops, Pat overgrows the dwarf female Dolores from which it sprang, swallowing her up as if she never existed. That’s really why scientists couldn’t find the mature females of the dulse world: they were overgrown by their offspring’s sporophyte fronds.
Mature sporophyte of the red seaweed Palmaria palmata (dulse), with darker sori of spores (thousands grouped in quadruplets) (photo credit: Thierry Chopin)
Once Dolores is squashed, Pat, having reached a large size, then produces many sets of quadruplet spores, grouped by the thousands to form dark spots, called sori (these dark spots make this the easiest stage of the life cycle to recognize). Every quadruplet has two spores that develop into boys and two that become girls. And these are the gametophytes that can sexually reproduce again.
But the girls can reproduce far sooner. They, like the overgrown Dolores, are nymphets, reaching sexual maturity within a few weeks. As Chopin puts it “and the boys being boys, the girls have to court the males from the older generation. Thus, it is generations after generations. And that’s where things get all Nabokov.”
So, the cycle of inter-generational coupling continues, as these new Lolitas court the males of Dolores’ generation, who are finally sexually mature (eight to twelve months later). Within the same generation, there is no way for one of these nubile females to mate with a guy her own age (of course, this also means she can’t mate with her brothers, which could be why the dulse does it this way).
Chopin concludes: 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 female-mates-with-mother’s-brother-bares-asexual-offspring-that-smothers-mother world out there for dulse. Figuring out this convoluted life cycle was an important step forward in our ability to cultivate this popular food—and learn how other seaweeds might be doing it.
Of course, there’s another bonus to understanding seaweed sex, besides the opportunities for food production, ecosystem restoration, and other advantages: whatever drives their sex could help our own sex drive, too. Something to consider next time you crunch through that sushi roll.