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The Night Lizards (Xantusia) of Arizona
Fig. 1. Arizona Night
Lizard (
) with the
color pattern most
frequently seen in
adults of the species.
Robert L. Bezy
Natural History Museum of Los Angeles County,
Los Angeles, CA 90007, USA.
1. Peralta Fever1. Peralta Fever
1. Peralta Fever1. Peralta Fever
1. Peralta Fever
In 1856 Spencer Fullerton Baird described
(Desert Night Lizard) and established the family
Xantusiidae on the basis of two specimens collected by
the eccentric Hungarian naturalist János Xántus at Fort
Tejon, California (Bezy 1988; Moll 2003), but it was
to be another 75 years before Night Lizards were
eventually discovered in Arizona. In August 1931, the
peerless Southwestern herpetologist Laurence M.
Klauber and his son Philip drove from San Diego to
northeastern Arizona to document the snake dances of
the Hopi at Mishongnovi (Klauber 1932). On their
return trip, motoring through the Weaver Mts.
(Yavapai Co.), Klauber was struck by the surprising
similarity of the habitat to areas in southern California
where he was familiar with
X. henshawi
Night Lizard). A true field biologist, Klauber followed
his instincts and ignored that he was hundreds of miles
from then-known populations of any species of
. The “inventor” of road-driving for snakes
stopped his vehicle, got out, and began searching for
Night Lizards. In very little time he discovered a
that was unlike any he had seen before. Later
he remarked that the discovery of a species new to
science “was a thrill such as the collector always
anticipates but (in this settled country, at least) all too
seldom achieves” (Klauber 1931:1).
In 1931, transporting live Night Lizards across the
Lower Colorado Desert in August was no easy task, but
Klauber managed to arrive back in San Diego with three
of the six
alive in a jar he had wrapped in a cloth
and continually moistened. One of the surviving females
gave birth to two dead off-spring, leading him to
conclude that the new species, like other
, is
Although academic tenure and promotion were
not a concern for this highly successful engineer, Klauber
was quick to see the results of his research into
publication. A month and a half after his discovery in the
Weaver Mts., he published the description of the new
Xantusia arizonae
, complete with photographs of
the habitat and of a live individual, together with a
summary of what was known at the time about all
members of the genus. He listed six features of scalation
and body proportions that easily distinguished the larger,
flatter, and more boldly spotted
X. arizonae
Night Lizard) found in rock-crevices from the then-
available specimens of
Xantusia vigilis
(Desert Night
Lizard) living in yuccas. From the publication it is clear
that the rock-crevice habitat and the presence of discrete
differences in scale counts were crucial to Klauber’s
decision to recognize the new
as a distinct
species rather than as a subspecies of the more widely
distributed yucca-inhabiting
X. vigilis
. My perusal of
Klauber’s extensive publications suggests that he usually
Fig. 3. Geographic
distribution of the three
species of Night Lizards
) in Arizona.
Solid symbols indicate
populations found
primarily in rock-
crevices; hollow dots
indicate those found
primarily in decaying
plants. Lines encompass
known localities and do
not imply continuous
Fig. 2. Arizona Night
Lizards (
) with a bold
color pattern (upper)
and with a fine color
pattern (middle) similar
to that of the Desert
Night Lizard (
lower). Note the
relatively short and
narrow head of
X. vigilis
judged populations with non-overlapping
scale characters to represent separate species,
whereas he considered that subspecies
represent populations with color pattern
differences and scale counts that are
statistically different but have overlapping
ranges of variation.
Not one to rest on his achievements,
Klauber continued to explore the
distribution of reptiles in Arizona and
elsewhere in the Southwest, extending the
range of
Xantusia arizonae
southeast to the
Superstition Mts. (Pinal Co) and northwest
to the McCloud (Yavapai Co.; Klauber
1938) and Cottonwood Mts. (Mohave Co.;
Klauber 1940). He was also the first to
X. vigilis
from Arizona, finding it
under yuccas at several localities north of the Hualapai
Mts. (Mojave Co.; Klauber, 1939).
