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Morphological variation in the endemic Colombian water snake, Helicops danieli Amaral, 1937 (Serpentes: Xenodontidae).

Resumen

Variacion en el patron de coloracion, asi mismo de caracteres meristicos y mensurales, se basa en el estudio de 45 ejemplares de esta culebra acuatica endemica en Colombia y previamente poca conocida.

Palabras clave: Colombia, Helicops danieli, Variacion, Xendodontidae.

Abstract

Variation in color pattern, as web as meristic and mensural characters, is based on 45 specimens of this previously little-known endemic Colombian watersnake.

Key words: Colombia, Helicops danieli, Variation, Xenodontidae.

Introduction

Helicops danieli was described (Amaral, 1937) on the basis of a single specimen from Carare, Santander, Colombia; a second specimen from Quibdo, Choco--previously identified as H. leopardinas (Amaral, 1932)--was also assigned to the new species. Most subsequent papers have added relatively little to our understanding of this northwesternmost species of the widespread aquatic snake genus Helicops beyond adding a few locality records. The most recent distributional summaries are those of Perez-Santos & Moreno (1988) and Yuki & Castano (1998). Significant morphological data have been provided only by Yuki (1996), who, in discussing two specimens of H. danieli that had been misidentified as H. carinicaudus, described them in considerable detail and figured an inverted hemipenis. Nevertheless, a comprehensive summary of variation in meristic and mensural characters, as well as color pattern, has yet to appear in print. The purpose of my paper is to do exactly that, within the larger context of an ongoing taxonomic review of the entire genus.

Materials and methods

In the course of this study, I personally examined 42 preserved specimens of H. danieli', in addition, John Lynch provided data on a few selected characters for two recently collected specimens, as did Rubens Yuki for the holotype (Instituto Butantan 9872). Meristic data were recorded for all undamaged specimens, but cephalic measurements were omitted for specimens having a snout-vent length less than 230 mm to avoid possible effects of allometry. Meristic counts included--ventrals (V); subcaudals (SC); supralabials (SL); infralabials (IL); anterior temporals (AT); dorsal scale rows (DSR) at the level of V10, at midbody, and two V anterior to the anal plate; maxillary teeth (Mx). Mensural characters included--tail length/total length (T/TL); head length/snout-vent length (HL/SVL); eye diameter/frontal length (ED/FL); frontal length/parietal length (FL/PL); muzzle length/frontal length (ML/ FL); muzzle width/frontal length (MW/FL); anterior frontal width/frontal length (FW/FL); posterior frontal width/ anterior frontal width (FWP/A); prefrontal length/internasal length (Prf/In); anterior/posterior chinshield length (ACS/PCS); dorsal loreal length/ventral loreal length (LD/ LV); loreal height/ventral loreal length (LHt/LV); ventral loreal length/muzzle length (LV/ML); total nasal length/ muzzle length (TN/ML). All of the preceeding ratios are expressed as percentages. I also recorded height of the outermost dorsal scale row/width of the vertebral row (DSR 1/VR), but expressed it as an absolute value rather than as a percentage. All counts and measurements were made by the methods described in Rossman et al. (1996).

Helicops danieli Amaral

Holotype: Instituto Butantan, IB 9872, a juvenile female, donated by Hermano Daniel.

Type-locality: Colombia, Santander, Carare.

Etymology: Named in honor of the holotype's donor, Hermano Daniel, a pioneer in Colombian herpetological research.

Definition: A very large (maximum recorded SVL 800 mm) species of Helicops characterized by having: a maximum of 19 DSR at midbody; the single internasal usually (ca 75%) in contact with the rostral; a large number of V (males 130-141, females 125-135); a moderately large number of SC (males 61-70, females 76-86); the dorsum with four or five rows of alternating dark spots; the light ventral color extending onto dorsum as high as DSR 2; the venter light with two rows of broad black semilunar markings, the same pattern extending onto the SC.

The combination of a spotted dorsum with a linear pattern of dark spots on a light venter readily distinguishes H. danieli from all other species in the genus.

Variation: Meristic and mensural variation are summarized in Tables 1 and 2. Many characters exhibit sexual dimorphism--some slight (e. g., relative headlength, number of maxillary teeth), some pronounced (e. g., relative tail length, number of subcaudals). Males tend to have fewer DSR, SL, IL, and V, but more SC and MX teeth. Females tend to have a proportionately shorter tail, shorter head (or longer body), smaller eye, shorter PCS, and a higher DSR 1.

