Tag: polymorphism

Central Park squirrel census

January 11, 2020 • 7:45 am

Because of a paucity of readers’ wildlife photos (I do have some, so if you sent them have patience), I’m deferring posting those till tomorrow, replacing them with a SQUIRREL CENSUS post by Greg:

by Greg Mayer

We’ve long been fans of squirrels here at WEIT, and so I was quite pleased to come across the following item in the New York Times, a combination of text, audio, video, and stills, on a census of the gray squirrels (Sciurus carolinensis) in Central Park. (Be sure to have the sound on for the squirrel vocalizations.)

https://www.nytimes.com/interactive/2020/01/08/nyregion/central-park-squirrel-census.html?

And it’s not just because it’s squirrels– it’s the location, too. Research takes me every year or two to the American Museum of Natural History, which is located on Central Park West between 77th and 81st Streets, and I often walk across to Central Park to have lunch, where I enjoy the wildlife, including the squirrels. Mike Klemens of the American Museum did a herpetological inventory of Central Park, which I’ve remarked upon here at WEIT (the only herps I’ve ever seen are turtles in Turtle Pond), so I’m glad to see the squirrels get their due.

The Times also had two earlier articles about the start of the census, here

and here:

Going through the multimedia piece on the results of the inventory, I noticed this photo. . .

Screenshot_2020-01-09 There are 2,373 squirrels in Central Park I know because I helped count them .png

. . . of a melanistic squirrel in the Park. This is interesting for two reasons. First, I didn’t know there were black squirrels in Central Park—I’ve never seen one. (In New York City, “black squirrels” are a color form of the gray squirrel; in other places, the “black squirrels” may be fox squirrels, Sciurus niger.) Second, it shows that the black squirrels are not all blacks (sorry, New Zealand!), but usually have some reddish color in them. In the one above, the belly is quite extensively reddish; in black squirrels I’ve gotten close enough to see, there’s usually some red color on the back, although their appearance depends on the lighting; and from a distance they may appear all black.

I was hoping to look at the report of the squirrel census to see the prevalence and distribution of the black squirrels (as well as to find other fun squirrel facts), but was disappointed to find that the report will cost you $75! But, a single ring chart was visible on the census website—in a copy of the report opened to show what you would be paying for—and this chart shows that there were 140 black squirrels out of 3938 squirrels whose color was recorded: a frequency of 3.56%. (There’s also mention of a more common “cinnamon” morph, but I’m not convinced that’s a distinct morph.)

The Times piece also provided some bits of data. From the following figure, I was able to determine that of 2969 squirrels with a known color depicted, 103 were black, for 3.47%. (The “white” squirrels in the figure, 54 of them, are actually blanks—squirrels with no color data recorded. The pie chart had 74 such missing-data squirrels.)

Screenshot_2020-01-09 2 There are 2,373 squirrels in Central Park I know because I helped count them .jpg

I’m not sure why there are 3023 squirrels total in the Times‘ figure, but 4012 in the ring chart, but the two estimates of the prevalence of the black phase, 3.56 and 3.47%, are very close. It’s no wonder then, that the handful of squirrels I would see during my Central park rambles would not include any black ones.

In a nice “squirrel map” of all the sightings in Central Park in the Times piece, there are about 3 or 4 black squirrels recorded in the part of the park between the American Museum and the Turtle Pond, so they do occur there, but, again, at low frequency, so no surprise I haven’t seen them.

(Here are some earlier WEIT posts on color polymorphism in squirrels.)

Albino squirrel update

March 29, 2010 • 10:39 am

by Greg Mayer

Observant reader Chris Helzer saw an albino squirrel outside the National Museum of Natural History a few days after I did, and got a much better picture of it, which he has kindly allowed me to post here.

Albino gray squirrel outside the USNM, Washington, DC, 28 March 2010.

This is probably the same squirrel I saw, and it seems to be on the same tree. In Chris’s much better picture you can see the pink eye, showing that it is a true albino, not merely albinistic.

UPDATE. I came across this posting at The Chicken or the Egg blog about white squirrels at the Museum of Comparative Zoology, my (and Jerry’s) alma mater. It seems that white squirrels have an affinity for natural history museums. Note that the MCZ white squirrel is albinistic, not true albino (it has a dark eye). Chicken also links to this wonderful site, the White Squirrel Research Institute, devoted to the white squirrels of Brevard, North Carolina. The Brevard squirrels, like the MCZ ones, are also albinistic rather than albino.

Caturday felid: the King Cheetah

March 27, 2010 • 8:42 am

by Greg Mayer

Of interest to both ecological geneticists studying vertebrate polymorphisms and cryptozoologists is the king cheetah.

King Cheetah, by Jurvetson. Source http://www.flickr.com/photos/jurvetson/12020752/

The king cheetah, known only from southern Africa, is a striking pattern variation of the common cheetah (Acinonyx jubatus). Instead of being spotted, the dark markings of the king cheetah coalesce into stripes and vermiculations, especially along the dorsal midline. King cheetahs are to common cheetahs as blotched tabbies are to spotted tabbies, not just in the similarity of the patterns, but in their genetic relationship: the king pattern is a variation within populations of the same species, and both patterns can occur in the same litter.