This was more or less what was known about
in Arizona when as a youngster I began
exploring lizards with my brother Bill on our
grandfather’s property in the Weaver Mts. Before I had
actually encountered my first Night Lizard there, my
grandfather started selling shares in a gold mine he had
discovered on his land and shortly thereafter was
hospitalized with a cerebral hemorrhage. The gold mine
was never re-located and unfortunately his property,
which included the type locality of
Xantusia arizonae
was sold to developers.
But my fascination with Night
Lizards continued. During my high
school years I began searching for
in central Arizona to better document
variation and distribution. With my
friend Jim Fitzsimmons, I climbed to the
summit of the Harquahala Mts. where we
Xantusia vigilis
under agaves
(reported 25 years later from the range by
Jones et al., 1982). I discovered Night
Lizards in several other ranges where they
were previously unrecorded, but despite
repeated attempts, I had not succeeded in
locating them in the Superstition Mts.
from which Klauber had reported a
specimen collected by Vic Householder.
Not to be deterred, I looked-up
Householder in the Phoenix phone book,
called to make an appointment, and
interviewed him. He reported that the
lizard had been taken somewhere deep in
the range possibly near Weaver’s Needle.
That did it. Not only were the
Superstitions and the Peralta Land Grant
alleged to be the home of the Lost
Dutchman’s Mine, an assortment of gold-
crazed murderous prospectors, and a
phantom band of Apaches, but now the area harbored
a lost
. I came down with a full-blown case of
Peralta Fever, from which I have never fully recovered.
in the Superstitions became an
obsession. When I arrived at the University of Arizona
as an incoming freshman, I asked my mentor-to-be, Dr.
Charles H. Lowe, if he knew where Night Lizards
occurred in that range. To my shock, he admitted he
did not know, but suggested I should look wherever
Rhus ovata
(Sugar Bush) is present. Some years later,
with the help of Wade Sherbrooke, I finally located
in the range, although at the time I was
worried that a sting received from a
Scorpion) might leave me the “Lost Herpetologist of the
2. Oculotaedium2. Oculotaedium
2. Oculotaedium2. Oculotaedium
2. Oculotaedium
Studying Night Lizards
from central Arizona I
was struck by the extraordinary variation in color
pattern (Figs. 1-2, 4-8). The size, number, and
arrangement of dark dorsal spots differed wildly among
individuals and mountain ranges. Some of the
differences appeared to be related to body size, as larger
individuals tended to be more boldly spotted than
smaller ones. In ranges where the lizards seemed to
attain a smaller maximum size they were less boldly
spotted. Some
Xantusia arizonae
from rock-crevice
habitats were virtually identical in color pattern to
specimens of
X. vigilis
found in yuccas. This dizzying
array of variation within and among mountain ranges
led me to the conclude that color pattern was not a
reliable feature for distinguishing the two species.
I embarked on the tedious, eye-straining task of
counting scales and measuring body proportions on
these tiny lizards to determine if there were any discrete
differences (i.e. features with non-overlapping ranges of
variation) between the samples of
from rock-
crevice habitats in Arizona and those from yuccas,
agaves, and other plants. I examined the characters that
Klauber had found useful in distinguishing
X. arizonae
X. vigilis
and added some of my own. The
resulting data were remarkably parallel to the variation I
had observed in color pattern. Lizards from some
mountain ranges reached not only larger body sizes and
had more boldly spotted color patterns, they also had
higher scale counts and relatively longer limbs and
heads compared to those from yuccas and agaves,
consistent with the original observations of Klauber
(1931). But lizards from some ranges were intermediate
X. arizonae
X. vigilis
in all external features
and the conclusion seemed inescapable that the two
forms represented the ends of an ecological and
morphological continuum and were not distinct species.
