Table Of ContentAMNHNOVITATES novi 00170 Mp 1
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PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3297, 37 pp., 5 figures, 8 tables June 28, 2000
Systematics of the Smooth-Toothed Pocket Gopher,
Thomomys umbrinus, in the Mexican
Transvolcanic Belt
ALONDRA CASTRO-CAMPILLO1 AND JOSE´ RAMI´REZ-PULIDO1,2
ABSTRACT
Difficulties in the subspecific identification of more than 200 specimens of Thomomys um-
brinusfromtheStateofTlaxcalaledustoexaminethesystematicstatusoftheeightsubspecies
recognized within the Mexican Transvolcanic Belt. We gathered representative samples of
those subspecies ((cid:1) 50) during three years of fieldwork. These were analyzed together with
samples from other populations not previously assigned to subspecies, as well as voucher
specimens from several collections. Thirty-seven variables, obtained from 1145 specimens,
wereanalyzedmorphometricallyusingunivariateandmultivariatestatistics.Within-population
variationwashighlyinfluencedbysexualdimorphism,andespeciallybyontogeneticvariation;
therefore, these two factors should be considered carefully when making systematic and tax-
onomic decisions. Our analysis of geographic variation determined only two recognizable
subspecies of Thomomys umbrinus within the Mexican Transvolcanic Belt:Thomomysumbri-
nus umbrinus (Richardson, 1829) and Thomomys umbrinus pullus Hall and Villa, 1948.
RESUMEN
Dificultades en la identificacio´n subespec´ıfica de ma´s de 200 espec´ımenes de Thomomys
umbrinus del estado de Tlaxcala, nos llevaron a examinar el estado sistema´tico de las ocho
subespecies reconocidas en el Eje Volca´nico Transversal. Obtuvimos muestrasrepresentativas
de esas subespecies ((cid:1) 50) durante tres an˜os de trabajo de campo. Estas fueron analizadas
junto con muestras de otras poblaciones no asignadas previamente a las subespecies y ejem-
1DepartamentodeBiolog´ıa,UniversidadAuto´nomaMetropolitanaUnidadIztapalapa.Apdo.Postal55-535,09340
Me´xicoD.F.
2ResearchAssociate,DivisionofVertebrateZoology(Mammalogy),AmericanMuseumofNaturalHistory.
Copyright(cid:2)AmericanMuseumofNaturalHistory2000 ISSN0003-0082/Price$4.70
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2 AMERICAN MUSEUM NOVITATES NO. 3297
plares de referencia de varias colecciones. Treinta y siete variables fueron obtenidas de 1145
ejemplares y fueron analizadas morfome´tricamente utilizando estad´ıstica uni y multivariada.
La variacio´n intrapoblacional resulto´ altamente influenciada por el dimorfismo sexual, pero
especialmente por la variacio´n ontogene´tica; por ende, estos dos factores deben ser conside-
radoscuidadosamentecuandosetomendecisionessistema´ticasytaxono´micas.Nuestroana´lisis
de la variacio´n geogra´fica determino´ que so´lo pueden reconocerse dos subespecies de Thom-
omys umbrinus en el Eje Volca´nico Transversal: Thomomys umbrinus umbrinus (Richardson,
1829) y Thomomys umbrinus pullus Hall y Villa, 1948.
INTRODUCTION graphic but not necessarily a genetic isola-
tion nor a wider morphological variation.
