This morning I took the compost bin down to the pile of decomposing organic waste behind the big azalea. As I hurled the orange and banana peels, coffee grinds, and assorted other stuff on top a veritable swarm of small flies rose up. So my daily bucket observation for today is that there are a lot of Drosophilid flies in my backyard on the northern outskirts of Tallahassee on August 13.
The Daily Bucket is a regular feature of the Backyard Science group. It is a place to note of any observations you have made of the world around you. Insects, weather, meteorites, climate, birds and/or flowers. All are worthy additions to the bucket. Please let us know what is going on around you in a comment. Include, as close as is comfortable for you, where you are located. Each note is a record that we can refer to in the future as we try to understand the patterns that are quietly unwinding around us.
|
Observations of
Drosophila species involve not just backyard science but kitchen science, supermarket science, and even trash bin science. This is diary about the natural history of one of the most important study organisms in biology as well as an annoyance around the fruit bowl: the 'fruit fly'.
The term fruit fly is applied to two completely different families of fly. Entomologists use the term as the common name for flies in the family Tephritidae. The Tephritids have attractively patterned wings and larvae all feed on vegetation. The apple maggot fly (Rhagoletis pomonella) is a typical example in which the larvae borrow into and feed on the flesh of apples. The Mediterranean fruit fly, Ceratitis capitata is another example that is a serious agricultural pest. The round galls on goldenrods are formed by yet another species. Tephritid flies have been studied intensively by agricultural biologists and also by evolutionary biologists interested in the role of plant/insect interactions in the formation of new species. However the amount of research on this group pales in comparison to the 'other fruit flies'
What non-biologists and even most non-entomologist biologists (e.g. geneticists) call fruit flies are members of the family Drosophilidae. Calling Drosophilids fruit flies is not very accurate as these flies do not feed on fruit but the species commonly experienced by the average person are closely associated with fruit and the name is in such wide use that the entomologists might as well give in. In a guide to insects they will usually be called vinegar flies or pomace flies.
The Drosophilids in general and one species, Drosophila melanogaster, in particular have been enormously important in the expansion of our knowledge of biology over the last century. Drosophila melanogaster was the first model organism used in biological research. D. melanogaster is native to tropical Africa but has spread around the world in association with humans. Like many/most members of the family the larvae and adults of D. melanogaster feed largely on yeast growing on over-ripe to rotten vegetable matter. Humans provide them with abundant sources of food.
In the early 20th century, biologist Thomas Hunt Morgan recognized that D. melanogaster would make a good organism for studying the inheritance of characteristic (i.e. genetics). The diet of the flies and the larvae could be easily provided by preparing a mixture of the appropriate plant matter and yeast. Flies could be mated and larvae reared in small vials with a minimum of maintenance. Very large numbers of these vials could be housed in a lab and large scale experiments conducted on a scale that would not be feasible with, for example, mice. Yet, as small as they are, the flies have complex bodies with lots of visible traits whose inheritance could be studied.
As a result D. melanogaster became the first model organism in biological research. The model organism as a research tool is based on the following facts and assumptions.
1) It is impossible to study everything about every species on earth.
2) Some species have attributes that make them easier to study than others for a particular area of inquiry.
3) Because of common ancestry we would expect closely related species to have similar biological characteristics.
Morgan didn't think that studying flies would give him specific details of the inheritance of particular human traits. However studies of Drosophila should reveal general principles of inheritance. As it turns out flies and humans are more genetically similar than Morgan and his colleagues could have imagined.
One important consequence of focusing on model organisms is that knowledge builds on itself. The more researchers learned about D. melanogaster, the greater the sophistication of the questions they could ask.
Unfortunately, D. melanogaster is a lousy model organism for field ecological research. It is small and highly mobile and it has turned out to be next to impossible to keep track of wild individuals for any length of time at all. So ironically, perhaps the best known animal on the planet from genetic standpoint is one in which almost nothing is known of its field ecology.
However there have been quite a few interesting field studies of evolutionary patterns of Drosophila species. I don't have time to go into all of them but here are a couple of interesting tidbits.
The invasion of D. melanogaster and other species such as the very similar D. simulans of much of the world has allowed researchers to observe the results of rapid evolution. For example the enzyme alcohol dehydrogenase exists in two different forms: fast and slow that are coded for by different alleles. The fast allele is more common in the north and the slow allele more common in the south. It turns out that the fast allele is better at breaking down alcohol but is less stable at higher temperature. Alcohol dehydrogenase is crucial to D. melanogaster as they often occur in high alcohol environments on fermenting fruit.
About 40% of the world's species of Drosophila occur on the Hawaiian islands where giant species (the size of house flies!) have evolved as well as a hammer-headed species.
Drosophila melanogaster is actually a much less common 'wild' species in North America than it was a century ago when Morgan began his experiments. D. simulans, an almost identical species, has become the dominant human-associated species. Recently, here in Florida, we have seen the invasion of another Drosophilid in a different genus. Zaprionus is a widespread genus in the old world tropics that is very closely related to Drosophila. One species, Zaprionus indianus was introduced to South America in the late 90s and has now spread to Florida and perhaps further north and west. It is a very attractively striped small fly. It does appear to attack fruit and is a genuine agricultural pest. I know that it was very common at baits we put out late last summer.
"Green Diary Rescue" is Back!
After a hiatus of over 1 1/2 years, Meteor Blades has revived his excellent series. As MB explained, this weekly diary is a "round-up with excerpts and links... of the hard work so many Kossacks put into bringing matters of environmental concern to the community... I'll be starting out with some commentary of my own on an issue related to the environment, a word I take in its broadest meaning."
"Green Diary Rescue" will be posted every Saturday at 1:00 pm Pacific Time on the Daily Kos front page. Be sure to recommend and comment in the diary.