I proposed (Bezy 1967) that there were two subspecies
in Arizona:
X. v. vigilis
found in yuccas, agaves, and
other decaying plants in western Arizona from the Kofa
Mts. (Yuma Co.) north to the Hualapai Valley (Mohave
Co.); and
X. v. arizonae
found primarily in rock-crevice
habitats from the Superstition Mts. (Pinal Co.)
northwest to the Cottonwood Mts. (Mohave Co.).
3. Molecular Degeneration3. Molecular Degeneration
3. Molecular Degeneration3. Molecular Degeneration
3. Molecular Degeneration
From its kaleidoscopic pattern of variation, I
suspected that
Xantusia v. arizonae
might not represent
even a legitimate subspecies, but rather a series of
populations that had independently evolved, to varying
degrees, specializations for the rock-crevice habitat.
Perhaps it was an ecomorph, akin to dark populations
of rodents and lizards found on various lava flows
scattered across the Southwest (Norris and Lowe 1964).
To test this idea I needed to look at features of
that were independent of their physical adaptation to
rock-crevice habitats.
My first step down the slippery slope of
reductionism was to focus on chromosomes. During the
mid 1960’s, I learned techniques for preparing,
documenting, and comparing karyotypes (photographs
revealing the number, size, and shape of the
chromosomes) from Jim Patton and Jay Cole who at the
time were fellow graduate students at the University of
Arizona. This was still the “space race” era and my
research was supported by NASA. Night Lizards turned
out not to be easy subjects due to their small size and
low metabolic rate, but I succeeded in obtaining
karyotypes of 10 species of the Xantusiidae (Bezy 1972).
Among the various results was the first clue that there
were deeper differences between the Arizona
populations of
X. v. arizonae
from the Weaver
Mts. differed in the centromere position on one pair of
chromosomes from
X .v. vigilis
in the nearby Arrastra
Mts. (Yavapai Co.) and in the Kofa Mts. (Yuma Co.), as
well as from populations in the Sonoran and Mohave
Deserts of California. But this difference was
complicated by variation found elsewhere in the range of
The next step was to compare gene products
(enzymes) among various xantusiids. Working with Jack
Sites at Brigham Young University, we found a large
number of differences among three rock-crevice
populations of
in Arizona: (1) the Mazatzal
Mts. (Maricopa Co.); (2) the Weaver Mts.; and (3) the
Cerbat Mts. (Mohave Co.). The lizards from rock-
crevice habitats in the Cerbats were nearly identical in
allozymes (but not in appearance) to the surrounding
populations of
X. v. vigilis
found in yuccas in the
Mohave Desert (Bezy and Sites 1987). It was the genetic
evidence that some of the Arizona rock-crevice
populations were actually
X. v. vigils
rather than X
. v.
that provided the key piece to the puzzle.
Focusing down to the molecular level, Sinclair et
al. (2004) compared nucleotide sequences for portions
of two mitochondrial genes from 87 localities
throughout the range of
The analyses
confirmed earlier data (Bezy and Sites 1987; Papenfuss
et al. 2001) and clearly indicated that there are actually
three species present in Arizona: two found
predominately in rock-crevices (X.
, X.
and one (
X. vigilis
) occurring in yuccas and other plants
at some localities, but in rock-crevices at others. Thus I
have come full circle in my appraisal of the species status
in Arizona. But even systematists are bound
by the methods of science and must reject hypotheses
that are no longer supported by the data at hand (see
Vitt 2003 for a similar discussion on species of Night
Lizards in Arizona). The 3 species found in Arizona are
summarized below.
Fig. 4. Bezy’s Night
Lizard (
) with the color
pattern most
frequently seen in
adults of the species.
Fig. 5. Bezy’s Night
Lizard (
). An adult with
large spots.
