1.1.   The next step in evolutionary efficiency was the arrival of organisms which didn’t waste all their time turning minerals into organic material using photosynthesis.  They let the phytoplankton do all the work, and then just ate the phytoplankton.  These first animals used superior powers of motion to move through the water, and the ability to manoeuvre food particles into their mouths, to graze on ocean vegetation like sheep on grass.  These herbivores evolved into worm like creatures called Rotifers, and tiny crustacean called Daphnia, that we see today (through microscopes) in Lake Annecy.

1.2.   If Cyanobacteria are the acclaimed hero/villain of this story the Rotifers and the Daphnia are the unsung heroes.  Rotifers were so named after the latin for wheel carrier, because their distinctive feature is generally two wheel-like structures at their head which sweep food into its mouth. They are multicelled animals just too small to be seen with the naked eye around 0.5 mm when full grown.  They are to be found in just about every fresh water habitat in the world, and are the good guys because they eat rotting organic material, algae and dead microorganisms ie they keep the lake clean.  They also provide an important food supply for the bigger zooplankton and fish. Rotifers are so interesting they have attracted a bit of a fan club since their first observation by leuwenheuk in 1685.  Some of their more interesting features a) they are almost entirely  a female population the amazons of the microbial world reproducing through parthenogenesis.  Occasionally they will produce a male but for very limited uses, so limited the male does not have an effective digestive system and so dies within a day or two of birth. Not much time for courtship then.  There are around 2000 species of rotifer with variations upon variations defying the tidy mind of the taxonomist.   In fact as one Rotiphile (as members of the Rotifer fan club are styled) remarked the taxonomy of the rotifer is very taxing. Rotifers are one of the most populous zooplankton in lake Annecy.

1.3 The arrival of the Copepods brings us to the next stage in efficiency of evolution. Another little creature realized they could let the phytoplankton do all the photosynthezing, and then the Daphnia and Rotifers do all their grazing for them, and then just eat the Daphnia and Rotifers.  This is the arrival of the the big boys on the environmental block. These guys rival Cyanobacteria for their importance for the global biosphere.  They are so cool that they don’t just have their fan-club, they have a whole society dedicated to their study.  One reason is that they are arguably the largest biomass on the planet by weight, exceeding for instance, homo sapiens.  Another is that the oceanic shoals of copepods play a crucial role in climate control sinking carbon dioxide out of the atmosphere equal to around a third of all human produced green house gases on the planet daily.  So Copepods, the microbial wolves of the oceans and lakes, to return to our analogy, definitely join the Rotifers, Daphnia and Dr Servettaz as heros of our story.

1.4   Copepods are the most populous form of microbial animal life in lake Annecy. And evolution didn’t stop there, because having learnt the trick of the herbivores, who let other organisms do the photosynthesis thing for them, and just eat them instead, another specious arose to eat the herbivores.  They are referred to as heterotrophs because they eat both plant and animal. And then heterotrophs started eating heterotrophs and the battle to survive started hotting up.  Both the herbivores and the heterotrophs are now referred to as zooplankton or water microanimals and are to be seen everywhere in the oceans and also lake Annecy.

1.5 Copepods are small crustaceans that have colonised virtually every aquatic habitat from the deep-sea floor to the high Himalayas. They are by far the dominant animal group in marine plankton and often in freshwater plankton also. They are abundant both on and in marine sediments from the intertidal zone to the abyss and can be found in damp terrestrial habitats in large numbers. The variety of freeliving forms is only part of the copepod success story since copepods have become associates or parasites of virtually every animal phylum from sponges and cnidarians up to chordate, including fish and mammals.

1.6  Perhaps as a result of this simple evolutionary idea, that it was easier to get complex nutrients by eating your neighbour rather than working the oceans, a great battle to survive arose with a flood of new organisms evolving trying to get the better of each other.  Or perhaps there was another reasons, no one quite knows.  But around 565 million years ago a remarkable thing happened.  Evolution, whose plodding pace which in the previous billion or so years had stayed at home in the oceans, and gotten from the first prokaryote to not much more than creating some photosynthesising bacteria (algae), and some  eukaryotic herbivores to graze on the them, went nuts. 

1.7 Within a space of some twenty million years or less all the thirty or so body plans of life – or phylae -  which we know today were laid down (as well as around another 60 or so that were so bizarre they never made it).  This was such an amazing evolutionary period that it has its own name.  Adam Sedgwick named it after Cambria, the Latinised form of Cymru, the Welsh name for Wales, where Britain's Cambrian rocks are best exposed. These are sites of exceptional preservation, where "soft" parts of organisms are preserved as well as their more resistant shells. This is why our understanding of Cambrian biology surpasses that of some later periods. Adam Sedgwick was one of the founders of modern geology. He proposed the Devonian period of the geological timescale. He had guided the young Charles Darwin in his early study of geology and continued to be on friendly terms, but was an opponent of Darwin's theory of evolution by means of natural selection.

1.8   The Cambrian marked a profound change in life on Earth; prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple; the Precambrian Charnia being exceptional. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized—hence readily fossilized—organisms became common.

1.9 The rapid diversification of life-forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.

1.10 Phylogenetic analysis has supported the view that during the Cambrian radiation, animals evolved from a single common ancestor, flagellated colonial eukaryotes similar to modern choanoflagellates. Dujardin, a French biologist interested in protozoan evolution, recorded the morphological similarities of choanoflagellates and sponge choanocytes and proposed the possibility of a close relationship as early as 1841.

1.11 Over the past decade, this hypothesized relationship between choanoflagellates and animals has been upheld by independent analyses of multiple unlinked sequences. (Interestingly, the choanoflagellates were included in the group Chrysophyceae (golden algae found mostly in freshwater, and forming one of the main types of algae in Lake Annecy, until work by Hibberd in 1975.) So when you go swimming in the Lake you are surrounding yourself with something very similar to closest known unicellular living relative of yourself. Not one of the most advertised pleasures of the lake, but an interesting one nevertheless.

1.12 Meanwhile our Rotifers, and Daphnia kept their heads down and continued to munch on their algae, and the Copepods munched on the Daphnia and Rotifers, while the world around them erupted.

Continue Reading   Chapter Eleven