San F ernanclo Valley State College
OLFACTORY DISCRIMINATION BETWEEN DIPODOMYS II -------
MERRIAM! AND DIPODOMYS PAt·U�.:tvUNTIT\:'US
A thesis submitted in partial satisfaction of the requirements for the degree o£ t-!IaE:ter of Science in
< j
Biology
by
Edward NeaJ 1v1irsky
June, 1971
The thesis of E�dward ��al Mirsky is approved:
-p·�---- ·--------------
Committee Chairman
San Fernando Valley State College
June , 197 1
ii
ACKNOWLEDGMENTS
I wish to express my appreciation to Dr. George F. Fisler for his
guidance and helpful criticism throughout this study, and for his critical
reading and improvements of this manuscript. I am indebted to Dr. John
Swanson for his many hours 6'1liding me in the chromatographic work and for
his criticism of this manuscript. I am further indebted to Dr. Andrew
Starrett for his radiant humor and for his many useful suggestions.
With sincere gratitude I wish to acknowledge the invaluable coop era
tion and aid of the following persons: Dr. John Kontogiannis for use of his
shed; J\1iss M. Sue Wensel for printing the photographs; Miss Joyce A.
Hayes and Mr. Russ Sprouse without whom the computer would have been
just another machine; Mrs. Barbara Peet for typing the final manuscript;
and Iny wife Phyllis for aid in every way.
Computations were performed at the San Fernando Valley State College
computation center using a Control Data Corporation 3170 electronic com
puter. The DAM analytical program was employed.
iii
TABLE OF C ONTENTS
Page ABSTRACT . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . .. . . . . .. . .. . "' . . . vii
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
MATERIALS AND METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ; • • . 3
Experimental Procedure . . . . . . • . . . . • • . . . . . . . . . . . . . • . . . . . . . . . 4
Collection of Lipids . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . • . . . . . . . . 9
Thin -layer Chromatography . . . . . . . . . . . . . . . . . • . . . . • . . . . . . . . . 1 1
Histological Techniques . . . . . • . . . . . . . • • . . . • . . . . • . . . • . . . . . . . 12
RE:SUL1"S . ., . . o • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • I' . . . .. . . . . . . . . . 14
Activ it)T Experin1el1tS . . 0 • • • • • • • Cl • • • • • • � • e • Cl • • • • • • • • • • • • " • • 14
Chromatographic Analysis . . . . . . . . • • . . . . o • • • • • • • • • • • • • • • • • • 16
Histological Studies . . . . . . . . . . . . . • . . . o . . . . . . . . . . . . . . . . . . . . 17
DISCUSSION AND C ONCLUSIONS . . . . . . . • . . . . . . . • . . • . . . . . . . . . . . . 18
LITEltATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
iv
Table
l.
TABLES
Page
Activity o{ D. !l1�_ETiar_ni i\bles, D. merriami Females ar1cl Qn. J2al���niJ!_0!.:_ltlS Nlales� Ol • • �. . . . . . . . . . . . . . . . . . . . •
. • • • • 2 1
2. Statistical Analysis of the Activity of D. !nerriami Males D. �1_!-�rr1���mi;. Fen,ales and .!2; panaminti�rs Females. . . . .. 24
3. Statistical Analysis of the Activity of D. merriami Males. . 26
-1:. A Comparison of the Activity of D. !nerriami Males Used in Experimental Sets One and Two . . • . . . . . . • • . . . • • . . 28
5. Activity of _Q_. rneJ;E��-mi_ Females . . . . . . . . . . • . . . . � • • . . • • • • 30
6 . Statistical An3.lysis of the Activity of D. merriami Fj e1Y18.. les e (t .. ' • • � • • • e • " " • • ll • • • � • • • • • • · e • • • • • • • • • • • • • • • • • • 32
7. /\ctivtty of De �er�j,::trt1i r::e1nales . . . .. . . . . . � . . . . . . . . . . . . .. 34
8. Statistical Ann-lysis of the .Activity of !2: merriami F E.'l11:11E:S .. II " • "" -.1 " • " • • • • • • • fl • • • • • • • • • • • Ill • • • • • • • • • • • • 0 • • • • 36
9 . Control Experiment. AcUvity of D. me!riam..J Males. . . .. . 38
10. Control Experiment. Statistical Analysis of the Activity of l)e rnerria.J11i JVIc:1les+ .. '" . " . s . . o . . . . . . . . . . . . . . . . . . . . . . . 40
H. Analytical Results of Thin -layer Chromatography. . . . . . . . . 42
F IGURES
Figure Page
1. Experimental apparatus . . . . • . . . . . . . . . . . . . . . • • . • . • . . . . . • 44
2 . Thin -layer chromatograph of l ipids . . . . . . . . . . . • . . . . . . . . . 46
3. Parasagittal section of the dorsal skin gland of a D. n1er11iami male • 0 6 6 0 e t e . 0 e e 1!- 0 8 e ,e 6 II e a e 0 0 � II S . e 0 0 6 • • II e 0 ft 6 48
4 . Tangential s ection of the dorsal skin gland of a D . pana.n� male . . . . . . . e • • • 0 , • • • • • • • .. • • • • • • • • • • • • • • • 50
vi
ABSTRACT
OLFACTORY DISCRIMINATION BETWEEN DIPODOMYS
:tv1ERRIAM1 AND DIPODOMYS PANAMINTINUS
by
Edward Neal Mirsky
lv1as.ter of Science in Biology
June, 1971
A s eries of experiments was desig11ed to determine the role of the dorsal
skin gland in olfactory discrimination and chemical communication in two
sympatric species of kangaroo rats , Dip_c_:�lomys merriami and Dipodomys
I?ana:r:ni�tinus . Experirnental animals \Vere tested for responses to odors of
the oppo site sex of both species. Thin layer chromatographic studies of
l ip ids of the back and of the dorsal s kin gland, as well as histological s:udies
of the latter, were performed . Results indicate that , at least under the con-
dit ions of these experiments, individuals of D . merri�m� md D . panamintinus
may distinguish bet\veen homospecific and heterospecific individuals by
chemical cues, although the source of the oclor -pmducing d1emical is not
known. Olfactory stimuli probably play a role in establishment of pair bonds
by orienting s earch behavior of both males and females toward conspecifics.