Fig. 6. Bezy’s Night
Lizard (
Xantusia bezyi
An adult with small
Xantusia arizonae Xantusia arizonae
Xantusia arizonae Xantusia arizonae
Xantusia arizonae
Klauber, 1931Klauber, 1931
Klauber, 1931Klauber, 1931
Klauber, 1931
Arizona Night LizardArizona Night Lizard
Arizona Night LizardArizona Night Lizard
Arizona Night Lizard
As re-defined by Sinclair et al. (2004),
is known only from Yavapai Co., Arizona, where
it has been found from the Weaver Mts. to the McCloud
Mts. and associated ranges (Fig. 3; Bezy 1967; Klauber,
1931, 1939). It extends from the Saguaro-Paloverde
association of the Arizona Upland Sonoran Desertscrub
at 760 m (2500 ft) elevation to Interior Chaparral at
5000 ft (Brown 1994). The species occurs primarily in
rock-crevice habitat, but also has been found in
(Pack Rat) nests and in decaying
Yucca baccata
Yucca; Bezy 1967; Klauber 1931, 1938; Gloyd 1937
and pers. comm.; Wood 1944). This is a relatively large
species, reaching a maximum snout-vent length of 60
mm (2.4 in). Most individuals are boldly spotted, and
there is often a tendency for the
dark spots to be linearly aligned.
In many individuals there is a
pair of dark spots on the
posterior dorsal head scales (Fig.
1-2). However, some
have a finely spotted
dorsum similar to that of X.
from which they can be
distinguished only by features
of scalation, by having a
relatively longer and broader
head (Fig. 2, Bezy 1967), and
by DNA (Sinclair et al. 2004). I
have found
X. arizonae
20 km (12 mi) of X.
. The
DNA evidence strongly
indicates that the nearest relative
X. arizonae
is a species of
found in Sonora, rather
than either
X. bezyi
X. vigilis
found nearby in Arizona
(Sinclair et al. 2004).
Little is known of the biology of the species
beyond habitat and distribution. The Arizona Night
Lizard gives birth to one (3 females) or two (4 females)
young around 1 September (Brattstrom 1951; Klauber
1931). The diet consists primarily of ants, with a few
flies, beetles, bugs, and soft-bodied larvae (Brattstrom
1952; Klauber 1931).
Xantusia bezyi Xantusia bezyi
Xantusia bezyi Xantusia bezyi
Xantusia bezyi
Papenfuss, Macey, and Schulte, Papenfuss, Macey, and Schulte,
Papenfuss, Macey, and Schulte, Papenfuss, Macey, and Schulte,
Papenfuss, Macey, and Schulte,
Bezy’s Night LizardBezy’s Night Lizard
Bezy’s Night LizardBezy’s Night Lizard
Bezy’s Night Lizard
The species ranges from the Mazatzal Mts.
(Maricopa Co.) south to the Galiuros. (Pinal Co.; Fig. 3;
Bezy 1967; Johnson et al. 2001; Klauber 1938;
Papenfuss et al. 2001; Sinclair et al. 2004). It is found
from the Saguaro-Paloverde Association of the Arizona
Upland Sonoran Desertscrub at 730 m (2400 ft)
elevation, through Semi-desert Grassland to Interior
Chaparral at 1770 m (5800 ft). It occurs primarily in
rock-crevices, but also has been found in decaying
Dasylirion wheeleri
(Sotol; Bezy 1967), under plant
debris on the desert floor (Vitt 2003), and in buildings
(Don Swann, pers. comm.).
The species is quite variable in maximum body
size and in color pattern within and among localities.
The largest (maximum snout-vent length, 60 mm, 2.4
in), most boldly spotted individuals (Figs. 4-5) occur in
the northern part of the range with smaller, more finely
spotted individuals (Fig. 6) predominating to the south.
