Black, white and stinky: Explaining coloration in skunks and other boldly colored animals

May 30, 2011
Striped Skunks (Mephitis mephitis) Image: Wikipedia, CCA3.

(PhysOrg.com) -- In a first-of-its-kind analysis of the evolution of warning coloration in carnivores published this week by University of Massachusetts Amherst evolutionary biologist Ted Stankowich and colleagues, the researchers explain why some species such as skunks use bold coloration to warn predators either that they risk being sprayed with stinky gas or getting into a vicious fight, while other species don't.

Stankowich says most evolutionary research attention to date on warning coloration in has been paid to like newts, poison dart and , so this new investigation is a rare comprehensive analysis of mammalian warning coloration, also known as aposematic coloration, such as the ’s bold stripes.

He adds, "It’s important to be clear that bold coloration is not just advertising the ability to spray your anal glands, it’s often an advertisement for ferocity. Some of these small black and white animals are extremely ferocious, for example the honey badger."

Stankowich, who is also a visiting postdoctoral and teaching fellow at Harvard, with Tim Caro of the University of California Davis and UMass Amherst undergraduate Matthew Cox, conducted this first systematic examination of the evolutionary drivers of bold coloration patterns and placement in carnivores such as skunks, badgers, civet cats and wolverines.

The researchers collected data on 188 species of mammalian and found those who are more boldly colored are more likely to be stocky, able to spray noxious chemicals from their anal glands, burrowing, nocturnal and living in exposed environments. Results appear in the current online edition of the journal .

"One question we’re asking is what are the possible evolutionary advantages of bold coloration in mammals," he says. "Why would you want to be so bold, calling more attention to yourself when camouflage is such an effective strategy? We’ve tested how certain aspects of species ecology and lifestyle might shape the evolution of this phenomenon."

Among the evolutionary advantages these strategies may carry is the ability to move into a new habitat that is relatively exposed to but not exploited by other animals or the ability to remain living in a habitat that suddenly experiences an influx of new predators.

To investigate eight factors that are potentially involved in the evolution of aposematic coloration, Stankowich and colleagues categorized 188 carnivore species by pelage: from a single color to extravagantly and boldly marked, which contributes to a feature they call salience, an expression of how well a species stands out in its environment due to its color pattern. Other variables included in the analyses are the ability to spray noxious anal gland secretions, body shape and habitat openness.

The researchers then used a series of statistical steps including phylogenetic independent contrast methods, which are based on information about species’ evolutionary relationships, to look at changes in a particular trait. They analyzed these contrast scores with a measure known as Akaike’s information criterion (AIC) to obtain the relative goodness of fit for variables to a statistical model. AIC analysis reveals which variables play the strongest role in explaining the variation in the data, Stankowich notes.

In this case, the authors identified the 10 strongest models, then looked at which variables most commonly occurred in those models. These strongest models were used to calculate summary weights for each factor, an indicator of the importance of each predictor. They found that the evolution of boldly colored body patterns was best explained by body length, habitat openness, anal spray ability and burrowing behavior.

They also found that species with horizontal stripes along the body leading to the tail are more likely to be able to spray their anal gland secretions at predators in defense, suggesting that the stripes also direct the predator’s attention to the area where the weapon is found. Similarly, a previous study found that facial stripes in this group were found in species that defend themselves by fighting, often with strong bites.

Overall, these anti-predator strategies appear to have evolved independently several times among the Carnivora, say Stankowich and colleagues. So, for example, other nocturnal, slow, stocky, small-to-medium animals with bold black-and-white signaling the presence of noxious anal gland secretions and/or the ability to fiercely defend themselves can be found living in open areas in Africa as well as North and South America and Europe.

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User comments : 9

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dogbert
not rated yet May 30, 2011
The study used an arbitrary small subset of mammals.

Try to apply the conclusions to, for example, a Zebra.
Twin
not rated yet May 30, 2011
This article is referring to statistical study which, I agree, the zebra does not fit. All data need not fit to reach a statistical conclusion.

The zebra's camo is indeed B&W but probably for intensity not warning. It is thought the zebra's stripe may have a dual function.
1. Dazzle or Disruptive camouflage see:
http://en.wikiped...mouflage
2. Protection from biting flies, many of which are attracted
to large dark areas.

Statistically, the authors conclusions about function may be correct. The conclusion that they result from evolution simply shows a prejudice toward a particular theory.
LEDman
5 / 5 (3) May 30, 2011
Dogbert,

If you re-read the article, it is not a small subset of random mammals, it is a study of mammalian carnivores. Last time I checked zebras preferred vegetation.

I would argue that for zebras, their coloration makes it much more difficult to distinguish individuals. A useful trait considering their predators single out individuals for attack.
dogbert
not rated yet May 30, 2011
If you re-read the article, it is not a small subset of random mammals, it is a study of mammalian carnivores.


I did not say it was a small subset of random animals. I said they used an "arbitrary small subset of mammals". I am aware that they used carnivores and that they used a small subset of carnivores.

Did they reach their conclusions after researching or did they select the arbitrary subset in order to reach the conclusion?

Either way, the research is mostly useless.

As for Zebras, they are rather fierce fighters but they did not fit the arbitrary group the study designers selected because they rejected herbivores.
Beard
5 / 5 (1) May 30, 2011
Stankowich, the skunk professor.
orsr
not rated yet May 31, 2011
Either way, the research is mostly useless.



Please present us your (or someone else's) research, which you consider useful on this topic. I am willing to learn.
dogbert
3 / 5 (2) May 31, 2011
Please present us your (or someone else's) research, which you consider useful on this topic. I am willing to learn.


Why? Why would anyone conduct research to conclude what is already known? Before this study determined that bold coloration indicates a creature capable of aggression, we already knew that bold markings indicates a creature capable of aggression.

I understand that obtaining grant money is dependent on publishing, but why not publish something which actually increases our knowledge?

I do not know of any useful studies on what is obvious without a research grant.
210
2.3 / 5 (3) May 31, 2011
Please present us your (or someone else's) research, which you consider useful on this topic. I am willing to learn.


Why? Why would anyone conduct research to conclude what is already known? Before this study determined that bold coloration indicates a creature capable of aggression, we already knew that bold markings indicates a creature capable of aggression.

I understand that obtaining grant money is dependent on publishing, but why not publish something which actually increases our knowledge?

I do not know of any useful studies on what is obvious without a research grant.

My friend, have you seen this blog?
http://www.uinnob...tem.html
It speaks to what you are alluding to, I believe: There is a problem in grant-dom and it is getting worse.
word-to-ya-muthas
DavidMcC
not rated yet Jun 10, 2011
The zebra's camo is indeed B&W but probably for intensity not warning. It is thought the zebra's stripe may have a dual function.
1. Dazzle or Disruptive camouflage see:
http://en.wikiped...mouflage

Indeed so. Specifically to confuse lions, whose eyes have a tapetum lucidum, which gives them better night vision than zebras, BUT also creates visual artifacts, the reason diurnal animals do not have a t.l.