Biomedical Engineering Reference
In-Depth Information
BODY SIZE AND INTEGUMENT
Size and Sexual Dimorphism
Variability is one of the outstanding features of nonhuman
primate morphology. The range in size among species is
tremendous. For example, an adult male pygmy marmoset
(Cebuella pygmaea) weighs less than 100 g whereas an
adult male gorilla (Gorilla gorilla) may weigh more than
200 kg (
Fleagle, 1999
). These are two extremes, but within
the order there is considerable variability even between
closely related species (
Napier and Napier, 1967
).
A second factor that affects body size is sexual
dimorphism. The most marked differences between the
sexes occur in species such as olive baboons (Papio
anubis) and Sumatran orangutans (Pongo pygmaeus
abelii) where adult female weight is approximately 50%
and 54% of adult male weight, respectively. In other
species, very little sexual dimorphism occurs. For
example, in spider monkeys (Ateles paniscus)orchim-
panzees (Pan troglodytes), adult female weight is
approximately 103% and 90% of adult male weight,
respectively. These comparisons of body weight differ-
ences are one index of the amount of sexual dimorphism in
a species. The relationship of body weight to body length
(crown
Notable external coloration in primates is not just
limited to hair. In some primates the skin on parts of the
body, such as the face or perineum, assumes a coloration
that is distinct for the species and/or phase of the repro-
ductive cycle. For example, the skin of the face and
perineum of adult male mandrills (Mandrillus sphinx)is
multicolored with blue, white, and red, whereas the peri-
neum of adult male patas monkeys displays a blue scrotum
below a red perianal triangle flanked by the white hair of
the posterior thighs. In many female primates near
ovulation and/or parturition the skin of the face and
perineum shows marked reddening, sometimes accompa-
nied by swelling and the tumescence may be quite
pronounced. All of these colorations are thought to be
integral parts of behavioral signaling within the context of
the social organization (
Setchell and Dixson, 2001; Gerald
et al., 2009
).
The skin of nonhuman primates is histologically very
similar to humans. Epidermal free (nonencapsulated)
sensory endings, Merkel cells (
G¨¸l¨ et al., 2008
), and
encapsulated endings, e.g. Meissner's and Pacinian
corpuscles, are present to transmit afferent impulses. As in
humans, the volar surfaces of the hands and feet (
Figures
4.3, 4.4
) are covered by tactile pads complete with dermal
ridges (dermatoglyphs) (
Cummins, 1933; Stewart, 1933
).
These pads have an abundance of afferent nerve endings
which provide detailed sensory information to the brain
(
Niemitz, 1990
). Some NewWorld monkeys, such as spider
(Ateles) or howler (Alouatta) monkeys, have prehensile
tails which they use extensively as a fifth appendage. In
these species, the ventral surface of the distal tail is also
covered by a tactile pad very similar to that on the hands
and feet. The skin of nonhuman primates includes seba-
ceous glands as well as eccrine and apocrine sweat glands,
although these are not as numerous as in human skin. Scent
glands, modified apocrine sweat glands, are present in some
species and, like urine, may be used for marking.
Depending on the species, scent glands may be present in
a variety of locations (sternal, brachial, suprapubic, sub-
caudal) and contribute to a variety of social functions
(
Hirano et al., 2003, 2008; Heymann, 2006
).
In Old World monkeys and gibbons (Hylobatidae) the
ischial tuberosities are covered by a callous formation:
the ischial callosities. The form and extent of these
callosities are species specific. In some species, such as
theGuineababoon(Papio papio), the two fuse across the
midline. There is, however, considerable variability
within a single genus as evidenced by the well-separated
ischial callosities of the rhesus monkey (Macaca mulatta)
and the fused callosities of the Barbary macaque
(Macaca sylvanus). The extent of these callosities is
thought to be related to sitting habits, but the correlation
between behavior and morphology has not been proven in
controlled studies.
rump or head height plus trunk length) is such
that those species in which the female weight is approxi-
mately 50% of the male weight, female body length is
approximately 81% of that of the male. In species with
little difference between body weight of males and
females, there is also little difference in body length
(
Napier and Napier, 1967
).
e
Skin
The skin of all primates is extensively covered with hair.
The thickness and density of the hair as well as its color and
length vary significantly among species. The major deter-
mining criteria for differentiating species within a single
genus are frequently coat (hair) color and coloration
patterning. Within a single species, however, coat color
may show considerable variability, as evident in rhesus
macaques in which coat color ranges from brown to gray or
even gold (
Kessler et al., 1986a; Napier and Napier, 1967
).
In addition to the basic coat coloration, many species also
show considerable sexual variability in the coloration
pattern of adults. For example, in patas monkeys (Eryth-
rocebus patas), not only is the pattern of coat coloration
different for males and females, but also the coloration of
the facial hairs of the female changes during pregnancy and
subsequent lactation (
Palmer et al., 1981
). New genetic
studies as well as more detailed morphology and field
studies of behavior and ecology are providing important
data which along with coat color help distinguish species
and/or subspecies.