One distinctive feature of some populations is the
presence of a narrow bar across the back of the head (i.e.
immediately behind the postparietals), but this (like
virtually all features of color pattern) varies among
populations (Figs. 4-6). The northern-most population
was discovered
1971 by Laurie Vitt and Justin
Fig. 7. Desert Night
Lizard (
) with the color
pattern most
frequently seen in
adults of the species in
Arizona. Photo by Erik
F. Enderson.
Congdon and they (and Don Tinkle) originally
perceived that it represented an undescribed species
(Vitt 2003), but were dissuaded from describing it due
to the variation found in other parts of the geographic
range (Bezy 1967). The allozyme (Sites and Bezy 1987)
and DNA (Papenfuss et al. 2001; Sinclair et al. 2004;)
data indicate that all Arizona populations east of the
Verde River represent a distinct species lineage (
), but it is quite variable in external features and its
morphological diagnosis requires further study.
Nothing has been published about the biology of the
6. 6.
6. 6.
Xantusia vigilisXantusia vigilis
Xantusia vigilisXantusia vigilis
Xantusia vigilis
Baird, 1859 Baird, 1859
Baird, 1859 Baird, 1859
Baird, 1859
Desert Night LizardDesert Night Lizard
Desert Night LizardDesert Night Lizard
Desert Night Lizard
The species occurs at widely scattered localities in
western Arizona (Fig. 3) from the Cabeza Prieta Mts.
(Yuma Co.) north to the Virgin Mts. (Mohave Co.) and
east to the Sierra Estrella (Maricopa and Pinal Cos.) and
into the Grand Canyon (Coconino Co.; Bezy 1967,
1972; Jones et al. 1981,1982; Klauber 1939, 1940;
Lowe 1964; Sinclair et al. 2004; Tomko 1975). In
Arizona, It lives primarily in Mohave and Arizona
Upland Sonoran Desertscrub where it has been found
in decaying plants of the following species:
(Joshua Tree),
Y. schidigera
(Mohave Yucca),
Y. baccata
(Banana Yucca),
Agave deserti
A. utahensis
(Utah Agave),
Nolina biglovii
(Biglow nolina),
Carnegiea gigantea
cf. englemannii
(Englemann Prickly Pear) and
(Velvet Mesquite); it also occurs inside houses
(Brattstrom pers. comm.), in rock-crevices (Klauber
1940 as
X. arizonae
), and in
(Pack Rat) nests.
This is the smallest species of Night Lizard in
Arizona, reaching a maximum snout-vent length of 45
mm (1.8 in) in most populations. Color pattern usually
consists of small dark dots on a tan to gray background
and a dark edged light stripe may be present on the sides
of the neck (Figs. 2, 7). Some Arizona individuals are
virtually patternless (Fig. 8).
Populations found in rock-crevice habitats in the
eastern Hualapai, Cottonwood, and Cerbat Mts. (Fig. 3)
were formerly considered to be
Xantusia (v.) arizonae
(Bezy 1967; Jones et al. 1981; Klauber 1940). They are
intermediate in maximum size and in appearance
X. arizonae
X. vigilis
and could be viewed
as hybrids or intergrades (Bezy 1967). Evidence from
allozymes (nuclear gene products; Sites and Bezy 1987)
and mitochondrial DNA (Sinclair et al. 2004) clearly
indicates that these populations are
X. vigilis
as they lack
any genetic markers identified with
X. arizonae
. There is
an extensive literature on the species largely based on
populations in California (e.g. Zweifel and Lowe 1966;
summaries in Bezy 1882, 1988), but little is known
about the biology of the species in Arizona.
7. Conservation Status7. Conservation Status
7. Conservation Status7. Conservation Status
7. Conservation Status
None of the three species of Night Lizards found
in Arizona is currently listed as Endangered or
Threatened or as a Candidate under the Endangered
Species Act.
Xantusia vigilis arizonae
is listed as a
sensitive species by the U. S. Forest Service. A small
portion of the range of
Xantusia bezyi
is protected by its
Fig. 8. Desert Night
Lizard (
). An Arizona
individual virtually
lacking color pattern.