Skin l ip ids alone, however, are not effective as agents of species discrimina
tion, but may still have a role in chemical communication .
vii
INTRODUCTION
Pheromones are chemical substances that s erve as signal s eliciting be
havioral reactions in individuals of the same species (Karlson and Luscher,
1959 ) and are important in species recognition and therefore may act as
ethological isolating mechanisms in mammal s . Species of mammals have
their own courtship and mating behavior; in some, behavior has become
ritualized and is often extraordinarily complex (see Eisenberg, 19 6.3; Marter
and Hamilton, 19 66; Tinbergen, 1954) . For the perpetuation of a mammalian
spec ies , it is necessary that there should be means of overcoming innate
aggressions so that the s exes may encounter each other, copulate , and pro
duc e offspring . Pheromones may be important in this role. Since many re
views of the l iterature on pheromones and their role in mammalian reproduc
tive physiology and behavior have been published (Bronson, 19 68; Bruce, 1966;
Ewer, 1968; Mykytowycz , 1970; Ralls , 197 1; Scholtz-Westrum, 1970;
Sebeok, 19 69 ; Whittaker and Feeny, 197 1; Whitten, 1970; Whitten and Bron
son, 1971) , it is unneces sary to elaborate on this here .
Quay ( 1953) and Eisenberg ( 19 63, 1967) have reported that all species of
�podomys (Heteromyidae) exhibit locus specificity in their sandbathing .
These authors suggest that sandbathing can serve the dual function of dressing
the pelage and marking . Quay ( 1953) showed that at least in D . agilis and D .
me�·riami (but not in both sexes of D . heermani and D. deserti), the dorsal
skin gland of males , but not females , increases in size nearly one-hundred
1
percent during the breeding season . Thus, there is the possibility that the
dorsal skin gland of male kangaroo rats may have a role in marking during
s andbathing and therefore have a function in communication.
Experimental studies of olfactory discrimination between individuals of
closely related mammalian species have 'been conducted by Godfrey (1958),
Moore (1965 ) , and Smith (19 65). Preliminary investigations into the possible
role of odorous secretions of various glands have been reported by Thiessen,
et al. (19 68 , 1969) and Mykytowycz (1958, 1959 , 19 66a, b , c, 19 67) , but only
in one case has a particular behavior been associated with a particular chem
ical or group of chemicals (Brownlee , et al . , 19 69 ; Muller - Schwarze, 1969) .
None of thes e investigators , however, has attempted to correlate olfactory
discrimination with the source of the odor . This inve stigation does . To
accomplish this , certain questions concerning species discrimination and
chemical communication with particular reference to the role of the dorsal
skin gland of D. mer:riami and D. _Eanamintinus must be answered . First ,
can individuals of D . merriami and D . panamintinus discriminate between
members of the opposite s ex of these two species by chemical cues alone?
Second, are there any differences betvveen the skin-surface lipids and the
lip ids of the dorsal skin gland which may serve as a basis for olfactory dis
crirnination? Finally, can the skin-surface lipids serve as a basi s for
species discrimination?
2
MATERIALS AND METI-IODS
Two species of kangaroo rats were used in this study, DiiJ.odomE
! merr� Mearns , Merriam kangaroo rat, and Dipodomys panamjntinus
(Grinnell), Mohave kangaroo rat. Individuals ·were captured at two locations
in the Mojave desert near Pearblossom , Cal ifornia, using Sherman l ive-traps
(3" x 3" x 10") baited with wild bird see� and p eanut butter . Animals were
housed individually in the animal care room at San F ernando Valley State
College.
Betvveen 2 July 1970 , and 29 April l97 1 , 60 experiments were performed
testing individuals for response to odors of the opposite sex of each species.
The apparatus (fig . 1) used in these preference experiments was a variation
of the Y -tube apparatus used by Godfrey (1958). It was constructed of ply
wood and painted with a white, washable oil base paint (Epoxy) to reduce odor
absorption . The internal dimension of all areas was s ix inches square . The
entrance runway was five feet long; the other three runways were each eight
feet long . To the ends of each of the three eight-foot runways was attached a
ten inch end -compartment . The s ide of the end -compartment common to the
runway had a hole four inches in diameter which was covered with hardware
cloth . At a distance of one -half inch from the common wall and attached to it
was placed a five inch metal plate. This plate , completely covering the hole ,
prevented the test animal from entering the end -compartment . It also pre
cluded any tactile or visual contact between the test animal and the interior of
3
the end -compartment .
At eight locations in the floor of the apparatus at the beginning and end of
each runway, a treadle suspended over a microswitch was placed (see "x 's ",
fig . 1) . The switches were s ensitive to a weight of approximately ten grams,
which is considerably less than the u sual weight of the kangaroo rats (32 gms)
used, and when depressed would close the c ircuit to an Esterline-Angus
Operation Recorder (Model AW) . Thus a sequential record of passage
through the runways was obtained . Tests were begun at dusk and run until
the next morning . The first 480 minutes (eight hours) were arbitrarily sel
ected as the activity period to be analysed . Records continued after eight
hours were not appreciably different . The chart speed was . 75 inches per
m inute . The data were treated by dividing the eight hour continuous chart
record into half-inch intervals and summing the intervals for each of the
four runways. The distance was multiplied by 1 . 3333 to convert the chart
distance into time in each of the four runways . The time in the central area
of the apparatus was obtained by subtracting the sum of the time in the four
runways from 480 minutes (eight hours) .
Experimenta! 2rocedure . -To determine whether individuals of D .
m erriami and D . panamintinus discriminate between members of the opposite
s ex of these same species by chemical cues alone, two types of experiments
were designed. In the first, two kangaroo rats, one of each species and both
' of the sex opposite to that of the test animal, were placed in the end -compart -
ments to provide a choice . The procedure in these first experiments did not
allow one to distinguish bet\veen olfactory and acoustic communication . Sec
ond, the odor left by a kangaroo rat after removal from the end -compartment
was used t{)/provide a choice . This eliminated the possibility of acoustic
communication, but did not establish the source of the odor. In add ition, to
see if lipids have a role in species discrimination and chemical communica
tion, a third s eries of experiments was conducted using only these lipids
(see beyond for extraction methods ) as the odor sourc e . A table o f random
numbers was used to determine which two of the three end -compartments was
to be used for each test .
Prior to each experiment the equipment was disassembled and vvashed in
soap and warm water to eliminate odors from the previous experiment . No
food or water was placed in the apparatus o There were no other animals in
the test area during an experiment . Also, cages used to transport the ani-·
mals were removed before the experiment was begun.
The apparatus was divided into five areas designated A , B, C , D and E
(fig . 1) . Two xnethods were employed to analyse the data for each experi
mental set of ten trials : Method I, comparison of activity of the test kangaroo
rats relative to odors in two end -compartments ; and Method II, comparison
of activity of the test kangaroo rats in each o,\ the five areas of the apparatus .
In Method I , the time spent in each of the following areas was totaled and
1 compared statistically: Domain 1, the runway with the odor of the homospe -
5
c ific kangaroo rat in the end -compartment; Domain 2 , the runway with the
odor of the heterospecific kangaroo rat in the end -compartment; Domain 3,
the runway with the empty end -compartment; Domain 4, area A; and Domain
5 , area E. For Method I I , the time spent in each of the five areas of the
apparatus (A -E) was totaled and compared statistically . It was assumed
that the test animals would distribute tbeir activity randomly in all four run
ways of the apparatus if odor were not useful in communication. Student's t
distribution test for comparison of means was made with the expectation of
equal use of all four runways . The level of s ignificance chosen was 0. 05 .
