Observations on garter snakes of the Thamnophis eques complex in the lakes of Mexico's transvolcanic belt, with descriptions of new taxa

64 Pages·2003·7.4 MB·English

by  Conant, Roger, 1909-2003

AMERICAN MUSEUM
Novitates
PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3406, 64 pp., 20 figures, 7 tables May 22, 2003
Observations on Garter Snakes of the
Thamnophis eques Complex in the Lakes of
Mexico’s Transvolcanic Belt, with
Descriptions of New Taxa
ROGER CONANT!
CONTENTS
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ICL AG eC MIZE G8 oe ereccers tears cpctice Sete RONPEY PURE ars cs, anaes coe he ORIOL TES Pel Paley eg ie
Thaninophis ques Culutzeoensis, NEW SUBSPECIES. «4 fe alae é 6 Sis dla le I2
Wao Ail Ce MUIRITTA , Fone Ble he yessm ea ate 52, aR a A kai usD y, gereelan ital all Wau de ny See Reee Le, 17
Bi Bard: de Patzeuaro: 8 sso. 2b tte. s nik Rhee eS a UE a DES VOR RRP eg SE 18
Thamnoplis-eques PalzCuaroensis, NEW, SUDSPECIES 2... arid bud Pa we ee week OLE hee 19
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‘Research Associate, Division of Vertebrate Zoology (Herpetology), American Museum of Natural History; Ad-
junct Professor, Department of Biology, University of New Mexico.
Copyright © American Museum of Natural History 2003 ISSN 0003-0082
2 AMERICAN MUSEUM NOVITATES NO. 3406
TRENOPUIS CQUES TUSHETATUIS; DEW SUDSDECIOS. 20: oh, BS errr ag? Wee tee tow, Coe eS 26
sa CES Cc WS aI VEIC ORC ANT, Bia Boers msc r TREES peg ga2 2 ice ede gina Del Gm MO cP wo fa FM nate Rr gee 27
Blilagocde © napalar near S Merc corse sey peg tay cease aire ak cle eclera ree Mere eat oe wea en Fairy sf 29
Thamnopnis. eques ObScuras, NEW SUDSPECIES 4a FA oe 4 ee eh np pee ee 29
Lass Caguiias-dé: Atotonileo- sya Cap ttre oo ance aan ale gcac ea mee's oe nae Gh ikh l arte teenage ee cate BS
TLR ATINOPUTS. CQUCS-GHAVIGLIS, MEW SUDSPECICS Pi cha cres lel ee alee iW wer eostshchas tests a7.
Pe) sao cea ARS core" te cee ve RRR oP aa acsecs, & comenets pI te Se I PRR Sista aes 2 sororone ricci 42
TRAMAOPIIS CGueS SCOHTIMEM SUDSPCCIES: stoner etek Hina wineries, AL eae See ee e 45
FRETHATKG secre) 5h iGe ieV n hohe alge hy ey acts uae oer ees, Uae Ulan he Was Jey.i m eae es eRC eg ek pe Il Bete we, 50
ETRValle:dé: MECxICOS g.38 lep 55 4 chk Rote Ge SERED RONAN Gg TR Sot A Pera D5 als oun ene DEL E 2 50
aM ASU Ce NCAT NCTN eelae neo 4 yest y BI Sia se lia tyB e PINEAL ge ye, cinta dsE A Re aaa ago chot ee 51
Thamnophis eques -carmenensis, NEW SUDSPECIES 2.56 ose ee eae es eae eee es a2
cel C060 << A Rede tt Pen Bee eee PUP ek aOR, citeT ete ae Pe Oru, ANY, 2 tak PEN Dy.