Photo by Erik F.
occurrence on Tonto National Monument. No species of
Night Lizards were included in the March 1996 list of
Wildlife of Special Concern in Arizona (Arizona Game
and Fish Department Non-game Branch 2004), but
AGFD regulation R12-4-303-C prohibits the use of
manual or powered jacking or prying devices to take
reptiles or amphibians, providing an important measure
of protection for
in the state.
8. Literature Cited.8. Literature Cited.
8. Literature Cited.8. Literature Cited.
8. Literature Cited.
Arizona Game and Fish Department Non-game Branch.
2004. Reptiles of Arizona. Sonoran Herpetologist
Baird, S. F. 1859. Description of new genera and species
of North American lizards in the Museum of the
Smithsonian Institution. Proceedings of the
Academy of Natural Sciences Philadelphia
Bezy, R. L. 1967. Variation, distribution, and taxonomic
status of the Arizona night lizard (
Xantusia arizonae
Copeia 1967:653-661.
Bezy, R. L. 1972. Karyotypic variation and evolution
of the lizards in the family Xantusiidae.
Contributions in Science 27:1-29.
Bezy, R. L. 1982.
Xantusia vigilis
. Catalogue of
American Amphibians and Reptiles 302:1-4.
Bezy, R. L. 1988. The natural history of the night
lizards, family Xantusiidae, pp. 1-12. In H. F.
De Lisle et al. (eds.), Proceedings of the
Conference on California Herpetology.
Southwestern Herpetologists Society Special
Publication 4:1-143.
Bezy, R. L., and J. W. Sites, Jr. 1987. A preliminary
study of allozyme evolution in the lizard family
Xantusiidae. Herpetologica 43:280-292.
Brattstrom, B. H. 1951. The number of young of
. Herpetologica 7:143-144.
Brattstrom, B. H. 1952. The food of the night lizards,
. Copeia 1952: 168-172.
Brown, D. E. 1994. Biotic Communities; Southwestern
United States and Northwestern Mexico.
University of Utah Press, Salt Lake City.
Gloyd, H. K. 1937. The Chicago Academy of Sciences
Arizona Expedition April-June, 1937. Program of
Activities of the Chicago Academy of Sciences 8:1-
Johnson, T. B., C. R. Schwalbe, R. L. Bezy, C. H.
Lowe, and R. B. Spicer. 2001. Geographic
Xantusia vigilis arizonae
Herpetological Review 32:121.
Jones, K. B., D. B. Abbas, and T. Bergstedt. 1981.
Herpetological records from central and northeastern
Arizona. Herpetological Review 12:16.
Jones, K. B., L. M. Porzer, and K. J. Bothwell. 1982.
Herpetological records from west-central Arizona.
Herpetological Review 13:54.
Klauber, L. M. 1931. A new species of
Arizona, with a synopsis of the genus. Transactions
of the San Diego Society of Natural History 7:1-16.
Klauber, L. M. 1932. A herpetological review of the
Hopi snake dance. Bulletin of the Zoological Society
of San Diego 9:1-93,
Klauber, L. M. 1938. Notes from a herpetological diary.
I. Copeia 1938:191-197.
Klauber, L. M. 1939. Studies of reptile life in the arid
Southwest. Bulletin of the Zoological Society of San
Diego (14):1-100.
Klauber, L. M. 1940. Notes from a herpetological diary,
II. Copeia 1940:15-18.
Lowe, C. H. 1964. Amphibians and reptiles of Arizona,
pp. 153-174.
C. H. Lowe (ed.), The Vertebrates
of Arizona. University of Arizona Press, Tucson. x +
270 pp.
Moll, E. O. 2003. János Xántus and Fort Tejon or how
the Night Lizards got their name. Sonoran
Herpetologist 16:26-29.
Norris, K. S,. and C. H. Lowe. 1964. An analysis of
background color-matching in amphibians and
reptiles. Ecology 45:565-580.‘
Papenfuss, T. J., J. R. Macy, and J. A. Schulte. 2001. A
new lizard species in the genus
Arizona. Scientific Papers of the Natural History
Museum, University of Kansas 23:1-9.
