Saturday, February 28, 2009
Recently, in the interests of finding some life-form with which to entertain the legions of avid readers of this blog (hem, hem), I decided to investigate what life might exist in a small pool of rainwater that had collected in the crevices of a sheet of polythene lying in my garden. Putting a drop under my hobbyist's microscope I was immediately confronted by large numbers of the creature seen in photo 1 (scale:1 small division = 1um). Some were motionless. More excitingly, others were highly active, 'zooming' through the water at a rate of knots (see later)
Some internet searching later, and with the help of photo's such as those on Ralf Wagner's microscopy site, and I'm tolerably confident I'm looking at a Heamatoccus alga.
The red colouration, motile behaviour and the presence of the transparent, gelatinous envelope surrounding the central green body all fit with the the species being H. pluvialis on this site ('Algaebase') . I don't claim any certainty over this identification however, since firstly I'm no expert, and secondly the same site lists 5 other species in the Haematoccus genus and a staggering 123,336 species of algae overall.
The family Haematoccae is part of the Volvocales order of algae, one example of which - Volvox - is a perennial favourite with microscopists. The Volvocales are equipped with two whip-like flagella - the secret to their ability to 'swim' through the water. The length and positioning of any flagella on an alga is an important aid to identification. Unfortunately the quality of my camera/microscope optics doesn't appear to be good enough to have caught these in the (dormant) Haematoccus specimen in photo 1 (or is it that flagella are lost in the dormant state?) - but the superb photo's by Wim van Egmond here show them clearly.
In researching the life in my garden I constantly come across what I imagine at first to be 'obscure' creatures. "Beyond naming it, surely no-one can have found the time to learn anything interesting or remarkable about this little critter!" I think to myself. It's a constant source of enjoyment to me to learn I'm wrong, and that for just about anything I come across, someone somewhere will have discovered some remarkable or interesting 'story' (which isn't to say that vast amounts don't remain unknown about the natural world of course).
So it was with H. pluvialis. Beyond a few dry descriptions in an obscure journal, surely there would be nothing say? Wrong again! It turns out H.pluvialis is an algae of significant commercial importance. It produces the highest known concentrations of astaxanthin of any living creature and is cultured on a commercial scale. Astaxanthins are chemicals used in the cosmetics, food and feed industries. They are antioxidants and have been studied for their potentially beneficial effects against everything from cataracts to colonic cancer. Guerin et.al. have produced a review (Trends in Biotechnology, 21(5), 2003). Astaxanthins are cartotinoid chemicals responsible for the red coloration in photo 1. They act as a 'sun block' against harmful UV rays. Those dormant algae I observed in my microscope sample seemed to contain more red pigment than mobile ones. I assume this is because dormancy is, in part, a mechanism to survive in dry conditions when cells can expect to need more protection from the sun.
Algae introducing astaxathanins into the food chain is the reason why animals higher up like shrimps, salmon and flamingos end up with pink flesh or feathers.
Returning to the issue of the mobility of H.pluvialis, Burchardt et.al (Biodiv. Res. Conserv. 1-2, 163-166, 2006) give a figure for their swimming speed of 200m/h. Given that their size is about 20um, scaling this up, and assuming a human about ~2m tall and I've got my maths right, this corresponds to a person swimming along at 20,000 km/h!
Finally, I can't end without mentioning one of the few books I have that gives a fairly detailed introductory guide to freshwater algae, namely Freshwater Microscopy by W.J. Garnett. Though it contains no real information about Haematoccus beyond a mention, it covers many common UK species in some detail. First published in 1953, I particularly like dipping into it for its evocation of a seemingly quieter more 'holistic' (for want of a better word) world, before out-of-town shopping centres and a life of frenzied commuting up-and-down packed motorways, when armies of amateur hobbyists seemed to spend their evenings and weekends learning the art of painting watercolour landscapes, investigating the geology of their county, or studying the lifeforms in their village pond. Or perhaps that's rose-tinted nonsense, though I do wonder how many hobbyists there are today, who, of a typical weekend, boil hay in rainwater in order to culture pond protozoa for study as Mr Garnet advises!