The area E of the apparatus was disproportionately smaller than the four run
ways; therefore , the time spent in it was not expected to be equal to the time
spent in any one of the four runways .
The following procedure was employed for Expe1imental Sets One, Two
and Three .
These experiments were carried out in an unused classroom located in
an air -conditioned building. An experiment was begun by assembling the test
apparatus and masking all seams with tape SJ that the apparatus would be air
tight . Females of both species were then placed in the end -compartments as
described . A hose connecting a vacuum. system to a nozzle at the center of
the apparatus was then turned on (see fig . 1) . After one hour the test anim,al
was introduced into the apparatus . At this time the vacuum hose was trans
ferred to the noz7le at the entrance ( see fig . 1). Once the test animal was in
6
the apparatus and the vacuum attached, the l ights in the room were turned
off and the activity of the test animal recorded .
EXPERIMENTAL SET ONE . Dipodomys merriami males were used as
test animals . Data ax1:�J.ysed by Method I .
EXPERIMENTAL SET TWO . Dipodomys merriarni males were used as
test animals . The s ame ten kangaroo· rats were used as in Experimental Set
One. This provided a control which tested whether previous experience in
the apparatus would influence the choices an animal made on suceeding tests.
Data analysed by Method I .
EXPERIJ\!IENT AL SET THREE. Dipodomys panamintinus males were
used as test animals. Data analysed by Method I .
The following procedure was employed for Experimental Sets Four, Five,
Six and Seven .
These four experiments were conducted in a roofed shed which was
screened on all four s ides . In o rder to fit the apparatus into the shed it was
necessary to shorten the entrance runway to three and one-half feet and to
angle runways B and D toward runway C so that the maximum width was seven
feet . There was no vacuum facility, so it was decided not to s eal the runways
with masking tape .
EXPERIMEI\lT AL SET FOU R . �odomys merriam� females were tested
for their activity in the apparatus with males of both species in the end -com
partments . Data analysed by Method I .
7
EXPERIMENTAL SET FIVE . Dipodomys marriami males were tested
for their response to odors only of females of each species . The experiment
was initiated as before; however, after one hour the females were removed
from the ,end -compartment . T:he 'H11i3;e to be tested was then introduced into
the apparatus and the experiment continued as before . Data analysed by
Method I .
EXPERIMENTAL SET SIX . Dipodomys me£!�iami females were tested
for their activity in the apparatus with odor in the end -compartments provided
by skin -surface l ipids of males of both species. Lipids were collected (see
beyond) and poured onto clean filter paper. The activity of the female was
recorded for 180 m inutes (three hours) . The initial area of the apparatus
entered by a female after passing through area E was also recorded . This
data was then statistically analysed in two ways as follows :
Experimental Set Six a . Data analysed by Method I.
Experimental Set Six b . Because of the non -random behavior in
the apparatus , and because chromatographic analysis indicated that
there is no difference between the lipids of males of both species
(see beyond) , a statistical comparison was performed by summing
the time spent in each of the ten possible combinations of Domains .
That is, the time spent in Domain 1 was added to the time spent in
Dmnain 2 . This sum was compared to the sum o f the times in two
other such Domains, producing forty -five comparisons .
8
EXPERIMENTAL SET SEVEN . A set of ten control experiments was
designed to test cleaning procedures used during the experiment, and to see
if the design of the apparatus prejudiced the results . A female of both
' species was .. placed in the end:,;ec;�mpartments as befme. After one hour the
females were removed and the apparatus washed with soap and warm water.
The apparatus was then reassembled o=md a male .!2_. m�rriami introduced.
His activity was recorded for 18 0 m inutes (three hours) . This data was then
statistically analysed in two ways as follow s :
Experimental Set Seven a. Data analys ed by Method I . This would
s erve as a cleaning control to test whether or not the method. of
cleaning the equipment prior to each experiment was adequate to
eliminate the odor of the previous experiment .
Experimental Set Seven b . Data analysed by Method II . This was
a control to test whether or not there were behavioral character
istics of kangaroo rats which the apparatus m ight elicit.
Collection of l ipids . -Samples of lipids were co1lected from kangaroo
rats which were washed the previous evening in acetone . Washing was done
to reduce the amount of free fatty acids which are not a product of the s eba
ceous glands, but come from triglycerides of the rebaceous glands by the
action of bacteria or endogenous enzymes, or both (Nikkare, 19 65) . Acetone
was chosen because it dissolves l ipids even in the presence of water, and
because it is known to be relatively nonirritating to the skin . Two methods
9
w ere employed for the collection of lipids . (I). Samples were taken from the
dorsal skin gland of adult male D. merrian:2:_ and Do panamintinus with a
sterile Q-tip dipped in acetone . Samples from ten animals were pooled to
make one sample for thin - layer chromatography . Two pooled samples of
each species were collected, and each spotted onto two chromatographic
plates . The gland area in female kangaroo rats is usually less than one milli -1
meter in length, making it impractical to collect enough lipids . (II).
1 Samples were collected by squirting approximatly 25 ml of acetone over the
back of a kangaroo rat . By this method sufficient s kin -surface lipid was
obtained to allow thin -layer chromatography of a single animal .
Each chromatographic plate consisted of fiv'e spots from each of two
s amples. Two types of samples were collected by this method . (A) . After
removing the lipids from the dorsal skin glands of five male kangaroo rats of
each species, skin -surface lipids of the back were collected . Five such
chromatographic plates \Vere male . It was assumed that each sample repre
sented skin -surface lipids and not gland lipid . (B) . Skin- surface lipids were
collected from the backs of five male and five female kangaroo rats of each
species, without previously washing the dorsal skin glands . Care was taken
not to collect from the anal area because of possible contamination by fecal
fats , and glands of the anal area . Ten chromatographic plates were made .
Cholesterol esters of one male of each species were collected (see beyond) .
Each sample was chromatographed twice . Thus ten spots of each sample
10
were made .
Thin -layer chromat(�graphy . -Conventional techniques of thin -layer
chromatography we1e used ( Stahl , 19 65) . A slurry of 25 gms of s ilica gel G
( E . Merck and Co . ) in 7 0 ml distilled water was layered (0 . 25 mm in thick
ness) onto 20 x 20 em glass plates with a. Des saga. -B rinkmann applicator .
The plates were air dried, then heat -activated for at least 3 0 minutes at 120
C , and allowed to coo l . Reference standards and animal l ipids were applied
to the activated chromatographic plates using capillary tubes . Reference
standards used were octa.decane, squalene, cholesterol oleate, cetyl palmi
tate, free fatty acids, cholesterol palmitate, triolein , oleic acid, and
cholesterol .
