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Scales Microstructure of Snakes from the Egyptian AreaAuthor(s): Ahmed A. Allam and Rasha E. Abo-EleneenSource: Zoological Science, 29(11):770-775. 2012.Published By: Zoological Society of JapanDOI: http://dx.doi.org/10.2108/zsj.29.770URL: http://www.bioone.org/doi/full/10.2108/zsj.29.770

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2012 Zoological Society of JapanZOOLOGICAL SCIENCE 29: 770–775 (2012)

Scales Microstructure of Snakes from the Egyptian Area

Ahmed A. Allam1,2* and Rasha E. Abo-Eleneen2

1King Saud University, College of Science, Zoology Department, P.O. Box 2455,Riyadh11451, Saudi Arabia

2Beni-Suef University, Faculty of Science, Zoology Department,Beni-Suef 65211, Egypt

The morphology of many organisms seems to be related to the environments in which they live.

Many snakes are so similar in their morphological patterns that it becomes quite difficult to distin-

guish any adaptive divergence that may have occurred. Many authors have suggested that the

microstructure of the reptile’s scales has important functional value. Herein, we investigate varia-

tions on the micromorphology of the external surface of dorsal scales on the head, the mid-body

region (trunk), and the tail of Rhomphotyphlops braminus (Typhlopidae), Eryx jaculus (Boidae),

Psammophis sibilans (Colubridae), Naja haje (Elapidae) and Echis carinatus (Viperidae). The spec-

imens were metallized and analyzed by scanning electron microscopy. All species displayed unique

dorsal scale surface microstructures of the investigated regions. The microstructural pattern of the

scales of head, trunk, and tail differs in different species of these snakes. In conclusion, we

detected ecomorphologic relationships between extant dorsal scale microstructures and snake

microhabitat, enabling us to hypothesize that environmental pressures have significant influences

not only on these animals’ macrostructure, but also on its microstructure as well.

Key words: snake, microstructure, Rhomphotyphlops braminus, Eryx jaculus, Psammophis sibilans,

Naja haje, Echis carinatus

INTRODUCTION

The morphology of organisms is generally well matched

to their environment, supposedly because gene expression

is tailored at the population or individual level to suit local

conditions (Aubret et al., 2004). Teixeira-Filho et al. (2001)

associated the use of different microhabitats, such as terres-

trial occupation of smooth bromeliad leaf surfaces, with vari-

ations in claw curvature of lizard species inhabiting resting

habitats. However, many snakes and other squamata are so

similar in their morphological patterns that it can be difficult

to distinguish their adaptive divergences, since these are

imperceptible to the naked eye. Scales protect the body of

the snake, aid in locomotion, allow moisture to be retained

within the body, alter surface characteristics, such as rough-

ness, to aid in camouflage, and in some cases even aid in

prey capture (Abo-Eleneen and Allam, 2011). The scales

are also modified over time to serve other functions such as

‘eyelash’ fringes, and protective covers for the eyes with the

most distinctive changes in the North American rattlesnakes.

The snake hatches with a fixed number of scales. The

scales neither increase in number as the snake matures nor

they reduce in number over time (Elwira and Rupik, 2010).

The scales however grow larger in size and may change

shape with each molt. Snake scales are made of keratin, the

protein present in human hair and fingernails. The scales

are cool and dry to touch (Licht and Bennett, 1972). The sur-

face of snake scales may be granular, smooth, or have a

longitudinal ridge or keel on it. Often, snake scales have

pits, tubercles, and other fine structures which may be visi-

ble to the naked eye or under a microscope (Cardwell,

2011).

Certain primitive snakes such as boas, pythons, and

certain advanced snakes such as vipers have small scales

arranged irregularly on the head. Other more advanced

snakes have special large symmetrical scales on the head

called shields or plates (Pernetta et al., 2011). Snake scales

occur in variety of shapes. They may even be cycloid, as in

some blind snake species (Vidal et al., 2010).