A large and highly heterogeneous sample Therefore,wedecidedtoallocatetheTlax-
of Thomomys umbrinus from Tlaxcala in- calan specimens according to the morpho-
cluded the whole variety of diagnostic char- metric variation of the subspecies within the
acters for the eight subspeciesacknowledged MTB, expecting that our results would mo-
in the MTB, Mexican Transvolcanic Belt, tivate a thoughtful study of variation in this
(Nelson and Goldman, 1934; Hall and Villa, taxon throughout its range. Such scope
1948).Infact,theTlaxcalanspecimenscould would enable greater comprehension of the
be assigned to any of the following subspe- systematics and taxonomy ofThomomysum-
cies: Thomomys umbrinus albigularis from brinus in the MTB. It might also contribute
Hidalgo; Thomomys umbrinus martinensis to a better understanding of the role of sub-
and Thomomys umbrinus orizabae from speciesasameansofrecognizinggeographic
Puebla; or Thomomys umbrinus vulcanius variants of the species (Mayr, 1969). This is
from Me´xico (Hall, 1981). possible if the subspecies is regarded ascon-
Examination of most of the holotypes and specific populations sharing their genetic
topotypes of the subspecies from the MTB pool through gene flow (Smith and Patton,
housed at National Museum of Natural His- 1988; Patton and Smith, 1989), on one hand,
tory (USNM) and the American Museum of but which have a particular morphometric
Natural History (AMNH), made clear the variation because they are adjusted to the
qualitativeness of the diagnostic characters. habitat conditions in their geographic area
For example, Thomomys umbrinus, vulcan- (Grinnell, 1935; Yates and Schmidly, 1977;
ius, T.u.tolucae,T.u.martinensis,T.u.um- Honeycutt and Schmidly, 1979; Patton and
brinus,T.u.albigularis,andT.u.peregrinus Smith, 1990).
are similar both in shade and in cranial char- Afterthreeyearsoffieldwork,wegathered
acteristics. In fact, some T. u. albigularis large sample sizes (n (cid:1) 50) along the MTB.
lack the allegedly diagnostic white spot on In addition, voucher specimens from the
theirthroat(NelsonandGoldman,1934),but MTB were examined in several collections.
some T. u. peregrinus and all of those of T. Qualitative examination of collected and
u. vulcanius do have it. In T. u. orizabae,the voucher specimens showed that persistence
holotype and most of the topotypes differ of morphological features was not consistent
from the preceding by their melanic shade; within a particular locality; on the contrary,
however, melanic individuals were also the variation was generally noticeable. The
found among Tlaxcalanspecimensaswellas only exception was the distinctlysmall-sized
in T. u. pullus collected in Michoaca´n. specimens of T. u. pullus. Moreover, in ad-
Those qualitative characters, togetherwith dition to the overlapping morphological var-
the apparently isolated distribution of the iation among the samples from MTB, stan-
populations along the MTB, were previously dard karyotypes and allozymic data showed
used in designating seven of the eight sub- no distinctions among some of them (Hafner
species in the MTB (Merriam, 1893; Bailey, et al., 1987). That is, T. u. pullus (Pa´tzcuaro,
1915; Nelson and Goldman, 1934). Since Michoaca´n), T. u. tolucae (Toluca, Me´xico),
only small sample sizes (n (cid:2) 15) were ex- T.u.vulcanius(Amecameca,EstadodeMe´x-
amined, investigators emphasized a geo- ico), and T. u. umbrinus (Boca de Monte,
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Veracruz) belong to the same chromosomic Hoffmeister, 1969; Patton and Dingman,
(NF (cid:1) 78) and allozymic groups (Hafner et 1968;Patton,1973;PattonandSmith,1990).
al., 1987). These data together certainly do Furthermore, changes includethesubsequent
not suggest distinct species, and perhaps not reorganization of the involved subspecies.
even separate subspecies. Before conclusive evidence was gathered
Therefore, the objective here was to ex- (Patton and Dingman, 1968; Patton, 1973;
amine geographic variation among the pop- PattonandSmith,1990)toformallyconsider
ulations of Thomomys umbrinus in the Mex- them as separate species (Patton, 1993),Hall
ican Transvolcanic Belt. Morphometric anal- (1981) combined Thomomys umbrinus with
yses include the eight previously recognized Thomomys bottae and included 229 subspe-
subspeciesandpopulationsnotpreviouslyal- cies.Therefore,thedistributionofThomomys
located from the states of Me´xico, Michoa- umbrinus started north of the United States
ca´n, and Tlaxcala. and extendedalongtheCalifornianmountain
ridges and the Sierra Madre Occidental and
DIAGNOSTIC CHARACTERS, TAXONOMY, AND Sierra Madre Oriental, all the way down to
DISTRIBUTION the MTB.
