Courtesy: POLYPHEMOS: May 2006

LEEWAY CORUCIA RESEARCH CENTER (LCRC)

Subspecies comparision of the Genus: Corucia

Brian L. Schnirel and Sherri L. Jones
Leeway Corucia Research Center (LCRC)
Blenheim, S.C. 29516 U.S.A.

_____________________________________________________________

Abstract:

Detailed measurements and observations differentiating the two
subspecies of Corucia zebrata (underlined), Corucia zebrata zebrata(underlined) and Corucia zebrata alfredschmidti (underlined), are described including new material not previously documented.

Key words: Corucia, Sclera, Parietal, Prefrontal, Rostral, Nasal

Introduction:

Corucia zebrata zebrata (underlined) described and named (Gray, 1855) and Corucia zebrata alfredschmidti (underlined) described and named (Kohler, 1997) represent the two subspecies of Corucia zebrata (underlined) – the prehensile tailed monkey skink.

The common monkey skink (Corucia zebrata zebrata) hails from the larger islands of the Solomon archipelago southeast of Buka and Bougainville. This includes Choiseul, Guadalcanal, Isabel, Malaita, Nggla, New Georgia, Santa Ana, San Cristobal, Shortlands, and Ugi (Balsai,1995). The North Solomon monkey skink (Corucia zebrata alfredschmidti) hails from the North Solomons which are comprised of Bougainville and Buka (Kohler,1997).

Bougainville is by far the largest island in the archipelago and being on the northeast fringe of these islands, supported the establishment of peripheral isolates evolving into the subspecies alfredschmidti. This is supported by the sheer number and larger distribution of the subspecies
zebrata in the southeastern islands. The core population of Corucia zebrata zebrata (underlined) appears to be from Quadalcanal (Balsai, 1995). The allopatric subspeciation of the Genus: Corucia reveals
a larger size of Corucia zebrata alfredschmidti compared to Corucia zebrata zebrata. Indeed, a semi-Wallace line appears to exist between Bougainville and Choiseul. "There is an affinity along the lines of Bougainville – Choiseul, separated by the Bougainville strait, in which the
faunal differences are relatively distinct (faunal differences 86%)" (Green/Slade,1968). Other animals show a size differential with the populations on Bougainville being generally larger than that on Choiseul. The monkey faced flying fox (Pteralopex anceps) on Bougainville is also
larger (255-280 mm). On Choiseul, next to Bougainville, the population is smaller (160-275mm) (E. Bowen-Jones 1997).

The differences between Corucia zebrata zebrata and Corucia zebrata alfredschmidti are described here in detail which should aid in better appreciating the comparative differences between the two subspecies. As such, identification will achieve a faster result. However, once one has seen both Corucia zebrata zebrata and Corucia zebrata alfredschmidti, the visual difference in size and body coloration alone is readily apparent, even from a distance.

Snout/Vent Length (SVL) & Length Overall (LOA)

common monkey skink
Corucia zebrata zebrata (underlined)

SVL:

Average: Males = 250 mm

Females = 270 mm

Range: Males = 230 – 270 mm

Females = 260 – 280 mm

LOA:

Average: Males = 550 mm

Females = 582.5 mm

Range: Males: = 520 – 580 mm

Females: = 560 – 605 mm

North Solomon monkey skink
Corucia zebrata alfredschmidti (underlined)

SVL:

Average: Males: = 320 mm

Females: = 330 mm

Range: Males: = 290 – 340 mm

Females: = 270 – 330 mm

LOA:

Average: Males: = 660 mm

Females: = 670 mm

Range: Males: = 630 – 680 mm

Females: = 640 – 690 mm

Number of individuals of equal proportions used in study: 96.

A noticable difference in size of neonates is also in evidence: (LOA)

Corucia zebrata zebrata (underlined) averages about 11 1/2" (Langerwerf, 2006, Schnirel, 2001)

Corucia zebrata alfredschmidti (underlined) averages just under 15" (Schnirel, 2004)

Czz / Cza neonate comparison:

Corucia zebrata zebrata LOA = 289 mm

Corucia zebrata alfredschmidti LOA = 370 mm

Note: Both subspecies of Corucia zebrata (underlined) reproduce by viviparous matrotrophy with the birth of a single very large neonate. Occasionally, twins are produced, there is one documented case of triplets (Langerwerf, 2003).

