Promising young algae …

Spring has arrived in Cassop Vale.  Leaves are appearing on many of the trees and the ground vegetation has the green flush of a new beginning.   More importantly, the herd of emo-fringed highland cows have been moved away, to give the plants more chance of flowering, and there is some warmth in the sun in the middle of the day.

From my point of view, the biggest change since I was last here is the appearance of an extensive floc of green algae covering much of the pond’s surface.   I had a hunch, from their appearance, that these would be predominately Spirogyra, but was not expecting the sight that greeted me when I put a small piece of a floc under the microscope. 

Flocs, predominately Spirogyra, in the margins of Cassop Pond, April 2021.

I find Spriogyra and its relatives quite regularly on my travels, but usually in the vegetative state.  It is relatively unusual to find them as they undergo sexual reproduction (see “Fifty shades of green …”).  But there was plenty of evidence of this process (termed “conjugation” in Cassop Pond’s green flocs.  There were plenty of vegetative filaments, each about 20 micrometres wide and with a single helical chloroplast.  But there were also many ellipsoidal zygotes apparent.   When I looked more closely, these were inside filaments which were linked to an adjacent filament by a narrow tube.   What started out as an early morning natural history trip has turned out to be the algal equivalent of Saturday night on Newcastle Quayside.   

For those of you unused to dating, Spirogyra style, here is a quick guide.   First, put on your best helical chloroplast (two or more, if you are daring), then head out to find a partner amongst the many other filaments in your particular floc.   Little is known about Spirogyra’s preferences, but we can assume that many species are not heterosexual, so don’t be shy: sidle up to any filament you fancy.   He/she/it might well play hard to get at first, so maybe you need to drop a hint.  Make sure your potential date gets a whiff of your aftershave (that’s what I assume “hormonal interactions between the paired filaments” means).  If he/she/it gets the hint, then you can indulge in a little mutual meiosis to get yourselves into the mood.    

Spirogyra from flocs in Cassop Pond, April 2021.   a. vegetative filament; b. two filaments undergoing sexual reproduction with zygotes in the lower filament.   Narrow filaments of Aphanizomenon gracile are also present.   Scale bar: 20 micrometres (= 1/50th of a millimetre).  

Now we’ve got that all-important emotional (okay … hormonal) connection, it is time to get physical.   An embarrassing bulge appears on the side of your filament but, fortunately, a similar one should appear on the side of your date’s filament at about the same time.   Eventually, these fuse to form a tube that links you both together.  The correct term for this is the “copulation canal” which is as frank as it is alliterative (it could also be called a “tupping tube”, I guess?). The protoplast of both cells now contracts and one (the “boy”, for want of a better analogy) crawls, amoeba-like, through the tube and fuses with the “girl” protoplast to form a zygote.  That’s as far as our frisky filaments in Cassop Pond have got.  If our phycological peep-show continued for longer, we would see the green zygotes gradually become brown in colour as thick, resistant walls grew around them, and the cell contents were processed into starch and lipid-rich food reserves.   They would then sink to the bottom of the pond and rest, dormant, until conditions were ripe for its germination.

Features of Spirogyra conjugation: a. a vegetative cell in one of the two aligned filaments; b. conjugation canals developing between the aligned filaments; c. a zygote.  Scale bar: 20 micrometres (= 1/50th of a millimetre).  

Why here, why now?   Nitrogen limitation has been quoted as one of the triggers for conjugation and the presence of a nitrogen-fixing cyanobacterium (Aphanizomenon gracile) plus nitrogen-fixing diatoms (Epithemia– see “Working their passage”) in the pond at the same time lends support to this hypothesis.  Also, the yellow-green appearance of the flocs is also a hint that they may be nitrogen-limited.   However, there are also reports of conjugation happening on a predictable annual pattern in some locations.  The two possibilities are not mutually exclusive, we should remember.  

Meanwhile, on dry land, there are plenty of other plants getting down to the complicated business of reproduction too.   We saw goat willow (Salix caprea) and hazel (Corylus aveana) as well as lesser celandine (Ficaria verna) in flower, and leaves of primroses yet to bloom.   You can read more about those here.   Just remember, when enjoying the sight of spring flowers, that the botanical bacchanalia takes place in less obvious ways in the water too.

Some other highlights from this week:

Wrote this whilst listening to:  Horses and Easter by the Patti Smith Group (see below).   And a 1977 BBC “Sight and Sound in Concert” recording of Jethro Tull, which I remembered seeing when it was first broadcast.

Cultural highlights:   The film Black Bear – a rather dark and challenging, but ultimately rewarding, film.

Currently reading:  Just Kids, by Patti Smith.  Best read with Horses and Easter as a soundtrack.  The geographer in me also reads it with a map of New York to hand, as it is a book with a very strong sense of place.

Culinary highlight:.our local Indian restaurant makes a rather good lamb shank, cooked in aromatic spices which, with basmati rice and a side order of bhindi, is just about unbeatable.

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