OF THOMOMYSUMBRINUS The distribution is discontinuous, particu-
larly in thestates oftheMexicanPlateauand
Thomomys umbrinus is a rodent speciesof the MTB. The presence of arid zones and,
fossorial habits belonging to the Geomyinae probably, the presence of some species of
within the Geomyidae. The genus is charac- Cratogeomys (Hall, 1981) have contributed
terized (Hall, 1981) by its small size and by to this pattern. Indeed, Nelson and Goldman
the rather delicate structure of its hands with (1934) noted that Cratogeomys merriami
fine claws, as opposed to the robust hands merriami restricted the distribution of Thom-
with strong claws of other genera (Geomys omys at 11,500 ft in the Popocatepetl Vol-
and Cratogeomys). The genus Thomomys cano, and that Cratogeomys tylorhinus plan-
does not show the basitemporalfossalocated iceps did the same at 8600 ft in the Nevado
between the lower third molar (m3) and the de Toluca Volcano. Observations by Nelson
lingual face of the coronoid process is rather and Goldman (1934) were confirmed during
a slight depression in some specimens in the fieldwork, especially in the Valley of Me´xi-
United States. Thomomys has the front sur- co, where Cratogeomys occurs in many lo-
face of the upper incisors smooth, but with a calities in which Thomomys umbrinus is no
very fine groove toward the inner limit, longer found.
while the other genera of the family have ei- Simpson (1961) strongly criticized the
ther one (Cratogeomys, Pappogeomys and large number of subspecies allocated to
Zygogeomys)ortwowell-defined(Orthogeo- Thomomys umbrinus (Smith and Patton,
mys) grooves. In addition, the third upper 1988), and in so doing, he placed this taxon
molar (M3) is elliptic, monoprismatic, and in the midst of a debate on the validity of
similar to the other two upper molars (M1, the subspecies (Grinnell, 1935; Davis, 1938;
M2) in Thomomys. Conversely, in othergen- Wilson and Brown, 1953; Brown and Wil-
era the M3 is rather biprismatic and differs son, 1954; Simpson, 1961; Choate and Wil-
from the M1 and M2 (Hall, 1981). liams, 1978; Smith and Patton, 1988; Patton
Within the genus, systematic and taxo- and Smith, 1990). In fact, studies by Patton
nomic status of Thomomys umbrinus has un- et al. (Patton, 1973; Patton and Feder, 1978;
dergonenumerouschanges(HallandKelson, Hafner et al., 1987) have raised new ques-
1959; Anderson, 1966; Hoffmeister, 1969; tions about the taxonomic and systematic
Patton and Dingman, 1968; Patton, 1973; population status of this species. Hafner et
Hall, 1981; Ram´ırez-Pulido et al., 1996). al. (1987) found three chromosomic groups
Such changes include: (1) synonymy with within Thomomys umbrinus that show genic
other congeneric species (Bailey, 1915; Hall differentiation at the allozymic level, sug-
and Kelson, 1959; Hall, 1981) and (2) rec- gesting more than one species of pocket go-
ognition of Thomomys bottae and T. town- pher as currently recognized.
sendii as separate species (Anderson, 1966; After the separation of Thomomys umbri-
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4 AMERICAN MUSEUM NOVITATES NO. 3297
nus and Thomomys bottae, 47 subspecies 1 million years (Fa and Morales, 1991, De-
fromthe78occurringinMexico(Hall,1981) mant, 1978; Nixon et al., 1987; Pasquare´ et
have been allocated to the latter (Patton and al., 1987a, 1987b) in the MTB.
