p. 226 The digestive tract of flies has to cope with a variety of food sources. Often the same individual is feeding on both blood and nectar, so the interior has been divided into a series of distinct regions, for consuming and processing meals, then for nutrient absorption, and finally for excretion or waste removal, the length and size of the different parts varying with species and food type.”

p. 227 The mid gut has been poorly studied, which is quite remarkable considering how essential a good diet is to the fly. Flues, like us, have a variety of micro-organisms that live inside them to aid difestion. It has been suggested that the number … could be greater than the number of cells in their entire body… it is more than likely .. the larvae of the mosquito Aedes aegypytii don’t start off with any gut fauna and the poor things can’t actually grow if they are prevented from establishing a healthy microbe environment, cultured from microbes they would have consumed from their environment.

The midgut bacteria have been shown to strengthen the immune response in mosquiots and protect them against any unwelcome pathogens… The bacteria in the gut of adult Anopheles mosquitos inhibits Plasmodium infection – it alerts the immune system of the mosquito to let tit know that these parasites have arrived and the mosquito needs to do something about it, but these bacteria are also directly attacking the Plasmodum by producing enzymes and toxins. Studying which bacteria are the most effective at tackling this will aid our war against malaria. As mosquitos are smaller, and less complicated than us humans, they also make a great model for understanding the interactions between the host, the good bacteria and the bad pathogens.

p. 231 There are further issues to overcome when feeding. Mosquitos and other blood-feeding species have to cope with the high internal temperatures of their hosts … many blood-feeding species are heterothermic ie they vary between self-regulating their temperature and using the external environment to regulate it. The ANopheles genus does this by excreting fluid droplets from the end of their abdomens. This reduces the temperature of the internal fluid by a process of evaporative gooling, where the external air cools the fluid. This mechanism prevents all gut symbionts, as well as the mosquito, from overheating.

p. 278 Many species of fly will allow themselves to fall into a coma to protect themselves during times of extreme temperature… they can take their bodies below freezing point without all the internal cells becoming solid. This allows them to survive during periods of extreme cold, by inducing a state called a chill-coma. Some species have glycerol in their cells that acts as antifreeze. One such fly is Chymomyza constata… another species of drosophilid… subjected the largae of this species to a series of lower and lower temperatures.. (t) cryopreservation at -196C (-321F). And some survived – to be fair there was quite a high death rate in the individuals at -196C 0 but still, some survived, which means that these flies are the most complex animals able to do so.”

p. 49 A mycorrhiza is a root infested with a particular type of generally beneficially fungus … The most widespread and ancient type, although not the most familiar, bears the cumbersome name of vesicular-arbuscular mycorrhiza (VAM)… form no visible external structures, so it is impossible to tell if a plant has the association without microscopic examination of stained roots. VAM are formed by a small group of fungi… can only survive in association with the roots of a plant. Their principal distinction is the size of their spores, which are quite enormous by fungal standards – in one species of Gigaspora they are over half a millimetre across, compared to a typical figure for most fungi of around 1/100th of a mm. … most plants that can form VAM do so nuder natural conditions because the fungus appears to offer a solution to an otherwise sever problem – the acquisition of the essential nutrient phosphorus… occurs in soil as phosphate ions which are so sparingly soluble that they move only very slowly through the soil… normally less than a millimetre through soil in a day … Remarkably, fossils of one of the first land plants Rhynia, about 400 million years old, have fungi associated with their rhizomes that appear almost identical to modern VAM fundgi.

p. 51 The best-known nonVAM mycorrhiza “is the ectomycorrhizal or sheathing mycorrhiza, characteristic of many forest trees, especially the Pinacae (pines, spruces, larchs firs), the Betlaceae (birches, alders) and the Fagacae (oaks, beeches).. almost all are toadstools, members of the Basidiomycetes. Some are well known and distinctive, such as fly agaric which forms a mycorrhiza with birch…. Ectomycorrhizal roots are stubby and often fork dichotomously, giving dense clusters. Each root tip is surrounded by a sheath of tightly woven fungal hyphae and other hyphae radiate away from this int the soil… The fine fungal threads penetrate the soil, picking up the immobile phosphate ions and transporting them back to the sheath. Meanwhile the fungal hyphae beneath the sheath, which are in contact with the root cells, obtain sugar from them to feed the fungal tissues.”

