Can genetics reveal the secrets of colour in nature?

The natural world is bursting full of colour everywhere you look.

A good example of how colour draws us into nature can be found in the humble robin. A frequent Christmas card image, the purpose of this bird’s bright orange-red breast is to ween off competitors for territory. By climbing to higher perches on trees and buildings they compete to ensure that they are the most visible.

Colour also acts to camouflage and hide individuals from potential prey. A brilliant example of this is the snow leopard – nicknamed ‘the ghost of the mountain’ for their slate grey coloration. Blending in with the surrounding environment reduces their risk of being seen prey. Artists often draw inspiration from the natural world for their work. Similarly, scientists also draw inspiration for their work and thanks to genetics the underlying mechanisms can now be studied in greater detail than ever before.

The agouti gene

Fur colour can vary across large areas for the same species. For example, the water vole exists across the Scottish Highlands in what is known as a ‘meta-population’ – a group of individuals that are capable of interbreeding but rarely do. What is unique about the Scottish voles is that most of them are black! In stark contrast to the ‘southern’ water vole that are entirely brown. But why do we see this difference?

Well the exact reason for this is still not entirely understood but it is widely believed by geneticists that the story behind this north-south divide begins 20,000 years ago. At that time, black water voles from Eastern Europe moved into the British Isles across the frozen English Channel covered in permafrost from the ‘Last Glacial Maximum’. The English Channel was still covered in an ice sheet, remnants of the last ice age.

Later, a second wave of brown water voles arrived 10,000 years ago from Central Europe. By this time only a few black water vole still existed in the south but were replaced by invading brown individuals. Whereas in the north they existed in sufficient number to maintain this genetic lineage that still exists today.

A clip from BBC Series ‘The Animal’s Guide to Britain’ where Chris Packham talks to Xaiver Lambin from the University of Aberdeen about Scottish black water voles. Credit BBC

Scientists from Harvard University and the University of California have studied the genetics of deer mice found living in the Nebraska Sand Hills. They found that fur was linked closely with the soil colour of the surrounding areas. Dark-coloured mice become more conspicuous on lighter soils and are more likely to be eaten by avian predators. So, over time these lighter mice survive better than darker mice.

By comparing the genes of darker and lighter deer mice researchers found a change arose in the last 8,000 years within the ‘agouti’ gene. Whilst this genetic mutation was absent from the original darker coloured mice it persisted throughout the adapted lighter mice. In evolutionary terms 8,000 years is an incredibly short time which makes the deer mouse a great example of adaptive evolution.

Batesian mimicry in butterflies

Colours and shapes in nature have evolved to maximise species fitness and their chance of survival. Mimicry is when one species copies the appearance of another to improve its own fitness, either by evolving to share warning colours, or by cheating and deterring predators even without by poisonous.

The African swallowtail from East Africa can mimic the forms of over 12 other species. Birds find the African swallowtail delicious, but the butterflies they imitate taste horrible and in some cases, are even poisonous. The African swallowtail is a natural shapeshifter capable of mimicking various shapes and colour patterns of other butterflies. Mimicking these distasteful butterflies protects them from being eaten. However, they cannot switch from this form once emerged from the chrysalis.

The African swallowtail is a brilliant example of ‘Batesian mimicry’. Named after the Leicester born naturalist Henry Walter Bates this term describes the process whereby vulnerable species imitate the forms of lethal ones.

But how is the African swallowtail capable of imitating so many different species? Researchers have delved into the genes of different African swallowtail variations and found that each of their forms were controlled by the ‘H supergene’. With each passing generation, the H supergene collects instructions on replicating the wing shape and colour of their associated models.

Similarly, to how a train can be diverted onto a different route through a track switch, the African swallowtail H supergene is controlled by the engrailed (en) gene. The en gene effectively acts as a genetic switch and mutations in this gene causes the African swallowtail butterfly to focus its attention towards a particular species to model itself on.

Papilodardinusmorphsabove.jpg

Various forms of African swallowtail – Models are above the horizontal line, mimetic forms of African swallowtail are underneath. Credit: Martin Thomson

Developments in genetics and technology have improved our understanding of how colour has evolved in nature. But whilst this is important, it is just as vital that we all look for our own wonders within nature. Look up within the trees when you are out and about – you might just be able to catch a glimpse of the humble robin.

http://www.discoverwildlife.com/blog/everything-you-need-know-about-robin

http://www.bbc.co.uk/programmes/p00g90d0

https://en.wikipedia.org/wiki/Last_Glacial_Maximum#Europe

http://news.bbc.co.uk/earth/hi/earth_news/newsid_8225000/8225219.stm

http://www.mimeticbutterflies.org

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s