Smith, 1990; Patton, 1993; Ram´ırez-Pulido Specimens were collected in the second
et al., 1996). Therefore, T. umbrinus is rep- through fifth districts recognized by Demant
resented by the remaining 31 subspecies (1978) in the MTB. The second district in
which occur along the Sierra Madre Occi- the east shows numerous monogenetic cones
dental from southern Sonora downward to and, except the Tanc´ıtaro Hill in Michoaca´n,
Durango and Nayarit. In the Mexican Pla- there are no stratified volcanoes. Four large
teau, the species is distributed in patchy ar- stratifiedvolcanoesarelocatedfromthethird
rangements in Chihuahua and Coahuila in to the fifth districts at the center of the MTB
the north but in more isolated populations in (Nevado de Toluca, Popocatepetl, Iztacc´ı-
Zacatecas, Aguascalientes, San Luis Potos´ı, huatl, and La Malinche) and oriented in a
and Guanajuato in the center. In the Sierra north-south direction within the lake depres-
Madre Oriental, T. umbrinus extends from sion corresponding to the Sierra Nevada.
mid-Coahuila to Nuevo Leo´n. The species Other small sierras, among which Chichi-
wasreportedtooccurintheMTBwithiniso- nautzinisfound,runinanortheast-southwest
lated populations in Michoaca´n, Me´xico, direction, on fissures closer to the southern-
Distrito Federal, Morelos, Tlaxcala, Puebla, most portion of the Valley of Me´xico. In the
Hidalgo, and Veracruz (Hall, 1981). fifthdistrict,theCofredePerote-PicodeOri-
The eight subspecies occurring in the zaba volcano chain, which is a recent lava
MTB (Hall, 1981) are Thomomys umbrinus cone on an older volcano, runs eastward.
umbrinus (Richardson) in Veracruz; Thomo- The sampled zones have a temperate cli-
mys umbrinus orizabae Merriam in Puebla; mate with rainfall at the end of spring and
Thomomys umbrinus peregrinus Merriam in fall, and the northern portions arelesshumid
Distrito Federal, Hidalgo, Me´xico, and Mo- than their southern counterparts. The annual
relos; Thomomys umbrinus albigularis Nel- average temperature is generally about 18(cid:2)C,
son and Goldman in Hidalgo, Puebla, and but it decreases as altitude increases(Garc´ıa,
Veracruz; Thomomys umbrinus martinensis 1981). The predominant vegetation in the
in Puebla; Thomomys umbrinus tolucae Nel- studiedareas(Rzedowski,1978)isoakforest
son and Goldman in the state of Me´xico; (Quercus sp.), pine-oak (Quercus-Pinus sp.)
Thomomys umbrinus vulcanius Nelson and and pine-spruce (Pinus-Abies religiosa) as
Goldman in Me´xico, Morelos, and Puebla; well as pine forest with fodder grass (Muhl-
and Thomomys umbrinus pullus Hall and enbergia sp. and Festuca sp.). Because the
Villa in Michoaca´n. parent rock is volcanic, the ground is sandy
near the volcanic uplifts and more clayey in
STUDY AREA the lower regions.
The Mexican Transvolcanic Belt (MTB) METHODS
includesthehighestregionsofMe´xico(2000
to 5650 m), located between 19(cid:2) and 20(cid:2)N COLLECTING AND EXAMINING SPECIMENS
and 96(cid:2) and 105(cid:2)W, and crossing thecountry Previously, specimens from the study area
from ocean to ocean. From west to east, the were less than 15 in most collections and no
volcanoes related to this study are Nevado extensive morphometric work had been con-
de Toluca (4624 m), Popocatepetl (5452 m), ducted. Therefore, we decided to collect in-
Iztaccihuatl (5460 m), La Malinche (4461 tensively and to examine voucher specimens
m), and Pico de Orizaba (5700 m). The re- in several mammal collections. After three
gion is 130 km deep and more than1000km years of exhaustive fieldwork, more than 50
long. It is bounded by the Sierra Madre Ori- representative samples of most of the rec-
ental in the east, by the Sierra MadredelSur ognized subspecies were obtained from the
in the south, and by the Sierra Madre Occi- type locality and neighboring areas. The two
dental in the west. There areabout 1000vol- exceptions were T. u. martinensis (n (cid:1) 47)
canoes from the Quaternary Age of lessthan and T. u. umbrinus (n (cid:1) 5). Specimens were
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alsocollectedfromunsampledareasbetween was also checked for sexual differences(i.e.,
populations of the recognized subspecies in alargerpubicforamenandawidersimphysis
the states of of Me´xico, Tlaxcala, and Mi- in females); however, if the postcranial skel-
choaca´n. Such samples suggest gene flow eton was not available,the specimenwasex-
among all populations of Thomomys umbri- cluded.
