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Observations and measurements on the North American Wood Turtle:
Glyptemys (Clemmys) insculpta
with notation of two different phenotypes.

- A 1985 study





Typical dimensions of Glyptemys insculpta



Based on eight live specimens

Research conducted 1985


Carapace length Carapace width Head width Carapace-
plastron length
("Carastron index"

inches / centimeters



Males -Yellowlegs phenotype



7 3/4 19.8 5 9/16 14.2 1 5/16 3.5 11/16 1.6


7 5/16 18.3 5 1/2 13.9 1 7/16 3.6 6/16 1.0



Males -redlegs phenotype



7 1/16 17.8 5 4/16 13.6 1 3/16 2.8 9/16 1.3



7 14/16 19.9 5 12/16 14.4 1 4/16 3.2 1 5/16 2.2


Females -yellowlegs phenotype



6 11/16 17.4 5 9/16 14.3 1 1/16 2.7 -1/16 -0.2


7 3/16 18.3 5 11/16 14.4 1 3/16 2.9 -2/16 -0.3


Females -redlegs phenotype



7 4/16 18.5 5 1/2 13.9 1 2/16 2.8 4/16 0.7


7 4/16 18.5 5 9/16 14.0 1 3/16 2.9 5/16 0.9



Abstract:



Research and observations were conducted in 1985 by Brian L. Schnirel on Glyptemys insculpta.

Live specimens were acquired and it was noted at that time that two distinct phenotypes were in

evidence with this species. The different color aspect of this species has been mentioned by Pope

(1938) and Harding (1997).



Both types of Glyptemys insculpta were measured for carapace and plastron length, head width,

and difference in length between the carapace and plastron ('carastron' index). Two of these

measurements (the head width and the 'carastron index are linked with sexual dimorphism of

Glyptemys insculpta. The two varieties were tested using variations of the Tinklepaugh labyrinth

experiment, Yerkes space reaction experiment, and mirror association experiments. Photographs

were taken at this time on these two phenotypes and were included in this report.


Introduction:



The third suborder of turtles to evolve from the Amphichelydia

are the Cryptodires- which are the most successful group of turtles

today. They possess the ability to pull their heads directly into their

shells without a full sideways motion. The largest family of

Cryptodirians are the Emydidae. Within this family, lies the genus

Glyptemys; which began in the Paleocene Epoch (55 million years

ago). The North American wood turtle (Glyptemys insculpta)- the

sculptured turtle- begins extensively in the Pleistocene

(approximately 1 million years ago). Voorhies (2000) reported a

discovery of a wood turtle shell from the Hemiphillian Miocene (6

million years ago. Pope (1939) mentions the remains of N.A. wood

turtles found in Pennsylvania that were at least ten's of thousands

of years old. As wiil be mentioned in the Geographic Range section,

ice age wood turtles were found in Tennessee and Georgia where

they have never been known from modern times. Since the advent

of Homo sapiens, the population has diminished considerably due to

overcollecting, highway deaths, extensive habitat destruction, etc.

In the past, native americans reduced some of the population for

rituals, shell helmets, rattles, and so on. For the white settler,

Insulptas were a convenient source of food. Indeed, in the early

part of the 20th century, quite a market developed for the 'Redleg'

as Glyptemys insculpta was called in the vernacular. Many

individuals were pulled out of muskrats holes in the winter using

sticks to locate something hard (Pope, 1939). The toughened

individual would then reach into the icy, cold water to claim his

prize.


Relationships:


The wood turtle, as stated belongs to the family Emydidae. The

Genus Clemmys, (as of 1985) consisted of the wood turtle Clemmys

insculpta, the bog turtle Clemmys muhlenbergi, the spotted turtle

Clemmys guttata, and the pacific pond Turtle Clemmys marmorata.

As 0f 2001, Mitochondrial DNA studies have now placed the wood

and bog turtles in the genus: Glyptemys and the pacific pond turtle

in the genus Actinemys. Only the spotted turtle remains in the now

monotypic genus Clemmys. The spotted turtle and the bog turtle

(although widely separated and rare) are also denizens of the

northeast. The pacific pond turtle is the most aquatic member of

this former group and resides along the Pacific coast.


An interesting example of parallel evolution or common ancestral

trait exists between the wood turtle and the semi-box turtle

Emydoidea blandingi , also known as the blanding turtle. The

plastron of both species is amazingly similar. The pattern is a

yellow-white background with black blotches on each of the scutes.

