Monday, February 11, 2008

Two Verrucaria lichens

I am an amateur naturalist attempting to identify all the life in my garden.

February is seeing Oxford hit by a succession of clear, frosty days. The cold weather means that many of my garden's plants, fungi and animals are tucked away out of sight or sitting out the winter in a dormant state. As I've remarked before, this is a good time for the amateur to take an interest in those humble lifeforms the mosses and lichens which, far from lying dormant, seem to positively relish the winter and the lack of competition it affords. My garden wall for example, is currently layered with a vibrant mat of fruiting mosses.
Photo 1 shows a closeup of two more denizens of my wall's stonework. For the uninitiated, no, this is not a mistake! What appears from a distance to be little than a collection of stains on the stonework is in fact my blog's first example of a crustose (=flat, crustlike - see here for more explanation) lichen. In fact there are two in photo 1. Photo 2 shows a zoomed-out image of the same region. Personally, I find it little short of miraculous to see life thriving on bare rock.

Photo 3 shows a 40x magnified view of the tiny black dots peppering the surface of the uppermost lichen in photo 1. These are perithecia - tiny flask shaped 'salt cellars' from which the lichen shoots out spores.

When it comes to species, as always, my identifications come with a health warning: I'm far from expert in identifying lichens and furthermore, without going to the lengths of studying spores under the microscope and applying chemical tests (lichenologists take these seriously: I even have a book - Microchemical Methods for the Identification of Lichens, Orange, James and White - that teaches the amateur how to perform chromatography!), it can be well-nigh impossible to definitively identify some lichens by visual appearance alone. With this disclaimer, let me say that my lichen's fruit bodies being set in little craters in the surface, and the black line delineating the thallus perimeter in photo 1, are both features that fit with the description of Verrucaria baldensis in my copy of Lichens:An Illustrated Guide to the British and Irish Species (F.S.Dobson).

A similar analysis for the lower, 'less spotty' (though you'll still see some perithecia if you look closely) lichen in photo 1 inclines me to an identification as Verrucaria muralis.

The Verrucaria genus of lichens is noteworthy for including a number of freshwater and maritime lichens. The next time you're at the seashore, look towards the high-tide line and in all likelihood you find the rocks everywhere stained black. This isn't oil (as is sometimes thought) but a result of the ubiquitous seashore lichen V.maura.

Amongst the many extreme features of the life of a crustose lichen is the extraordinarily slow growth of some. According to my copy of Lichens (O. Gilbert, New Naturalist series) lichens are amongst the oldest and slowest growing organisms in the world: Rhizocarpon geographicum, for example, puts on a mere 0.09mm of growth-radius per year. A patch of the lichen Aspicilia calcerea, growing on the Rollright Stones, a stone circle in Oxfordshire, is estimated to have begun life there in 1195AD. It's thought some Icelandic lichens might be 9000 years old! I'll have nothing quite so extreme in my garden, but I am curious to track the growth rates of at least a few of the crustose patches on my garden wall. Watch this space!

Harlequin ladybird Harmonia axyridis succinea

I am an amateur naturalist attempting to discover all the life in my garden.

Early last October I found a pair of ladybirds sitting on some of the rust-afflicted Groundsel growing in my garden (at (0.2,1.9) - see here). Photo 1 shows a front view and photo 2 a view from the side which more easily permits my ladybird's 19-spots to be counted.

In seeking to identify my ladybird I turned first to my recently acquired copy of Ladybirds (Richmond Publishing, 1989) by Majerus (he of moth book fame) and Kearns. Despite the book containing beautiful colour illustrations of all 42 of the traditionally accepted British species of ladybird, I was surprised to find my 19-spot not included. All became clear however when a search of the internet bought me to David Element's webpage and I learnt that my ladybird is The Harlequin Ladybird (Harmonia axyridia), an invasive alien species that has only recently arrived in Britian (it was first recorded here in summer 2004).

In fact, H. axyridia comes in a variety of subspecies with different colouring and number of spots. My 19-spot variety is termed H. axyridia succinea.

Sadly, despite it's attrative appearance, it's a bad sign to find a Harlequin ladybird in my garden. The Harlequin is a voracious aphid predator, so varacious in fact that there is considerable concern about the damage the Harlequin may do to the native ladybird- and lacewing-species that also rely on aphids for their food. The Harlequin ladybird survey has been set up to monitor the invasion threat and people are encouraged to register sightings (I have).

To cheer us all up I'll leave us with the nursery rhyme, which, though I used to recite the first two lines as a child, I enjoyed learning from Majerus' and Kearns' book contains two extra lines

"Ladybird, ladybird fly away home,
Your house is on fire and your children all gone,
All except one, and her name is Anne,
And she crept under the porridge pan"

Sunday, February 3, 2008

Soft-tufted Beard Moss Didymodon (Barbula) vinealis

I am an amateur naturalist trying to identify all the lifeforms in my garden.