Weight (Average)

Adult Neonate

Common monkey skink = 500 Grams 81 Grams
Corucia zebrata zebrata

North Solomon monkey skink = 845 Grams 173 Grams
Corucia zebrata alfredschmidti

Number of adult Corucia used in study : 96. , Number of neonate Corucia used in study : 39.

common monkey skink

Corucia zebrata zebrata (underlined)
(Gray,1855)

Czz
Description:

Size:

Smaller size than Northern Solomon monkey skink
(Corucia zebrata alfredschmidti (underlined)).
Average adult: LOA = 572mm (22"), SVL = 262mm
(10").

Scalation:

Head
Scalation: The original description by Kohler indicates that common
monkey skinks possess five parietal scales. The
arrangement has, from left to right-head facing
observer, parietal scale one and two larger and less
cramped in width than comparable parietal scales in the
North Solomon monkey skink (width/length ratio-
parietal scale one = 9/13, parietal
scale two = 18/27). Parietal scales encompass nearly
the entire left side of the region (front facing away from
observer) of the upper head. Parietal
scale three is positioned centrally comparable in position
to parietal scale four in the Northern Solomon
subspecies. It is larger (length ratio Czz/Cza = 9/7,
Width ratio Czz/Cza = 7/5). Parietal scale three is
triangular with the tapered point directed towards the
rear of the head (width/length ratio
= 7/24). Parietal scale four is right of center. It is
more round in shape (length ratio Czz/Cza = 5/8, width
ratio Czz/Cza = 7/9, width/length ratio = 7/8).
Parietal scale five is on the right edge of the head and
positioned more to the rear than the other four parietals
(width/length ratio = 13/30). Unlike the Northern
Solomon subspecies, the common Solomon monkey
skink has no number six and seven parietal scales.
The parietal description is a guide however, and
should not be taken as absolute except for the total
number. In practice, the head scales are as varied
as fingerprints in size and shape. The prefrontals of
Corucia vary in size and number. Common
monkey skinks possess two to three.

Body
Scalation: Dorsal and ventral scales are in a different ratio.
Common monkey skinks are more elongated with a
length/width dorsal scale ratio of 4/9.
Northern Solomon skinks have a length/width dorsal
scale ratio of 6/9. Length/width ventral scale ratio for
the common subspecies is 3/7. The
Northern Solomon subspecies length/width ratio = 1/2.

Eyes:

Sclera: A consistent distinquishing feature separating the two
Corucia subspecies is scleral color. Corucia zebrata
zebrata (underlined) has a white sclera. Corucia
zebrata alfredschmidti (underlined) has a black sclera.

Iris: The iris color can vary from dark green, green,
greenish yellow, orange, and jet-black. A green
background iris can be stippled with brown or black
pigment. The green or yellow-green pigmented iris
could be autosomal dominant as is with a brown-black
pigmented iris in humans. This
means only one copy of this gene from a parent is
needed in order for a green-yellow pigment to be
manifested in the individual. For a total
black pigmented iris in a Corucia (which is the least
seen); this would signify the black pigmented gene
would have to be contributed by both
parents to achieve this color phase. Unlike the
Northern Solomon subspecies, there is no
establishment of iris color linked to specific islands
or cooresponding phenotypes with the common
subspecies.

Body
Coloration:

Holotype
Description: The classic holotype description by John Edward Gray
describes Corucia zebrata zebrata (underlined) as
having prominent banding. The bands
are alternating dark brown-black/ green. The green
portion can be of various shades. The mid body
bands are vertical to a twenty degree forward slope
as compared to Corucia zebrata alfredschmidti
(underlined) with a fifty degree
forward slope. Gray also described a play of colors
effect from the body scales, hence the origin of the
scientific name. The Genus name Corucia derives
from the latin coruscus – definition: shimmering.
zebrata is a latinized form of the word zebra;
pertaining to the zebra-like banding. Black
spots are varied throughout the body. The green in
the body is often blended with brown. The locus
typicus of gray’s work with
Corucia was on San Cristobal.

