The Variations in the Number of Vertabrae and Ventral Scutes in Two Snakes of the Genus Regina

Ruthven, Alexander G.; Thompson, Crystal

doi:10.1086/279376

Cited by 10 publications

(9 citation statements)

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“…However, sample sizes (numbers of species, and specimens per species) are often low. For example, the only published data that I could find on this topic for New World natricines was an early study on Regina ( Ruthven & Thompson, 1908), which reported a 1 : 1 correspondence between vertebrae and scales. Because gartersnakes display particularly unusual patterns in vertebral numbers (above), six specimens (three male, three female) of Thamnophis sirtalis were X‐rayed and scale‐counted.…”

Section: Resultsmentioning

confidence: 99%

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Vertebral numbers in male and female snakes: the roles of natural, sexual and fecundity selection

Shine

2000

Journal of Evolutionary Biology

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The relative numbers of trunk (body) and caudal (tail) vertebrae in snakes might be influenced by at least four processes: (1) natural selection for crawling speed, (2) fecundity selection for larger trunk size in females, (3) sexual selection for longer bodies or tails in males and/or (4) developmental constraints (if an increase in the number of body vertebrae requires a decrease in the number of tail vertebrae, or vice versa). These four hypotheses generate different predictions about the relationship between sex differences in the numbers of body vertebrae vs. tail vertebrae. I collated published data to test these predictions, both with raw data and using phylogenetically independent contrasts. Some snake lineages show a negative correlation between the magnitude of sex disparities in trunk vs. caudal vertebrae whereas other lineages show the reverse pattern, or no correlation. Thus, different selective pressures seem to have been important in different lineages. Vertebral numbers in snakes may offer a useful model system in which to explore the conflicts between natural, fecundity and sexual selection.

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Section: Resultsmentioning

confidence: 99%

“…4 in most snake species, vertebral numbers correspond to the numbers of scales under the body (ventrals) and under the tail (subcaudals) ( Ruthven & Thompson, 1908; Gans & Taub, 1965; Alexander & Gans, 1966; Voris, 1975), traits commonly measured and reported for taxonomic purposes; and…”

Section: Introductionmentioning

confidence: 99%

Vertebral numbers in male and female snakes: the roles of natural, sexual and fecundity selection

Shine

2000

Journal of Evolutionary Biology

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“…There is a correlation between the number of precloacal ventral scales and the number of precaudal vertebrae among alethinophidian snakes (excluding Acrochordus and many members of Hydrophinae) (Ruthven and Thompson 1913;Alexander and Gans 1966;Voris 1975). However, if each ventral scale does develop aligned to each somite, they are therefore not directly aligned with each vertebra given that each vertebra originates from adjoining portions of two consecutive somites (Aoyama and Asamoto, 2000).…”

Section: R a F Tmentioning

confidence: 99%

Differential growth of body segments explains ontogenetic shifts in organ position for the Diamondback Water Snake (Nerodia rhombifer)

Anderson

Secor

2016

Can. J. Zool.

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As snakes grow, their organs move anteriorly relative to body size. We explored a developmental explanation for the ontogenetic shift in the relative position of internal organs for snakes using the Diamondback Water Snake (Nerodia rhombifer (Hallowell, 1852)). With age, this water snake’s heart, liver, small intestine, and right kidney move anteriorly by 2.5–5.0 percentage points of snout–vent length. The number of precaudal vertebrae did not vary due to size or sex. The anterior edge of the heart, liver, small intestine, and right kidney were typically aligned within a span of 4–8 vertebrae that likewise did not differ as a function of size or sex. Snakes exhibited a positive relationship between the number of precaudal vertebrae and the vertebra number aligned with each organ. Total length, centrum length, centrum width, ball width, height, and mass of eight vertebrae sampled at consistent vertebral number revealed that vertebrae in the middle region of the body grow at a greater rate than vertebrae at the anterior or distal ends of the body. For N. rhombifer, the observed forward shift in relative organ positions is the product of regional differences in the growth of body segments. Predictably, these differences arise from a developmental program generated by the differential expression of Hox genes.

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“…The usual condition among snakes is a ratio of one ventral scale to one vertebra (e.g. Ruthven &Thompson, 1913;Kramer, 1961;Alexander & Gans, 1966;Voris, 1975), although some primitive snakes deviate from this ratio (Bellairs & Underwood, 1951;Gans & Taub, 1965). Consequently, in VQera, the number of ventral scales has been shown to correlate with number of vertebrae (Kramer, 1961).…”

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Variation in number of ventral scales in snakes: effects on body size, growth rate and survival in the adder, Vipera berus

1993

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With 3 figures in the text)The relationship between number of ventral scales, correlating with number of body vertebrae, and body size of adders, Vipera berus, was investigated using captive-born young and wild-caught adults (snout-vent length >400 mm) from six populations in eastern Sweden. Females had significantly more ventral scales, and were larger, than males in all populations. Among adult individuals, snout-vent length was highly positively correlated with the number of ventral scales when differences due to sex and locality were controlled for. The same pattern was true for newborn individuals when differences due to litter and sex were controlled for. The influence of number of ventral scales on survival and growth rate as possible causes of this positive correlation was examined. Mean number of ventral scales was lower in new-born snakes than in adults, indicating selection against individuals with a low scale count. Since this selection appears to take place in the early juvenile phase, it is inadequate to explain the relationship between adult body size and number of ventral scales. However, individuals with many ventral scales had significantly higher growth rates than individuals with few ventrals. This suggests that individuals with many ventral scales enjoy a higher growth rate and therefore are able to reach a larger size than their conspecifics of the same age with few ventral scales. This would explain the positive relationship between body size and ventral scale number observed in new-born and adult snakes.

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The Variations in the Number of Vertabrae and Ventral Scutes in Two Snakes of the Genus Regina

Cited by 10 publications

References 0 publications

Vertebral numbers in male and female snakes: the roles of natural, sexual and fecundity selection

Vertebral numbers in male and female snakes: the roles of natural, sexual and fecundity selection

Differential growth of body segments explains ontogenetic shifts in organ position for the Diamondback Water Snake (Nerodia rhombifer)

Variation in number of ventral scales in snakes: effects on body size, growth rate and survival in the adder, Vipera berus

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