Posts Tagged ‘Mephitis mephitis’

Striped Skunk (Mephitis mephitis) Dispersal During the Pleistocene

May 30, 2017

Most people don’t even think about where and when the various species of wildlife inhabiting their neighborhood originated. No matter how common a particular species may seem, it has not always been there.  The striped skunk is a generalist species that occurs all across the United States, and it is quite common in many regions, especially rural farm country. It is found in forests, fields, wilderness and suburbs.  They are an adaptable species, thanks to their omnivorous diet and unique defense strategy.  Yet, striped skunks have not always existed over their present day range.

The ancestors of all American skunk species came to this continent by crossing the Bering Land Bridge over 5 million years ago.  Paleontologists assign fossils of this ancestral species to the extinct  Martinogale genus.  About 2 million years ago striped skunks in the Mephitis genus diverged from spotted skunks in the Spilogale genus.  There is fossil evidence of early species of Mephitis skunks from the early and mid-Pleistocene in Nebraska, Colorado, and Florida.  However, this early species must have gone extinct over much of its range.  By 300,000 years ago, Mephitis skunks were restricted to what today is northern Mexico and southern Texas.  All present day striped skunks descend from this ancestral population, according to a study of striped skunk genetics.  Scientists studied genetic information from 314 specimens chosen from 20 states and determined striped skunks spread east and west from this population.  Early striped skunks, like their closest living relative–the hooded skunk (M. macroura), were probably well adapted to desert environments but evolved characteristics that helped them survive in woodlands and grasslands.  Over 250,000 years ago, striped skunks crossed the Mississippi River and colonized the entire southeast.  This probably occurred during a glacial stage when the river ran low and numerous sandbars facilitated the crossing.  The lower Mississippi River has served as a barrier, isolating populations of striped skunks ever since.

Geographic distribution striped skunk phylogroups based on 601 base pairs of cytochrome-b gene in mitochondrial DNA. Pie charts indicate the proportional representation of groups in each state. The hypothesized Pleistocene and Holocene dispersal patterns for striped skunk phylogroups are indicated by unique dash marks.

Dispersal of striped skunk population during the Pleistocene based on genetic evidence from 314 specimens taken from 20 states. Map from the below referenced study.

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The hooded skunk (Mephitis macroura) is the closest living relative of the striped skunk.  Its range is Mexico and the extreme southwestern U.S.  Genetic evidence suggests this is also the geographic range where striped skunks originated.

Image result for striped skunk

Nice photo showing coat variation within the striped skunk population.  Striped skunks colonized southeastern North America about 300,000 years ago.  A primitive closely related species occupied this region before that.  It’s unclear when this predecessor became extinct.

~200,000 years ago striped skunks advanced up the Rocky Mountains from their southwestern refugium.  This population split into 2 clades on either side of the Great Basin 130,000 years ago.  This western population expanded east and colonized the Midwest.  Following the end of the last Ice Age, southeastern skunks colonized New England and expanded west, coming into contact with western populations in the Midwest.  This has resulted in an admixture of once genetically distinct populations.  The history of this dispersal explains why skunk physical characteristics vary so much. The upper Mississippi River is smaller than the lower part and is not an insurmountable barrier.  Admixtures occur along the upper part of the river.  Genetic studies of raccoons, deer mice, northern short-tailed shrews, 5-lined skinks, and leopard frogs show similar dispersal histories with the Mississippi River acting as a barrier isolating populations from each other.

Reference:

Barton, Heather; and Samantha Wisely

“Phylogeography of Striped Skunk (Mephitis mephitis) in North America: Pleistocene Dispersal and Contemporary Population Structure”

Journal of Mammalogy 93 (1) 2012

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Pleistocene Skunks

April 7, 2013

The skunk’s black and white markings warn predators, even those lacking color vision, to beware of the noxious spray this animal is capable of unleashing.  The skunk’s defense mechanism is so effective they seem to fear no other animal.  When threatened they often run toward much larger animals and chase them away.  Nevertheless, skunks do suffer predation.  Most notably, great horned owls (Bubo virginianus) specialize in taking skunks, and the owls seem to be immune to the spray.  For this reason some great horned owls smell like skunk.  Cougars stalk and kill skunks before the skunk has time to respond.  Formerly, some Native Americans preferred skunk to other types of meat such as turkey.

Scientists no longer consider skunks to be members of the weasel family, the mustelidae.  Instead, skunks and old world stink badgers belong to a family all their own known as the mephitidae.  Today, Georgia is h0me to 2 species of skunks–the striped (Mephitis mephitis) and the spotted (Spilogale putorious).  During the Pleistocene hog-nosed skunks (Conepatus leuconotus) lived throughout the south as well, leaving fossils at Ladds Mountain, Bartow County, Georgia and several sites in Florida.  The extinct short-faced skunk (Brachyprotoma obtusata)  may have extended its range into the upper south but was more of a boreal species.  Fossils of this species have been found as far south as Arkansas.

Striped skunk–the most common species found in Georgia today and probably during the Pleistocene.

Striped skunks are the most common skunk in Georgia today, and are the only species found in more than 1 fossil site in state, so they likely were the most common species throughout the Pleistocene.  Striped skunks are omnivorous, feeding on small mammals, reptiles, birds, insects, and fruit.  I’ve never seen a live individual, but I have frequently seen road-killed skunks in rural areas of north Georgia.  They prefer broken country with a mix of fields and woods.  Curiously, they’re rare near Augusta, Georgia, perhaps because there aren’t many farms with stores of grain that attract enough mice to entice skunks.

Spotted skunk.  When a spotted skunk displays a handstand flee the scene immediately…it’s about to spray.

I did see a live spotted skunk once in 1990, while I was throwing a paper route at about 5:00 am on Sand Bar Ferry Road located east of downtown Augusta.  Spotted skunks are attractive little animals that climb trees–an unusual behavior for a skunk.  Spotted skunks prefer forest edge and prairie habitats and are common in the middle part of North America but less abundant on the edges.

Hog-nosed skunk.  Note the claws for digging up grubs.

Current range of hog-nosed skunk and closely related South American species.  During the Ice Age its range expanded into the southeast of North America because there was more brushy arid habitat then.

Hog-nosed skunks prefer arid brush and grassland habitats, thus explaining why they occupied the south during the Ice Age but no longer occur here.  Arid scrub habitat expanded across the southeast during the Ice Age because the climate was drier then.  Like striped and spotted skunks, hog-nosed skunks are omnivorous but rely more on insects for a greater part of their diet than other skunk species.

Little is known about the extinct short-faced skunk.  It was a small skunk, more like the spotted skunk than any other extant species.  Based on its fossil distribution, it was an animal of the boreal forests that predominated south of the ice sheet.  It co-existed with the other 3 species of skunks, but unlike them, it failed to adapt to the environmental changes that occurred ~8,000 years BP.  Perhaps, they were more vulnerable to diseases carried by an increased population of parasites in the warming climate.