Other
Phenotypes: Unfortunately, not enough research has been done
on wild populations on specific islands with Corucia
zebrata zebrata (underlined).
Certain phenotypes may correspond to separate
islands. The Leeway Corucia
Research Center has found that different phenotypes
within Corucia zebrata zebrata (underlined) will
breed with complete success. In other words, there
appears to be no genetic drift towards speciation to
the point of non-viability
of the embryo. All phenotypes can have black spot
pigmentation throughout the body
in various sizes, numbers, and patterns. The spots
may overlap. Dark green
body coloration may occur with little or no black
pigmentation. This may coincide with the report of
the darkest individuals coming from Malaita (McCoy, 1980). There are individuals having
incomplete banding. The incomplete banding
consists of blotches. The blotches are green to
greenish aqua. Some will have no banding or
blotches period. One phenotype from this category
is an army green color often with
little or no black spots. Often, as previously
indicated, the body is flushed with patches of light
brown at various parts of the body but
in addition, there can be brick red around the head.
Yellow is generally less
prominent in Corucia zebrata zebrata (underlined)
than with Corucia zebrata alfredschmidti
(underlined. Some yellow can be seen usually in the
throat or spotted only on parts of the head compared
to cases of almost full yellow on
the head of the North Solomon subspecies. In one
documented case, a highly pigmented (light and dark
spots) female (LCRC/Czz/34) exhibits yellow
spots on the tail. To date, this is the only Corucia
seen with this color pigmentation in the tail region.
Some common monkey skinks have
white on the head and throat (i.e.LCRC/Czz/36).
The nasal and rostral scales of all types are
generally darker in color in Corucia zebrata zebrata
than with Corucia zebrata alfredschmidti. North
Solomon monkey skinks have a distinctive yellowish-
cream color to the nasal and rostral scales which
appears striking in contrast to the generally turquoise
head.

North Solomon monkey skink

Corucia zebrata alfredschmidti (underlined)

(Kohler,1997)

Cza
Description:

Size: Larger size than the common monkey skink (Corucia
zebrata zebrata).

Average LOA = 690mm (27"), SVL = 335mm (13").

Head
Scalation: As based on Kohler, North Solomon monkey skinks
possess seven parietal scales. The arrangement has,
from left to right-head facing observer, parietal scale
one and two smaller and more cramped in width
than comparable parietal scales in the common
monkey skink (width/length ratio: parietal scale one = 4/6, parietal scale two = 13/25). Parietal scale

three is smaller in length and width (width/length ratio = 13/16) than

comparable scale in Corucia zebrata zebrata (pointed towards the rear of

the skull). Parietal scale four is centralized and elongated with a bottleneck

appearance near vertical center (narrowest point width/length ratio = 2/19,

total width variation ratio = 4/17,). However, the original description of the

holotype and paratypes has no mention of parietal scale four ever pinched-

off completely rather than bottlenecked. The illustration in Salamandrae gives

the impression that the bottleneck configuration is standard. Head scales

actually vary in size and shape as much as the black pigment spots on the

body. In common observation, most specimens of Corucia zebrata

alfredschmidti have the pinced-off version. Parietal scale five is just right of

center rather than at the dextral edge as in the common monkey skink

(width/length ratio = 13/17). Parietal scale five is also more symmetrical in

shape and squarer than parietal scale five in the common monkey skink.

Parietal scale six (not found in Corucia zebrata zebrata) is comparable in size

and shape to parietal scale three (width/length ratio = 12/17). Parietel scale

seven (not found in Corucia zebrata zebrata) is elongated and more pointed

to the front of the skull (width/length ratio = 7/12). Parietal scale seven is at

the dextral edge of the head. Prefrontal scalation varies from two to four

compared to two-three in the common monkey skink.

In summation, head scales are not the best indicator of Corucia

subspecies classification. It takes a trained eye and much close up viewing to

get an accurate determination. The unwavering criteria to utilize is that

Corucia zebrata alfredschmidti has 2 more parietals (six and seven) than with

Corucia zebrata zebrata.