Reduction in the number of DSR from 19 to 17 results either from the fusion of rows 3 and 4 or the loss of row 4. The point of reduction lies 82% of the body length posteriorly (as determined by V location) in the eleven specimens examined for this feature. The internasal is clearly in contact with the rostral in 25 specimens, they are separated by contact between the opposing nasals in seven, and the four scales meet in a single point in three. The ten largest females average 673 mm (500-800) in SVL and the nine largest males average 413 mm (355-457). Mature males (>350 mm SVL) have tubercles on the chinshields and anterior infralabials.

The scales of DSR 1 and 2 are white, or cream, like the adjacent venter. The dorsum is some shade of olive brown with four or five rows of alternating dark spots, those of the ventral row (when present) often less distinct than those in the dorsolateral and lateral rows. Spots in the latter two rows are 1-2 scales long; those in the lateral row extend from DSR 3-5 (or 6), in the dorsolateral row from DSR 7-9. The dark spots are much more distinct in smaller individuals (Figs. 1-2), often becoming obscured by the brown pigment in larger individuals (Fig. 3). Ontogenetic variation in dorsal pattern also is apparent in the nuchal region, where, in juveniles, a prominent yellowish collar is interupted middorsally by the anterior extension of the dark nuchal band (Fig. 1). The light collar soon disappears as an individual increases in size (Fig. 2), but the dark nuchal band and its anterior extension remain visible even in large adults (Fig. 3). The top of the head is olive brown, and this color extends ventrally across SL 1-3 to the lip and across the dorsal portions of DSR 4-8 to a varying extent.

The venter is cream in life with two rows of black semilunar marks. These black marks range in size from being fairly small (Fig. 4) to so expanded that they fuse midventrally (Fig. 5). Paired black spots also appear on the SC, being confined to the anterior scales in some individuals (Fig. 4) and extending nearly the entire length of the tail in others (Fig. 5). The chin and throat areas also are marked by varying amounts of black pigment. There invariably is at least some pigment along the lower margin of the IL, but the extent--or even presence--of pigment on the chinshields may differ dramatically (Figs. 4-5). This statement also applies to whether or not there is a black bar connecting the spots on the gular scales to an area of dark pigment on the posterior SL (Figs. 4-5).

Renjifo & Lundberg (1999) included two color photographs of living H. danieli in their book (the head and a section of body of an adult appears on page 86, and a smaller individual in the process of being ingested by an immature Clelia clelia appears on the front cover).

Distribution: With two exceptions (discussed below), Helicops danieli appears to be confined to northwestern Colombia (Fig. 6) in drainages that empty into the Caribbean, directly or indirectly (the Atrato, Sinu, Cauca, and Magdalena rivers). Most records are from low elevations (below 500 m) and the record for Medellin should be verified. Perez-Santos & Moreno (1988) plotted a H. danieli record from the general vincity of Cucata, Norte de Santander, in the Maracaibo drainage, but they did" not include that region in their text where they characterized the distribution of the species. No museum specimen was cited, so it isn't possible to determine if the record is valid or in error.

On the other hand, the range extension reported by Yuki & Castano (1998) is based on ICN 242, an adult male purportedly from Mitu, Vaupes, in the Amazonian drainage. Rubens Yuki kindly provided me with a photograph of this specimen, and there is no doubt that it was correctly identified by them. However, the fact that this locality lies east of the Andes, more than 700 km removed from the main range of the species, raises some question as to whether or not the specimen might have been inadvertently mislabeled. Acquisition of additional material from Mitu--or other localities in the Amazon drainage--would remove any certainity surrounding this specimen.

On their map, Yuki & Castano (1998) mistakenly plotted the type-locality of H. danieli (Carare, Santander--middle Magdalena drainage) in the general vicinity of Popayan, Cauca (upper Cauca drainage). The type-locality is correctly placed in my map (Fig. 6).