nus in the MTB. In total, 857 specimens Hair color of holotypes, topotypes, and
were gathered from 67 localities in thestates other specimens (n (cid:1) 76, 55(cid:3); 21(cid:4)) was
of Hidalgo, Me´xico, Michoaca´n, Morelos, reviewed. We looked for qualitative taxo-
Puebla, Tlaxcala, and Veracruz. The collect- nomic characteristics that might distinguish
ed specimens were prepared as skins and the subspecies. Likewise, in order to obtain
skulls (Hall, 1981; Ram´ırez-Pulido et al., data about the habitat and the exact capture
1989) and they are housed at Coleccio´n de localities,theoriginalcollectors’notesonthe
Mam´ıferosdelaUniversidadAuto´nomaMe- specimens were reviewed. Among others,
tropolitana, Unidad Iztapalapa (UAMI). The notes of W. Dalquest in 1946 (KU), S. An-
skulls were cleaned with dermestid beetles derson in 1952 (KU), and E. W. Nelson in
(Hall and Russell, 1933; Ram´ırez-Pulido et 1892 (USNM), were examined.
al., 1989).
In addition, 288 specimens from nine lo- MEASUREMENTS
calities, were examined in other collections:
Coleccio´n de Mam´ıferos del Laboratorio de Four conventional external measurements
Cordados Terrestres, Escuela Nacional de (Hall, 1981) together with 33 skull measure-
Ciencias Biolo´gicas, Instituto Polite´cnico ments (fig. 1) were recorded from eachspec-
Nacional (CB) at Me´xico City; American imen. The external measurements are the to-
MuseumofNaturalHistory(AMNH)atNew tal length of the body (TOL); length of the
York; National Museum of Natural History, vertebral tail (LVT); length of the right hind
SmithsonianInstitution(USNM)atWashing- foot (HFT); and length of the ear (LOE).
ton, D.C.; Texas Cooperative Wildlife Col- Measurements were taken from the skin la-
lections (TCWC) of the Texas A&M Uni- bels of voucher specimens.
versity in College Station; Museum of Nat- Someskullmeasurementsweretakenfrom
ural History (KU) of the University of Kan- the literature (Thaeler, 1968; Heaney and
sas, Lawrence. Among specimens in other Timm, 1983) and others were suggested by
museums, most holotypes (USNM) and sev- Dr. Michael Smolen (Texas A&M Universi-
eral topotypes (AMNH, CB, KU, UAMI) of ty, Nov. 1989). However, most measure-
the mentioned species were examined. Ex- ments were selected during direct examina-
ceptions include the holotype of Thomomys tion of the specimens by one of us (ACC).
umbrinus pullus, at the University of Mich- Cranial measurements (fig. 1) were taken
igan, and that of Thomomys umbrinus um- withcalipersandrecordedtothenearest0.01
brinus, at the Natural History Museum,Lon- mm. The following list contains the names
don. andabbreviationsofmeasurements(numbers
We examined 1145 specimens of Thomo- in parentheses correspond to fig. 1).
mys umbrinus from 76 localities in the six
mentioned states. However, the number of BRAINCASE AND ROSTRUM
specimens included varied with the type of
statistical analysis. In addition, some very GLS (1–1(cid:3)) greatest length of skull
young specimens or damaged skulls were LNA (1–2) length of nasals
eliminated. The numbers of specimens in LMX (2(cid:3)–2(cid:4)) length of maxilla
LFO (3–3(cid:3)) length of frontal
each calculation is mentioned inthemethods
LZA (4–4(cid:3)) length of zygomatic arch
or in the tables for each study.
