Saturday, 28 May 2011

Amazing animalcules: or how to create a jungle in a coffee jar

With frequently cloudy night skies preventing astrophotography of Saturn (even a few clouds are enough to ruin seeing, since they reflect the light pollution over London) I decided to head in the other direction, so to speak, and investigate the world of the very small. Last year my daughters and I had mixed success raising a batch of tadpole shrimp, a.k.a. Triops longicaudatus. Having seen the creatures lay their eggs in the adult tank, I kept some of the substrate in case we wanted to try round two this year. Therefore having had some warmer weather recently, I thought last week would be a good time for Triops Trek: the Next Generation.

Some enthusiasts - I can't really call them owners/keepers for such short-lived 'pets' - sift the half-millimetre diameter triops eggs from their tank substrate as if gold panning, but with the coral sand I used that frankly looked far too much like hard work. Therefore I just added about a 5mm deep layer of last year's substrate into a hatching tank of deionised water and hoped for the best. And...

...Success! Out of the thirty-five or so that hatched about half are still alive a week later, which surprised the hell out of me. The only problem being that the main tank is really only big enough for five or six adults. That is if they survive the transition and don't fall prey to problems with osmotic pressure, Ph balance, the nitrification cycle, etc, ad nauseum.

Meanwhile, a bit of research later, I discovered that each adult female (and most are) T. longicaudatus lays between 60 to 200 eggs per clutch. With up to one clutch a day, that's potentially an enormous number of eggs in my substrate. Looking at the nursery tank today I could see about sixty unhatched eggs stuck to the sides just above the water line, the latter having dropped slightly due to evaporation. All I have to do now is find a way of scraping them out...
Triops longicaudatus A.K.A. tadpole shrimps
Back to the current batch. The first problem was what to feed the nauplii (hatchlings for the uninitiated), as for the first few days they are too small to manage the shrimp food left over from last year's kit and I certainly wasn't going to bother buying anything. Luckily, last year I had found grow-your-own-infusoria instructions so had collected dried leaves from the local park during winter. So here's my recipe for happy hatchlings: collect some dead leaves, the more spore-covered the better; tear them into small pieces; soak them in rain or mineral water for three or four hours in a clean jar (e.g. coffee jar); tip out the water and dry the leaves; add them back to jar with fresh rain or mineral water and leave for three to four days. Voila - infusoria in abundance!

For those like me not in possession of a microscope, the best way to observe your new ecosystem (a slight Dr Frankensteinian moment) is at night. Place the jar against a dark background, turn off all the lights and view them via a torch and a magnifying glass with at least 3 times magnification. You'll be amazed at all the activity, especially the spiralling dance of the bdelloid rotifer. These half-millimetre creatures are extremely common but at this size it's perhaps not surprising that I've never noticed them before. There are hundreds of species, all of which seem to be asexual (or entirely female, depending on your viewpoint). But even these are just the tip of the diversity iceberg that is the world of the neo-microscopic. NASA has been experimenting on other similar-sized denizens, tardigrades, which can survive exposure to the vacuum, extreme temperatures and radiation of space. Otherwise known as water bears (despite their eight legs) tardigrades look more like a something off The Muppet Show than Doctor Who, but research has shown they can survive hundreds of times the lethal X-ray dose for humans, so perhaps long-duration spaceflights in the future will in some way benefit from the current endurance-testing of these remarkable little animals.

Back to the home-grown micro-jungle. Having reared a jarful of infusoria, I happily injected a few siphons' worth into the triops hatching tank. And then I felt a bit uneasy. I had heard that some fresh water aquarium owners breed triops just as food for their fish - perish the thought. And yet here I was, happily throwing the seals into the shark tank, as it were. Last year I had allowed a fairy shrimp and clam shrimp to go to their doom, along with countless daphnia (water fleas). So why was I worried now? Is there a threshold above which I consider a species should not become food (triops, obviously), whilst those below it can be eaten without qualms (clearly daphnia) and presumably bdelloid rotifers?

As a Westerner, I haven't grown up with Buddhist or other Eastern notions concerning animal welfare, ranging from veganism to reincarnation (although the latter clearly has self-interest at its core). Morals and empathy have a place in science too, and I consider pharmaceutical experimentation on animals as a necessary evil not to be thought about too often, but with the home-grown infusoria was it a case of size-based vulnerability or just cuteness that worried me how easily I had bred one animal as lunch for another? I suppose it's easy to argue that daphnia have the stigma of the name 'flea' with all its connotations, but the triops kit literature has an interestingly dismissive approach about associated fauna: it states that they won't live long (compared to triops, that is), but fails to mention that a primary reason for this is that the triops will hoover up the smaller species in next to no time.

Perhaps it was nothing more than the graceful, balletic movements of the rotifers that gave me pangs of guilt about serving them at the Café de Triops, but next time you pass a small puddle of dirty rainwater why not spare a moment's thought for the astonishing animalcules that live, largely unobserved, all around us? It really is a jungle out there!