Each plate was developed in three successive solvent systems : hexane;
benzene; and hexane, ether, and acetic acid (70 : 30: 1). The l ipids were
visualized by �praying the plates with 5 . O% concentrated sulfuric acid in 100%
ethyl alcohol and then charred by heating at 120° C for five minutes (Downing
et al. , 19 69) .
Separation of the cholesterol esters was accomplished by first developing
the plates as described previously . The area of chromatographed plates con
taining the cholesterol esters were scraped off with a. razor blade cleaned in
; acetone, Each plate was then sprayed as befon; and charred. Collected
fractions were eluted with petroleum ether and centrifuged to separate the
si l ica gel G. Ead1 sample vvas dried over boiling water and resuspended in
1:1
petroleum ether.
Each plate was developed in three successive solvents of freshly distilled
carbon tetrachloride. The chromatographed plates were sprayed with either
5. O% sulfuric acid, or animony tri-chloride, and heated for five minutes at
ll0° C (Stahl, 1965).
Histological techniques. -Microtome sections were made of dorsal skin
glands without extracting the lipids (Procedure I) and following lipid extrac
tion inherent in paraffin embedding (Procedure II) . A total of 250 slides
were made of five male and three female D. merriami, and two male and one
female D. panamintinus.
Procedure I; the sudan black B technique vvas used for all unsaturated
lipids. Tissue was first fixed in 1% calcium acetate-10% formalin, to pre-
vent loss of polar lipids through extraction by water (Humason, 1967). The
·.tissue was then embedded in 20% aqueous gelatin and sectioned either para
sagittally or tangentially using a Reichert sliding microtome with a Yomaro
Koki electro -freeze microtome attachment ret at -28° C. Sections were
made at 1� , floated on water, transferred onto clean slides coated with egg
albumin, and dried. The tissue was then stained for 15 minutes in. sudan
black B (Adams, 1969). Some slides were counterstained in hematoxylin
(Humason, 1967).
Procedure II; the hematoxylin and eosin technique, was used to stain
tissue after extraction of lipids. The tissue was embedded in paraffin after
12
fixation in Zenker's fluid (Humason, 1967). All sections were cut either
parasagittally or tangentially at "f# on a Spencer microtome. TI1e tissue was
then stained in Harris' hematoxylin and countemtained in eosin (Davenport,
1960).
13
RESULTS
Activity experiments. -The test animal entered each compartment dur
ing the first few minutes of each experiment and thus was exposed to all odors
in the apparatus. After the first half -hour of each experiment, the test
animal tended to remain in a single runway for longer periods of time. The
first half -hour was the time of greatest activity, probably due to exploratory
behavior.
EXPERIMENTAL SET ON E. 12!:£odon� merriam� males showed no
statistically significant difference in ·their activity within the five Domains
(tables 1 and 2).
EXPERIMENTAL S ET TWO. Dipodomzs merriamj males showed no
statistically significant difference in their activity within the five Domains
on the basis of t -tests (tables 1 and 2) . However, F -ratios (table 3) showed
that samples compared were significantly different (P >. 05). Therefore there
is reason to believe that D. merriami males were not random in their activity
between the runways with the D. merriami female in the end-compartment
and the runway with the D. panamintinus female in the end -compartment.
A comparison of the activity of D. merriami males used in Experimental
Sets One and Two indicate that in only two behavior tests did a kangaroo rat
choose the same Domain in both trials (table tl). Thus previous experience
in the apparatus does not influence the behavior of a kangaroo rat on subse
quent trials in the same apparatus.
EXP ERIMEJ\lT AL S ET THREE. Dipodo�y_E panamintinus males were not
14
random in their behavior in the test apparatus, they spent the greatest
amount of time in the runway with the conspecific female in the end -compart
ment (tables 1 and 2).
EXPERIMENTAL SET FOUR. D�podomy� merriami females spent a
statistically significant greater amount of time in the runway with the con
specific male in the end -compartment {tables 1 and 2).
EXPERTh.1ENT AL SET F NE. Dipodomys merriami males were not ran
dom in their activity vvithin the apparatus (tables 1 and 2), the odor left by a
female kangaroo rat is a sufficient stimulus to elicit non -mndom behavior in
the male. It should be pointed out that Experimental Sets One and Two were
conducted during July through September, which is outside of the breeding
season (Quay, 1953) , when�as, this experimental set was conducted during
February, at the beginning of the breeding seas::m. This may acmunt for the
apparent stronger response of male !2.· _merriami to odors left by female D.
merriami than to the females themselves. However, the results are compli
cated by the possibility of acoustic communication in Experimental Sets One
and Two.
Experimental Set Six a. Dipodomys merriami females were not random
in their behavior in the apparatus. Their behavior was least random with
respect to area E and the runways with the lipids in the end -compartments
; (tables 5 and 6).
Experimental Set Six b. The activity of the females was not random in
15
the apparatus. Indeed, they spent a statistically significantly shorter time
in the runway with the lipids in the end -compartments. Female D. merriami
also spent significantly more time in area E than would be expected by chance
(tables 7 and 8 ) .
Experimental Sets Seven a and b. Dipodomys merriami males were
statistically random in their activity fQr both methods of analysing the data
(tables 9 and 1 0).
ghromatographic ana!:Jsis. -The lipids of the dorsal skin gland and of
the back were found to be identical in both species. There were no observ
able differences between the skin-surface lipids of either sex of both species
(table 11; fig. 2). Qualitative tests of the chemical nature of the skin-surface
lipids indicate that they are composed mainly of cholesterol and cholesterol
esters. Fatty acids, triglycerides and particularly wax esters are present in
trace amounts. Squalene, which is a major constituent of human skin -surface
lipids (Downing et al., 19 69), was not present in the kangaroo rats tested.
Analysis of the cholesterol esters indicates that the only ester present in both
species of kangaroo rat appears to be cholesterol palmitate (table 1 1).
These results are similar to those reported by Wheatly and James ( 1957)
for the guinea pig, Cavia porcellus, the laboratory mouse, Mus musculus,
and the laboratory rabbit, which have all been shown to have skin -surface
lipids lacking in squalene and low in triglycerides and fatty acids. Further
more, the guinea pig was shown to have a high concentration of cholesterol.
16
Histological studies.: -Quay (195 4) reports that the dorsal skin gland is
a holocrine gland, derived from basal cells of the gland unit (figs. 3 and 4) .
These cells proliferate to form a hard pillar of secretion which extends
through the neck of the gland. The center of the dorsal skin gland is the area
of greatest development. At the periphery are the sebaceous glands of least
development, showing the transition Hom unmodified to modified gland (fig.