LBC (4–5) length of braincase
Sex of most specimens was gatheredfrom ICO (6–6(cid:3)) interorbital constriction
museumcatalogsandlabels.Inthefewcases WRO (7–7(cid:3)) width of rostrum
in which sex was unrecorded, the skins were AZB (8–8(cid:3)) anterior zygomatic breadth
examined for evidence such as well-devel- MZB (9–9(cid:3)) medial zygomatic breadth
opedscrotumornipples.Thepelvicstructure PZB (10–10(cid:3)) posterior zygomatic breadth
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6 AMERICAN MUSEUM NOVITATES NO. 3297
SBP (11–11(cid:3)) skull breadth across parietals State of Mexico, during the three years of
(i.e., braincase) fieldwork. Fortunately, 40 individuals refer-
LDI (12–12(cid:3)) length of diastema able to T. u. martinensis were located at the
LMT (12–13) length of molar toothrow
USNM.
LPF (14–14(cid:3)) length from the pterygoid fossa
Nelson and Goldman (1934) described
to the basioccipital
BAM (15–15(cid:3)) breadth across molars (M1-M1) Thomomys umbrinus orizabae and, especial-
BAB (16–16(cid:3)) breadth across bullae ly, T. u. tolucae and T. u. vulcanius with im-
BOP (17–17(cid:3))breadthacrossbasioccipitalpro- precise localities. Therefore, our sampling
cesses was conducted as close as possible to the lo-
HRO (18–18(cid:3)) height of rostrum calities described in the fieldnotes. Accord-
HMC (19–19(cid:3)) height of maxillary crests ingly, specimens of T. u. orizabae were ex-
MHS (20–20(cid:3)) maximum height of skull amined from Miguel Hidalgo y Costilla,
HBP (21–21(cid:3)) height from the bulla to the pa- Puebla. In the state of Me´xico, we collected
rietal
specimens of T. u. tolucae at several locali-
ties near the Nevado de Toluca Volcano, and
MANDIBLE
the same was done with T. u. vulcanius at
BCP (22–22(cid:3)) breadth across coronoid pro- the Paso de Corte´s.
cesses Sampled localities (SL) are mappedinfig-
BJT (23–23(cid:3)) breadth across jaw teeth (m2- ure 2 and are detailed underExaminedSpec-
m2)
imens. Samples of Thomomys umbrinus col-
AWD (24–24(cid:3)) anterior width of dentary
lected in zones not previously recorded, but
GWM (25–25(cid:3)) greatest width of mandible
MWD (26–26(cid:3)) medial width of dentary which were in the gaps between two recog-
GLD (27–27(cid:3)) greatest length of dentary nizedsubspecies,areconsideredtobevouch-
LCP (28–28(cid:3)) length to coronoid process ers for corridors of genetic continuity be-
BML (28–29) basal mandible length tween the eight subspecies inhabiting the
DHI (27–30) dentary height from basis of in- MTB (fig. 2).
cisive alveolum
AHM (28–31) anterior height of mandible NONGEOGRAPHIC VARIATION
PHM (29–28(cid:3)) posterior height of mandible
Individual variation,ontogeneticvariation,
andsexualdimorphismwereexaminedinthe
SAMPLED LOCALITIES
population of the Sierra de Tlaxco, Tlaxcala
Sampling was carried out within: (a) lo- (n (cid:1) 356). We considered fouragegroups(1
calities represented by few specimens (n (cid:5) (cid:1) young; 2 (cid:1) subadults; 3 (cid:1) adults;4 (cid:1) old
50); (b) localities in potential corridors for specimens) among 214 females and 142
gene flow among previously recognizedsub- males according to the expansion of the zy-
species;(c)localitiesstilloccupiedbyThom- gomaticarchesand theelongationoftheros-
omys umbrinus; or (d) topotypic localitiesof trum relative to the braincase (Castro-Cam-
subspecies not represented in Mexican col- pillo et al., 1993).
lections (i.e., T. u. albigularis, T. u. marti- Individual variation in each external and
nensis, T. u. orizabae, T. u. pullus, T. u. to- cranialmeasurementwasanalyzedbyobtain-
lucae, and T. u. umbrinus). ing the standard statistics (mean, x¯; standard
In the field, we noticed that T. u. albigu- error, SE; minimum value, MIN; maximum
laris, T. u. pullus, and T. u.martinensiswere value MAX; coefficient of variation, CV)
becoming scarce at the type localities. This with the routine PROC UNIVARIATE SAS
rarity results from habitat modifications and (SAS, 1985). These analyses also served to
from displacement by Cratogeomys merria- corroborate the normal distribution of the
mi. In fact, only one topotypical femaleofT. data and helped in finding outlier values.