p. 52 It does seem that extomycorrhizal trees are better able to colonize poor soils than VAM trees, and this is probably because the former get more benefit from the more active fungi. Of course there is a cost to this: the ectomycorrhizal tree probably has to give up more of the carbon that it fixes than does the VAM tree so the latter may be at an advantage on better soils.
Another remarkable feature of mycorrhizas that has recently come to light is their ability to link plants together. .. BY labelling trees with radioactive isotopes, it has been found that materials can pass from plant to plant by means of these links… there is intriguing evidence that seedlings establish in swards more readily if they become mycorrhizal than if they remain uninfected… If this turns out to be widespread and important phenomenon t may force us to rethink our view of plant communities: ecologists have in the past tended to view them as dominated by intense competition between plants; it may be there is more cooperation than we thought.”

p. 57 Soil fauna – flatworms, rotifers or wheel animalcules, hairy backs, land nemerteans, eelworms, earthworms, bear animalcules (Tardigrada), woodlice, terrestrial sand-hopppers, mites, spiders, millipedes, centipedes.

pp. 158 Like an unpredictable genie, pesticides have proved to be a somewhat mixed blessing, for their overall effects can seldom be fully predicted. There are few if any pesticides that are completely specific to their target organisms: discrimination between harmful and harmless organisms is rarely adequate.

(A shorter version was first published on Blogcritics)

The early evolution of life on Earth is a subject I’ve always found fascinating, but it’s a couple of decades since I last revisited the subject in any depth, and having read Oxygen: A Four Billion Year History by Donald E Canfield I now know that pretty well everything I’ve ever read or been taught on the subject was wrong. The idea that gradually algae spread around the earth, pumping out oxygen in a steady-growing stream, well it simply isn’t true.

It’s not surprising my teachers were so wrong, for as I read in Oxygen, a big breakthrough in understanding early life on Earth came in only 1999, when a colleague and friend of the author, James Farquahar, found some highly unexpected results on a study of sulfur isotopes, in Archaen rocks aged from 2.3-2.4 billion years ago. That led to the conclusion that at this time there’d been interaction between UV light and sulfur dioxide gas from volcanoes. Today, that’s absorbed by ozone, of course from oxygen. Further studies on the form some molybdenum takes in rocks of this age from some parts of the world, however, show that in some places there was free oxygen – what’s come to be known as a “whiff” of oxygen.

What was happening was that by around 2.5 billion years ago, the production of oxygen by photosynthesis more or less balanced the consumption of it by volcanic gases. Sometimes the balance shifted one way, so the oxygen disappeared, sometimes the cyanobacteria were beating the volcanoes.

It was between 2.3 and 2.4 billion years ago that “the great oxidation event” (GOE) changed that. Quite what caused it is still up for grabs. Canfield has a favourite, not evolution of cyanobacteria but a less active mantle, as it gradually cooled, cutting the production of reducing gases. Seems entirely plausible to this interested amateur.

But the GOE wasn’t entirely even – it was Canfield suggests concentrated in the atmosphere, the oceans remaining anoxic and rich in sulfide, with more sulfur being weathered from the land through oxidative weathering of sulfides. This is now known as the “Canfield Ocean” – yes after the author, we’re in seriously expert hands here.

Related to that is the likelihood that for much of the Earth’s “middle ages” atmospheric oxygen levels were much lower than today’s. (Any time machine travellers would need to take oxygen cylinders.) The author’s theory is just 10% of today’s levels, others suggest 40-50%.
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