Scale arrangements are important, not only for taxo-

nomic utility, but also for forensic reasons and conservation

of snake species (Pontes et al., 2009). Except for the head,

snakes have imbricate scales, overlapping like the tiles on a

roof. Snakes have rows of scales along the whole or part of

their length and also many other specialized scales, either

single or in pairs, occurring on the head and other regions

of the body. The dorsal (or body) scales are arranged in

rows along the length of their bodies. Adjacent rows are

diagonally offset from each other. Most snakes have an odd

number of rows across the body, although certain species

have an even number of rows, e.g. Zaocys sp. (Zhang et al.,

1997). In some aquatic and marine snakes, the scales are

granular and the rows cannot be counted (Berthé et al.,

2009). The part of the body beyond the anal scale is consid-

ered to be the tail, where snakes sometimes have enlarged

scales, either single or paired. These scales may be smooth

or keeled as in Bitis arietans somalica (Hu et al., 2009). The

end of the tail may simply taper into a tip (as in the case of

* Corresponding author. Tel. : +966-544265061;

Fax : +966-4678514;

E-mail : allam1081981@yahoo.com

doi:10.2108/zsj.29.770

Scales Micromorphology 771

most snakes), it may form a spine (as in Acanthophis), end

in a bony spur (as in Lachesis), a rattle (as in Crotalus), or

a rudder as seen in many sea snakes (Rabosky and

Lovette, 2008).

Scales do not play an important role in distinguishing

between the families but are important at the generic and

specific levels (Rocha-Barbosa and Moraes e Silva, 2009).

Electron microscopy thus becomes a very important tool in

uncovering such differences, for it allows the analysis of

microstructures present in squamates. Several studies have

suggested a functional significance for microornamentation

(Porter, 1967; Steward and Daniel, 1973; Gans and Baic,

1977; Smith et al., 1982; Renous, et al., 1985; Gower, 2003)

or have simply described microanatomy (Arroyo and

Cerdas, 1985; Chiasson and Lowe, 1989; Velloso et al.,

2005). Microstructure of scales has also been used as tools

in taxonomy (Hoge and Santos 1953; Dowling et al., 1972;

Stewart and Daniel, 1975) and in ontogenetic and/or evolu-

tionary studies of squamates (Peterson, 1985; Harvery

1993; Harvery and Gutberlet Jr, 1995).

Studies on the relationship between ecology and mor-

phology (i.e., ecomorphology) of animals may account for

some natural selection issues based on the partitioning of

resources, such as space and food in a given community

(Ribas et al., 2004). The scales of squamate reptiles are

composed of several histologically discrete layers formed

from cells of a living basal layer, the stratum germinativum.

The outermost epidermal layer is rigid and composed of ker-

atin, and this is overlaid by the oberhautchen (Irish et al.,

1988), which is often composed of cell-like divisions that

may bear complex three-dimensional features. The overall

arrangement of these cells and their surface features are

termed microornamentation (Ruibal, 1968; Arnold, 2002),

and these features are readily studied with scanning elec-

tron microscopy.

There have been several studies of micro-ornamenta-

tion in various groups of squamates (Arnold, 2002). An early

concern of this research was whether taxonomic variations

in micro-ornamentation were associated with systematics or

ecology; that is, whether taxonomic patterns are determined

more by phylogenetic history or by functional requirements.

Earlier works often considered one of these factors over the

other. Strong correlation between micro-ornamentation and

general ecology was not found (Gower, 2003), but phyloge-

netic utility was advocated (Harvey and Gutberlet, 1995).

Burstein et al. (1974) stated that since the ultrastructural

features of scales may be relatively free from direct adapta-

tional pressures, they could well be more reliable indicators

of interspecific relationships. Price (1982) noted that micro-

ornamentation patterns reflect phylogenetic relationship

rather than ecological or habitat factors and there is no case

to make for a correlation between ecology or habitat and

microornamentation. There was an understanding that both

history and function had a bearing on the taxonomic pat-

terns observed (Renous and Gasc, 1989). Arnold (2002)

applied a thorough, explicit approach to the understanding

of microornamentation in lacertid lizards by attempting to

explain variations in morphology through an integrated his-

torical (phylogenetic) and functional analysis. For lacertids,

a broad correlation between microornamentation and gen-

eral habitat was found.