u. albigularis from the National Park ‘‘El We determined ontogenetic or age varia-
Chico,’’ at the Sierra de Pachuca, Hidalgo, tionandthepresenceofsecondarysexualdi-
was collected and most of the 58 inividuals morphism for each taxonomic character,
ofT.u.pulluswerecollectedatLosTanques, through a one-way analysis of variance with
Michoaca´n. We collected no specimens of T. ANOVA routine. When significant differen-
u. martinensis at San Martin Texmelucan, ces (p (cid:5) 0.05) between ages or sexes were
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Fig. 1. Cranial measurements (33) taken in 1145 Thomomys umbrinus from 72 localities in the
Mexican Transvolcanic Belt. A, a: dorsal view; B, b: ventral view; C, c: lateral view. See pp. 13 – 15
for explanations of measurements.
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8 AMERICAN MUSEUM NOVITATES NO. 3297
found, Duncan’s Test for Multiple Means or GEOGRAPHIC VARIATION
Tukey’s Test for the Student-Type Range
(PROC GLM) were used, respectively (Ott, We examined the morphometric similari-
1984), in order to determine subgroups tiesamongthepopulationsofThomomysum-
among the means. brinus from the MTB by arranging the sam-
We considered age variationseparatelyfor plelocalities(n(cid:1)76)into17grouplocalities
males and females and, at the beginning, all (GL, table 1, fig. 2). Both nearness and eco-
of the specimens were included. However, logical homogeneity were considered in at-
since young (age class 1) became separated tempting to selectgroupswithnogeographic
from the others in 86.65% of all features,we orecologicalbarriersthatwouldrestrictgene
eliminated class 1. Both analyses are pre- flow within each group (Patton and Smith,
sented, but emphasis is given from subadults 1990).
on (age classes 2–4). Accordingly, for sec- Based on the analysis of intrapopulation
ondary sexual dimorphism, analyses includ- variation, we calculated the nature and mag-
ed each age group separately, and the young nitude of geographic variation of T. umbri-
specimens were excluded. nusintheMTBseparatelyforbothsexesand
We ran two-way analysis of variance fol- age classes (2–4).
lowed by Duncan’s test (PROC GLM) to de- Statistical programs exclude individuals
termine the effect of sex, age, and the inter- lacking information in any of the variables;
action between sex and age on the variance therefore, to include the greatest number of
in the examined sample (Hollander, 1990; specimens and GLs, a regression analysis
Stangl et al., 1991). In Duncan’s tests on sex (PROC GLM, SAS) was developed to esti-
and age, only the specimens aged 2 and up mate themissingvaluesinindividuals.Spec-
were considered. Finally, in order to under- imens lacking more than two measurements
stand the role played by sex, age, and their were excluded from the analysis (n (cid:1) 30).
interaction within total nongeographic vari- Likewise, some measurements were elimi-
ation in Thomomys umbrinus, we analyzed nated because they were missing in several
the components of the variance (Straney, specimens (BCP, BJT, AWD,GWM,MWD);
1978; Leamy,1983;PattonandSmith,1990) were too variable (TOL, LVT, HFT, LOE;
using the VARCOMP routine. BOP; and BML); contributed no information
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Fig. 2. Group localities (GL’s) analyzed in the geographic variation of Thomomys umbrinus from the Mexican Transvolcanic Belt.Numbered 0
dots signal sample localities according to specimens examined in text. Circling lines show the group localities according to table 1. F01
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10 AMERICAN MUSEUM NOVITATES NO. 3297
todifferentiateamongtheGLs;orwerehigh- and Legendre, 1992) and to compare the re-
ly correlated to other variables like MWZ sults, Mantel’s tests were developed on the
and PWZ (R (cid:1) 0.8, Castro-Campillo et al., correlation and similarity matrices (Mantel,
1993). 1967; Rohlf and Fisher, 1968; Sokal, 1979;
Geographic variation was examined by Smouse et al., 1986).