On the other hand I may be entirely wrong and there are legions of you hay-boilers out there! If you're one such, do leave a message to say hello.
Saturday, February 14, 2009
Handsome fellow isn't he! Photo 1 shows one of two male Common Pheasants (Phasianus colchicus) that visited my garden recently. Living as I do in rural Oxfordshire, meeting one isn't unusual; their rearing and shooting is common hereabouts.
The RSPB estimates there are 1.8million breeding female pheasants in the UK.
From a search of the internet a few random facts I've turned up about pheasants include some evidence that pheasants are sensitive to noises beyond the range of human hearing (Stewart, The Ohio Journal of Science. v55 n2 (March, 1955), 122-125). Secondly, given a choice, the 'stuff' (sand, loam, straw, feathers...) in which an adult pheasant will choose to take a dustbath can be predicted ahead of time by noting the material a bird prefers to peck at when still a chick (Vestergaard&Bildsoe, B Acta Vet. Brno, 1999,68, p141). This may seem an esoteric piece of knowledge, but as anyone who has ever watched a documentary about battery chickens will know, feather plucking is a damaging problem among livestock birds under confined conditions and an understanding of pecking behavior in birds can have worthwhile commercial implications.
The Common Pheasant is native to Asia. Like the peacocks, the Common Pheasant is an example of a sexually dimorphic species - a species in which males and females show consistent difference in form. Male pheasants are brightly coloured; Females are cryptically camouflaged. Photo 2 shows a female I spotted lurking in my garden shrubbery early last summer.
Sexual dimorphism is a much studied topic in the theory of evolution. Scientists would like to understand more deeply what forces encourage it and what advantages follow.
An internet search led me to a number of papers on sexual dimorphism in pheasants but unfortunately most were on the pay-to-view sites of commercial publishing firms. This always irritates me as it's typically you and I, the taxpayer, that has paid for the research contained in these papers. To be asked to pay again to read the results seems a bit much! Anyway, I did manage to find a few freely available papers from which I learn that female pheasants choose male mates based, in part, on the length of their spurs. Studies have shown spur length to be an honest indicator (see my peacock posting) of male health - males with longer spurs really do seem to be fitter than less well endowed males.
Spurs are a secondary sexual characteristic - a characteristic that differs between the sexes.
Girl pheasants also appear to judge their men folk according to the quality of their wattles (the red cheek patches in photo 1). Smith et.al. provide one study of this. My (amateur) understanding of their work is as follows:
Biologists had previously worked out that certain 'carotinoid' chemicals were associated with coloured appendages in some animals. At the same time, animals getting a good diet were known (perhaps unsurprisingly!) to have stronger immune systems than poorly nourished specimens. Smith et.al. wondered whether carotinoids were the root cause of both i.e. whether both the strength of a male's disease immunity and their wattle quality were directly controlled by the amount of carotinoids in their diet. If so, this might provide a very natural explanation of why females have 'a thing' for wattles -good wattles would be an honest indicator of the disease resistance of a suitor.
And the answer...after a series of detailed experiments Smith et.al. found no such correlation! Back to the drawing board in terms of discovering the deeper explanation of what's going on, but a nice example for those who might question whether science isn't ultimately a process of rigorous enquiry.
Sunday, February 8, 2009
Those following my recent posts will know I have been on something of a mission to blog the lichen-life on the exterior of my house. Photo 1 shows yet another inhabitant - another crustose lichen (for those unfamilar with lichens, see my post here).
Incidentally, photo 1 also captures (upper left) our old friend, the moss, Tortula muralis.
After a little research I'm confident the lichen here is Aspicilia calcarea. Characteristic features include the cracked, white thallus (the main body of the lichen) and the irregularly shaped apothecia (the black, spore-liberating cups) sunk into the thallus. The books tell me that A. calcarea is common on hard calcareous walls etc. in lowland Britain. Photo 2 shows a closeup.
For those wanting a cheap photographic key to some common, British, urban lichens incidentally, I recommend the short-form guide sold by the good people of the Field Studies Council . For something more detailed the book Lichens (Frank S.Dobson) is especially good.