Other studies indicate a close genetic relationship between the two

(See 2003 update in Morphs and Ancestral Relationships). The semi-

box turtle, a cold hardy species, also resides in the northeast;

overlapping the range of the wood turtle. This turtle's range-like so

many others- is slowly shrinking. At one time, it may well indeed

have had the exact same range as the wood turtle.


Behavior and Intelligence:



Tinklepaugh (1932) conducted experiments to

determine the intellegence of the wood turtle. Using a

labyrinth, he concluded Glyptemys (Clemmys) insculpta had

the learning capacity of a rat. In personal experiments

and observations(B. Schnirel,1985,1998) the wood turtle

does indeed show great resourcefulness in problem

solving. One male in particular was quite adroit at

climbing and would systematically probe for weaknesses at

all levels in the outdoor fencing he was kept in. In a

variation to the labyrinth experiment, a three

dimensional approach was conducted in 1985. Ramps were

used to allow choices at 3 different heights. Wood

turtles in the experiment quickly learned the right route

to find food or females placed in a consistent area.


Yerkes (1901) conducted the famous 'space

reaction'experiments. Included on his guest list was

none other than our friend, the wood turtle. The

experiments tested the animal's fear of heights. What

was learned was the more aquatic the species, the more

careless the species is in regards to heights. This is

due to aquatic animals being used to dropping off stones,

logs, or whatever into boyount water. How did the wood

turtle make out? It was found to have less fear of

heights than the more aquatic spotted turtle. In tests

performed (B.Schnirel,1985) at various heights up to 20

feet, great fear and respect of height was demonstrated

by the wood turtle. The turtles would stick their heads

way over to inspect the untouchable surface with a note

of displeasure. More aquatic species would simply walk

straight off the edge. No turtles were hurt in the

experiments and special precautions were taken.



Glyptemys (Clemmys) insculpta appears more cognizant

of it's own reflections when facing mirrors. Experiments

conducted (B. Schnirel, 1985) with wood turtles showed

that individuals would stop, lower their heads and touch

'noses' with their reflections. Other turtles and

tortoises tested (Geocheleone carbonaria, Geocheleone

denticulata,Geochelone chilensis, Testudo horsfieldi,

Kinixys belliana belliana, Gopherus polyphemus, Terrapene

carolina carolina,Terrapene carolina bauri,and

Rhinoclemmys pulcherima showed no interest in their

mirrored image.

Results:


Dimensional Parameters:


The 1985 measurements on the eight insculpta's showed the following pertaining to sexual

dimorphism: Carapace length - males: 7 1/16 - 7 14/16 inches (17.8 - 19.9 centimeters).

Carapace length - females: 6 11/16 - 7 4/16 inches (17.4 - 18.5 centimeters). All test subjects

were mature adults and as such, males showed a larger ultimate size. Carapace width - males:

5 4/16- 5 12/16 inches (13.6 - 14.4 centimeters). Carapace width - females: 5 1/2 - 5 11/16

inches (13.9 - 14.4 centimeters). Again, males were slightly larger. Width of head - males:

1 3/16 - 1 7/16 inches (2.8 - 3.6 centimeters). Width of head - females: 1 1/16 - 1 3/16 inches

(2.7 - 2.9 centimeters). Males show a significant difference. Carapace minus Plastron length

(Carastron index) - Males: 6/16 - 15/16 inches ( 1.0 - 2.2 centimeters). Carapace minus

Plastron length (Carastron index) - females: 5/16 - 2/16 inches ( 0.9- -0.3 centimeters). This

was a sizeable difference with males possessing a large carapace overhang. In subsequent

observations, this is always the case. Female redlegs phenotype insculpta have a narrower

overhang but in the case of the yellowlegs phenotype insculpta, the plastron was actually longer

than the carapace (giving a minus Carastron value). One yellowlegs female that had a Carastron

value of -.06 (not included in parameter table) was unusual in having a completely round

carapace similar to a dinner plate. One thought is that she was a member of a peripheral isolate

population. Another thought was paedomorphism of the carapace. Hatchling

Glyptemys insculpta display a round carapace which develops into a more oval shape during

development towards adulthood.


Results: (Continued)


Tinklepaugh Labyrinth Experiments:


Glyptemys insculpta indeed showed great resourcefulness and speed in problem solving. In

addition to finding escape routes quickly, subjects in variation quickly found correct pathways

to food and male Glyptemys insculpta to females in different sections of the labyrinth. Male

insculpta had been observed in 1985 lying in ambush near pools for females to happen by

looking to soak or a drink. The male would proceed to jump on the back of the female to

mate. A three dimensional approach in the labyrinth experiments did not slow down the

wood turtles in their quest. One male in particular was very adroit in climbing and would

systematically probe for weaknessess. This was done at all levels in the outdoor fencing he

was kept in.