univariate and multivariate statistical analy- Furthermore, a classification discriminant
ses. Standard statistics were calculated for analysis (DISCRIM, SAS) was used to de-
each variablewithUNIVARIATE(SAS)and termine the number of specimens correctly
then a one-way ANOVA (GLM, SAS) was assigned accordingtotheacknowledgeddes-
run to disclose significant (p (cid:5) 0.05) inter- ignation or to the GL of origin (Castro-Cam-
population differences among means of the pillo et al., 1993). This analysis also deter-
GLs. This analysis was completed by Dun- mined the degree of overlap among the GLs
can’s Test for Multiple Means (SAS) to find because of misclassified specimens (Castro-
population subgroups with no significantdif- Campillo et al., 1993).
ferences.TheANOVAwasmadeontheGLs Finally, a brief analysis relatedpelagecol-
having four or more specimens. oration to original descriptions (Nelson and
Principal Components Analysis (PCA) Goldman, 1934; Hall and Villa, 1948). For
with the PRINCOMP (SAS) routine on the thisanalysis,onlythetypespecimensandthe
measurements of each specimen determined material deposited at UAMI were reviewed.
thetrendsinthevariationpattern.Resultsare Pelage shade is described according to
summarized in a bidimensional graphic of Smithe (1974a, 1974b) with the names and
the first (PC I) and third (PC III) principal color numbers in parentheses after the de-
components where the distribution of each scription.
GL is represented by polygons with their re-
spective centroids. We present PC III instead SPECIMENS EXAMINED
of PC II in this plot for the sake of clarity,
since in the plot of PC I vs PC II, there was Group localities of previously recognized
an overall massive overlapping of the poly- subspecies and other populations of Thomo-
gons. We developed another PCA on the mys umbrinus examined along the MTB are
population measurements of the GLs and for listed from west to east according to table 1
thetridimensionalrepresentationofthisanal- and figure 2. Taxonomic names are followed
ysis, we used the statistical package Numer- by the abbreviated (table 1) and the spelled-
ical Taxonomy System NT-SYS (Rohlf and out name corresponding to the group locali-
Kishpaugh, 1972; Rohlf, 1988). A minimum ties (GLs) mentioned in tables, figures, and
spanning distance tree (MST), calculated text. Next, thetotalnumberofspecimensex-
from the correlation matrices, was projected amined is indicated in parentheses. Within
onto the first three PCs (Gower and Ross, the sampled localities (SL), the type locality
1969; Rohlf, 1970, 1973, 1975). In thatanal- isindicatedbyanasteriskandiftheholotype
ysis, as in the rest of the multivariate anal- was examined, its sex, age, catalog number,
yses, all specimens were included. and the abbreviation for its institutional lo-
Cluster analyses were run on the sample cation are indicated also after the name of
meansofallthevariablesineachGL(Sneath the GL. The SLs are preceded by their as-
and Sokal, 1973), using NT-SYS program. signed number according to figure 2 and fol-
Group populations with a greater phenetic lowed by the number of examinedmales((cid:4))
similarity were obtained, using the average and females((cid:3)),andhousingmuseuminpa-
taxonomic distance as a similarity measure- rentheses.
ment and the unweighted pair-group method Thomomys umbrinus pullus. P (cid:1) Pa´tzcuaro
based on arithmetic averages (UPGMA). We (45). Michoaca´n: 2. – 7 km SE Pa´tzcuaro,
followed this procedure for all age groups 2380 m * (8(cid:3) 5(cid:4) CB); 3. – Los Tanques,
withsexesseparate,aswellasin12localities 2450 m (21(cid:3) 11(cid:4) UAMI).
where subadult (2) and adult (3) specimens Thomomys umbrinus ssp. N (cid:1) Cerro de San
werecollected.Thecopheneticcoefficient(r) Andre´s (26). Michoaca´n: 4. – Laguna
of each phenogram was calculated(Lapointe Verde, 12.5 km N, 18 km W Cd. Hidalgo,
