B.
c. melanogaster Natural History Articles
We
wish to thank Jim Pomaville, Jr. for kindly providing this article. A
New Subspecies of The
species Boa constrictor as currently recognized, with its many and varied
mainland and insular races, has one of the largest distributions among
land-dwelling vertebrates. Almost
central to the historically accepted range of the species and nestled
against the eastern flank of the Andes in Ecuador is a little-known
population that has the highest meristic count for circumferential body
scales and a readily recognizable and distinctive color and pattern.
This subspecies is herein named Boa constrictor melanogaster
and is compared to all its conspecifics recognized as valid taxa in the
last century. The
boa constrictor of legend and of popular literary and cinematographic
infamy bears little relation to the peaceful and handsome creature so
familiar to hobbyists and to scientists who have knowledge of the
herpetofauna of tropical America. The
species' formal description is attributed to Linnaeus as Boa
constrictor in 1758, although a long list of literary references
dating from 1648 is given by Bibron and Dumeril (1844).
Since 1758 the species has been juggled between the generic
assignments of Boa and Constrictor on a frequent basis as
the result of a probably irresolvable difference of opinion as to the
systematic relationships of the American tree boas, Corallus caninus,
C. enydris, and C. annulatus (Forcart, 1951).
For the moment I accept the present consensus that Boa is
the best generic assignment for the boa constrictor. Following
Linnaeus's original description, a number of additional populations were
given specific recognition but later were relegated to subspecific status
when the mainland ranges were found to be continuous so that, with the
exception of the isolated insular races, a large clinal entity seems to
exist. Boa constrictor is a remarkably adaptable species and
ranges from sea level to elevations of at least 350 meters (Lazell, 1964;
Duellman, 1978), with its southernmost range approximately 35degrees South
latitude in Argentina and the northernmost range nearly 30degrees North
latitude in western Mexico. Cope
(1877) records B. c. ortonii ( = B. c. imperator)
from 3000 feet (923 meters), which, if correct, is probably far above the
habitat of most populations of the species.
Although never really aquatic, the species inhabits wet tropical
jungles, rain forests, xeric (dry)
jungles (Yucatan), and even
the deserts of Sonora (Mexico) and coastal Peru, where remarkable upper
and lower extremes of temperature tolerance are required. Repeated
trips to Ecuador have drawn my attention to a distinctive population of Boa
constrictor that needs formal recognition-not only to facilitate the
scientific study of the species and its ecological associates, but also to
provide a reference to a race that has assumed the dubious distinction of
being the most desirable and valuable boa constrictor to reptile
collectors and exhibitors. Prior
to my trip to Ecuador in 1968, I'm not sure anyone realized that the
so-called "red-tailed boas" were actually a stable population
rather than exceptionally handsome individuals of an extremely variable
species. Since neither a
formal description nor a valid scientific name has ever existed for this
population, the trade has sold these animals under various names such as
"red-tailed boas" or "Peruvian red-tailed boas."
Erroneously, the specimens were labeled as Boa constrictor rubricauda
(a name having no apparent validity) or as B. c. ortonii or B.
c. amarali (both
legitimate scientific names but for pallid races totally different from
the strongly patterned red-tailed creature being offered for sale). To
further complicate matters, the boas offered for sale as "red-tailed
boas" actually seem to represent two different stocks.
The one described herein as B.
c. melanogaster has a deep mahogany-red coloration to the tail
blotches, but the other has a bright orange-red color to the tail on a
body typical in all other respects of the boas of the Amazon basin
referred to Boa constrictor constrictor.
For this reason I have decided to avoid the confusion that
continued use of the name "red-tailed" would be certain to
engender among collectors and have named the Ecuadorian race the
black-bellied boa, based upon a character quite reliably used to
differentiate it from the eastern Amazonian population.
With a formal name available and access to the identifying
characteristics provided herein, hobbyists should be able to be certain
that they are getting what they are paying for, and both the hobby and the
scientific communities will hopefully have a better understanding and
appreciation of the entire species complex. Boa constrictor Holotype. -Adult female, University of Michigan Museum of
Zoology (UMMZ) 172680, total length 233 cm.
Collected by Jivaro Indians in December, 1968, near the Rio Yaupi
Catholic Mission upstream from the Rio Santiago in the Morona Santiago
province of Ecuador. Topoparatypes.