Yerkes Space Reaction Experiments:


At all levels up to twenty feet, great fear and respect of heights was demonstrated by

Geochelone carbonaria. Glyptemys insculpta and Terrapene carolina carolina showed

respect for all distances but did not show fear at the two foot height. Clemmys guttata

showed respect and fear at ten and twenty feet, but did not so at two and five feet. Indeed, at

the latter two heights, the subjects tried to drop off as aquatic species would be expected to

into buoyant water.





Results: (Continued)


Mirror Experiment:


All test species with the exception of Glyptemys insculpta, showed no interest in their reflected

images. Glyptemys insculpta appeared more cognizant of it's own reflections when facing

mirrors. test subjects would stop, lower their heads, and touch 'noses' with their reflections.

This behavior has been noted between encounters between two Glyptemys insculpta. In addition

to the head lowering and nose tipping, individuals will often tip their heads and sniff each other

in the manner of dogs. They seem to treat each other on an individual basis. Knowlton describes

the behavior of insculpta in an encounter in the following manner: "Their heads were slowly

lowered when the turtles were with eight inches of each other. Next, their heads were

swung from side to side for up to an hour without cessation. Mating occurred in a nearby

pool. " Harding also mentions that Glyptemys insculpta conduct a mating dance initiated by

both parties. They position themselves in front of one another and swing their heads in a

sideways swing.


Text (Introduction):



The North American wood turtle belongs to the Family Emydidae. The Genus Clemmys

(as of 1985) consisted of the wood turtle Clemmys insculpta, the bog turtle

Clemmys muhlenbergi, the spotted turtle Clemmys guttata, and the Pacific pond turtle

Clemmys marmorata. As of 2002, mitochrondrial DNA studies have now placed the wood

and bog turtles in the Genus: Glyptemys and the pacific pond turtle in the Genus: Actinemys.

Only the spotted turtle remains in the now monotypic Genus: Clemmys.



In 1985, several live Glyptemys insculpa were acquired for study. Individuals were selected

from extreme ends of their natural range. Some individuals came from Wisconsin

(Oneida county). This represented the western end of the range. Other individuals hailed

from Northern Virginia. This represented the eastern as well as the southern part of their range.

It immediately became apparent that there were consistent differences in coloration between the

geographically separated groups. The eastern group consisted of the standard reddish orange

color phase known in the vernacular as the "redlegs" (Pope, 1939). This standard morph also is

characteristic of having a yellow-ringed iris. The western group of Glyptemys insculpta was

different in that the skin color was yellow instead of reddish-orange and the iris was entirely

black with no yellow ring. This phenotype will be referred to as the "yellowlegs" for the duration

of this paper. Photographs of both phenotypes were taken and accompany this report. In the

early twentieth century, Clifford Pope mentions having specimens of the yellowlegs phenotype

which he describes as follows: " The soft parts lack the normal salmon red color of the adult,

Text (Introduction) - Continued:




the plastron is dark except for a narrow light margin and a little light mottling ".

Harding (1997) also mentions the color variation aspect and geographical distinctiveness of

Glyptemys insculpta.



Measurements were recorded on eight selected individuals (4 males, 4 females- divided by 2

from each region). The data recorded was significant in regards to sexual dimorphism.

Typically, male Glyptemys insculpta are noted for having wider heads, carapace's significantly

longer than the plastron (always), longer claws, concave plastron, and thicker tails with the vent

further out from the shell than the female. Female Glyptemys insculpta posses narrower heads,

a carapace slightly longer than the plastron or in some cases, the plastron is longer than the

carapace, shorter claws, flat plastron, and thinner tails with the vent close to the edge of the

shell.



Tinklepaugh (1932) conducted experiments to determine the intelligence of Glyptemys insculpta.

He concluded that this species had the learning capacity of a rat. The 1985 experiments of the

same were done with a labyrinth constructed of 2 x 4's. The width of the corridors were ten

inches wide with area covering twenty feet by twenty feet. In a variation of the original

experiment, a three dimensional approach was conducted. Ramps were used to allow choices

at three different levels. Incentives included food and females placed at specific locations.



