Observations and measurements on the North American Wood Turtle: Glyptemys (Clemmys) insculpta with notation of two different phenotypes - A 1985 study
Courtesy of POLYPHEMOS (2004)
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 (In most cases). 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.
Contributed by Brian - LCRC.
Accepted on October 8, 2007.
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.
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.
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.
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.
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.
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.
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, 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.
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 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.
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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