Arnold explains derived patterns in which microorna-

mentation becomes more elaborate in species and morpho-

logical regions (e.g., dorsal surface of the body) that are not

in contact with particularly moist substrates. Mapping fea-

tures onto a phylogeny and reconstructing states for internal

branches indicated that lineage effects were probably impor-

tant because reversals in microornamentation appeared to

be extremely limited, but also that many of the derived pat-

terns had evolved many times independently, and that there

seem to be limits on the variations that can be produced

(Arnold, 2002; Gower, 2003).

This study aimed at explaining the microstructure varia-

tion on the scales surface of the snakes occupying different

microhabitats (terricolous, arboreal, aquatic and fossorial) to

search for the existence of ecomorphology relations

between the species studied and their environment.

MATERIALS AND METHODS

In the present study, 40 specimens from five different species

of adult snakes from different families were used. These snakes

were captured from the different Egyptian regions of Egypt. The first

snake, Rhomphotyphlops braminus (Typhlopidae), is known locally

as known locally as Baha kibeer. It lives under dense vegetation

near irrigation ditches and it occurs in southern Nile Delta. The sec-

ond, Eryx jaculus (Boidae) commonly known as the Dassas baladi

snake, inhabits sandy areas near cultivated land and is collected

from Upper Egypt and Lower Valley as well as northern Sinai. The

third is the Abu essuyur snake, Psammophis sibilans (Colubridae),

a snake of riverine habitats and agricultural fields usually found in

gardens and cultivated areas. It appears to climb trees occasionally

and its distribution includes the Nile Valley and Delta. The fourth is

the Egyptian cobra snake, Naja haje (Elapidae), which inhabits agri-

cultural fields of the Nile Delta. It is most frequently encountered on

densely vegetated banks of rivers or irrigation canals, and is distrib-

uted in the Nile Valley, Delta, and Faiyum regions. The fifth, Echis carinatus (Viperidae), is commonly called is the Haiya ghariba

snake and inhabits sandy desert areas with a distribution in the

northern oases of the western desert, including western area of

Faiyum and Cairo. The distribution of the snakes examined in this

study is as described by Saleh (1997).

Dorsal sections of skin scales were taken from the head, the

mid-region, and the tail of the body of eight adult individuals of each

species. The skin sections were placed in numbered tubes and

identified for each species. Distilled water and neutral soap were

added to the tubes. Each tube was manually shaken for about one

minute to remove any probable impurities. The small parts were

then removed, washed, and left to dry at room temperature for

about five minutes. The fixation was done in 5% glutaraldehyde.

The skins were then washed in 0.1 M cacodylate buffer and post-

fixed in a solution of 1% osmium tetroxide at 37°C for two hours.

This procedure was followed by dehydration, critical point drying,

and platinum-palladium ion sputtering. The specimens were then

examined under a scanning electron microscope (Jeol, JSM-

5400LV). Scales were later analyzed and photographed under a

scanning electron microscope under various magnifications.

RESULTS

In the R. braminus , the microstructure of the external

surfaces of the head scales showed zigzag ventilations like

structure (Fig. 1A). The surface of the trunk scales appeared

smooth, but showed wide grooves at high magnification

(Fig. 1B). The tail scales appeared cycloid, smooth, and bril-

liant at low magnifications (Fig. 1C) while at high magnifica-

tions, showed lines similar to those on the head scales’ sur-

A. A. Allam and R. E. Abo-Eleneen772

face (Fig. 1D). The head scales appeared darker than the

scales of the trunk and tail, respectively.

The microstructure of the E. jaculus scales surface of

head and trunk regions appeared similar however, scales

surface were found to be corrugated and contain black

patches (Fig. 2A, B). The scales surface appeared darker as

heading backward and resembled the surface of sandy

dunes. The microstructure of the tail scales surface from the

region after the anus showed some parallel lines that may

resemble microornamentation (Fig. 2C). The scales from the

top region of the tail appeared small, cycloid, rough and

hard (Fig. 2D).