Growing on a stone next to my vegetable patch (at (0.2,1.6) - see here) is the moss seen in photo 1 (click photo's to enlarge).

For this posting I was fortunate enough to gain access to a low power stereo dissecting microscope. My usual technique of balancing my cheap digital camera on the eyepiece didn't deliver such good results as it does with my own higher-power microscope, but the stereo' did allow me to capture some photo's at 16x magnification of the moss in its wet state (photo 2) and (photo 3) the remarkable 'twisted-rope' structure the leaves adopt if the moss is left to dry out. Mosses are able to withstand considerable drying incidentally, all that's needed to bring them back to full greeness being a few drops of water.

Previously, I've talked at length (here, here and here) about some of the features to look for when identifying mosses. For this posting, suffice to say that the combination of elongated leaves with their circular cells and nerve running their full length, together with a few other features and reference to my copy of British Mosses and Liverworts (Watson, Cambridge) and a recently acquired copy of The Moss Flora of Britain and Ireland (Smith, Cambridge), leads me to conclude I've got Didymodon (Barbula) vinealis growing in my garden (though as always, my identifications come with a 'health warning' - I'm always happy to be corrected). The website of the British Bryological Society gives the common name as Soft-tufted Beard Moss.

Though I realise the following will be decidedly 'old news' to the experts out there, I can't end today's posting without relaying a fascinating feature of mosses that I discovered recently from leafing through some botany textbooks. As most people know, DNA inside living cells gets packaged up into chromosomes. Human cells contain 2 sets of 23 chromosomes (i.e. 46 in all) and are said to be diploid. The exceptions are sperm and eggs; These contain only 1 set of (23) chromosomes and are said to be haploid. This pattern is common across almost all mammals. Mosses do things differently however; When you look at a moss you are seeing a mass of haploid cells, except, however, where you see stalk-like setae (you can see a number in photo 1. Photo 4 shows a closeup). These are the a moss's spore-filled fruits. In contrast to the rest of the moss, the cells comprising the setae are diploid. In a sense therefore, your or my diploid arms 'sprouting' from our diploid torsos, are a genetically 'closer match', than a moss's diploid setae sprouting from its haploid host.

There are more things in heaven and earth, Horatio, than are dreamt of in your philosphy!

Friday, February 1, 2008

The Common Frog Rana temporaria

I am an amateur naturalist trying to find out what lives in my garden.

Have you spotted it yet?

Photo 1 (click to enlarge) taken in late summer, shows, squatting camouflaged against the undergrowth, my blog's first amphibian, (at (0.8,0.4) - see here).

Identification wasn't difficult. There are only two native British toads: the Common and the Natterjack. These have warty skin and an altogether more robust stature than my amphibian. There are also only two frogs: The Common and the Pool Frog. The latter is rare and in fact has only recently been recognised as an indigenous species. There are also a handful of introduced alien species of frog and toad in Britain, but again none is like mine. In all therefore, I've little heitation in indentifying my frog as The Common Frog (Rana temporaria).

To learn something about frogs I have been reading The British Amphibians and Reptiles (M. Smith, New Naturalist). Published in the 1950's, the book has a more 'robust' (a.k.a. cruel!) approach to studying nature than most amateurs would find acceptable today. I learn for example, that toads dropped into formalin will (surprise, surprise!) adopt a defensive posture; that Goldfinches injected with toad venom, die; and that a convenient way to mark frogs for identification is to cut one of their fingers off! Despite this, the book contains a lot of fascinating and surprising information: For example I hadn't previously known that, lacking a rib cage, frogs are unable to inflate their lungs as mammels do. Instead they absorb oxygen through their skin and by rhythmically 'gulping' air, which they can do up to 140 times a minute. Croaking is achieved by passing air backwards and forwards over the vocal chords. Since this does not require air to be expelled from the body, frogs can, and commonly do, croak underwater.

The skin colouring of the Common Frog is highly variable. Black patches (see photo 2) are due to accumulations of melanin. More melanin is produced in colder weather and during hibernation (typically mid October to early March) Common frogs may turn quite a dark brown. As they grow, frogs periodically moult a thin outer layer of their skin.

Male Common Frogs can be distinguished from females by the presence of thickened black nuptial pads on their hands. These help the male to grip onto the female's back during mating. As the female releases her eggs, the male fertilises them by releasing sperm into the water. Common Frogs can spawn suprisingly early in the year. March and April are most common, but the book describes records of spawning as early as mid-January and says that it is not uncommon to find spawn floating amongst the ice on freezing ponds.

Frogs have a 'homing instinct' and can find their way back to breeding pools from some distance. When the book above was written (the 1950's), how they achieved this wasn't known. Can anyone comment on whether this problem has been solved since?