3) . There were no morphological or histological differences observed be
tween the species studied, except that, generally, the overall gland size is
larger in ;Q_. panamintinus. Glands of the females of both Epedes, though
smaller, are neither morphologically nor histologically different from glands
of the males. These results are consistent with the findings of Quay (1954) .
17
DISCUSSION AND CONCLUSIONS
Difficulties with the design of the experimental apparatus used in this
study make conclusions concerning the role of chemical communication in
1 species discrimination tenuous. Firstly, its size and shape may elicite
maze running behavior in individuals. Secondly, the apparatus may elicite
exploratory behavior. Thirdly, even in experiments where the vacuum was
attached, it cannot be said with certainty that the odors were restricted to
a single runway. If, as Rosenberg (1968) points out, the nose is the most
sensitive chemical detector known, sensitive to a small number of odorous
molecules per receptor cell at threshold, the test animal conceivably may
be receiving threshold olfactory stimulation anyvvhere in the apparatus.
Fourthly, in the central area of the apparatus the test animal was confronted
with several choices, that is, he may stay where he was or go into any one
of four runways. Furthermore, one may assume that odors placed in any
end -compartnwnts will converge in this area, thus providing multiple
chemical excitation. Perhaps being confronted with several choices and
multiple chemical excitation, the test animal chooses to remain in the cen
tral area.
Under the conditions of the experiments )1owever, individuals of both
sexes of D. merriarni and male D. panamintinus may have discriminated
between homospecific and heterospecific individuals by chemical cues (al
though the source of these odor-producing chemicals is not known). Time
1 8
spent with the homospecific was usually greater than time spent with the
heterospecific, although, time spent with the homospecHic was often less
than time spent in some other area of the apparatus. Nevertheless, olfactory
stimuli probably play a role in establishment of pair bonds by directing
search behavior of both males and females to con specifics. Indeed, the
similar responses observed for male and female D. merriami. under the con
ditions of this study suggest that odors may provide stimuli in mate selection.
Unfortunately, these results are difficult to interpret vvithout information on
the social organization systems of the kangaroo rats in their natural en
vironments (see Manson and Kessler, 1940 ; and Reynold, 19 60 for prelim
inary reports on social organization).
Evidence presented by Kelly ( 19 69) and Csuti ( 19 69 , 1971) indicates
that there are isolating mechanisms in Dipodomys which would prevent inter
specific hybridization if sexual promiscuity were to occur between species
in sympatry. Results of the present study suggest that olfaction may be
important in sexual isolation in kangaroo rats.
Chromatographic methods employed for this investigation could not
discern qualitative differences between skin -surface lipids and lipids of the
dorsal skin gland. Furthermore, no differences vvere discerned between the
skin-surface lipids of D. merriami and D. panamintinus or between males
and females. However, there is always the possibility that there is a com
pound or group of compounds other than lipids which may be important in
19
species discrimination.
Results of the present study suggest that lipids were not effective as
agents of species discrimination. The results indicate that female D.
men�iami respond to the lipids of males of both species similarly by spend
ing less time in those runways with these lipids. However, this does not
preclude the possibility that they may have a role in chemical communication
within or between the two species.
Studies such as these may only suggest the purpose a particular be
havior pattern or chemical compound may serve in the natural environment
of the species. Since the social organization and chemical communication
systems of a species are an adaptive product of interaction of the species
with the environment, laboratory studies should be used largely for the·
erection of hypotheses which may be tested by field studies. Olfaction is
probably only one element of a complex interaction of sensory stimuli where
by kangaroo rats direct sexual behavior toward members of their own
species, minimizing the likelihood of interspecific hybridization through
species specific discrimination.
2.0
21
Table 1 . Activity of D. merri�E:!:� males (Dm cf), D. merriami_ females (Dm �) and D. panamintinus males (Dp �) with odors in t\vo end -compartments. In Experimental Sets One through Four, t\vo kangaroo rats, one of each species and both of the sex opposite to that of the test animal ·were used to provide a choice. In Experimental Set Five, the experiment was initiated as before, however, after one hour the feinales were removed from the end -compartments. The male D. _r_::wrriami was then introduced into the apparatus and the experiment continued as before. Each experimental set consists of ten 480 minute (eight hour) trials. The time spent in each of the following areas was totaled and compared statistically: Domain 1, the runway with the odor of the homospecific kangaroo rat in the end -compartment. Domain 2, the runway with the odor of the heterospecific kangaroo rat in the end -compartment. Domain 3 , the runway with the empty end -compartment. Domain 4, area A. Domain 5 , area E. (see fig. 1).
i I I
! i i I I
i l !
� -��--J
22
Table 1 . Activity of Kangaroo Rats
-----�
Mean with Standard Ranae Standan:I Error Deviation
EXPERIMEJ\lT AL SET ONE (Dm d')
Domain 1 15.0 - 367 . 0 130.000 + 45.3:31 143 .350 2 5.0-297.0 5 1.000 + 28 . 239 89 . 301
-
3 9 . 0 - 388 . 0 1 3 1 . 000 + 44. 490 1 40.689 4 19 . 0 - .139. 0 55.600 + 12.992 41 .08.3
-
5 23.0 -295.0 lll. 700 + 27.296 8 6.31 6
EXPERIMENTAL SET TWO (Dm cf)
Domain 1 29 . 0 - 435.0 1 44,200 + 4L1.42 1 1 40 . 47 0 -
2 6.0 - 20 1.0 5 4.000 + 18 . 324 57.9 46 -
3 8. 0 - 242 . 0 79.000 + 34.31 6 108.5 1 7 -
4 3.0 - 350 . 0 ll9 . 500 + 37.680 1 19.154 -
5 20.0 - 309.0 8 3.300 + 27.144 8 5 . 8 37
EXPERltviENT AL SET THREE (Dp cr't)
Domain 1 32.0 - 339.0 190.200 + 27.8 45 88, 05L1 -
2 3.0 - 95.0 49 . 100 + 9 . 7 1 6 30 . 726 -
3 10 . 0 - 95 . 0 45.800 + 8.785 27.780 -·
4 5.0- 33 1.0 1 10.700 + 32.601 103.093 -
5 43 . 0 - 140.0 8 4,200 + 10. 8 16 31± . 205
EXPERIMENTAL SET FOUR I (Dm �)
Domain 1 17 . 0- 3 1LO 162 . 400 + 33. 232 105 . 090 -
2 5.0 - 85 . 0 30 . 700 + 9 . 158 28 . 9 60 --
3 1 4.0 - 303.0 9 0.200 + 27.0 17 85.436 4 3. 0 -338.0 105.800 + 33.922 107 . 272
-
5 13.0 - 200.0 9 0 . 900 + 15.669 49 . 550 --·------- r_.,,. __
23
Table 1 . continued
Mean with Standard Range Standa1u Error Deviation
EXP ERIM ENTAL S ET FIVE (Dm a')
Domain 1 2 . 0 - 428 . 0 1 21.9 00 + 40 . 220 127.187 2 3. 0 - 63.0 18 . 9 00 + 5 . 718 18.083 3 9 . 0: 366.0
-
109 . 200 + 37.5 8 0 1 1 8 . 840 -
4 5 . 0 ·- 343.0 1 12 . 300 + 40 . 167 127.018 5 9 . 0 - 321 . 0 1 17 . 7 00 + 3 1 . 235 9 8 . 774
Table 2 . Statistical analysis of the activity of D. rnerriarni males, D. merrian2l females and D. panamintinus males. See explanation in legend for table 1 . Level of significance (P) = 0. 05 . Degrees of freedom (D. F . ) = 18 .