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FASCTA IO E cic Leintete Samet Ble e Secdeh Peed wana icles EES eter ce ed Cas Yt gare EE 58
‘ablessai-Scutelhationy, 3.9et. ace y yur oe eas. + xcecorycu cite NY EO PIS Says. 2 conecize”y 29
Ute TER PLOnAtOn n AL, pe: Fiti abet a 15 Al see a ee Ele a iar a, A ee ee 59
PAE IO NVC CV MITOTIDS: —u de he Sos Nn cae Bete aa ie foF atih ach con e a ie 0: See ee teem £2s use ncle atis Sat-% 59
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eete) Cdel1 G eae ae ORS ee eee Ln ELE Se OP RL Oe EA Cy aS he, MRR rie 62
This report is dedicated to my late wife, Isabelle Hunt Conant, who was
my constant companion during our full year of peregrinations throughout
Mexico. Her presence has caused me to use the plural pronouns ‘‘our’’ and
‘““we” many times in my text. She shared our hardships, hazards, and
triumphs. She ran the camp, tended to our culinary needs, photographed
habitats and living examples of our catch, including all the photographs that
appear in this publication, and helped in too many ways to list. This analysis
of the garter snakes of the Thamnophis eques complex across Mexico’s
transvolcanic belt would not have been possible without her constant and
enthusiastic support. We were pair-bonded and always acted as one. I deeply
regret that she did not live to see this opus, the result of our joint efforts.
2003 CONANT: GARTER SNAKES IN MEXICO’S TRANSVOLCANIC BELT
ABSTRACT
There are many isolated endorheic lakes in the transvolcanic belt of Mexico, which are
the result of volcanism or extreme flooding. Organisms living in the lakes have had ample
time to differentiate, and endemism is well known and documented, especially among the
fishes. Other organisms also show endemism, including salamanders, crayfish, and even birds
and mammals. The same is true for the garter snake, Thamnophis eques (Reuss). Seven new
subspecies are described in this paper, each from a different lake or from the remnants of a
former large lake. Based on morphological differences in coloration and pattern, they are
Thamnophis eques cuitzeoensis from El Lago de Cuitzeo, Thamnophis eques patzcuaroensis
from El Lago de Patzcuaro, Thamnophis eques insperatus from La Laguna de Zacapu, Tham-
nophis eques obscurus from El Lago de Chapala, Thamnophis eques diluvialis from Las
Lagunas Atotonilco and Cajititlan and several isolated localities, Thamnophis eques scotti
from El Lago de Magdalena, and Thamnophis eques carmenensis from La Lagunilla del
Carmen. Among six of these, series of specimens were collected and studied in detail. The
seventh (insperatus) is known only from a single imperfect individual.
RESUMEN
Hay muchos lagos endorhéicos en el cinturé6n transvolcanico de México, que son el resultado
de vulcanismo e inundaciones extremas. Los organismos que viven en los lagos han tenido
un tiempo amplio para diferenciar, y el endemismo ha sido bién documentado, especialmente
para los peces. Otros organismos también exhiben endemismo, entre ellos, salamandras, lan-
gostinos, e incluso aves y mamiferos. Lo mismo es cierto de la culebra ranera, Thamnophis
eques (Reuss). Siete nuevas subespecies se describen en este papel, cada una de un lago
distinto o de los remanentes de lo que fue un gran lago. Basado en diferencias morfolégicas
de coloraci6n y patroén, estas son Thamnophis eques cuitzeoensis de El Lago de Cuitzeo,
Thamnophis eques patzcuaroensis de El Lago de Patzcuaro, Thamnophis eques insperatus de
La Laguna de Zacapu, Thamnophis eques obscurus de El Lago de Chapala, Thamnophis eques
diluvialis de Las Lagunas de Atotonilco y Cajititlan y varias localidades aisladas, Thamnophis
eques scotti de El Lago de Magdalena, y Thamnophis eques carmenensis de La Lagunilla del
Carmen. De cada una de seis de estas subespecies, una serie de ejemplares fue colectada y
estudiada en detalle. La séptima (insperatus) es conocida de un solo ejemplar en mal estado.
