Allometry of cranial morphology, gape size and ingestion performance in the banded watersnake (Nerodia fasciata) feeding on two types of prey

Abstract

Small body size imposes limitations on the feeding capabilities of juveniles, particularly in species that consume their prey whole. It has been hypothesized that juveniles exhibit exceptional performance measures to compensate for their small size. However, few studies have examined whether juveniles have better feeding performance relative to adults and investigations of snake feeding ontogeny have not shown enhanced performance in smaller snakes. I tested the hypothesis that juvenile snakes have better feeding performance by comparing maximum gape circumference and ingestion performance (time and number of pterygoid protractions) in a series of banded watersnakes (Nerodia fasciata) of different sizes fed fish and frogs. I also measured several external and osteological dimensions of the head and used Akaike's information criterion to determine which morphological measurements were the strongest predictors of relative gape. All skull measurements and maximum gape circumference showed negative allometry relative to snout-vent length (SVL). Given the available models, Akaike information criterion (AIC) analysis indicated that both skull length and mandible length were the strongest predictors of gape circumference for both external and osteological measurements. Multiple regression analysis of ingestion performance indicated SVL was negatively correlated with the time and number of pterygoid protractions required to consume fish or frogs, indicating that juveniles do not have a higher ingestion performance than adults. While exaggerated morphology in juvenile snakes does not appear to improve ingestion performance, a larger gape should increase the ability of juvenile snakes to consume a wide range of encountered prey shapes and sizes.

Allometric growth in the skull of Tylosaurus proriger (Squamata: Mosasauridae) and its taxonomic implications

“…Some insight might be gained through consideration of their purported closest living relatives, snakes and varanids (Lee 1997;Conrad 2008). In the banded watersnake (Nerodia fasciata), frontal width and maxilla length are isometric, and quadrate length (= height in this study) and mandible length are positively allometric (Hampton 2014). Growth in other skull variables is also significantly allometric, but these have no equivalent in this study.…”

Patterns of morphological variation following colonization of a novel prey environment

“…Carrier () hypothesized that juveniles have exaggerated features that increase performance thus compensating for their smaller size. However, more recent investigators have found little evidence to support this hypothesis in feeding structure (Herrel & Gibb, ; Hampton, ). The patterns revealed in our study are consistent with these latter studies.…”

“…With only one exception (quadrate), each trait exhibited a negative allometry; a finding consistent with other studies of cranial morphology in snakes (e.g. Vincent et al ., ; Hampton, ). Both males and females were found to vary in scaling relationships among populations, at least for head length and lower jaw length.…”

“…For each snake captured, we measured the snout‐vent length (cm; SVL), mass (g), head length (mm; measured from the tip of the rostrum to the caudal end of the skull where it articulates with C1), lower jaw length (mm; measured from the rostral tip of the mandible to the caudal tip of the mandible) and quadrate length (mm; measured from the dorsal tip where it articulates with the supratemportal bone to the ventral tip where it articulates with the mandible). We chose to measure these cranial elements because they are common metrics for the study of head size in snakes, together they contribute to gape size, and their importance has been demonstrated in previous studies (Vincent et al ., ; Hampton, , ). Upon capture, we gently forced snakes with food in their guts to regurgintate prey and the prey item was identified and weighed (g) (Table ).…”

Relative Growth by the Elongated Jaws of Gars: A Perspective on Polyphasic Loglinear Allometry

“…b and c and b).Polyphasic loglinear allometry has been criticized on several occasions over the years (e.g., Ford and Horn, ’59; Gould, ), with one of the first critiques being coauthored by none other than Huxley himself (Reeve and Huxley, , p. 144). Despite the many expressions of concern, however, the procedure continues in wide use by contemporary biologists (e.g., Clemente et al., ; Glazier, ; Hampton, ; Lemaître et al., ; Pescinelli et al., ; Snelling et al., ). The current investigation confirms that reservations of the critics were well founded and that studies relying on polyphasic loglinear allometry are unlikely to provide accurate representations for patterns of variation in bivariate displays of untransformed variables. The best model fitted to both datasets by nonlinear regression is a power function with an unchanging exponent (Tables and ).…”