Sinclair, E. A., R. L. Bezy, K. Bolles, J. Camarillo R.,
K. A. Crandall, and J. W. Sites. 2004. Testing
species boundaries in an ancient species complex
with deep phylogeographic history: genus
(Squamata: Xantusiidae). American
Naturalist 163:396-414.
Tomko, D. S. 1975. The reptiles and amphibians of the
Grand Canyon. Plateau 47:161-166.
Vitt, L. J. 2003. Secrets in the rocks, p. 209.
E. R.
Pianka and L. J. Vitt, Lizards. Windows to the
Evolution of Diversity. University of California,
Berkeley. xii + 333 pp.
Wood, S. F. 1944. The reptile associates of wood rats
and cone-nosed bugs. Bulletin of the Southern
California Academy of Sciences 43:44-48.
Zweifel, R. G., and C. H. Lowe. 1966. Ecology of a
population of
Xantusia vigilis
, the Desert Night
Lizard. American Museum Novitates 2247:1-57.
... Since Klauber's 1939 report of Desert Night Lizards in Arizona, our knowledge of the distribution of the species in the state has grown steadily. It is now known at many localities in western Arizona scattered from Utah to Sonora (Fig. 3; Klauber 1940;Bezy 1967Bezy , 1982Bezy , 2005Lowe 1964;Tomko 1975;Jones et al. 1981Jones et al. , 1982Bezy and Sites 1987;Smith et al. 2008). ...
... Decaying branches and trunks of Joshua Trees Desert they have been found in decaying Desert Agaves (Agave deserti; Fig. 6) and Saguaros (Carnegiea gigantea) in the Estrella, Harquahala, Kofa, Castle Dome, Cabeza Prieta, and Tinajas Altas mountains (see also Bezy 2005 andSmith et al. 2008). Packrat (Neotoma spp.) nests provide important habitat throughout the range (Zweifel and Lowe 1966). ...
... v. vigilis), found in yuccas and agaves predominately in the Mohave Desert, rather than Arizona Night Lizards (X. v. arizonae), found mostly in rock crevices in central Arizona (see Bezy [2005] for additional details and discussion of Xantusia in Arizona). At about this time, a second population of X. vigilis south of the Gila River was discovered by Clay May in the Cabeza Prieta Mountains in far western Arizona. ...
... The map also suggests sympatry for X. arizonae and X. bezyi, when in fact these two species are allopatric (separated by the Verde River). The triangle icon marking the type locality for X. bezyi is misleading in that this species is now known from several other sites, all east of X. arizonae, which is restricted to the McCloud, Weaver, and Date Creek mountains (Bezy, 2005). In addition, contrary to the authors' statement (p. ...
The thermal quality of the habitat is key for the regulation of body temperature in terrestrial ectotherms and, therefore, permits them to carry out their fundamental biological activities. In thermally heterogeneous environments, ectotherms might follow different behavioral or physiological strategies to maintain their body temperature within biologically adequate boundaries, for which they depend on microhabitat selection. These aspects are, thus, relevant in the context of habitat degradation and land-use change. In this study, we characterized the thermal ecology of three lizard species (genus Xantusia) that differ in microhabitat use along the Baja California peninsula, Mexico. We made three predictions: (1) the three species will follow different thermoregulatory strategies according to habitat thermal quality; (2) the thermal requirements and tolerances of these species will match the environmental or microenvironmental thermal conditions; and (3) due to their habitat and range restriction, the species studied will be highly vulnerable to climate change. Our results indicate the existence of thermoregulatory mechanisms in Xantusia to face thermal heterogeneity, including behavioral thermoregulation by choosing different microhabitats, shifts in activity periods, and adaptation to particular high thermal quality microhabitats. Furthermore, despite their association to specific microhabitats and specialized physiology, the studied species will not be adversely affected by climate change, as the increased microenvironmental temperatures will lead to a higher habitat thermal quality and lower costs of thermoregulation. However, we do not discard other indirect adverse effects of climate change not considered in this study.