Body
Scalation: North Solomon monkey skinks have been described as
having larger ventral and dorsal scales than the common
monkey skink (Kohler,1997). The scales are larger in
general due to the larger ultimate size of this

subspecies of Corucia. However, in a ratio comparison of width/length,

there is a difference as noted in the common monkey skink section.

LCRC research data shows that in a width/length ratio of dorsal scales,

North Solomon monkey skinks have a ratio of 6/9. Common monkey

skinks have a ratio of 4/9. The ventral width/length ratio is 1/2 for the

Northern Solomon monkey skink and 3/7 for the common monkey skink.

Eyes:
Sclera: As noted earlier, Corucia zebrata alfredschmidti
(underlined) has a black sclera and Corucia zebrata
zebrata (underlined) has a white sclera. This is
unvaried.

Iris: The iris color of Corucia zebrata alfredschmidti
does not seem to vary as much as in Corucia
zebrata zebrata. The color is almost always a
green-yellow mix – at least in Corucia zebrata
alfredschmidti from Bougainville.
However, Corucia zebrata alfredschmidti from Buka
appear to have a more intense green iris.
Besides the striking head color and larger ultimate
size, the eyes of Corucia zebrata alfredschmidti
(underlined)are another very prominent and
stunning attribute of this subspecies. The yellow-
green iris coloration surrounded by the black sclera
makes this so.

Body
Coloration: The top of the head in the North Solomon Monkey skink
is a striking

turquoise often suffused with yellow. This concurs with the holotype

description by Kohler. Most of the yellow is prominent in the throat and

chin region but may occur on top of the head as well in several areas including

the region around the ear openings. There has not been observed in Corucia zebrata alfredschmidti, a yellow spotted individual in the tail region like the

LCRC / Czz /34 specimen. From imports of highly questionable legal

passage but traced and personally seen, it appears that North Solomon

Corucia that hail from Buka differ from the main pennisula contingent in that

the Buka contingent of Corucia shows a light brownish component overlaying

the bright turquoise on the head. In addition, as mentioned, the iris is an

intense green. Otherwise, all other aspects of Buka Corucia zebrata

alfredschmidti are germane to that of Bougainville Corucia zebrata alfredschmidti. It would appear, that the Buka Corucia are a polytypic

variant but would not constitute a separate subspecies classification.

As with the common monkey skink, North Solomon monkey skinks

are found with and without banding. The banded individuals have central

bands that slope at a 50 degree angle. Common monkey skinks have a

0 – 20 degree angle to the transverse torso of the body. This has also been

noted by Burt Langerwerf of Agama International. The bands on the

North Solomon monkey skinks are a consistent light brown whereas

common monkey skinks are darker brown to black. The lighter brown

banding in contrast to the aqua bands gives a more faded appearance to the

North Solomon subspecies compared to the common subspecies. Blotched

North Solomon individuals are occasionally encountered. Both banded and

unbanded North Solomon monkey skinks may have black spots. Northern

Solomon monkey skinks have the light brown tone mentioned in the bands

often intermixed with the aqua of the body. Common monkey skinks often

have a brown wash with the green/aqua color of the body but the brown is

usually darker. All North Solomon monkey skinks have a distinctive

yellowish-cream color to the nasal and rostral scales in contrast to a darker

color in common monkey skinks as noted in the common monkey skink section.

The cream color of these scales also shows a significant contrast to the turquoise

color of the head of the North Solomon subspecies.

Kohler lists the holotype of Corucia zebrata alfredschmidti as holotypes SMF 77587 with locus typicus being the island of Bougainville (Mekamuri or North Solomons). The Holotype resides in the Senckenberg Museum, Frankfort Germany (Museum Franfort Senckenberg an lage 25 60325 Frankfort am main D.

Germany tel +49 06917542-0 fax ++90691746238). The holotype is described as being an adult Male.

The Paratype of Corucia zebrata alfredschmidti is listed as MTKD – 39481. The paratype resides in the Staatiches Museum Fur tierkunole Augustus strasse 2 Dresden Germany. The Paratype is described as being unknown in gender.