INTRODUCTION did fieldwork, chiefly in the early 1960s, at
a number of lakes in or close to the trans-
In essence, this is a historic review of volcanic belt, including Alchichica, Atoton-
some of my work on natricine snakes in ilco, Cajititlan, Chapala, Cuitzeo, Patzcuaro,
Mexico. Beginning in 1949 and continuing Yuriria, and remnants of Magdalena and To-
through 1965, my late wife, Isabelle Hunt tolcingo. We also briefly explored the highly
Conant, and I undertook fieldwork with the saline and nonproductive Laguna Sayula, but
objective of studying geographical distribu- we failed to reach the lagunas San Marcos
tion and speciation among the water and gar- and Zirahuén because their access roads were
ter snakes of the genera Natrix (= Nerodia) choked by deep mud. We visited what was
and Thamnophis inhabiting Mexico. Our 10 left of Texcoco and Xochimilco, and planned
trips were mostly lengthy, but they varied in to return to all those areas and as many other
duration from a few days to more than two lakes as possible. After our 1965 expedition,
months; in all, we spent a full year in the however, my administrative duties at the
field in Mexico. We visited all 31 states and Philadelphia Zoo increased so enormously
the Federal District, and amassed a large rep- that we were unable to visit Mexico again,
resentative collection of both genera that was except for a brief vacation excursion to Creel
deposited in the herpetological collection of and the Barranca del Cobre in the state of
the American Museum of Natural History. Chihuahua.
During our peregrinations in Mexico we A number of papers based on our activities
- AMERICAN MUSEUM NOVITATES NO. 3406
in Mexico have been published, as well as scribe herein was widely accepted three de-
those listed in the References. The most thor- cades ago. Several herpetologists have es-
ough was a monographic review of the water chewed subspecies in recent years, but the
snakes (Conant, 1969). Similar lengthy con- status of that category has been restored by
tributions on Thamnophis eques, T. melano- a blue-ribbon “‘Standard Names’’ committee
gaster, and T. rufipunctatus, three species of sanctioned by the Society for the Study of
garter snakes that occupy the water snake Amphibians and Reptiles, the American So-
niche over wide areas of Mexico, were con- ciety of Ichthyologists and Herpetologists,
templated, but I was forced eventually to and the Herpetologists’ League (Moriarty,
abandon them because of lack of time. The 2001).
extraordinary variations in coloration and Descriptions of the lakes and their envi-
pattern of the populations of 7. eques in the rons where we collected reflect conditions as
lakes of Mexico’s transvolcanic belt have they were during the early 1960s, although I
continued to intrigue me, however, and I have added some recent information.
herewith summarize many facts about those
snakes and their environments, the lakes that PROCEDURES
vary greatly from one another.
It was our practice, while in the field, to
Because our fieldwork in the many isolat-
preserve most material in formalin for later
ed lakes, or remnants thereof, was terminated
transfer to alcohol. The largest and most pho-
in the 1960s, I am nearly 40 years in arrears.
togenic snakes and all gravid females, how-
It would be helpful to return to Mexico, but
ever, were transported alive to our bases at
current restrictions concerning collecting and
the Philadelphia Zoological Garden and the
personal physical handicaps preclude any re-
Spacious study in our residence. At the latter,
sumption of the activities that Isabelle and I
portrait photography could be done under
endured and enjoyed so many years ago. Fur-
studio conditions. Both at home and in my
ther, the lakes are under severe anthropogen-
office at the zoo, I maintained series of cages
ic pressure. More water is being diverted for
where the snakes were observed and where
human use from many; others suffer from
young were born. Neonates were weighed
pollution, including the inflow of raw sew-
and measured as soon as possible. Many also
age, silting, the development of eutrophic
were photographed, and pertinent details, in-
conditions, and the introduction of exotic
cluding coloration and pattern, were record-
species of fish. Alterations in the environ-
ed. Incidentally, live captives, whenever pos-
ment were evident to us in the 1960s, but
sible, were preserved immediately after shed-
they are continuing with increased velocity
ding their skins in an effort to reduce shed-
(Chaco6n, 1993; Leon and Escalante, 1993;
ding in the bottle and loss of scales, when
Lyons et al., 1998; Flores-Villela, personal
the snakes needed to be handled at later
commun.).
dates.
