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Thread: Observations/measurements on NA wood turtle phenotypes

  1. #1 Observations/measurements on NA wood turtle phenotypes 
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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


    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).

    The Redlegs (Pope, 1938) phenotype has reddish - orange skin and a yellow ringed iris.

    The Yellowlegs (Schnirel, 1985) phenotype has yellowish skin and no yellow iris ring. The eye is completely black.

    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.


    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



    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.


    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


    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.

    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


    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.


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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
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    Pope, C. H. 1939. Turtles of the United States and Canada. Alfred A. Knolpf, New
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    Pritchard, P. 1979. Encyclopedia of turtles. T.F.H. Publications, Neptune, New
    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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  3. #2 two phenotypes G. insculpta 
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    The Redlegs (Pope, 1938) phenotype has reddish orange skin with a yellow - ringed iris.

    The Yellowlegs (Schnirel, 1985) phenotype has yellowish skin with no yellow iris ring. The eye is completely black.

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