Text (Introduction) - Continued:




Yerkes (1901) conducted the famous 'space' reaction experiments. Included on his guest list was

Glyptemys insculpta. The experiment tested the animal's fear of heights. What was learned was

the more aquatic the species, the more careless the species is in regards to heights. This behavior

has evolved due to aquatic turtles being used to dropping off stones, logs, or whatever into

buoyant water. The following test heights were chosen: two feet, five feet, ten feet, and twenty

feet. In addition to Glyptemys insculpta, other species tested were the spotted turtle:

Clemmys guttata, the redfoot tortoise: Geochelone carbonaria, and the Eastern box turtle,

Terrapene carolina carolina.



The last series of experiments involved reaction to reflections in mirrors. The mirror used was

twenty four inches wide. In addition to the North American wood turtle: Glyptemys insculpta,

the following chelonian species were tested: the redfoot tortoise: Geochelone carbonaria, the

yellowfoot tortoise: Geochelone denticulata, The Chaco tortoise: Geochelone chilensis, the

Afghan tortoise: Testudo horsefieldi, the hingeback tortoise: Kinixys belliana, The Eastern

gopher tortoise: Gopherus polyphemus, the Eastern box turtle: Terrapene carolina carolina,

the Florida box turtle: Terrapene carolina bauri, and the Central American wood turtle:

Rhinoclemmys pulcherima.
Discussion:



The differences between the redlegs and yellowlegs phenotypes of Glyptemys insculpta are suttle

but distinctive. Present evidence suggests the yellowlegs phenotype resides in the western part

of the biozone. The yellowlegs form may exist as peripheral isolates evolving eventually into a

new subspecies if not disturbed by Homo sapiens. However, an alternative view may have the

yellowlegs as ancestral stock. Harding (1999) mentions hybrids between Emydoidea blandingi

and Glyptemys insculpta. The range of these two species overlaps with the greatest core

concentration (as of 1985) remaining in the Great Lakes region. During the 1985 research,

individuals of Emydoidea blandingi were present and studied with similarities noted with

Glyptemys insculpta. The plastron of both species is very similar with the same arrangement

of black spots on the plastral scutes. The skin color is yellowish on blandingii as is with the

yellowlegs insculpta. It might be possible that a common emydid ancestor to both species

resided in the same region and the ancestral color trait being yellow in regards to skin color.

This would be a pre-Miocene event as the earliest known wood turtle (an adult male) found

(Voorhies, 2000) was in the Hemphillian Miocene. If this is the case, the redlegs phenotype

would be a derived apomorphic trait.

Ernest, Lovitch and Barborn in 1994 reported that in the cooler climes of

the ice age, the wood turtle had a more southern distribution. The evidence

suggested that the species could be found as far south as Tennessee and

Georgia.




The noted differences in the phenotypes with dimensional measurements were the females with

the Carastron values. Plastrons seem to be longer than the carapace with the yellowlegs

phenotype. However, more measurements on more yellowlegs and redlegs individuals would

be needed to draw an absolute conclusion.


Discussion: (Continued)




In behavior, both phenotypes acted along similar lines and showed no differences in intelligence.

This was true for the Tinklepaugh labyrinth experiment, the Yerkes space reaction experiment

and the mirror reflection experiment.





References:




Behler/King. 1979. Audubon Society field guide to North American reptiles and amphibians.
Knopf, New York. 744 pp.

Bickman, J. 1996. Molecular systematics of the genus Clemmys and the intergeneric
Lamb, T. Minx, P. relationships of Emydid turtles. Herpetologica. Bainbridge, Ga.
Patton, J. 521 (1) pp.89-97.


Burton, M. 1973. The world of reptiles and amphibians. Bounty Books, London-New
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Carr, A.F. 1952. Handbook of turtles. Comstock Publ. Associates, Cornell University
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Conant, R. 1958. A field guide to reptiles and amphibians of Eastern North America.
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Ernest, C. H./ 1972. Turtles of the United States. University of Kentucky Press. 347 pp.
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Harding, James 2003. Clemmys Insculpta. Animal Diversity Web - Michigan State University
Museum of Zoology 7 pp.

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Jersey. 895 pp.

Roberts, M. 1980. Turtles. T.F.H. Publications, Neptune, New Jersey. 93 pp.

Tinklepaugh, 1932. Maze learning of a turtle. Journal Comprehensive Psychology 13:
O. pp. 210-206.

Zim, H. 1953. Reptiles and amphibians (North America). Golden Press, New

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