One of the
most famous examples of domestication is Darwin and his pigeons (Freeman
et. al., 2007). Darwin
held much interest in the artificial selection of pigeons with elaborately
shaped and coloured feathers to support his research into evolution. The
domestic pigeon (Columba livia), originated 5000 years ago from Mediterranean rock doves. They were domesticated for food, fancy
looks and pigeon racing. At around 350 domestic breeds there is enormous variation in size, shape, and colour.
Now a new generation of feral pigeons (domestic breeds released/escaped into the wild) inhabit cities around the world (Cookson, 2013). Sol (2008) examined the outcome of pigeon domestication and its flow on effects that hinder survival to its feral descendant’s populations. Artificial selection is known to displace individuals from their ‘adaptive peak’ that enhances species survival in the wild. This can be seen in the disproportionally long tarsus-metatarsus bones (leg bone) in the domestic and feral pigeon. The size of the leg bone is hereditary and influential in how an animal utilizes its environment (stride length, speed and perching stability).
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| Fancy Pigeon Photo courtsey of John Ross. http://charlesdarwintrust.org/content/86/galleries_pigeons |
Now a new generation of feral pigeons (domestic breeds released/escaped into the wild) inhabit cities around the world (Cookson, 2013). Sol (2008) examined the outcome of pigeon domestication and its flow on effects that hinder survival to its feral descendant’s populations. Artificial selection is known to displace individuals from their ‘adaptive peak’ that enhances species survival in the wild. This can be seen in the disproportionally long tarsus-metatarsus bones (leg bone) in the domestic and feral pigeon. The size of the leg bone is hereditary and influential in how an animal utilizes its environment (stride length, speed and perching stability).
It was found that longer leg bones are a hindrance and
resulted in higher mortality in feral pigeons due to inefficient locomotion required
in active food searching. Surprisingly, instead of the demise of the feral
pigeon, it appears re-adaption has occurred independently with feral pigeon
populations reverting back to their ancestral rock dove skeletal sizes and
shapes, steering away from their most direct domestic ancestors. This suggests
that selective pressures of the wild environment (a phenotype–ecology association)
has driven natural selection to ‘undo’ domestication and assert the size and
shape phenotypes of the original, wild ancestors.
Is human interference in the evolution of species through
domestication beneficial or detrimental?
As seen in the domestic pigeon,
the traits selected for
that are deemed ‘fit’ & ‘better’ in reality no longer allow for the species
to successfully function in its native ecosystem from whence it originated.
Will feral pigeons ever fully revert back to their
ancestral physiology?
Some populations may not have
had enough time yet to re-adapt OR possibly a new niche in human-made habitats
has created a unique morphological optimum for feral pigeons, rather than their
ancestors open rocky environment.
That's interesting how the pigeons are able to re-adapt to their ancestral skeletal sizes and shapes. Did it say how the longer leg bones benefited the domesticated pigeons in the first place?
ReplyDeleteHey Courtney, I couldn't find exactly why they were selected for long legs but I believe it is a combination of appearance (for winning breeding shows etc) as well as the fact that as they were domesticated to be kept in cages. Caged pigeons didn't need to walk extensively on the ground to find food but rather to perch and wait for humans, and staying stationary in a perched position led to longer legs (stability etc). I hope that helps! Google images of fancy pigeons and the wide range of appearance is amazing.
DeleteNice post! I like that you’ve used a classic example of artificial selection here and that you’ve explained it quite eloquently. This is a good example of how natural selection pressures are often very different to the selection pressures humans imposed on animals. Feral pigeons are amazingly successful birds, so I wonder what other types of adaptations could promote their continued success in human environments?
ReplyDeleteHey Tasmin, other than reverting back to their ancestral morphology I found that feral pigeons have two other adaptations that could explain their abundance in human environments. They have very unfussy nesting needs and use very rudimentary sites like window ledges & abandoned buildings as well as mass nesting/flocking tendencies. So they are not struggling to find shelter/keep warm. But most importantly I think it is their breeding habits that promote their success. Breeding is strongly dependent on food availability, and in cities food is abundant all year round therefore individuals can successfully reproduce up to six times a year. Its amazing : )
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