From the above circumstances, it became
apparent that I should prepare this paper as
INSTRUMENTS USED FOR RECORDING DATA
though it were written a few years following
our fieldwork, and in a style then prevalent. We recorded temperatures of air, water,
After much thought and consultation with and snakes, as well as the relative alkalinity
several colleagues, I decided to compile the of the lakes and other bodies of water where
following text, in part, as a historic record we worked. Because I briefly summarized
based almost exclusively on our own abun- our methods and procedures previously for
dant material and other specimens in the water snakes, Natrix = Nerodia (Conant,
American Museum collection. I have chosen 1969: 127-128), I quote as follows:
to consider the new taxa described below as Temperatures were obtained through the use of
subspecies, even though I can demonstrate quick-recording thermometers distributed by the
morphological intergradation in some in- Schultheis Corporation of Brooklyn, New York. Wa-
stances but not in others. They are obviously ter temperatures were usually noted at a depth of one
or two inches beneath the surface. Air temperatures
closely related (see The Species Model). The
were taken within one foot of the surface and shaded,
use of subspecific names for the taxa I de- if necessary, by my own shadow. Most were recorded
2003 CONANT: GARTER SNAKES IN MEXICO’S TRANSVOLCANIC BELT 5
at night, and care was taken to make sure the instru- an intergrading population, and the reference
ment was perfectly dry so the reading would not be to figure 4 follows the name of the lake.
affected by evaporation. Temperature of a snake was
made by inserting the bulb in the cloaca and keeping
the fingers as far removed as possible in order to ne- PROBLEMS
gate heat transfer from them to the body wall of the
live snake and secondarily to the thermometer. It was our practice to photograph samples
Power of hydrogen readings were obtained of each population of Thamnophis eques as
through the use of a pHydrion paper dispenser (AB
soon as possible after our return from Mex-
pH 1-11) manufactured by the Micro Essential Lab-
ico. It could be done quickly and easily in
oratory, Inc., Brooklyn, New York.
our home studio. I often preserved such
All snake temperatures were taken as
specimens as soon as we knew we had good
quickly as possible after capture. Because
pictures. Sometimes the AMNH numbered
garter snakes are chiefly diurnal, air and wa-
tags did not arrive for weeks, and because
ter readings were made virtually simulta-
we always had series of adult specimens and
neously during daylight hours.
cage space was at a premium, I could not
Unless otherwise stated, lengths of speci-
always be sure which number was assigned
mens are total lengths. In those with incom-
to the animal portrayed. That proved embar-
plete tails the numeral is followed by +.
rassing when it came time to prepare the fig-
ures to accompany this report. In an effort to
ILLUSTRATIONS remedy the situation I examined dozens of
Isabelle took many black-and-white field preserved specimens, usually in vain because
pictures and studio close-ups of snakes and of look-alikes and postmortem changes. As
other amphibians and reptiles we collected. a result, the AMNH numbers are missing
We had experimented in depth with color from several specimens shown on the illus-
film while working on our field guides dur- trations. Sex, locality, and live lengths are
ing the 1950s and 1960s, but found it unsat- included for all, however, inasmuch as those
isfactory. Pictures or slides returned to us data were typed on the negative holders.
from commercial developers were invariably Another problem arose because we took
off-color. The enormous recent improve- all gravid females back alive with us. These
ments in film, lenses, cameras, and especially gave birth to their litters and several adults
the skill of developers were not available to were kept alive for observation, often with
us at the time we were working in Mexico. live males, and they bore young again in sub-
Isabelle executed the color plate that accom- sequent years. As a result, we eventually had
panies this report by using the same tech- a plethora of neonates of a few taxa (207 of
nique of applying watercolor dyes to toned the population named herein as Thamnophis
black-and-white prints that she employed in eques diluvialis, for example). It was futile
our field guides (Conant, 1958, 1975). All to tag and make scale counts on all of them.
illustrations herein, unless otherwise credit- So there are a number of untagged neonates
ed, are by Isabelle Hunt Conant. in the AMNH collection, but most of them
Colors were recorded from live snakes, or bear locality data and dates.
more frequently from specimens that had just My unexpected major chore of having to
been euthanized but before they were pre- take over the management of the Philadel-
served. Care was taken to avoid snakes ap- phia Zoological Garden as acting director
proaching ecdysis. I recorded the colors in immediately after our return from Mexico in
my notes or wrote them on photographic 1965 prevented my close attention, as in pre-
matte prints of the animals involved. Specific vious years, to the snakes I kept alive. In-
color names are from the 1115 swatches pub- evitably, some data were lost, as well as a
lished by Ridgway (1912). female that had given birth to young.
