Date of birth, litter and neonate size of a diamondback water snake, Nerodia rhombifer, from southernmost Texas.
Three of the 39 neonates were either born dead or died before they were measured. Mean snout-vent length (SVL) of all 39 neonates was 228 mm (range 202-240, SD = 9.6, CV = 4.2). This is significantly smaller (P < .01, 523 df) than the mean of 246.1 mm (SE = 0.6) reported by Plummer (1992) for 486 neonates from Arkansas. Ford et al. (1990) reported a mean SVL of 214.8 mm for 55 neonates (two litters) from northeastern Texas. The neonates from southernmost Texas were significantly larger (t=8.57, 92 df, P<.001) than the neonates from northeastern Texas. Aldridge et al. (1995) reported a mean SVL of 213 mm (range 204-221) for neonates from Veracruz, Mexico, but did not give a sample size or a measure of variance. Consequently, a statistical comparison of neonate SVL of these specimens is not possible.
The data reported here are the first available for a subtropical population of N. rhombifer. The information on geographic variation in litter size suggests that there is no clinal latitudinal variation in neonate size in N. rhombifer.
The litter size (39) observed in this study is beyond the range (8-36) reported for N. rhombifer from Veracruz, Mexico, (Aldridge et al. 1995) and it is larger than the litter sizes of 26, 33, and 37 reported by Ford et al. (1990) for three litters from northeastern Texas. Conversely, it is within the ranges reported by Cagle (1937) for Tennessee (13-42) and Plummer (1992) for Arkansas (12-48). Aldridge et al. (1995) reported that clutch size was significantly smaller in the tropical Veracruz, Mexico, population than in temperate populations. While caution should be used in drawing inferences based on the meager data currently available for Texas populations, it appears that litter size in N. rhombifer from southernmost Texas may be typical of that of temperate populations and significantly larger than that of tropical populations.
We are grateful to B. Autry, T. Hyde and J. Gable for assistance in the field and laboratory.
Aldridge, R. D., W. P. Flanagan & J. T. Swarthout. 1995. Reproductive biology of the water snake Nerodia rhombifer from Veracruz, Mexico, with comparisons of tropical and temperate snakes. Herpetologica, 51:182-192.
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Ford, N. B., V. A. Cobb & W. W. Lamar. 1990. Reproductive data on snakes from northeastern Texas. Texas J. Sci., 42(4):355-368.
Plummer, M. V. 1992. Relationships among mothers, litters, and neonates in diamondback water snakes (Nerodia rhombifer). Copeia, 1992:1096-1098.
Tennant, A. 1985. A field guide to Texas snakes. Texas Monthly Press, Austin, Texas. 1-260 pp.
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Frank W. Judd and Martin Bray
Department of Biology, University of Texas-Pan American, Edinburg, Texas 78539 and U.S. Fish and Wildlife Service, Rt. 2 Box 202A, Alamo, Texas 78516
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|Title Annotation:||GENERAL NOTE|
|Author:||Judd, Frank W.; Bray, Martin|
|Publication:||The Texas Journal of Science|
|Date:||Feb 1, 1996|
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