In P. sibilans, the microstructure of the head scales

showed the presence of extended surface grooves and

microvilli-like structures (Fig. 3A). At low magnification, the

trunk scales showed a flattened shape (Fig. 3B). The high

magnification of the trunk and tail scales revealed ventila-

tion-like structures, as in tree leaves (Fig. 3C, D). The tail

scale ventilations appear darker than those of the trunk.

The microstructure of the head scales of the N. haje appeared wavy, similar to the head scale surface of E. jaculus (Fig. 4A). Also, small black patches were observed

in the bright microimage of head scales (Fig. 4B). The

surface of trunk scales appears rough and without any

prominent structures (Fig. 4C). The tail showed the pres-

ence of small undulated regions (Fig. 4D).

In E. carinatus, head scale surface is similar to a moun-

tain or hill while trunk scales showed some structures as in

Figure (5A, B, C). These structures are like an aggregation

Fig. 1. (A–D) Scanning electron micrographs show the microstruc-

ture of skin scales of Rhomphotyphlops braminus. (A) head scales,

Scale bar = 3 μm. (B) trunk scales, Scale bar = 4 μm. (C) tail scales,

Scale bar = 60 μm. (D) tail scales, Scale bar = 4 μm.

Fig. 2. (A–D) Scanning electron micrographs show the microstruc-

ture of skin scales of Eryx jaculus. (A) head scales, Scale bar = 3

μm. (B) trunk scales, Scale bar = 4 μm. (C) fore-region tail scales,

Scale bar = 4 μm. (D) hind-region tail scales, Scale bar = 4 μm.

Fig. 3. (A–D) Scanning electron micrographs show the microstruc-

ture of skin scales of Psammophis sibilans. (A) head scales, Scale

bar = 4 μm. (B) trunk scales, Scale bar = 240 μm. (C) trunk scales,

Scale bar = 4 μm. (D) tail scales, Scale bar = 4 μm.

Scales Micromorphology 773

of stones. The tail scales appeared as small raised peaks of

some remnant materials (Fig. 5D).

DISCUSSION

Previous studies of microstructures in squamate skin

have found intraspecific variation associated with the ontog-

eny, body region, scales size and structures (Price and

Kelly, 1989; Harvey, 1993; Gower, 2003; Rocha-Barbosa

and Moraes e Silva, 2009). Observation of widely diverging

microstructural patterns allows us to conclude that, over the

course of evolution, modifications arose not only in macro-

but also in microstructures, and that such alterations allowed

optimal adaptation of organisms to their environmental niche

(Velloso et al., 2005). Stewart and Daniel (1973) underscore

that differences in microornamentation allow a functional

interpretation. Williams and Peterson (1982) state that the

investigation of significant adaptation in cases of morpholog-

ical divergences may provide insights into new evolutionary

adaptive complexes. Gower (2003) does not discard the

idea that variation in scale microstructure corresponds to dif-

ferent environmental conditions to which the organisms were

exposed during the acquisition of the micro-ornamentations.

The study of microstructural variation thus must take into

account the effects of selective pressures brought about by

the peculiarities of each environment.

The present study used five species of snakes from

different families gradient in the evolution scale and inhabit

different habitats except of N. haje and E. jaculus snakes,

may be seen in the same habitat in some cases. It is likely

that small differences in microstructure conformation may

bring great benefit to the occupation of distinct microhabi-

tats, and during squamate evolution, synapomorphies may

have arisen giving the same solution to different adaptive

problems. Even when the microstructural form is similar, the

distribution and organization pattern differ, which gives a

characteristic microstructure to each snake (Arroyo and

Cerdas, 1985).

The R. braminus is a fossorial, blind, and primitive

snake that lives underground inside muddy soil and decayed

organic soils (Yan et al., 2008). The microstructure of scales

surface of head, trunk and tail are not the same. Some lines

on the surface of head and tail scales bear resemblance in

the micro-ornamentations reported by Rocha-Barbosa and

Moraes e Silva (2009) for fossorial snakes. The absence of

these lines in the trunk scales makes the surface smooth.

