Birds are a diverse class of vertebrates that include over 10,000 living species. They are found worldwide and occupy a wide range of ecological niches. Understanding the genetics, development, physiology and behavior of birds requires model organisms that can act as representatives for the class Aves as a whole. An ideal model organism for birds exhibits some key characteristics:
Key Criteria for Avian Model Organisms
- Be easy and inexpensive to acquire and house in a lab setting.
- Have a short generation time allowing for rapid selective breeding.
- Be amenable to genetic manipulation and molecular techniques.
- Have a well-characterized, high-quality genome sequence.
- Exhibit traits and behaviors representative of birds in general.
There are a handful of bird species that fit these criteria and have become important model organisms providing insights into genetics, development, physiology, neurobiology, behavior and disease in avian biology. The most commonly used and thoroughly studied avian models are:
Domestic Chicken
The domestic chicken (Gallus gallus domesticus) is the predominant model organism used for avian biological research. Some key advantages of the chicken include:
- Chickens are easy to acquire and available year round.
- They have a short generation interval, reaching maturity in 5-6 months.
- Housing costs are low and they can be kept in high densities.
- There are many genetic lines and breeds to choose from.
- The chicken was the first bird to have its genome sequenced.
- Their embryos develop externally allowing easy access.
- A wide range of genetic tools exist for chicken research.
Chickens exhibit complex social behaviors and are used to study topics ranging from cognition to disease transmission. Some limitations are that they cannot fly, have poor vision, and altered digestive anatomy compared to wild birds.
Zebra Finch
The zebra finch (Taeniopygia guttata) is a highly gregarious songbird species native to Australia. Advantages include:
- They breed readily in captivity.
- Have a short generation time of 2-3 months.
- Small size makes them easy to house.
- Genome has been fully sequenced.
- Utilized for studies of neurobiology, song learning, and sexual selection.
- Drawbacks are a lack of sophisticated genetic tools and limited embryos
Neuroscientists often study song learning in juvenile zebra finches. Their complex vocal communication provides insights on human language acquisition and development. Zebra finches are also a model for research into monogamy and pair bonding behavior.
Japanese Quail
The Japanese quail (Coturnix japonica) has features making it a useful alternative to chickens such as:
- Smaller size making housing easier.
- Shorter generation interval of 2-3 months.
- Exhibit more natural wild behavior than domestic chickens.
- Have a well-defined genetic lineage.
- Widely used in studies of embryo development, nutrition, and physiology.
Limitations of quail include more stringent housing requirements, lack of genetic tools, and relative difficulty of egg and embryo access compared to chickens. They show promise as a model for research into avian domestication and evolution.
Pigeon
Pigeons and doves (Family Columbidae) are sometimes used as models for visual perception, learning, cognition and behavior. Benefits include:
- Readily available urban populations of feral pigeons.
- Adaptable behavior and ability to thrive in captivity.
- Excellent eyesight and visual acuity.
- Highly developed homing abilities.
- Have served as traditional subjects for studies of learning and memory.
Limitations are a lack of genetic tools, limited embryos, and highly derived digestive system. The most common subject is the domestic pigeon used for racing and shows.
Budgerigar
The budgerigar or common parakeet (Melopsittacus undulatus) is a small Australian parrot sometimes used as a model for research into bird behavior and neurology. Benefits include:
- Their small size makes them easy to house.
- Breed readily in captivity.
- Exhibit flocking behavior, vocal learning, and visual abilities representative of parrots.
- Have served as models for studies of bird speech and song learning.
Limitations include scarce genetic tools, limited embryos, and a non-native habitat compared to wild parrots. Budgerigars remain an underutilized model species in avian research.
Duck and Goose
Domestic ducks and geese provide alternative avian models to the standard chicken. Benefits include:
- Readily available due to agricultural usage.
- Exhibit more wild-type aquatic behaviors than chickens.
- Embryos are readily accessible and comparable to chicken embryos.
- Particularly suitable as models for studies of influenza viruses and hepatology.
Limitations are behavioral differences from wild waterfowl, scarce genetic tools, and housing challenges due to size. Various duck and goose breeds are used but Pekin and White Leghorn are common.
Turkey
The domestic turkey (Meleagris gallopavo) has some advantages as an alternative avian model. These include:
- Similar husbandry requirements to chickens but exhibits more active wild behaviors.
- Amenable to having embryos accessed for developmental studies.
- Increasing number of genomic resources.
- Comparable immune system to chickens.
Disadvantages of turkeys are longer generation intervals, challenges collecting eggs, limited genetic tools, and a large size requiring more housing space. Various breeds are utilized for research purposes.
Conclusion
Birds provide important model organisms that allow researchers to tackle questions relevant to avian biology itself along with providing general insights into topics like development, behavior, neurology, genetics and disease. The predominant avian model is the domestic chicken due to its ease of use, wealth of genetic knowledge, and similarities to wild junglefowl. For specific research aims, alternate species like pigeons, quail, finches, parakeets, waterfowl and turkeys can offer complementary advantages. Avian models will continue to advance our understanding of fundamental biological processes in this diverse vertebrate class.