I'm fond of lichens. Their ability to shrug off the worst the elements can throw at them gives them, for me, an appealing minature 'feistiness' - I picture them squatting on exposed boulders on windswept mountain sides goading the rain "Come on! Give me your best shot! Is that all you've got pal !?"
On a more rational note (!), something that intrigues me is the diverse array of colours and shapes lichens adopt. I have no deep expertise in evolutionary ecology but as I understand it, there is nothing haphazard about the forms taken by species. Life is hard and an ever-present scarcity of resources and the threat of predation and disease is a constant imperative, forcing species to individually specialise in unique methods of suvival. A famous example is of course the beaks of finches, with different species having been driven to evolve different beak-shapes to allow them to eat different nuts and seeds. Different birds evolving different beaks to help them occupy different feeding niches is one thing. The distinct environmental pressures or purposes that drive two lichens such as A. calcerea and C. citrina to adopt such different colours and (once you look closely) really quite different textural forms, when both seemingly occupy the same ecological niche of lowland stone (indeed, the same household windowsill in my case!) - I struggle to guess. Do leave a comment if you can help me.
Monday, February 2, 2009
Photo 1 (click to enlarge) shows the handsome insect I found lying dead on a windowsill in my house some months ago. I am not expert at insect identification so at first I wasn't sure what I was looking at, but a little internet browsing and I'm confident I've found a European Hornet (Vespa Crabo): of the half dozen-or-so social wasps one might encounter in a British garden, the hornet is the only one with a distinctly brown coloured thorax. Much the most extensive introductory source I've come across online is Dieter Kosmeier's excellent hornet website.
Despite their fearsome reputation hornets are no more likely to attack humans than other wasps, nor is their sting notably worse. They are voracious predators of other insects however; a nest colony can take up to half-a-kilo a day. There are even records of hornets taking down pairs of copulating dragon flies (see Dijkstra et. al., Int. J. of Odonatol. 4(1),17-21, 2001).
Queen hornets hibernate over winter - the site of the Bees, Ants and Wasps Recording Society gives a record of a queen discovered beneath a rotting branch of cherry wood. She emerges around May and begins the process of constructing a nest and egg laying. By mid summer the nest is in full swing and may contain in excess of 500 individuals. Nests of one species of hornet (Vespa wilemani) have been recorded at altitudes of 2300m (Martin, Jpn.J.Ent.61(4), 679-682,1993). Come winter the nest is permanently abandoned (hornets do not reuse a nest the next year).
Figure 2 (click to further enlarge - if you dare!) shows a close up of my hornet's feasome jaws and, atop the head, the circle of small primitive light sentive 'eyes' (ocelli). Counting the number of segments on the antennae (=12) tells me my hornet is a female (males have 13)
A debate amongst professional naturalists concerns the mechanism and role of 'brood policing' in Vespa crabo. In brief the debate surrounds the question of why only the eggs of the queen, and not of the workers, are allowed to hatch (I was surprised to learn that the workers are not in fact sterile, and are quite capable of producing progeny). In the 60's the British evolutionary theorist W.Hamilton, argued mathematically that, other things being equal, in order to benefit their gene-line organisms ought to behave in ways that favour their close relatives (kin). Genetically however, a Vespa crabo worker is closer to its own offspring or indeed the offspring of a fellow worker than that of the queen. Despite this, workers ruthlessly seek out the eggs of fellow workers and discard them. Foster et.al. argue (Molecular Ecology (2000) 9, 735-742) that this may be due to the queen chemically controlling the 'minds' of the workers, hence the title of their paper 'Do hornets have zombie workers?' - although overall the jury seems still out.
Or at least that's my loose understanding of things. As I say often, I'm not a professional. I'm happy to be corrected and in particular I've not managed to follow the quantitative aspects of this debate. For example, Foster et. al. begin:
"In a colony headed by a singly mated queen, workers should prefer rearing sons (r= 0.5) and other workers’ sons (r= 0.375) to their mother’s sons(r= 0.25)'
I get the general idea, but can anyone give me a simple explanation of what these numbers mean and how they're calculated?