Illustrations of each taxon are noted below Whenever we stopped in Mexico near vil-
the appropriate new names. Also included for lages we invariably were joined by small
quick orientation are references to pertinent boys who seemed to be drawn to us as
maps or habitat pictures. An exception in- though we were magnets. Some, especially
volves the Laguna Yuriria in which there is along the highways, were looking for pro-
6 AMERICAN MUSEUM NOVITATES NO. 3406
pinas (tips) in exchange for favors—helping eques are summarized briefly as follows: Ho-
to change a tire, for example. Farther away, lotype soft and end of tail missing (head—
they sensed adventure and stayed with us for body length 639 mm). Body shriveled in
hours. Sometimes we could put them to work SMF 17180. In both males, the tail tip had
doing minor chores, but when they joined us been desiccated in life and subcaudals were
at night while we were snake hunting they uncountable (head—body lengths 509 and 539
could be unmitigated nuisances. That was the mm, respectively). Maximum number of dor-
case when two boys spoiled my once-in-a- sal scale rows 21 in all three snakes. Ventrals
lifetime chance to study a ball of snakes near 153 in the female holotype, and 164 and 167
Magdalena, Jalisco. in the males, respectively. Pale lateral stripe
on third and fourth scale rows, only third row
USE OF THE NAME posteriorly. Pale middorsal row occupying
THAMNOPHIS EQUES vertebral and most of the paravertebral rows
on both sides of the body.
The taxonomy of the garter snakes was Rossman et al. (1996: 171, 175) reviewed
long confused, partly because many of the the synonymy and commented on the variety
species are similar in appearance and scutel- of names that were applied over the years to
lation, and partly because many of the early the species of garter snake now known as
museum specimens were in such poor or fad- Thamnophis eques.
ed condition that it was difficult to study If time had permitted, I had intended to
them. Some early workers, including G.A. search for color and pattern characteristics
Boulenger, according to Smith (1951), even among our live and freshly preserved mate-
lumped together several closely related spe- rial to assist in separating T. eques eques
cies and subspecies from the southwestern from T. eques megalops. They are now rec-
United States and Mexico. ognized as two subspecific forms solely on
Hobart M. Smith, long a leading authority the basis of ventral and subcaudal counts that
on Mexican herpetology, validated eqgues as widely overlap (Smith, 1942: 115). Smith
the proper specific name by resurrecting Col- discussed them under Thamnophis m. ma-
uber eques Reuss, described in 1834. Smith’s crostemma, now a synonym of eques.
(1951) conclusion was accompanied by a re-
production of a photograph of the type spec-
THE SPECIES MODEL
imen labeled, in part, ““Senckenberg Muse-
um, No. 7209a’’. That number has since been Thamnophis eques is a relatively large gar-
changed, as I discovered while on a tour of ter snake that attains a known maximum
European zoos. I spent November 8, 1967, length of 1216 mm (a female from the Lago
examining natricine snakes at the Sencken- de Chapala). It is widespread in Mexico,
berg Museum in Frankfurt am Main, Ger- ranging from the vicinity of the Pico de Ori-
many. The type, an adult female, is now zaba northwestward to and through Sonora
SMF 17179. In the bottle with it was a loose and Chihuahua to Arizona and New Mexico.
tag bearing the following: ““EA. Dillenbur- Rossman et al. (1996: 173) mapped the range
ger, d. 1832 (Bttgr. Kat. 7209a)’’. There were and showed disjunct colonies in Oaxaca and
also two male paratypes (SMF 17180, Nuevo Leon.
17181) with the same accession data as the Rossman et al. also indicated the ranges of
holotype. the subspecies heretofore recognized. Tham-
Konrad Klemmer, custodian of the Senck- nophis eques eques occurred to the south and
enberg collection, stated that determining the southwest, and 7. e. megalops throughout
provenance of the type is impossible. Dillen- most of the rest of the range. The third sub-
burger was a casual (commercial?) collector. species, 7. e. virgatenuis, was described by
The best guess is that, at the early date of Conant (1963: 490) as a dark snake with an
1832, the snakes may have come from Mex- exceptionally narrow middorsal stripe; ap-
ico City or were shipped from there after be- parently it is confined to the highlands of Du-
ing obtained elsewhere. rango and Chihuahua.
