Reclassification in de genealogy of life

The kinship of animals and plants was established on the basis of visible similarities. DNA research now introduces substantial corrections into this genealogy of life. Willem Prud’homme van Reine, working at the Leiden branch of the National Herbarium, is responsible, together with two of his colleagues, for a drastic reclassification of brown algae. The kinship of animals and plants was established on the basis of visible similarities. DNA research now introduces substantial corrections into this genealogy of life. Willem Prud’homme van Reine, working at the Leiden branch of the National Herbarium, is responsible, together with two of his colleagues, for a drastic reclassification of brown algae.

Oxygen producer and food source

Algae may not be very cuddly, but they are nevertheless very important. ‘Without algae there would be no life on earth,’ says Willem Prud’homme van Reine, although he would not go so far as to claim that this is also independently true for the Sphacelariales family, a sub-group of brown algae. Algae were the first, and are still one of the most important producers of oxygen on earth. What’s more, they form an important food source in the oceans. Some brown algae are also suitable for human consumption.

Publication in European Journal of Phycology

In collaboration with Stefano Draisma and Hiroshi Kawai, who work in Kuala Lumpur and Kobe respectively, Prud’homme van Reine published in late August in the European Journal of Phycology a new genealogy of Sphacelariales. Brown algae can be found in all the oceans of the world, but they are most frequent in colder waters. Prud’homme van Reine: ‘In the Netherlands, there are four types of Sphacelariales, but you have to know what you are looking for if you want to find them. They vary in size from 1 to 5 centimetres and are found mostly on dikes, in tidal waters and in pools.’

International collaboration

The three authors examined the DNA of dozens of specimens of Sphacelariales from all over the world. Accidental mutations occur at a constant pace in DNA, so that corresponding genes in populations which no longer exchange genes – i.e. different species – become increasingly divergent from each other. By mapping the differences and submitting them to statistical methods, you can draw up a reliable genealogy of a group of related species. The researchers examined the mutual relationship of two genes, which each encode a light-sensitive substance in the chloroplast of these brown algae, comparable to chlorophyll in plants. The reason for this choice is that studying and comparing the entire DNA sequence would take many years of work.

Reclassificatin of brown algae

Biologists classify life forms into a hierarchy of groups: related species form a genus, related genera form a family, and above that there are orders and classes. Sphacelariales form an order which has been quite seriously shaken up as a result of this research; of the thirty species examined, quite a few have now ended up in a different family.

To give a comparison: within the class of mammals, the carnivores form an order. An equally drastic reclassification to that which took place within the Sphacelariales order might involve, for instance, the wolf being moved from the dog family to the cat family, or the otter moving to the bear family.

As a result of the reclassification, the Dutch brown algae now also include the three genera Battersia, Sphaceloderma and Protohalopteris (the latter is a new scientific name) and the Stypocaulaceae and Sphacelodermaceae families. Battersia and Sphaceloderma were until recently considered to be species within the Sphacelaria genus. The Stypocaulaceae family already existed, but now this family includes the new Protohalopteris genus, and the family therefore also occurs in the Netherlands.