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Analysis of seven morphological characters in eight granite-dwelling and five yucca-dwelling populations of night lizards from Arizona and California reveals an ecologically-based morphological gradient from a "granitoform" to a "yuccaform" morphotype. The intermediate position of a population along this gradient is correlated with (1) occurrence in both yuccas and granite, (2) occurrence in small fields of poorly exfoliated granite, and (3) ecogeographic and genetic continuity with essentially yucca-dwelling populations. The conspicuous morphological, ecological, and genetic continuum between Xantusia vigilis and X. arizonae indicates that the two taxa are conspecific. Xantusia vigilis arizonae is a valid subspecies, and is convergent with X. v. sierrae of the Sierra Nevada in California.
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Identification of species in natural populations has recently received increased attention with a number of investigators proposing rigorous methods for species delimitation. Morphologically conservative species (or species complexes) with deep phylogenetic histories (and limited gene flow) are likely to pose particular problems when attempting to delimit species, yet this is crucial to comparative studies of the geography of speciation. We apply two methods of species delimitation to an ancient group of lizards (genus Xantusia) that occur throughout southwestern North America. Mitochondrial cytochrome b and nicotinamide adenine dinucleotide dehydrogenase subunit 4 gene sequences were generated from samples taken throughout the geographic range of Xantusia. Maximum likelihood, Bayesian, and nested cladogram analyses were used to estimate relationships among haplotypes and to infer evolutionary processes. We found multiple well-supported independent lineages within Xantusia, for which there is considerable discordance with the currently recognized taxonomy. High levels of sequence divergence (21.3%) suggest that the pattern in Xantusia may predate the vicariant events usually hypothesized for the fauna of the Baja California peninsula, and the existence of deeply divergent clades (18.8%-26.9%) elsewhere in the complex indicates the occurrence of ancient sundering events whose genetic signatures were not erased by the late Wisconsin vegetation changes. We present a revised taxonomic arrangement for this genus consistent with the distinct mtDNA lineages and discuss the phylogeographic history of this genus as a model system for studies of speciation in North American deserts.
The colors of living amphibians and reptiles have been studied, using a General Electric recording reflectance spectrophotometer. The animals were brought to activity temperature levels and the appropriate surface pressed over the reflectance port of the machine while a color record was taken. Background samples from the localities at which the animals were taken were also recorded. Reptiles and amphibians living on backgrounds of relatively uniform color tend to match that background through superposition with considerable fidelity. The animal's color curve is superimposed over that of the background. Ventral color in most forms tested was lighter than the dorsal surfaces of the same animal. It was darker only in some forest-dwelling salamanders and in desert lava-dwelling species. The difference results primarily from the highly reflective ventral surfaces of these forms. The ventral surfaces of white-bellied amphibia show clear oxyhaemoglobin absorption peaks, as do the dorsal surfaces of some amphibia. These effects are entirely absent in curves recorded from reptiles. It is concluded that the degree of background color-matching is related to: (a) the degree of color uniformity of the animal's background, (b) the degree of exposure of the color-matched species to predator, (c) the illumination level prevalent in the habitat, (d) the size range of the color-matched species, (e) the ecological restriction of the species, (f) the qualities of the visual apparatus of predators upon the species, and (g) the adaptive compromise struck by the species. The size of a color-matched animal, or the size of the part of its body that is normally exposed, is related to the point at which such color-matching breaks down. This point of just noticeable difference between animal and background is also determined by the wave-length discrimination curves of the predators, the closeness of the match involved, the uniformity of the background color and its texture, and the presence of absence of concealing patterns. Background color-matching varies greatly in its degree of perfection. This variation is the result of adaptive compromise and balance between this adaptive characteristic and many others that in one way or another affect its complete expression.