F Rosa Rubicondior: Unintelligent Design - Why Skunks Have Evolved Different Colour Patterns

Sunday 26 November 2023

Unintelligent Design - Why Skunks Have Evolved Different Colour Patterns

Striped skunk, Mephitis mephitis
November: Skunks' warning stripes | News and features | University of Bristol

It's better to warn than to attack because attacking is costly and carries risks, but a warning is often free or takes minimal effort.

This is why many creatures advertise the fact that they can be dangerous so leave them alone - yellow and black wasps; the warning rattle of a rattlesnake, the bright colours of a poison dart frog, or the black and white pattern of a skunk, for example.

But these patterns only work as a deterrent, if the potential threat has some experience or has evolved in their presence so has a genetic aversion.
What information do you have about skunks, their evolution, color patterns and distribution of sub-species in North America? Skunks are small to medium-sized mammals known for their distinctive black and white coloration and the ability to spray a foul-smelling liquid as a defense mechanism. Here's some information about skunks, including their evolution, color patterns, and distribution of sub-species in North America:

Skunks are members of the family Mephitidae and are part of the order Carnivora, which includes other mammals such as dogs, cats, and bears. The evolution of skunks can be traced back to the Miocene epoch, with fossils suggesting that their ancestors were weasel-like animals. Over time, skunks developed their unique characteristics, including the ability to produce a noxious spray.

Color Patterns:
The most well-known feature of skunks is their black and white coloration. This serves as a warning signal to predators, indicating that they possess a potent defense mechanism. The specific patterns can vary among skunk species, but generally, they have a black body with one or more white stripes running down their back and tail.

Distribution of Sub-species in North America:
There are several species of skunks in North America, and their distribution can vary. The two most common species are the striped skunk (Mephitis mephitis) and the spotted skunk (Spilogale putorius). The striped skunk is found throughout most of North America, from Canada to Mexico. The spotted skunk has a more limited distribution and is found in various regions, including the western United States and parts of Mexico.

Within these species, there may be regional variations and subspecies. For example, the Eastern spotted skunk (Spilogale putorius) is found in the eastern United States, while the Western spotted skunk (Spilogale gracilis) inhabits the western part of the country.

Skunks are adaptable animals and can thrive in a variety of habitats, including forests, grasslands, and urban areas. They are primarily nocturnal, foraging for food during the night, and are omnivorous, feeding on a diet that includes insects, small mammals, fruits, and plants.

It's worth noting that while skunks are generally harmless if left undisturbed, they can spray a strong-smelling liquid as a defense mechanism when they feel threatened. This spray can be an effective deterrent against predators, and it's best to give skunks a wide berth to avoid any unpleasant encounters.

So why then, do the warning patterns on a skunk vary across its range and from sub-species to sub-species?

The only answer an intelligent [sic] design advocate could come up with, leaving aside the belief that it designed predators to prey on skunk, then gave the skunk a means of deterring predators from doing what they were designed to do, is that their putative designer never does anything simply when a more complicated way of doing it exists, so it designed lots of different warning patterns for skunks, some of which work less well than others.

But of course, as usual, there is a much simpler explanation and one which doesn't involve a supposedly supremely intelligent magic entity doing utterly stupid things for no apparent reason. That explanation is provided by the mindless, utilitarian process of evolution by natural selection, as a team of researchers from the Universities of Bristol, UK and Montana and Long Beach, California, USA have discovered.

Their research shows something that is predictable from the first principles of evolution by natural selection - when the environmental selectors are different, the result will be different. They have shown that skunk patterns vary according to the type and abundance of potential predators in different parts of the range.

They have published their findings in the journal Evolution, and a news release from the University of Bristol explains it's significance:
Striped skunks are less likely to evolve with their famous [black] and white markings where the threat of predation from mammals is low, scientists from the University of Bristol, Montana and Long Beach, California have discovered.

Skunks’ iconic black and white colouration signals its toxic anal spray. However, some skunks show very varied fur colour ranging from all black to thin or thick black and white bands to all white individuals. Variation is huge across the North American continent.

Findings published today in Evolution, suggest that this is a result of relaxed selection, when environmental change eliminates or weakens the selection of a normally important trait – in this case black and white pelage.

Warning coloration is an antipredator defence whereby a conspicuous signal advertises the ability of prey to escape predation, often because it is toxic or has spines or is pugnacious. Usually, predators have to learn the significance of this signal and so it is predicted that warning colouration will look very similar across prey individuals of the same, as well as perhaps different, prey species to be an effective education tool. Yet some warningly coloured prey show rather different advertisements even within the same species.

Professor Tim Caro, co-author
School of Biological Sciences
University of Bristol, Bristol, UK.
Graphic of variations of markings.
Professor Tim Caro
Researcher Hannah Walker from the University of Montana documented the distribution of these different pelage colours across their range in North America using museum specimens. She plotted these against a menu of variables that the team thought might drive this variation in coloration.

The team found that in locations in which skunks overlapped with rather few mammalian predators that might be capable of killing them, fur colour was varied even within the same litter.

Where there were many species of predators that were a danger to them, they showed little variation.

The team also examined owl and raptorial predators however while the effects were the same, they were not as evident. This is perhaps because birds have a poorer sense of smell and are less deterred by smelly anal defences.

Our results indicate that relaxed predation pressure is key to warning signal variation in this species, whereas stronger pressure leads to signal conformity and stronger signals. We now know why not all skunks look alike, and perhaps why members of other warningly coloured species look different from each other. If relaxed selection operates within species, it should do so across prey species too. More broadly, this study provides another brick in the wall of explaining the evolution of coloration in nature.

Professor Tim Caro
Now the team plan to see if this occurs across other skunk species whose geographic ranges overlap in North America.
Sadly, the team's paper in Evolution is behind a paywall, but the abstract is freely available.

Contrary to expectations regarding efficient predator education mediated by lack of ambiguity and enhanced prey recognition, aposematic signals often show considerable intraspecific variability. For example, some striped skunks (Mephitis mephitis) are almost entirely white, others have black-and-white stripes of equivalent thicknesses, yet others are mostly black. We tested the ecological correlates of this variation in patterning using 749 museum skins collected across North America. Skunks had longer white–black borders and more bilaterally symmetrical stripes in areas with a greater number of potential predator species, and this effect was more marked for mammalian than avian predators, the latter of which may be less deterred by noxious defenses. Skunks from locations with greater predator diversity were less variable in the extent of whiteness on their dorsa and less variable in the length of their white–black borders, suggesting strong selection from predators leads to greater conformity in stripe patterns, even at the same location, but weak selection from predators leads to relaxed selection on pattern conformity. Skunks exhibited greater areas of black pelage in areas of greater humidity conforming to Gloger’s rule. Our results indicate that relaxed predation pressure is key to warning signal variation in this iconic species, whereas stronger pressure leads to signal conformity and stronger signals.

To summarise then, what we have here is a group of scientists with absolutely no doubt that the Theory of Evolution provides the explanation for an observed phenomenon, in contrast to a creationist explanation in which the supposedly intelligent designer looks like an incompetent fool having an arms race with itself and giving skunks different warning patterns according to which predators it want to deter from doing what it designed them to do and which don't work as well as a perfectly good alternative pattern if the skunk strays outside its normal range.

Creationists need to remain stoically ignorant of much of nature to retain the delusion that a magic designer of it is worthy of worship.

Thank you for sharing!

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