Model organisms are non-human species that are studied to understand specific biological phenomena, diseases, molecular pathways and behaviours.
They harbour the expectation that the discoveries they lead to will provide insight into the workings of other organisms, such as humans. Model organisms are widely used in biological research since human experimentation would be unethical and/or unfeasible.
Model organisms are characterised by the following features:
- The metabolic/molecular/developmental pathway under study is conserved (comparable) with the one found in humans.
- Model organisms are easy to handle and cheap to maintain in laboratory conditions.
- There is a trade-off between their genetic complexity and research utility. Simple organisms are easy to understand, but not very informative.
Within the INsecTIME consortium, we use four different organisms.
They are listed below, together with the features which make them the best model organisms for out chronobiology studies.
D. melanogaster was among the first organisms used for genetic analysis. Thomas Hunt Morgan began using fruit flies in experimental studies of heredity at Columbia University in 1910, and today this insect is one of the most widely used and genetically best-known of all eukaryotic organisms. Not surprisingly D. melanogaster flies have been used since the beginning of molecular chronobiology. The first clock mutants, generated by Konoka and Benzer back in 1969, were isolated in D. melanogaster, and they paved the way for the molecular dissection of the circadian clock. What makes D. melanogaster so famous?
- It is small, easy and cheap to grow in the laboratory
- It has a short generation time (about 10 days at room temperature) so several generations can be studied within a few months
- It has a high fecundity (females lay up to 100 eggs per day)
- It has only four pairs of chromosomes
- Males do not show meiotic recombination, facilitating genetic studies.
- Genetic transformation techniques have been available since 1982 and its complete genome was sequenced and first published in 2000
- it has a complete but simple nervous system, consisting of around 100,000 neurons, as opposed to the 85 billion in the human brain
The molecular components of the clock machinery in D. melanogaster and humans are very similar. Moreover, D. melanogaster flies not only show circadian behaviours which are easy to monitor and measure in the laboratory (such as rhythmic locomotor activity and sleep patterns), but they are also characterised by a seasonal behaviour: diapause. These features make D. melanogaster flies an excellent model organism to study both circadian and seasonal clocks.
This short video shows an interview with Prof. C. P. Kyriacou, INsecTIME coordinator, who introduces the value of Drosophila as a model organism and explains about the importance of biorhythms, including their relevance to human health.
Nasonia ia a small parasitoid wasp that stings and lays eggs in the pupae of various flies. The fly species that Nasonia usually parasitize are primarily blowflies and fleshflies, making Nasonia a useful tool for biocontrol of these pests.
In 2010 the National Human Genome Research Institute announced the release of the Nasonia genome. Nasonia vitripennis is a primary model for parasitoid genetics. The unique aspects of its natural history include large family sizes, its cosmopolitan distribution, haplodiploidy, the ability to inbreed and produce healthy isogenic inbred lines, a wealth of visible and molecular markers and the ease of performing complete genome screenings in search of mutations. Of interest for our purposes, N. vitripennis flies display a strong, maternally induced larval diapause, the insect equivalent of mammal hibernation.
Within INsecTIME Nasonia wasps will be used in WP2, WP3 and WP6.
Bactrocera oleae is also known as the Olive fruit fly. It is found throughout the Mediterranean basin and in South Africa and since the late 1990s it has also been present in California. It is considered the most serious pest for olives, significantly affecting both the amount and quality of production in most olive growing areas.
The females lay their eggs in the summer by making a puncture into the skin of the olive. Hatching occurs over a variable period depending on weather conditions and time of year. The newly hatched larva initially digs a tunnel on the surface, and then later moves deeper into the flesh to the core. Larvae at their third stage move toward the surface again and during this phase the olive clearly shows signs of the attack.
The development cycle is closely linked to environmental conditions. This species does not conform to the definition of model organism given above, but it is of clear economic relevance. Investigating the molecular mechanism behind its overwintering strategy, and its sexual behaviour is key to developing a successful and effective management program.
Within INsecTIME the Olive fly will be used in WP6 and WP12.
The firebug Pyrrhocoris apterus is a very common insect, and as is the case for the Olive fruit fly, it is not a canonical model organism used in genetics research and as a consequence it is not genetically well-characterised. Nevertheless, what makes this bug special, is its solid and robust photoperiodic seasonal character. Furthermore, it belongs to the Pyrrhocoridae family, making it “phylogenetically distant” (and therefore genetically different) from the most commonly used insect model species such as Diptera and Lepidoptera. How is that an advantage? The firebug represents a new resource for comparative studies aimed at unraveling the evolutionary history of insect timing. Indeed, whereas much of biology tends to focus on a single exemplar organism or a small subset of model organisms, comparative biology is a cross-lineage approach to understanding the evolutionary history and interactions among different species.