My notes on the three type specimens of As the title implies, we are concerned in
2003 CONANT: GARTER SNAKES IN MEXICO’S TRANSVOLCANIC BELT 7
this paper with Thamnophis eques and its re- another. They are described in detail for each
lationships to the lakes of Mexico’s trans- taxon.
volcanic belt, lakes that because of volcanic PATTERN: A few more or less constant pat-
activity, extraordinary flooding, and isolation tern details are as follows: When three pale
under endorheic conditions for millions of longitudinal stripes are present, the central
years offer a wide variety of habitats. Spe- one occupies the middorsal row of scales and
ciation has been widespread. My studies, parts of adjacent rows depending on the sub-
based on scale counts of more than 600 spec- species involved. The lateral stripes occupy
imens and copious notes on coloration and scale rows 3 and 4 anteriorly and rows 2 and
pattern, reveal that scutellation is more or 3 or row 3 only posteriorly. Small paired yel-
less constant, whereas the snakes, even in lowish parietal spots. Labials whitish or yel-
lakes that are fairly close together, look very lowish, the sutures of the labials black. A
yellowish crescent two scales wide posterior
different. I have seven new taxa to describe.
To avoid repetition in the descriptive mat- to the temporals, followed posteriorly by a
ter below, a hypothetical Thamnophis eques black semicrescent two scales wide. When
markings are present between the light
is herewith created based on specimens from
stripes they are usually black or dark brown,
Mexico’s transvolcanic belt, but none of
paired but variable in size and position. Ven-
which is associated with any of the lakes,
ter often gray. A black crossline at the base
endorheic or otherwise. This should be con-
of each ventral, but hidden or not by the
sidered as the “‘model” of a typical Tham-
overlapping preceding scute. Underside of
nophis eques of the region. Describing its
tail, chin, and throat whitish or yellowish and
scalation and pattern characteristics will
unmarked. Anal plate similar in coloration or
serve to avoid writing details over and over
same color as venter in general.
again that are applicable to all members of
In the descriptions of holotypes in the text
the species. The composite description fol-
below all scutellation features are the same
lows.
as those in the hypothetical specimen, except
SCUTELLATION: Nine crown scutes (paired
as indicated. Patterns and coloration are de-
internasals, prefrontals, supraoculars, and pa-
scribed in full.
rietals, and a single frontal). Rostral wider
than high and barely visible from above. Two
MEXICO’S TRANSVOLCANIC BELT
nasals, the anterior bearing the nostril entire-
ly within it. Loreal subtrapezoidal, about as
A high mountainous volcanic belt crosses
wide as high. One preocular; 3 postoculars.
southern Mexico from the Pacific Ocean to
One temporal anteriorly; 2 posteriorly. Su-
the coastal plain of the Gulf of Mexico. On
pralabials 8, sixth and seventh largest, fourth the north it is bordered by the altiplano (high
and fifth entering orbit. Infralabials 10, sixth plain) and on the south by the Balsas—Tepal-
the largest, and first pair meeting on the mid-
catepec Depression. It approximates 900 km
ventral line; first five on each side in contact in extent from east to west, and is 130 km
with the corresponding chin shield. Two wide in the vicinity of Tepic, Nayarit. It
pairs of chin shields, the posterior longer
swings southward to include the Nevado and
than the anterior. Volcan de Colima, then narrows and extends
Dorsal scales carinate throughout the eastward roughly near the 19th parallel of
length of the body and most of the tail; keels north latitude. The belt is highly irregular in
weak on the first row of scales on each side shape, however, and has a northward exten-
of body. Apical pits, if present, are most apt sion that includes the towering Popocatépetl
to be found in the nuchal region. Scale rows and Iztaccihuatl southeast of Mexico City.
most frequently 21-19-17. Anal plate single The belt terminates in the east at Citlaltépetl
(undivided). Ventrals variable, subcaudals (Orizaba), the highest mountain in Mexico,
variable, and total and tail lengths variable. but with an extension north to the Cofre de
Whereas the scutellation is relatively sim- Perote. East of those two peaks is a Gulf
ilar in the separate populations, coloration Coastal Plain of variable width.
