Big­ger Pic­ture

Cli­mate change is bring­ing about sub­tle changes in an­i­mal colour­ing. What does it mean for fu­ture sur­vival?

Canadian Wildlife - - CONTENTS - By Alanna Mitchell Il­lus­tra­tion by Pete Ryan

Cli­mate change is bring­ing about sub­tle changes in an­i­mal colour­ing. What does it mean for fu­ture sur­vival?

WHAT IF THE AC­CU­MU­LA­TION OF HU­MAN ef­fects on the planet is al­ter­ing the colour of a green­finch’s tail feather, the hue of a lizard’s belly, the tint of a trout fin? What if, in other words, we are de­ter­min­ing not just the big stuff — whether we still have glaciers and per­mafrost, where the sea level set­tles, how many droughts, floods and heat waves we en­dure — but also the small?

This is the sur­pris­ing ques­tion ex­plored in a new pa­per in the U.K.’S Pro­ceed­ings of the Royal So­ci­ety B by (among oth­ers) Andrew Hendry, a bi­ol­o­gist at Mcgill Univer­sity in Mon­treal. But why do an­i­mals have dif­fer­ent colours — or any colours — in the first place?

For a lot of rea­sons, as it turns out. Cam­ou­flage is an ob­vi­ous one: your colour­ing can make you blend into the back­ground, hid­ing you from preda­tors, or make you stand out like a tasty sore thumb. Think about the Arc­tic hare, whose thick fur coat turns snow-white in the frosty win­ter and bluey-grey — the colour of tun­dra rocks — in the spring.

Coloura­tion can de­ter­mine whether you get the mate you want. For ex­am­ple, fe­male ci­ch­lid fish in Africa’s Lake Vic­to­ria are choosy about the pre­cise hue of metal­lic blue on their male mates’ dor­sal fins.

But the sig­nif­i­cance of colour­ing goes far beyond that. Colours, some of which are de­ter­mined by in­her­ited melanin pig­ments, have be­wil­der­ingly vast ef­fects on how an an­i­mal’s body works. For in­stance, colour can de­flect ul­tra­vi­o­let rays or let them in. Colour can soak up heat or push it away.

Darker crea­tures are gen­er­ally more phys­i­cally ac­tive and burn more calo­ries. Lighter-coloured an­i­mals can make do with less food. Darker colours have the bizarre abil­ity to fend off pol­lu­tion by toxic heavy met­als. Dark feath­ers don’t de­grade un­der bac­te­rial as­sault as quickly as light feath­ers. Colour­ing helps de­ter­mine how ef­fec­tive your im­mune sys­tem is, in­clud­ing how many an­ti­bod­ies you make.

But apart from af­fect­ing a crea­ture’s in­ner work­ings, colour can also af­fect how an an­i­mal be­haves. The darker the colour of your fur, feath­ers, skin and scales, the bolder you are. Darker an­i­mals are more so­cially dom­i­nant, more sex­u­ally ac­tive and more likely to live in groups, for rea­sons that are not fully un­der­stood.

All of th­ese char­ac­ter­is­tics af­fect how a crea­ture con­tracts dis­ease and par­a­sites and how it fends them off.

But as the world warms and changes in a raft of other ways, ver­te­brates face un­prece­dented new stresses that make them more sus­cep­ti­ble to dis­ease. Sure, all those heat waves, cold snaps, hur­ri­canes and mon­soonal rain­storms af­fect hu­mans, but they af­fect wild an­i­mals, too. In­va­sive species bring in new bugs. Pol­lu­tion de­presses im­mune sys­tems. How will colour play out in this new world of path­o­genic abun­dance?

Take green­finches as an ex­am­ple of the chal­lenges on the hori­zon. In 2005, a new in­fec­tious par­a­sitic dis­ease, Tri­chomonas gal­li­nae, be­gan killing off vast num­bers of green­finches across the United King­dom and north­ern Europe. (Emerg­ing in­fec­tious dis­eases are linked to the warm­ing world.) One small study from Es­to­nia pub­lished in 2014 showed that the tail feath­ers of green­finches that didn’t die from the dis­ease were 22 per cent darker than those of birds that did. Darker tail feath­ers some­how pro­tected the birds from the par­a­site. Per­haps it was be­cause lighter birds didn’t get good ac­cess to food and were weak­ened. Maybe it was some­thing else.

When you look at this find­ing through the lens of evo­lu­tion, it means green­finches with dark tail feath­ers are more likely to be left alive, more likely to breed, more likely to pass on their genes and colour­ing. And that means green­finches are more likely in the fu­ture to have darker tails.

Why does that mat­ter? The im­pli­ca­tions could be far-reach­ing, but they re­main un­known. Will other species also be af­fected? Likely. Global change is in­flu­enc­ing the spread of dis­ease. It may also shift an­i­mals’ colour­ing and their abil­ity to sur­vive in­fec­tion. How do the two in­ter­act? Could bi­ol­o­gists be­gin to use coloura­tion to pre­dict an­i­mals’ re­sponse to this weird world we’re creat­ing?

This ques­tion fas­ci­nates me. It speaks to the epic na­ture of the change hu­mans are un­leash­ing. Now, it’s not just the Bib­li­cal plagues that we al­ready no­tice and track. Now, it goes right down to the colour of the hair in a squir­rel’s tail.

We are dab­bling in evo­lu­tion in ways we barely com­pre­hend. There are dan­gers, of course. But there is also an af­front to the soul. If we are get­ting rid of colours na­ture has so painstak­ingly cre­ated, what sort of a species can we be?a

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