Dipsas catesbyi (Sentzen 1796)

Dipsas catesbyi

NATURAL HISTORY

Dipsas catesbyi is a small (snout-vent length to 590 mm, most adults less than 500 mm), thin-bodied nocturnal snake. It is predominantly a denizen of shrubs and low trees in primary and secondary forests below 1000 m but may descend to the ground occasionally in search of prey. Snails are the major prey, although soft-bodied insects are also eaten (Beebe, 1946).

BODY SIZE

HATCHLINGS.—Only one snake (148 mm snout-vent length) possessed a yolk-sac scar. Peters (1956) found 39 such specimens but did not report their sizes; we were unable to find his original data. Our total Dipsas sample contained four individuals 148 mm or smaller. The mean snout-vent length of these four hatchlings is 141.0 mm (standard deviation,±10.5 mm; range, 123–148 mm).

GROWTH AND SEXUAL MATURITY.—The smallest female with oviducal eggs is 338 mm snout-vent length, with class V follicles 356 mm. Thus, we assume that most females greater than 335 mm snout-vent length are sexually mature. Presumably males of this length are also sexually mature, for Peters (1956) could not discern any difference in growth rate between the two sexes.

The average snout-vent length of sexually mature females (N = 51) is 402.1 ± 48.6 with a range of 338–542 mm. The mean snout-vent length of females (8) with oviducal eggs and class V follicles is slightly smaller, 399.1 ± 47.8 mm (338–492 mm). The sexually mature females from Ecuador (13) have a mean snout-vent length of 401.9 ± 55.8 mm (338–502 mm), from Bolivia (9) 384.4 ± 44.0 mm (340–455), from Iquitos, Peru (19) 414.1 ± 53.0 mm (340–542), and all Peru localities (29) 407.6 ± 46.9 mm (340–542). In spite of the disparity in sample sizes, the mean length of mature females at each locality is approximately 400 mm. Without an unequivocal identifier for the attainment of sexual maturity in males, we hesitate to document mean length of mature males.

Various body size-month matrices were constructed in order to estimate growth rate from hatching to sexual maturity. None showed sufficient segregation of size classes to provide a reasonably accurate estimate. At best, we can guess that sexual maturity is attained in not less than two years. Peters (1956, fig. 16) estimates the age of size classes of D. catesbyi from Iquitos, Peru. From these estimates, the snakes do not reach sexual maturity until three and a half years—roughly 1 mm/week

SEXUAL DIMORPHISM

BODY AND TAIL LENGTH.—Peters (1956) notes that the tail length of females (32–41 percent of body length) was less than that of males (35–43 percent). He further observes that tail length is proportionately greater in larger, hence older, individuals of both sexes. Three of our samples, Pastaza, Bolivia (Figure 9), and Tingo Maria show the tendency for adult males to have longer tails than females. The Napo and Iquitos (Figure 9) samples, however, show a strikingly different trend. Juvenile and most adult males have shorter tails than females and only at body lengths greater than 400 mm do tail lengths of females and males overlap.

GONAD POSITION.—The relative position of the gonads is identical in both sexes. Comparison of the sexes by a one-way analysis of variance yields nonsignificant F values, e.g., 6.79, df 1/101 for Peruvian sample to 0.21 df 1/12 for Napo sample. The posterior edge of the left gonad lies 14 to 16 percent of snout-vent length from the vent.

TAIL BREAKAGE.—The frequency of broken tails is low (ca. 1 percent) in the entire Dipsas catesbyi sample. Most samples have no snakes with broken tails. Only the Bolivian sample differs strikingly with a 10 percent incidence of broken tails, which was evenly distributed between the sexes (x2=0.006).

SEX RATIO

Combining all samples, the 1:1 ratio is a perfect fit (150 females: 150 males), but including only sexually mature snakes (83:109; x2 = 1.51), males dominate. At a local level, the Guyana (all sizes and mature), Santa Cecilia (all sizes), Río Bobonaza (all sizes), and Iquitos (all sizes) samples deviate significantly (x2 ≥ 1.32) from a 1:1 ratio and all except Iquitos with males most numerous. Thus, the majority of the samples indicates an equality of sexes in Dipsas catesbyi.

REPRODUCTION

CLUTCH SIZE.—The modal clutch size for oviducal eggs in D. catesbyi is two. Classes IV and V follicles show a modal clutch of three (Table 4). The range for the entire Dipsas sample is one to four eggs. Clutches of four occur only in the Tingo Maria and Alto Río samples and only as class IV follicles. The potential for a clutch of four eggs may exist only in these populations or may indicate atrophy of follicles continuing into class V follicle development. Within classes II and III follicles, potential clutch size ranges from 2–23 with 7–9 follicles dominating in class II and 4–6 follicles dominating in class III. As an aside, the difference in number of gravid females in our examination of the Bassler Iquitos collection and that of Fitch (1970) results from his inclusion of any enlarged yolk follicles (Fitch, pers. comm.), some of which fall in our classes III and IV groupings.

With such small clutch size and our limited samples, regional differences in clutch size are not apparent. In spite of the positive regression of clutch size on body size (Figure 10), we doubt that an actual correlation exists, for the slope of the line is nearly zero. The production of a clutch of one, two, or three eggs may be more dependent upon a female's physical well-being than on her actual body size.

Dixon and Soini (1977) reported the capture of three females, each with two oviducal eggs, from Iquitos, Peru. Oviducal egg size in our sample ranges from 21.5 to 34.1 mm long with a mean of 27.7 ± 4.1 mm.

REPRODUCTIVE CYCLE.—The Dipsas data, like that for Coniophanes, is inadequate to draw definite conclusions on the cyclic-acyclic nature of reproduction. Our data (Table 5) does show that the Ecuadorian population lays eggs from April to June and the Peruvian population in June. February reproduction is implied for the Bolivian population, since hatchlings appear in May. Reproduction may occur at other times but cannot be discerned from our data. The addition of Dixon and Soini's (1977) observations of females with oviducal eggs in February, September, and December to our April and June records strongly indicates that the Iquitos population reproduces continually.

Catesby's snail-eater (Dipsas catesbyi), also commonly known as Catesby's snail sucker, is a nocturnal species of nonvenomous snake in the family Colubridae. The species is native to northern South America.

Dipsas catesbyi es una especie de serpiente no venenosa que pertenece a la familia Colubridae. Es una culebra nocturna, nativa del norte de América del Sur,​ que se alimenta principalmente de caracoles arbóreas. No tiene subespecies reconocidas.​

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Dipsas catesbyi Dipsas generoko animalia da. Narrastien barruko Dipsadidae familian sailkatuta dago.

Dipsas catesbyi est une espèce de serpents de la famille des Dipsadidae.

Dipsas catesbyi este o specie de șerpi din genul Dipsas, familia Colubridae, descrisă de Sentzen 1796. A fost clasificată de IUCN ca specie cu risc scăzut. Conform Catalogue of Life specia Dipsas catesbyi nu are subspecii cunoscute.

Dipsas catesbyi là một loài rắn trong họ Rắn nước. Loài này được Sentzen mô tả khoa học đầu tiên năm 1796.