- UMMZ 172676-172679 and 172681; also University of Kansas Museum of
Natural History (KU) 192081-192083. Etymology.-The subspecific name melanogaster literally translated means
"black belly" and refers to the nearly uniform distribution of
black pigmentation over the ventral surfaces of adults of this race. Diagnosis.-Boa constrictor melanogaster has the smallest and the most
numerous dorsal body scales of all the conspecifics, ranging from 86-94 in
circumferential count. The
dorsal pattern between head and anus consists of 20-21 dark blotches or
saddles that at their narrowest (usually the tenth blotch behind the head)
are typically only 4-7 scale lengths long at midbody (Fig. 3). These dorsal body blotches are usually very dark blackish
brown on a gray to pale yellow ground and typically show no light-colored
centers in the area dorsal to the vertebral column.
Shortly before the anus, the dorsal blotches become elongate and
are almost circular in outline on the tail.
These posterior dorsal blotches and their lateral counterparts are
usually black-bordered with mahogany-red centers. The Description of the holotype (Figs. 1, 2, and 3).-UMMZ 172680 is an adult female
of total length 233 cm and has a complete tail. Circumferentially there are 72 neck scales, 94 scales at the
level of the tenth dark dorsal blotch behind the head, and 45 scales at
the anus. There are 244
ventral scutes and 49 subcaudals. The
tenth dark dorsal blotch is 5 scale lengths long at its narrowest
transect. Variation.-Scutellation varies among the nine specimens (the holotype and eight
topoparatypes) as follows: circumferential body scales at the neck 69-74
(avg. 71.1), at midbody (= tenth dorsal dark blotch) 86-94 (avg. 89.6), at
the anus 43-49 (avg. 46); ventral scutes 237-252 (avg. 241.5); subcaudal
scutes 45-54 (avg. 49.7). The tenth dark dorsal blotch varies in its
narrowest transect from 4-7 scale lengths (avg. 5.7). Distribution.-Although all the type specimens came from the vicinity of the
convergence of the Rio Yaupi and the Rio Santiago in the Morona Santiago
province in Ecuador, the author has seen and examined identical material
from Tena on the Rio Napo in the Napo province of Ecuador. Also, the photograph on page 225 of Duellman (1978) would
indicate that the range continues northward in the Napo province to Santa
Cecilia on the Rio Aguarico. The
Amazonian jungles of eastern Ecuador are still relatively inaccessible, so
the eastern limits of the range of B.
c. melanogaster will remain unknown for some time.
It can be expected that the range will overlap into the adjacent
Amazonian areas of southern Colombia and northern Peru. Comparison The
relationships of the races or subspecies of Boa constrictor to one
another can only be understood if one realizes that all the mainland races
form a continuous clinal entity-each race merges genetically with one or
more adjacent races. In the
traditional sense, only the insular races B.
c. sigma, B.
c. sabogae, B. c. orophias,
and B. c. nebulosa are
perhaps worthy of subspecific status, having gene pools isolated from
continuous genetic drift. Even
so, these isolated gene pools are undoubtedly diluted and in all
probability were established when tropical storms carried specimens of
mainland Boa constrictor to these remote habitats.
The following remarks when used with the key and Table 1 should
help considerably to clarify the relationships and physical
characteristics of the published subspecies of Boa constrictor.
(1) B. c. constrictor Linnaeus, 1758 is the only subspecies with which B. c. melanogaster
is likely to be confused. B.
c. melanogaster differs
from this subspecies by having more dorsal scale rows at midbody, 86-94
(avg. 89.6) versus 81-89; In most of
the literature, the higher midbody scale counts for B. c. constrictor
of up to 95 (Boulenger, 1893; Lazell, 1964) are suspect as being
representative of specimens now being assigned to B c. melanogaster.
No specimens of B. c. constrictor
known to this author exceed 88 dorsal scale rows, and Stull (1932)
accepted 89 as the upper limit for this taxon without dealing with the
higher counts of earlier authors. Unquestionably,
B. c. constrictor
is the race to the east of B. c.
melanogaster and probably to the north as well, separating it from B.
c. imperator. (2)
B. c. occidentalis
(Philippi, 1873) is a southern neighbor in Bolivia and Argentina of B.