Specimens examined (or verified): ANTIOQUIA: Rio Porce, near estacion Botero (ILS 2085); Turbo (ANSP 25072, ILS 737); Puerto Berrio (AMNH 20397); Rio Cauca, Caucasia (ILS 2132); Rio Cauca, Yarumal (ILS 1811); Medellin (AMNH 35608, 35718). ATLANTICO: Barranquilla (ANSP 25668, ILS 736, MZUSP 2144-45, ZMH R04338-39); Cienega de Amajahuevo, CVM fishery station (FMNH 165216-19, 165524). BOLIVAR: vincinity of Cartagena (FMNH 165276); Canal de Duque, San Cristobal (AMNH 97459-62); Rio Cauca, Magangue (ILS 734); Santa Catalina, Hacienda El Ceibal (ICN 997172). CHOCO: "Isthmus of Panama, Atrato River" (ANSP 11659); Cienega!,] Agua Clara River (AMNH 18239); Quibdo (ICN 1391, ILS 735); vicinity of Opagado (LACM 7275). CORDOBA: Rio Sinu, Monteria (ILS 2139, 223435); upper Rio Ure, close to CVM camp (FMNH 165298); Rio Sinu, Urra (Renjifo.& Lundberg, 1999, cover, p. 86). SANTANDER: Barrancabermeja (ICN 11548); Carare (IB 9872, holotype). SUCRE: Cano Frances, E of Tolu (FMNH 165625); between Tolu and Sincelejo (FMNH 165895). NO SPECIFIC LOCALITY: "Magdalena Valley (BM[NH]) 1905.5.15.3-4); "New Grenada" (ANSP 22994-99); "Central America" (LSUMZ 83319); no data (USNM 12475).

Acknowlegments

For the loan of specimens or information, I am indebted to the curators and collection managers of the following institutions (with acronyms): American Museum of Natural History, New York (AMNH); Academy of Natural Sciences of Philadelphia (ANSP); British Museum (Natural History), London (BM[NH]); Field Museum of Natural History, Chicago (FMNH); Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogota (ICN); Instituto de La Salle, Bogota (ILS); Louisiana State University Museum of Natural Science, Baton Rouge (LSUMZ); Museu de Zoologia, Universidade de Sao Paulo (MZUSP); National Museum of Natural History, Smithsonian Institution, Washington (USNM); and Zoologisches Museum Hamburg (ZMH).

I also wish to thank Rubens Nobuo Yuki (Facultades Integradas do Tapajos, Santarem, Brasil) for providing data and/or photographs of specimens that he had examined--but which were not available to me directly--so I could verify the identifications; John D. Lynch (Instituto de Ciencias Naturales, Universidad Nacional de Colombia, Bogota) for providing data on two ICN specimens that he had collected, for providing the photograph of one of them that appears in this paper, for translating my abstract into Spanish, and for numerous other courtesies; Linda Ford and Tom Trombone (American Museum of Natural History) and Alan Resetar (Field Museum of Natural History) for helping me track down obscure localities; and Mark Kleiner (Louisiana State University) for taking the black-and-white photographs.

Literature Cited

Amaral, A. do. 1932. Estudos sobre ophidios neotropicos. 29. Novas notas sobre especies da Colombia. Memorias do Instituto Butantan (Sao Paulo) 7: 105-123.

--. 1937. Estudos sobre ophidios neotropicos. 34. Novas notas sobre a fauna da Colombia e descipcao de uma especie nova de Colubridae aglypho. Memorias do Instituto Butantan (Sao Paulo) 11: 231-240.

Perez-Santos, C. & A. G. Moreno. 1988. Ofidios de Colombia. Museu Regionale di Scienze Naturali Torino, Monogr. 6: 1-517.

Renjifo, J. M. & M. Lundberg. 1999. Guia de campo/ Anfibios y reptiles de Urra. Editorial Colina, Medellin.

Rossman, D. A., N. B. Ford & R. A. Seigel. 1996. The Garter Snakes: Evolution and Ecology. University of Oklahoma Press. Norman.

Yuki, R. N. 1996 ["1994"]. Sobre Helicops danieli Amaral, 1937, com a descipcao do hemipenis (Serpentes, Colubridae, Xenodontinae). Boi. Museu Paraense Emilio Goeldi, ser. Zool. 10 (2): 203-209.

--& O. V. Castano. 1998. Geographic distribution note of water-snake Helicops danieli Amaral, 1937 (Colubridae: Xenodontinae). The Snake 28: 90-91.

Douglas A. Rossman (1)

(1) Curator Emeritus, Museum of Natural Science, Louisiana State University, Baton Rouge, Louisiana 70803, USA; Research Associate, Department of Biology, Luther College, Decorah, Iowa 52101, USA (mailing address); and Research Associate, Milwaukee Public Museum, Milwaukee, Wisconsin 53233, USA.

Caption: Figure 1. Dorsal view of juvenile (148 mm SVL) female Helicops danieli (ANSP 22996) from "New Grenada."