Table 2. Statistical Analysis of the Activity of Kangaroo Rats
Test EXPERIM ENTAL SET ONE Between (Dm d') Dornains t -statistic Shmificance -------
1 and 2 l. L1792 p (. 1 1 and 3 -0. 0173 p <. 1 1 and 4 1. 5820 p <. 1 1 and 5 0. 3496 p ( .1 2 and 3 -1. 5201 p < . 1 2 and 4 -0. 1415 p <·1 2 and 5 -1. 5404 p <. 1 3 and 4 1. 6333 P<. 1 3 and 5 0. 3755 p (. 1 4 and 5 -1.8558 .I< p (. 05 ---
Test EXPERIMENTAL S ET THREE Between (Dp if) Domains t-statistic Significance
1 and 2 4. 784�1 . 02<.P 1 and 3 4. 9455 . 02<P 1 and 4 1. 854·.3 . H p 0 05 1 and 5 3. 5485 . 02( p 2 and 3 0. 2519 P < . 1 2 and 4 -1.8108 . 1< p (, 05 2 and 5 -2.4141 • 05 { p <. 02 3 and 4 -1. 9222 . 1 <P (. 05 3 and 5 -2. 7558 . 02 <P 4 and 5 0.7715 P<. 1
---------Test Between Domains -----
1 and 2 1 and 3 1 and 4 1 and 5 2 and 3 2 and 4· 2 and 5 3 and 4 3 and 5 4 and 5
EXPERIMENTAL SET FIVE (Dn1 d') t-staUstic Significance
2.5354 . OS<P<. 02 0.2307 p <.1 0. 1689 P< . 1 0.0825 P < . 1
-2. 3755 . OS< P <.02 -2. 3021 . 05 < p (.02 -3. 1114 . 02( p -0.0564 P<.1 -0.1739 P(. 1 -0.1061 p <. 1
EXPERIMENTAL S ET TWO (Dm 0"') t-statistic Significance
1. 8771 . 1 < p <. 05 1. 1615 p (. 1 0. 4240 p <.1 1.1699 p (. 1
-0.6426 p < . 1 -1. 5633 p (. 1 -0. 8946 p (. 1 -0. 7947 p {. 1 -0. 0983 p ( . 1
0.7795 P<. 1
EXPERIMENTAL SET FOUR (Dm 9) t-statistic Si�ificance -
3.8206 . 02 {P 1. 6858 p < • .1 1. 1919 P<. 1 1.9461 . l(P <. 05 .
-2. 0857 .HP ( . 05 -2. 1374 • 05 ( p {. 02 -3.3170 . 02< p -0.3597 p {. 1 -0. 0224 P<. 1
0. 3988 p < . 1
---------·-----------------------
25
Table 3 . Statistical analysis of the activity of D . merriami males. See explanation in le$end for table 1 . P = 0 . 05 . D . F . = 9 . Largest variance value has been placed in the numerator.
Table 3 . Statistical Analysis of the Activity of D. merriarpJ Males
Test EXPERIMENTAL SET TWO Between Domains F -ratio Significance 1 and 2 5 . 8765 . 02< p 1 and 3 1 . 675 6 P<. 1 1 and 4 1. 3898 P< . 1 1 and 5 2 . 67 8 1 p < . 1 2 and 3 3 . 507 1 . 1 (P < . 05 2 and 4 4 . 2283 . 05 ( p <. 02 2 and 5 2 . 19 43 p (. 1 3 and 4 1 . 2056 P< . 1 3 and 5 1 . 59 8 3 p { . 1 4 and 5 l. 9 2 69 P< .1
27
8
Table 4. Control experiments. A comparison of the activity of the same ten D. �males used in Experimental Sets One and Two (table 1), with female D. me�riami and .Q_. 12.ana�int1nus in two end -compartments. Each experimental set consists of ten 480 minute (eight hour) trials. * = test male spent more time in Domain 2 than in Domain 1 . Box around two experimental sets indicates the test animal chose the same area in both experiments.
Expmt . Cat . No. Set 100 ONE
TWO 1 1 1 ONE
TWO 1 16 ONE
TWO 8 3 ONE
TWO 8 8 ONE
TWO 71 ONE
TWO 109 ONE
TWO 87 ONE
TWO 102 ONE
TWO 75 ONE
TWO
Table 4 . Control Experiments . A Comparison of the Activity of D . merriami Males Used in Experimental Sets One and Two
area A area B area C area D
1 16 . 0 135.0 Dp 19 . 0 Dm 45.0 47 . 0 Dm 29 . 0';' 8.0 Dp 87 . 0 69 . 0 38.0 f'l �-'P 297.0 Dm 15 . 0*
350 . 0 Dm 63.0 13.0 Dp 17 . 0 53 . 0 Dni 367 .ot Dp 5 . 0 14 . 0
131 . 0 Dp 201 . 0 13 . 0 Dm 78 . 0* 27 . 0 126.0 Dp 8.0 Dm 27.0
175.0 Dp 60.0 Dm 80.0 69.0 41 . 0 Dp 18 . 0 Dm 10.0':' 388.0· 73 . 0 130 . 0 Dp 35.0 Dm 1 1 1 . 0
9 . 0 Dp 12 . 0 Dm 3 19.0 27 . 0 23 . 0 Dp 19.0 14 . 0 Dm 377 . 0 19.0 Dm 8 1 . 0 Dp 75 . 0 1 69 . 0 70.0 Dm 435 . 0 9.0 Dp 9 . 0 36.0 139.0 Dm 65.0 Dp 5 3.0
287.0 23 . 0 Dp 43 . 0 Dm 73 . 0 27 . 0 Dm 55 . 0 Dp 5.0 3 65 . 0 99 . 0 Dm 95 . 0 169 . 0 Dp 6.3 . 0 41.0 Dp 20,0 Dm 3 18 . 0 33 . 0
3 . 0 342 . 0 Dm 101.0 6.0
area E
37 . 0 41 . 0 57 . 0
295 . 0 9 6.0 23 . 0
' 13 1.0 1 1 3 . 0
54 . 0 136 . 0
20 . 0 187 . 0 54.0 28 . 0 54 . 0 68.0 28.0
['..) '-()
0
Table 5 . Activity of D. p1erriami females with odors in two end compartments p rovided by skin - surface Lipids of male D . merriami and D. panamintinus . This experimental s et consists of ten 180 minute (three hour) trials. See explanation in legend for table 1.