c. melanogaster and, due to the upper range of its dorsal scale
counts (reported to be as high as 87 but unverified by me), populational
intermediates may exist. When
compared to B. c. melanogaster,
the more typical lower range of the extremely variable (65-87, per
Boulenger, 1893) dorsal scale counts and the always higher (22-30) dorsal
blotch count of B. c. occidentalis
suggest to me that B. C. imperator may have in ancient times moved
across the Andes from the west and become the phylogenetic source of B. c. occidentalis
and B. c. amarali. The
geographical barrier of the present Andean range raises formidable doubts
to such a hypothesis, and I am not sufficiently knowledgeable to defend
the hypothesis myself. Schmidt
and Walker (1943) suggest that Peruvian faunal elements are known to have
moved eastward from coastal Piura and Lambayeque and westward from
Amazonian Cajamarca through Andean passes below 8,000 feet (=2,500
meters). These particular passes are too far north to support the
present hypothesis, which probably would require passage across the Andes
farther to the south, perhaps in Chile (south of 35 degrees South
latitude) where the Andean chain once again is crossed by passes at low
elevations (Schmidt and Walker, 1943; Duellman, 1979).
This latter possibility means, of course, that historically the
coastal population of B. c. imperator had to have ranged much farther to the south than
its present terminus near Libertad, Peru, which does not seem implausible
to me. In
B. c. occidentalis
the dorsal blotches almost always include light middorsal pattern
elements, and the blotches are interconnected with one another and with
the lower lateral blotches to form a dark reticular pattern of great
complexity (Fig. 6). Occasionally
in B. c. melanogaster the dorsal blotches coalesce
dorsolaterally to form a simple chain-like pattern (Fig. 1). (3)
B. c. amarali
(Stull, 1932) is known from southern Brazil, eastern Bolivia, and Paraguay
and would not seem to be related to B. c. melanogaster, having only
71-79 dorsal scale rows versus 86-94 in the latter.
However, one of Stull's paratypes (UMMZ 68005) of B. c. amarali from
Buena Vista, Department Santa Cruz, Bolivia, has the distinctive dorsal
pattern of B. c. melanogaster,
although in scale counts it conforms to its type series. B. c. amarali
typically also differs from B. c. melanogaster in its pallid
coloration and in having more numerous (22 or more) dorsal blotches (Fig.
7) At middorsum the blotches are usually more than 10 scale lengths long,
versus 4-7 in B. c. melanogaster. (4)
B. c. imperator (Daudin,
1803) probably has no direct genetic influence on
B. c. melanogaster,
with which it shares no common borders to their ranges.
B. c. imperator inhabits the tropical Pacific coast of South
America northward throughout most of Central America and Mexico.
B. c. imperator
almost certainly is the original stock for the taxa that follow (# 5-13),
with all of which it shares proximal ranges, 22 or more dorsal blotches,
and fewer than 80 dorsal scale rows.
All are easily differentiated from B. c. melanogaster, which
has 21 or fewer dorsal blotches and 86 or more dorsal scale rows.
See the accompanying key for the criteria to differentiate those
latter taxa that are considered valid. (5)
B. c. orophias (Linnaeus,
1758) is an insular race restricted to Saint Lucia in the Caribbean.
Much confusion exists in the older literature regarding its
distribution, but Lazell (1964) cleared this up to the satisfaction of
most workers. See the key and
Table 1 for diagnostic characters. (6)
B. c. diviniloqua (Dumeril
and Bibron, 1844) is considered by Lazell (1964) to be synonymous with B.
c. orophias. (7)
B. c. nebulosa Lazell, 1964 is a distinctive insular race restricted
to Dominica in the Caribbean. See
the key and Table I for diagnostic characters. (8)
B. c. sigma (Smith,
1943) is restricted to the Tres Marias Islands, Mexico.
Nine specimens were known in 1963 (Smith, personal correspondence),
with ventral scale counts of 253 to 260, slightly in excess of the high
for B. c. imperator of
253. (Stull, 1932). Zweifel
(1960) - synonymized it with B. c. imperator,
but Stull still recognized it in 1964 (personal correspondence), as did
Smith in 1963 (personal correspondence). It
would be wise to evaluate carefully the role of elevated ventral and
subcaudal scale counts as the sole basis for taxonomically recognizing
insular populations of snakes such as B. c. sigma.
Bogert and Oliver (1945, pp. 360-1) and Zweifel (1960) believe the
character to be unreliable. The
embryogeny of many cold-blooded vertebrates is known to be affected by
minor temperature differences between litters, with resultant differences
of sex ratio, vertebral elements, and scale meristics.