The smooth surface of the scales in R. braminus may be

related to its living in a smooth environment. Gower (2003)

proposed that a “smoother” and more regular micro-orna-

mentation may confer an advantage to underground living,

possibly by reducing the adhesive force of moist soils on the

scales of these snakes.

The E. jaculus snake lives in sandy area. This snake

occupies an intermediate position in the evolutionary scale

(Yan et al., 2008). The black patches distributed on the sur-

face of head and trunk scales that resulted from the distri-

bution of pigments in the skin (Abo-Eleneen and Allam,

2011). The surface patterns of head and trunk scales are

similar to sandy waves. This may be related to the sandy

environments of this snake. The tail scales are not similar to

the head and trunk scales, but they also have two shapes

on the dorsal region of the tail. The surface of the scales of

Fig. 4. (A–D) Scanning electron micrographs show the microstruc-

ture of skin scales of Naja haje. (A) head scales, Scale bar = 4 μm.

(B) head scales, Scale bar = 4 μm. (C) trunk scales, Scale bar = 2.4

μm. (D) tail scales, Scale bar = 4 μm.

Fig. 5. (A–D) Scanning electron micrographs show the microstruc-

ture of skin scales of Echis carinatus. (A) head scales, Scale bar = 4

μm. (B) trunk scales, Scale bar = 4 μm. (C) trunk scales, Scale bar =

4 μm. (D) tail scales, Scale bar = 4 μm.

A. A. Allam and R. E. Abo-Eleneen774

the fore-region of the tail has some lines that bear similari-

ties in microornamentation (Gower, 2003). The scales of the

hind-region appeared rough and hard, which is likely an

adaptation to the mode of locomotion in sandy areas (Pough

et al., 2003).

The P. sibilans snake has intermediate evolutionary

position. It has been found in the gardens and cultivated

area and spends time of its day over trees (Kelly et al.,

2008). The microstructures of the head scales are different

from trunk and tail. The trunk and tail scales show a special

type of surface microstructure. It has been observed that the

surface of the scales has ventilations similar to those of

some tree and plant leaves. More studies are required to

confirm whether this similarity is significant or is merely a

coincidence.

The N. haje is a member of the Elapidae snakes. These

snakes occupy an advanced position in the evolutionary

scale (Vidal and David, 2004). Our results show similarities

between the microstructure of head scales of N. haje and E. jaculus. This may be due to the similarity in their niches, or

because the two snakes belong to a group of snake called

Macrostomata (Saleh, 1997). Price (1982) found morpholog-

ical similarities in the micrornamentation of the scales of

aquatic, arboreal, and fossorial snakes, and concluded that

microornamentation has a more taxonomic than adaptive

function. The appearance of trunk and tail scales microstruc-

ture may be resulted from the adaptation with their environ-

ment (Ribas et al., 2004).

The viperidae are the most advanced snakes on the

evolutionary scale (Yan et al., 2008). Echis carinatus is a

desert snake, and lives between rocks and stones (Aubret

et al., 2004). The detected microstructures of the scales sur-

face are unique where it resembles to a certain extent to the

topography of its habitats. Ribas et al. (2004) give an

account on the relationship between ecology and morphol-

ogy. The scales of head, trunk and tail are different in the

microstructure. The surface of the tail scales appeared very

hard and rough in the present micrograph because of the

role of tail in the locomotion (Pough et al., 2003).

In conclusion, the dorsal surfaces of the scales of the

head, trunk, and tail regions of each of the snakes examined

in this study are not the same or even similar, so the scale

microstructures are species-specific even when some of the

species share the same habitats. The present study sug-

gests an inter-relationship between snake habitat and scale

microstructure.

ACKNOWLEDGEMENTS

This project was supported by King Saud University, College of

Science Research Center.

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(Received December 27, 2011 / Accepted May 31, 2012)