·--------> - - - · . · · - q ·--·-·� • • • - • • ' . ' -·-�· . " ' j
Table 5 . Activity of D. merr�ami Female
---·
Mean with Range Standard Error
--
Experimental Set Six a Domain 1 1 . 0 - 87.0 17.500 + 8.490
2 1 . 0- 7 3 . 0 26 . 000 + 8 . 897 3 1 . 0- 67.0 3 1.800 + 9 . 235
-
4 5 . 0 - 13'4 . 0 5 1 . 900 + 1 6 . 650 5 19 . 0 - 9 3.0 52 . 800+ 7 . 560
31
Standard Deviation
26 . 846 28 . 135 29 . 204 5 2 . 653 23.906
2
Table 6 . Statistical analysis of the activity of D. m�riami females . See explanation in legend for table 1 . P = 0. 05. D. F . = 18 .
.33
Table 6 . Statistical Analysis of Activity of D . merriami Females
----Test Experimental Set Six a Between Domains t -statistic Signifiamce
----� ... ..--..-----�
1 and 2 -0 . 69 12 p ( . 1 1 and 3 - 1 . 1400 p (. 1 1 and 4 -1 . 8 406 . 1< p ( . 05 1 and 5 -3 . 1053 . 02< p 2 and 3 -0 . 4523 p < . 1 2 and 4 - 1 . 3720 p < . 1 2 and 5 -2.2955 . 05 ( p ( . 02 3 and 4 - 1 . 0557 p < . 1 3 and 5 - 1.759 6 .1 < p (. 05 4 and 5 -0 . 049 2 P < . 1
-------------·---·-----�-----------
34
Table 7. Activity of D . _!Perriami females with odors in two endcompartments provided by skin - surface lipids of male D . m�_gJ�mi and D. panamintinus . Statistical comparison performed by summing the time in each of the ten pos sible pairs of Domains in table 2.
35
Table 7 . Activity of D . merriami Females
Experimental Set Six b . (Dm � )
Mean with Standard Domain Range Standard Error Deviation
1+ 2 2 . 0 - 126 . 0 43 . 500 + 12 . 902 40 . 79 8 1+ 3 2 . 0 - 10 1 . 0 49 . 300 + 1 1 . 7 40 37 . 1 25 1+ 4 15 . 0 - 141 . 0 69 . 400 + 1 6 . 139 59 . 03 6 1+ 5 28 . 0 - 106. 0 7 0 . 300 + 8 . 844 27 . 9 68 2+ 3 2. 0 - 139 . 0 57 . 800 + 14 . 035 44 . 382
-
2+ 4 14 .. 0 - 140 . 0 7 7 . 9 00 + 13 . 7 12 43 . 362 -
2+ 5 3 0 . 0 - 138 . 0 78 . 800+ 9 . 9 30 3 1 . 400 3+ 4 34. 0 - 143.0 8 3 . 700 + 11 . 614 36 . 7 27 3+ 5 23 . 0 - 152 . 0 8 4 . 600 + 13 . 65 6 43 . 185 4+ 5 39 0 0 - 177 . 0 104. 700 + 16 . 27 1 5 1 . 45 2
36
Table 8. Statistical analysis of the activity of D. merriami females . See explanation in legend for table 2 . The sum of the time in each of the ten possible combinations of Domains is com pared to the time in two other such combinations . Comb ina tions not in this table are all P ( . 1 . P = 0 . 05 . D . F . = 18 .
37
Table 8 . Statistical Analysis of Activity of D. merriami Females
Experimental Set Six b Test Between Combined Domains t -stati stic Sign�j.cance
1 + 2 and 2 + 4 - 1 . 82 7 1 . 1 < P (. 05 1 + 2 and 2 + 5 -2 . 1683 . 05 ( p { . 02 1 + 2 and 3 + 4 -2 . 3 158 • 05 < p < . 02 1 + 2 and 3 + 5 -2 . 18 77 . 05 ( p < . 02 1 + 2 and 4 + 5 - 2 . 9 473 . 02< P 1 + 3 and 3 + 4 -2 . 08 3 1 . 1 < p ( . 05 1 + 3 and 3 + 5 - 1 . 9 602 . 1 < p < . 05 1 + 3 and 4 + 5 -2 . 7612 . 02 < p 1 + 5 and 4 + 5 - 1 . 8575 . 1 < p ( . 05 2 + 3 and 4 + 5 -2 . 18 27 . 05 < p < . 02
38
Table 9 . Control experiments . Activity of D . merriami males. A female of both species was placed in two end -compartments . Mter one hour the females were removed and the apparatus washed with soap and warm water . The apparatus was then reassembled and a male introduced . Statistical comparisons performed : (a) . Wash control . See explanation in legend for table 1 . (b) . Behavior control . The time spent in the five areas of the appaTatus , A - E (see fig . 1 ) , were totaled and compared statistically . This experimental set consists of ten 1 8 0 m inute (three hour) trial s .
i ·-· "· · · ·····--·- . .... . ...... - . .. ...... -.,. .. . . . ... ...... ......... . . .. J
Table 9 . Control Experiment s . Activity of D . merriami Males
Experimental Set Seven a Domain 1
2 3 4 5
Experimental Set Seven b area A
B c D E
Rano-e Q.
5 . 0 - 1 0 1 . 6 2 . 0 -· 1 2 1 . 0 1 . 0 - 58 . 0 3 . 0 - 87 . 0 2 . 0 - 65 . 0
3 . 0 - 8 7 . 0 1 . 0 - 121 . 0 2 . 0 - 101 . 0
14 . 0 - 65 . 0 2 . 0 - 65 . 0
.
