Time for a Change
The scientific naming of new plants and animals follows international rules designed to provide stability. But what happens when following the rules means having to change the name of the world’s most famous laboratory species? Shane McEvey reports.
The descent of … ferment flies
A handful of insects are found nearly everywhere we live. They associate with the food we eat, the plants we farm, or the human body as a habitat. Thousands of years ago swarms of little flies drawn to the odours of ferment were being inadvertently carried by our ancestors on ripening fruit up and down the Nile. Ferment flies were passengers on the trade routes stretching from central Africa to the ancient civilisations skirting the Mediterranean Sea and the Indian Ocean; from there into the Orient and throughout the South-East Asian archipelago and thence via ancient trading routes of coastal New Guinea to the islands of the Pacific.
Just as we can trace the first movements of humans out of Africa by tracing the patterns of inheritance in mutant genes, so too can we establish that the ferment fly Drosophila melanogaster – which is found nearly everywhere we live, even in the kitchens of remote Polynesian islands – probably originated thousands of years ago in Africa.
It is an interesting twist that we owe our understanding of DNA, and the advances in knowledge of the human genome that are revealing so much about our own biology and origins, largely to a century of genetic research using our little travelling companion Drosophila melanogaster as a model.
A motley genus
Unlike our genus, Homo, with just one extant species, Drosophila has, at last count, 1146 species – far more than any of the other 72 genera in the family Drosophilidae (3950 extant species). Genera can become very large for two main reasons: (1) there are lots of species that form a natural group, or (2) there is a loose understanding of the conditions that determine whether a species is included in or excluded from the genus.
In the case of Drosophila, both causes have had an impact. There are lots of very similar species within Drosophila and there are also some very odd flies, homeless or incertae sedis species – good candidates for their own genera but placed within Drosophila because no suitable alternative is available.
A comprehensive study in 1990 by entomologist David Grimaldi at the American Museum of Natural History took the bold step of moving hundreds of species out of Drosophila and placing them in other more carefully defined genera. One-third of all species in the genus underwent a name change, including 134 species (42%) of the Australian drosophilid fauna.
This renaming passed more or less unnoticed in the scientific community at large because that most famous of species – no other binomen is so widely used in the scientific literature – Drosophila melanogaster, was unaffected. Most drosophilid workers around the world adopted the new nomenclature without fuss; Sydney gardeners didn’t mind that Drosophila hibisci Bock became Scaptodrosophila hibisci (Bock); Melbourne mushroom growers didn’t get upset that Drosophila mycetophaga Malloch became Hirtodrosophila mycetophaga (Malloch) – mainly because these scientific names were generally unknown either before or after 1990. However, Drosophila still remained ill-defined, large and with internal irregularities.
Every genus has its typical representative – its type species – around which the genus, when it is first constructed, is defined. But some untidy genera, like Drosophila, can contain more than one distinctive natural grouping. One such group in Drosophila is the subgenus Sophophora.
The type species of Sophophora is Drosophila melanogaster, but the type species of the genus Drosophila is Drosophila funebris – a very different species to Drosophila melanogaster. It makes taxonomic sense to move those species of the subgenus Sophophora out of the genus Drosophila into a genus of their own, Sophophora. This legitimate manoeuvre would preserve the integrity of the genus Drosophila – indeed it would strengthen our concept of that genus and its boundaries.
If this were to happen, about 340 species would undergo a name change. But most importantly the name Drosophila melanogaster would become Sophophora melanogaster. This might prove so unpopular that we could end up with two names for the same species. And we can’t have that!
A remarkable solution was proposed in late 2007, designed to preserve the popular name by swapping the type species of Drosophila – usurping Drosophila funebris from its lofty central position in the genus and replacing it with Drosophila melanogaster. A case was put before the International Commission of Zoological Nomenclature in late December 2007 but it was more than two years before a decision was reached.
Since this unusual case for bending the rules was proposed, the level of controversy has made it clear that people, even scientists, don’t really like name changes, but nor do they like fiddling around with the rules and definitions of established concepts.
There are those who want to follow the rules and change the name and those who want to bend them and preserve the name.
Naturally, quite a few scientists were disappointed when the Commission handed down its official opinion that Drosophila funebris should remain the type species of Drosophila.
That decision means that Drosophila melanogaster may yet change to Sophophora melanogaster – and if it does you can bet it will be many years before we hear the end of the grumbling.
Dr Shane McEvey,
Entomologist and Editor Scientific Publications.
First published in Explore 32(4).
Michael Hugill , Online Producer