Common cheetahs, by Picture Taker 2, source http://www.flickr.com/photos/80835774@N00/4360426464/in/photostream/

In 1927, R.I. Pocock of the British Museum named the king cheetah as a new species, Acinonyx rex, the holotype being a specimen at the Queen Victoria Memorial Library and Museum in Rhodesia (now Zimbabwe). In 1932 the zoologist Angel Cabrera suggested that the king cheetah was merely a coat pattern variant of the common cheetah. For many decades after that the question of the status of the king cheetah was unresolved, as few specimens were known, and genetic experiments on cheetahs not possible. Cryptozoologists became interested in the king cheetah as a ‘semi-cryptid’– a not quite undiscovered species of large mammal, but at least a mysterious one.

In the 1970s more king cheetahs turned up, and methods of captive breeding of cheetahs, developed for conservation purposes, had advanced to the point where it was possible to investigate the question. In 1986, R.J. van Arde and Ann van Dyk of Pretoria University and the National Zoo in Pretoria, South Africa, showed that the king coat pattern was due to a recessive mutation at a single autosomal locus, thus vindicating Cabrera’s hypothesis from 50 years earlier. King cheetahs are now found in several animal parks in South Africa, and can be easily seen and photographed.

The story of the king cheetah shows that even when a new species is described and named according to the best practices, including insuring a publicly available holotype, it doesn’t guarantee that the species so named is new. It might be a new species, but it might also be a geographic or within-population variation of a known species (the latter in the case of the king cheetah), or in some cases nothing new at all (as when the describer is unaware that a description had been published previously).

Polymorphism in vertebrates

March 26, 2010 • 1:04 pm

by Greg Mayer

Darwin’s theory of evolution (and ours), unlike that of Lamarck, is variational, rather than transformational: the process of evolution is a change in frequency of different variants within a population, not a transformation of the individuals.  Darwin thus made the origin, nature, and inheritance of variation key problems for biology; indeed, for much of the 20th century, evolution and genetics were often taught as a single course at universities.

One of the most distinctive sorts of variation is polymorphism, in which two or more discontinuous forms are found in a single species (this is distinct from sexual or age related variation). Darwin himself pioneered the study of polymorphisms. Such discontinuous variation often has a simple genetic basis, with allelic variation at one genetic locus accounting for all (or most) of the variability.The color polymorphism in peppered moths (Biston betularia) is a well known and well studied case involving industrial melanism, in which light and dark forms are adapted to polluted and unpolluted environments, respectively. A well known case of polymorphism in vertebrates are the two color phases of Cuban sparrow hawk (Falco sparverius sparverioides). This case is not well studied, though, and we know nothing about the genetics, nor the adaptive significance (if any) of the polymorphism.

Light and rufous phase male Cuban sparrow hawks (Falco sparverius sparverioides).

A polymorphism in vertebrates that many Americans and Canadians are familiar with are the melanistic and gray forms of the gray squirrel (Sciurus carolinensis). The most frequent color form is gray, but blackish or dark brownish individuals are widely distributed, and in places quite frequent. I have seen them in Illinois (Cook County), Wisconsin (Racine and Kenosha Cos.) and Michigan (Ingham Co.), and also on the campus of Princeton University. (I was told at Princeton that, during football season, black squirrels are captured, and orange stripes applied to them, so that they resemble diminutive arboreal tigers, the tiger being Princeton’s mascot.)

A demonic gray squirrel (locally known as 'yard dogs'), Annapolis, MD, 23 June 2008.

A much less common color morph is the leucistic or albinistic form, which is whitish, cream or yellowish. They are famously common in Olney, Illinois (due to an introduction of two albinistic individuals to an area previously lacking any gray squirrels at all), and also occur regularly in Stevens Point, Wisconsin, but I had never seen one before my recent trip to Washington, DC, where I saw one on the tree right across from the steps on the Mall entrance to the USNM.  (The picture was taken through a bus window.)

Leucistic or albinistic gray squirrel, Washington, DC, 16 March 2010.

Vertebrate polymorphisms are often less well understood than those of invertebrates, because their generally greater size and longer generation times make experimental study more difficult. Melanism in squirrels, for example, has been related to thermoregulation and fire frequency, but no thoroughly compelling explanation has been found. One exception to this is coat color variation in mice of the genus Peromyscus, where coat color seems to be an adaptation for camouflage in varying environments.

Light and dark forms of Peromyscus polionotus from sandy and dark soils (P. p. leucocephalus on the left, P. p. polionotus on the right, I think).

In the 1930s, F.B. Sumner conducted classic field and lab studies on light colored mice living on sandy soils and dark mice on dark soils. Unlike the melanistic and albinistic squirrels, which are variant individuals within a populations, there is an element of geographic variation in the mice, which live in distinct, though adjacent, places. Sumner’s studies showed that there were several (not just one) genetic loci involved in coat color, and the color forms intergrade where their habitats meet and they interbreed. Hopi Hoekstra of the Museum of Comparative Zoology is currently conducting exciting studies of some of the same species studied by Sumner.

Although the mice occur in distinct modal forms (white vs. brown), the intergradation where they meet shows an underlying continuous variation. The frogs below show that although we can pick out distinctly different individuals, the range of pattern from plain to mottled to striped makes it difficult to recognize a small number of discrete color morphs, and the variation approaches a continuous dictribution. Such continuous variations were thought by Darwin, and most biologists today as well, to be important raw material for the evolutionary process.

Leotpdactylus albilabris from Isla Vieques.