Mean with Standard Standard Error Deviation
-
39 . 000 + 9 . 433 29 . 829 33 . 000 + 1 1 . 02 1 34 . 85 1 35 . 400 + 6 . 8 64 2 1 . 70 6
-
40 . 300 + 9 . 7 1 6 40 . 300 -
3 1. 500+ 6 . 766 2 1 . 397
3 4 AOO + 9 . 840 3 1 . 1 17 37 . 900 + 1 1 . 5 46 36 . 5 1 3 3 4 . 600 + 9 . 229 3 4 . 600
-
4 1 . 600 + 5 . 989 18 . 9 40 3 1 . 500 + 6 .7 66 2 1 . 397
39
- - ---� •'<·-�.-��---� -�- - · �·--- · -·-· --� .... ____ •. -�-- -- ·· · j
Table 10 . Control experiment . Statistical analysis of the activity of D . merriami males . See explanation in legend for table 4 . P = 0 . 0 5 . D . F . = 1 8 .
i I
Table 1.0 . Control Experiments . Statistical Analysis of the Activity of D . merriami Males - -----
Experimental Set Seven a
Test ' Test Between Between Domains t - statistic Significance Areas t -statistic Sig-nificance
1 and 2 0 . 3585 p { . 1 A and B -0 . 23)7 P ( . 1 1 and 3 0 . 3086 p ( . 1 A and C -0 . 0148 P < . 1 1 and 4 -0 . 0960 p < . 1 A and D - 0 . 6250 p ( . 1 1 and 5 0 . 6461 P < . 1 A and E 0 . 2428 P < . 1 2 and 3 -0 . 1232 p ( . 1 B and C 0 . 2232 p < . 1 2 and 4 -0 . 4424 p < . 1 B and D -0 . 2845 P < . 1 2 and 5 0 . 1778 p { . 1 B and E 0 . 4782 p ( . 1 3 and 4 -0 . 4 1 19 p < . 1 C and D -0 . 6352 p < . 1 3 and 5 0 . 4046 P < . 1 C and E 0 . 2709 P < . 1 4 and 5 0 . 7 432 p < . 1 D and E 1 . 1 177 P < . l
41
42
Table 1 1 . Analytical results of thin -layer chromatography of the l ipids of D. E_lerriami and D_. panamintinu s . At least ten spots were made of ead1 sample collected . Samples from the dorsal skin gland were pooled, ten animals in ,each sample . Cholesterol esters were pn�pared from samples from one male of ecch species . MF = major fraction, T = trace, 0 = not detected .
Table 1 1 . Analytical Results of Thin -layer Chromatography
Dorsal Skin Gland
Back Less Gland
Whole Back
Dm d' D� Dm d" DJ2 cl' Dm d' Dm9- Dp o" Dp � Cholesterol MF MF MF MF MF MF MF MF Fatty Acids T T . T T T T T T Triglycericles T T T T T T T T Wax Esters T T T T T T T T Cholesterol Esters MF MF MF MF MF MF MF MF
cholesterol palmitate MF MF cholesterol sterate 0 0 cholesterol acetate 0 0
Sgualene 0 0 0 0 0 0
43
44
Figure 1 . Experimental apparatus . After modification to fit into shed . Five areas of apparatus are designated A, B , C , D and E . At eight locations in the floor indicated by "x" are the treadles suspended over mocroswitches . End -compartments are designated a , b and c . The nozzle at the entrance = 1 ; the nozzle to the center of the apparatus == 2 .
._.
.·
. . · ; ...
:,. ·· .
.. ... � -
. . - � " ('� _:'. ·.- r
.. � , . ...
46
Figure 2 . Thin-layer chromatography of lipids . Separation pe:rformed on silica gel G . Solvents : hexane; benzene ; hexane, eth er ; acetic acid (70 : 30 : 1) . Permanent laboratory records were made by xeroxing the charred plates . A tracing of the xerox copy was photographed to produce this record . C = cholesterol S = s qualene, CP = cholesterol palmitate, CTYP = cetyle palmitate , T = triglyceride .
Top . --Lipids from the back of D . merriami fem�le (Dm �) and D . panare�ntiws fcmale (Dp <_f.) .
Bottom . - Lipids from the back of D . _!P�rriami male (Dm if} and D. panamintinus male (Dp if) .
rl , .. , ,-, ,, " "' ,,.., ,, ... ., , ... , \.- , ... ,_, ( ... , '"
'" .. _,
,, ... .,
l ... , , .... .....
'" , .. .. _, 1..) ,- , ... ... _, \ .,.'
2. 7 ApR 7/ l-In BEN 70 :30 : 1
t') {l ... -, . ( .... .. ) , __ ,
-.,. ... _, "�' \. ) I I ,_,. � -· ,-, r -, , - , , -.. - � , - , , .. , , .... , , , .... �\ (_ ) ', )\ _ _,, _ .... , _ ) ',_.
c
�-"' " - " - ' ... _, \ . ..'
S C P CYTP �Dp / 2 4
-- - - - -- -.... --, � -... - -.. , - -,,- ..._ ,-, ,- ) _ , '"' � .... , ... __ _ _ .,� ... _, ,.,. __ , ... _,) ,_.,, ... _ , , __ , \_,, - ' ... � 1 ,_, '- """
c s
,-
') , .... , , ..... , , .. \ ,-
. , ... , ... -, ,--
, , ..
, , ... , \. ' I ( J \ , I ) \ 1_1 , _ 1 \_1 \ _ _,
- .... . ,.... .... ... ... ..,_ /
c/!1., SJ
c
2.13ApR7 1 l H�� I
,. -. I I ........
r
;>o : �0 : 1
...... I I \.._,.,...
c
i
CHOL E STEROL E STER WAX E STER
T R I G LYC E R I DE FAT TY AC I D
CHOLEST EROL
CHOLEST E ROL E STER WAX E STER
TRIGLYC ERIDE
FATTY ACI D
CHOLESTEROL
48
Figure 3 . Parasagittal section of the dorsal gland of D . merriami male, showing tra.ns ition f:com groups of hair follicles in unmodified skin to enlarged ho locrine sebaceous glands in the dorsal gland area . The gla_ncl shown is typ ical of the active gland in both species . Sudan black B . Dm d" 9 4 . 15_;.& X 2 4 .
5 0
Figure 4 . Tangential section of dorsal gland of D . panamintinus male, showing holocJine papi lla . Hematoxylin and eos in . Dp c:f' 82 . 7,.,. X 2 1 6 .
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Csuti, B . A . 19 69 . Interrelationships of five species of kangaroo rats (genu s PJE.�_domys) in southern Cal ifornia . Unpubl . M. S. Thesis , San F ernando Valley State College, Northridge , Calif .
197 1 . Karyotypes of kangaroo rats from southern California . J . Mammalogy, 5 2 : 202 -206.
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Ewer, R . F . 19 68 . Ethology of mammal s . New York, Plenum Press .
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5 2
Humason, G . L . 19 67 . Animal tissue techniques . 2d ed . San Francisco , W . H. Freeman .
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Kelly, T . S . 19 69 . The comparative morphology of the male phallus in the genus Dipodomys . Unpubl . M . S . Thesis , San F ernando Valley State College , Northridge, Calif .
Manson, G . , and W . Kessler . 1940 . . Life history notes on the banner tailed kangaroo rat, Merriam ' s kangaroo rat, and the white -throated woodrat in Arizona and New Mexico . J . vVildlife Managem ent, 4 : 37 -43 .
Marler , P . , and W . J . Hamilton III . 1966 . Mechanisms of animal behavior . New York, John Wiley & Sons , Inc .
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Muller - &..::hwarze, D . 19 69 . Complexity and relative specificity in a mammalian phermone . Nature, 223 : 525 -526 .
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