I set out for Cattle Point early one morning with one thing on my mind…sex. Now you may not be surprised that I had sex on the brain, seeing as it is the highest biological imperative, but the sex I had in mind was like nothing your average beachcomber could imagine. It was stranger and more bizarre than the boring old ‘birds and bees’, it was a botanist’s dream — seaweed sex!
Now if you think that human sexual reproduction can be complex, it pales in comparison to the strange and exciting world of algal nookie. Sporophytes, gametophytes, carpospores and tetraspores are just the beginning. The mind boggles with the sheer variety of strategies and processes employed. In order to wrap my head around this vast topic, I decided to select three algae at random from the rocky shore, identify them, and delve into the seedy underbelly of their reproductive habits.
The first specimen I stumbled upon was kelpy in appearance with a thick midrib (or rachis, as I would later learn), and small blades projecting off of either side interspersed with floats, or pneumatocysts. This was Egregia menziesii.
It was indeed a kelp which makes it a member of the Order Laminariales. It turns out that the second alga that I chose was also a member of Laminariales, though definitely more traditional in it’s kelp-like appearance. This was Cymathaere triplicata.
Now as these two algae are members of the same order, they have similar reproductive strategies. Organisms within a single order tend to share life histories. For kelp, this means a biphasic lifestyle with a free-living, microscopic haploid phase, and a diploid macroscopic phase. This is called the heteromorphic alternation of generations. What that means in English, is that the big kelps we see floating around are only half the story. These guys pass through two distinct forms in their life cycle, on the one hand we have the large kelp we are used to seeing (this is called a sporophyte.) These sporophytes produce spores (no surprise there) which are released into the water and then settle on the bottom. From these freshly settled spores grow little microscopic, fillamentous structures (the gametophyte) which will produce the gametes that come together to form another sporophyte! Algae within Laminariales are oogamous. This means that there are two distinct gametes, a spermatozoid which swims around in the water column after being released from the gametophyte, and the egg which is retained and sends out sexy chemicals that attract the spermatozoids. In this way, a big leafy kelp springs up in the place that the gametophyte settled. Hot.
If you think that is complicated, then the next sexy alga will be downright ridiculous. This is Corallina vancouveriensis, one of the red branching species found in our local waters.
Red algae are true superfreaks of nature when it comes to sweet lovin’ down by the fire. C. vancouveriensis has what is called an isomorphic triphasic life-cycle involving a carposporphyte, a tetrasporophyte and a male or female gametophyte. Basically what happens is this, a lonely gametophyte will produce male and/or female gametes, the male version of which are released into the water as spermatia. These spermatia are carried on the current until they bump into a female gamete (called a carpogonium). This carpogonium is then fertilized and begins to develop within the tissues of the female gametophyte as a diploid carposphorophyte. This carposporophyte will then release diploid carpospores which settle and become diploid tetrasporophytes. The tetrasporophytes produce haploid tetraspores which will be released and develop into a gametophyte. Now here’s the tricky part, the gametophytes and the tetrasporophytes are isomorphic, which means that they look identical to each other, except that one is diploid and one is haploid. That would be like if humans had eggs and sperm that looked identical to the individual that produced them, a very disturbing thought indeed. The complexity of this sex is ridiculous, so the take home message is this: most red algae have three distinct life-phases, two of which often look identical to each other and one that develops on the tissues of one of the others. Score!
And so ends my quest for sex at Cattle Point. It’s clear that the possibilities are endless when it comes to algal love, and I have taken from it a true appreciation of the comparable simplicity of good-ole’ mammal coitus. Triphasic life-cycle? Fascinating, but not for me, thanks.
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