Perhaps the differences in ventral scale counts seen in B.
c. sigma, B. c.
orophias, and B. c. nebulosa may
have a basis in microclimatic conditions and might disappear if the
different stocks were reproduced under similarly controlled conditions.
Although such elevated counts are not generally recognized in
mainland populations of B. c. imperator,
Smith (1943, 1964) mentions an odd specimen with 261 ventrals from
Tehuantepec and thus undermines his own reluctance to merge B c. sigma into B.
c. imperator.
(9)
B. c. sabogae (Barbour, 1906)
from Taboga Island, Panama, differs from the typical mainland B.
c. imperator only in being dark reddish brown with the pattern largely
obscured. Stull (personal
correspondence, 1964) found it indistinguishable from some aberrant
mainland individuals and felt it should be synonymized with B.
c. imperator.
(10)
B. c. var. isthmica Garman, 1883 is
considered a synonym of B. c.
imperator by Peters and Orejas-Miranda (1970).
It was described from the Isthmus of Darien, Panama. (11)
B. c. mexicana (Jan, 1863) was described from a single specimen
from Mexico with 55 dorsal scale rows but which was otherwise like B. c. imperator.
Most authors have synonymized this taxon with B.
c. imperator on the assumption that the type was an atypical
specimen or was simply miscounted. Smith
(1963) states that no Mexican specimens of known provenance have ever
shown 55 dorsal scale rows. However,
it appears that most workers have missed Andrew's report (1937) of four
Mexican specimens (Field Museum 26989-92) from Chichen Itza having dorsals
of 56 to 62. These counts
completely bridge the gap between B.
c. mexicana (= 55) and
B. c. imperator
(= 61-79 in Boulenger, 1893) and should allay any remaining doubts that B.
c. mexicana should be
suppressed. (12)
B. c. ortonii Cope,
1877 is a desert population of pallid coloration found from Perico and the
Upper Maranon valley to Piura and south to Libertad in northwestern Peru.
It was thought by Cope to be different from B.
c. imperator in having
a higher ventral count which Schmidt and Walker (1943) give as 246-252,
well within the range of B. c. imperator's
225-252 (Boulenger, 1893) or 235-253 (Stull, 1932)-and in having small
scales separating the suborbital and labial scales-which Schmidt and
Walker found to be inconsistent in their study.
Stull (personal correspondence, 1964) considers it to be a synonym
of B. c.
imperator, which seems logical without additional data. (13)
B. c. eques (Eydoux
and Souleyet, 1842) is based on a single specimen and is almost certainly
an aberrant B. c. imperator, with which it has been synonymized by most
workers. The specimen came
from Payta, Peru, and was characterized by one preorbital scale that was
larger than all other scales in the orbital ring and equal in size to the
eye itself. Other scales of
the head were mentioned as being unusually large also.
Since no further examples are known, it seems not to be a valid
taxon. Before terminating this brief discussion of the subspecific taxa of Boa constrictor, I would like to suggest that Lazell (1964) was almost certainly in error in believing that an evolutionary continuity existed as a stepped-cline series from B. c. constrictor through B. c. orophias to B. c. nebulosa. The latter two insular populations are admittedly distinct subspecific taxa, but Lazell somehow failed to discuss their potential derivation from mainland populations of B. c. imperator to the west. B. c. imperator is much more closely allied to the two Lesser Antillean taxa in Lazell's critical characters of dorsal scale rows, dorsal blotches, coloration, and patterning than is B. c. constrictor. Furthermore, the insular B. c. sigma off the Pacific coast of Mexico shares the elevated ventral scale counts of B. c. orophias and B. c. nebulosa. In my opinion the northward migration of B. c. constrictor ended with its colonization of Trinidad and Tobago. Table 1. Comparison of subspecies and synonyms of Boa constrictor discussed in the text
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Photo courtesy of Craig McSherry. Taken in May of 1982, this 10 year old docile male was about 10 feet long. It had a jet black belly with very little speckling. Photo courtesy of Craig McSherry. Taken in May of 1982, this 10 year old vicious female was 14+ feet long. She had a black belly except in the chin area where the first 12 inches was 50% cream color. This female (next four photos) was taken
out of the wild in April, 1999 by John Johnson and his wife of TN.
She was found near the Aquaro River close to Santa Cecilia in the Napo
Province of Ecuador. She is 8 feet in lenght and feeding on rabbits.
Her scale counts are:
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