Caption: Figure 2. Dorsal view of subadult (316 mm SVL) female Helicops danieli (ANSP 25668) from Barranquilla, Atlantico, Colombia.

Caption: Figure 3. Dorsolateral view of living adult (800 mm SVL) female Helicops danieli (ICN 9972) from Hda. El Ceibal, Santa Catalina, Bolivar, Colombia.

Caption: Figure 4. Ventral view of subadult (316 mm SVL) female Helicops danieli (ANSP 25668) from Barranquilla, Atlantico, Colombia.

Caption: Figure 5. Ventral view of adult (442 mm SVL) male Helicops danieli (ANSP 25668) from Turbo, Antioquia, Colombia.

Caption: Figure 6. Map of northwestern South America showing the known distribution of Helicops danieli. Solid circles represent specimens personally examined or verified, hollow circles unverified but probably valid records, and the solid triange the type- locality
Table 1. Individual and sexual variation of selected meristic
characters in Helicops danieli. Values represent number of
scales (number of specimens-percentage of sample).
M = males, F = females.

Character        Sex   Values

Anterior DSR      M    19(13-81.3), 20(1-6.3), 21(2-12.5)
                  F    19(21-77.8), 20(5-18.5), 21(1-3.7)

Midbody DSR       M    19(16-100.0)
                  F    19(26-96.3), 20(1-3.7)

Posterior DSR     M    16(2-12.5), 17(12-75.0), 18(1-6.3),
                       19(1-6.3)
                  F    16(2-7.4), 17(19-70.4), 18(6-22.2)

Total SL          M    16(16-100.0)
                  F    16(24-85.7), 17(3-10.7), 18(1-3.6)

Total IL          M    20(12-80.0), 21(3-20.0)
                  F    20(15-57.7), 21(6-23.1), 22(5-19.2)

Total AT          M    2(15-93.8), 4(1-6.3)
                  F    2(26-100.0)

Table 2. Individual and sexual variation of selected meristic
and mensural characters in Helicops danieli. Values represent
mean [+ or -] one S. D. (range of variation) number of specimens

Character          Sex   Values

No. of V            M    129.4 [+ or -] 2.66(125-135)16
                    F    135.4 [+ or -] 2.97(130-141)29

No. of SC           M    79.8 [+ or -] 2.70(76-86)15
                    F    65.3 [+ or -] 2.75(61-70)20

No. of Mx teeth     M    17.8 [+ or -] 0.71(17-19)8
                    F    17.1 [+ or -] 1.04(16-20)13

T/TL (%)            M    30.3 [+ or -] 2.10(26.4-33.4)15
                    F    23.5 [+ or -] 0.95(20.7-25.2)20

HL/SVL (%)          M    5.5 [+ or -] 0.36(4.7-6.0)9
                    F    5.2 [+ or -] 0.19(4.9-5.5)8

ED/FL (%)                M50.7 [+ or -] 2.76(47.2-56.1)11
                    F    48.0 [+ or -] 4.96(41.9-56.9)14

FL/PL (%)                83.6 [+ or -] 6.03(68.2-91.6)25

ML/FL (%)                64.9 [+ or -] 6.01(55.5-82.4)25

MW/FL (%)                51.3 [+ or -] 5.36(43.0-62.5)19

FW/FL (%)                41.6 [+ or -] 5.01(34.4-55.6)26

FWP/A (%)                126.7 [+ or -] 9.70(100.0-151.5)26

Prf/In (%)               73.6 [+ or -] 9.35(54.2-89.7)25

ACS/PCS (%)         M    88.8 [+ or -] 7.19(78.9-101.1)10
                    F    100.8 [+ or -] 8.39(89.4-119.6)15

LD/LV (%)                53.2 [+ or -] 6.30(41.0-63.2)19

LHt/LV (%)               94.6 [+ or -] 10.27(69.0-113.2)19

LV/ML (%)                43.8 [+ or -] 4.37(36.0-52.4)16

TN/ML (%)                58.5 [+ or -] 5.27(50.3-71.4)16

DSR 1/VR            M    1.74 [+ or -] 0.12(1.58-1.94)9
                    F    1.82 [+ or -] 0.09(1.67-1.92)8
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Title Annotation:Zoologia
Author:Rossman, Douglas A.
Publication:Revista de la Academia Colombiana de Ciencias Exactas, Fisicas y Naturales
Date:Dec 1, 2002
Words:2695
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