The Leeway Corucia Research Center (LCRC) Studbook classification system is as follows:

LCRC / Czz / 34

LCRC = Corucia Research Center of individual

Czz = Subspecies classification Czz = Corucia zebrata zebrata

Cza = Corucia zebrata alfredschmidti

34 = Individual number at research center

Discussion:

Although Genetic drift of the peripheral isolates of the
Corucia population resulted in the subspeciation of Corucia zebrata alfredschmidti (underlined), the ecological niche in this subspecies remained constant. This is based on a pattern in the Scincidae where the more arboreal the species, the proportionally longer the digits. A smooth, non-varying, numerical progression can be seen from species of various niches based on anterior foot length (the junction of the ulna / radius carpal bones to longest digit) divided by the snout to vent length (SVL)(Schnirel, 2004). In the case of Corucia, both subspecies occupy a high canopy arboreal niche with the same numerical value.

Although no viable cross subspeciation has been documented resulting in ‘whatticles’ (Jones, 1984), being subspecies, it is theoretically possible to cross North Solomon Corucia with common Corucia. Balsai (1995) has theorized that common Corucia from various islands have been genetically apart enough based on miscarriages that have occurred in captivity. However, many breeding centers have had great success rates in breeding of this species of different phenotypes. The South Florida Corucia Research Center had a 100% success rate of over thirty births. Agama International also shows a positive record. Other factors may be the reasons for the miscarriages resulting in slugs (miscarriages) or stillbirths other than genetic incompatibility that need to be explored. For instance, improper environmental conditions (humidity, temperature, diet, etc.), stress, disease, exposure to toxins, the possibility of too much genetic closeness if the mated pair came from the same island canopy and were closely related, etc. Other than Corucia zebrata zebrata (underlined) and Corucia zebrata alfredschmidti (underlined, there appear no other candidates for subspecies classification. As such, genetic incompatibilty between the common subspecies of Corucia is a topic that requires further research. Although common Solomon monkey skinks may not exhibit miscarrages due to genetic drift, it would be logical to conclude that between subspecies (Corucia zebrata zebrata (underlined) and Corucia zebrata alfredschmidti(underlined)), they could be enough apart that breeding between the two
would result in genetic misfires to some degree. This, of course, would be
based on the time honored rule of distinct speciation depending on a species being unable to produce a viable species with another. Whether or not the two subspecies straddle the fence of genetic compatibilty is also a future topic of research.

To distinquish Corucia subspecies in summation, if one cannot see the
two subspecies in comparison or a photograph, look for the following. In
Corucia zebrata alfredschmidti(underlined), two extra parietal scales, or
up to two extra pre-frontal scales, a black sclera, bright turquoise head (in most cases), and in banded individuals, a 50 degree slope in banding. In a visual comparison, look for a reduced ratio in dorsal and ventral
scale ratios of width/length of Corucia zebrata alfredschmidti (underlined) compared to Corucia zebrata zebrata (underlined). A larger size of approximately 17%, a lighter brownish coloration – especially a faded
appearance in the banded individual, and a noticeable contrast between body coloration and nasal and rostral scales – with the scales having a distinctive yellow cream coloration.

Addendum:

The color, banding, blotches and spots mentioned are adaxial in general for both subspecies. The abaxial area (lower chest and belly region to vent) is void of bands and spots. It is generally a solid green or aqua.

References:

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islands prehensile-
tailed skink (Corucia zebrata). The Vivarium,
Escondido,
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Bowens, E.; Jones; 1997. Flying foxes on Choiseul (Solomon islands) –
the need for
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Coburn, John; 1996. Prehensile tailed skinks. T.F.H. Publications
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De Vosjoli, Phillippe
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Green, Slade; 1968. Island patterns in the Solomon islands bird
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Langerwerf, Burt; 2003. Agama International; Personal
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McCoy, Michael; 1980. Reptiles of the Solomon islands. Wau
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Parker, F.; 1983. The prehensile tailed skink (Corucia
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island, Papua New Guinea. Advances in
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Schnirel, Brian L. 2004. Seni biometric analysis on the extinct
Scincidae species:
Macroscincus coctei. Underlined)
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Last edited by Brian – LCRC on Thu Aug 03, 2006 6:31 am; edited 4 times in total