and pattern vary distinctly from one lake to The transvolcanic belt, designated as the
8 AMERICAN MUSEUM NOVITATES NO. 3406
Cordillera Neo-Volcanica by Tamayo (1949, proposed six biotic provinces for Mexico,
I: 368), is a rugged region, the highest in one of which he named the “‘Transverse Vol-
Mexico, with snow persisting on the tallest canic’’. Smith (1940), as an offshoot of his
peaks during and after the rainy season and extensive studies on the lizards of the genus
sometimes year round. In an accompanying Sceloporus, with 85 forms then known to oc-
infolded page, credited to Ramiro Robles Ra- cur in Mexico, proposed 23 regions, subre-
mos, Tamayo showed a profile of the Cor- gions, and provinces, of which several fell
dillera, a cross-section giving elevations of within the transvolcanic belt.
the highest volcanos and also indicating a Biotic provinces are now seldom used.
few cities and high-level lakes. (This profile Differences of opinion caused confusion, and
was reproduced on page 29 of the Atlas the usefulness of such designations gradually
Goodrich Euzkadi, Caminos de México, diminished.
1964, 1966.)
There are fertile valleys occupying many TRANSVOLCANIC BELT ENDEMISM
parts of the transvolcanic belt, but volcanos
of various sizes dominate much of the re- Tamayo with West (1964: fig. 4) published
gion. The Volcan Paricutin erupted in a farm- an excellent map showing a series of lentic
er’s field in 1943. At one point on the east— basins that existed circa A.D. 1500, shortly
west highway across Michoacan there is an before the arrival of the conquistadors. Those
overlook called Mirador de Mil Cumbres (a authors indicated that a large series of iso-
thousand peaks). Volcanism created many lated basins, all lying within the transvolcan-
lakes with interior drainage, and it was to ic belt, were formed when normal drainage
them that we directed a large part of our field was disrupted by volcanic activity. As an ex-
studies on Thamnophis eques. ample, they included an aerial photograph
I could be spared from my duties at the (their fig. 6) showing how a lava flow cut off
Philadelphia Zoo chiefly in late summer. a portion of the Lago de Patzcuaro to form
That coincided with the rainy season in the the Laguna de Zirahuén. Figure 1 of the cur-
transvolcanic belt when amphibians and rep- rent paper was adapted from the Tamayo
tiles were most frequently in evidence. Often with West map.
it meant, however, that we and they were ex- Robert R. Miller, a noted authority on
posed to intermittent cold rains, especially at Mexican fishes, stated (personal commun.)
high elevations, such as at the Lago de Patz- that the Rio Lerma “‘wandered all over the
cuaro at 2035 m. map.’ The Rio Lerma formerly flowed
northeastward across Michoacan, but today,
INTERNATIONAL INTEREST some millions of years later, it rises in marsh-
es and lakes east and southeast of Toluca and
The transvolcanic belt of Mexico has long flows essentially westward. A probable sce-
been an important topic for scientists of nario was that its course was blocked by vol-
many disciplines both in North America and canic upheaval, a lake formed that eventually
Europe. A considerable number of their pa- found another outlet, and the Rio Lerma fol-
pers are cited in the following text, particu- lowed a different course, often leaving the
larly those originating on this continent. Eu- lake isolated. The process was repeated at
ropean interest is reflected by the two con- successively lower elevations.
tributions of Alcocer et al. (1997, 1998), of Organisms living in the lakes have had am-
which one was printed in the Netherlands ple time to differentiate, and endemism is well
and the other in Stuttgart, Germany. The pa- known and documented, especially among the
per by Metcalfe et al. (1994) came from the fishes. Barbour (1973b: 533) analyzed the evo-
United Kingdom, and that by Tricart (1985) lution of the 18 species and 6 subspecies of
from Strasbourg, France. fishes of the genus Chirostoma in the southern
During the 1940s and thereabouts it was part of the Mexican Plateau. He wrote, “The
fashionable to create biotic provinces based Mesa Central has a long history of geological
on genera, families, or groups of animals or instability. Tectonic movements associated
plants. To cite two examples, Moore (1945) with the Laramide Orogeny, mid-Tertiary and
2003 CONANT: GARTER SNAKES IN MEXICO’S TRANSVOLCANIC BELT

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10 AMERICAN MUSEUM NOVITATES NO. 3406
Plio-Pleistocene vulcanism and mid-Pleisto- volcanic belt, three of which he personally
cene uplift and associated vulcanism have re- described as new, and two others in collab-
sulted in continuously changing drainage pat- oration with a colleague. A population from
terns. During the Tertiary and early Pleisto- the marshes at the east end of the Lago de
cene, the ancestral Rio Lerma probably flowed Chapala may now be extinct. Dickerman
westward, perhaps through a series of lakes, to (1965, 1970) also showed that endemism as
the Pacific Ocean.” Barbour (1973a: 98) also a result of splitting occurs in at least two oth-
stated, “*... in the westward flowing Lerma- er birds of the transvolcanic belt. In the first
Santiago river system and contiguous fluvial of two papers he described a new race of the
and lacustrine basins, endemism reaches ge- red-winged blackbird, Agelaius phoeniceus;
neric and familial levels.” in the second a new subspecies of the black-
Robert R. Miller, in a letter to me dated polled yellowthroat, Geothlypis speciosa. He
November 11, 1958, wrote, ‘““The Rio Lerma also called my attention to two small mam-
system, which rises above Toluca and once mals, of the genera Neotomodon and Reith-
included such lakes as Patzcuaro and Cuitzeo rodontomys, listed and mapped by Hall
. contains a fascinating fish fauna. It is the (1981), that have similarly split into two sep-
home of an endemic family of viviparous arate subspecies in parts of their wide ranges
fishes, the Goodeidae, and also of the endem- in the transvolcanic belt.
ic silverside genus Chirostoma, belonging to Crayfish of the genus Cambarellus also vary
an otherwise largely maritime family. Both from lake to lake. Two leading astacologists,
groups have flowered in what was once a rel- Horton H. Hobbs, Jr., of the U.S. National Mu-
atively unsaturated environment.”’ seum, and Alejandro Villalobos Figueroa, of
Other kinds of organisms inhabiting the Mexico’s Instituto de Biologia, agreed, but
transvolcanic belt also show endemism. The they differed on whether they were species or
late James D. Anderson, our companion in subspecies. Villalobos Figueroa (1943) pre-
the field twice in Mexico, suspected that sal- ferred subspecies, as when he described a new
amanders of the genus Ambystoma would race from the Lago de Patzcuaro. Hobbs
vary from lake to lake and also occur in (1971), in listing the hosts of ostracods from
some habitats that were unsuitable for garter the lakes, also used subspecies for the crayfish,
snakes. His ambitious plans to investigate but in later papers (Hobbs, 1972, 1974) he el-
were thwarted by his early death, but one of evated them all to full species.
his students, Salome Litwin Krebs, armed Hobbs succinctly summarized the situation
with Anderson’s notes, data, and a partially in a letter to me dated November 12, 1965,
written manuscript, joined with Ronald A. in which he wrote, ‘‘Present data indicate
Brandon (Krebs and Brandon, 1984) in de- very much the same thing that you have
scribing Ambystoma andersoni as a new spe- found with your Thamnophis eques, for at
cies. The type locality was the Laguna de least many of the lakes have their own pe-
Zacapu, Michoacan. Brandon was already culiar form of the crayfish that we are calling
aware of the new species and had previously Cambarellus montezumae.”’
begun studies in depth on the general topic Other organisms, including additional in-
and continued to do so. In his Natural His- vertebrates and vegetation, doubtless show
tory of the Axolotl and Its Relationships to splitting into two or more closely related taxa
Other Ambystomatid Salamanders, Brandon within the transvolcanic belt.
(1989: 18) listed 19 then-recognized species Flores-Villela (1993), in writing about the
of Ambystoma in Central Mexico. The status distribution and endemism of the herpetofau-
of some was in question, and a number were na of Mexico, stated:
known only from their type localities. It was
Mexico’s rugged topography has resulted in a great
obvious, however, that they collectively ex-
variety of habitats and microhabitats that are subject
hibited endemism. to variable environmental conditions. Consequently,
Robert W. Dickerman (1963) reported on there are different ecological conditions that allow the
establishment of distinct animal populations isolated
endemism among the song sparrows, Melos-
in small areas. Amphibians and reptiles are organisms
piza melodia, indigenous to the region. He
of low vagility with a few exceptions [sea snakes and
recognized seven subspecies from the trans- sea turtles]; their tolerance levels of climatic and eco-