The scaling of tongue projection in the veiled chameleon, Chamaeleo calyptratus.

Within a year of hatching, chameleons can grow by up to two orders of magnitude in body mass. Rapid growth of the feeding mechanism means that bones, muscles, and movements change as chameleons grow while needing to maintain function. A previous morphological study showed that the musculoskeletal components of the feeding apparatus grow with negative allometry relative to snout-vent length (SVL) in chameleons. Here, we investigate the scaling of prey capture kinematics and muscle physiological cross-sectional area in the veiled chameleon, Chamaeleo calyptratus. The chameleons used in this study varied in size from approximately 3 to 18 cm SVL (1-200 g). Feeding sequences of 12 chameleons of different sizes were filmed and the timing of movements and the displacements and velocities of the jaws, tongue, and the hyolingual apparatus were quantified. Our results show that most muscle cross-sectional areas as well as tongue and hyoid mass scaled with isometry relative to mandible length, yet with negative allometry relative to SVL. Durations of movement also scaled with negative allometry relative to SVL and mandible length. Distances and angles generally scaled as predicted under geometric similarity (slopes of 1 and 0, respectively), while velocities generally scaled with slopes greater than 0 relative to SVL and mandible length. These data indicate that the velocity of jaw and tongue movements is generally greater in adults compared to juveniles. The discrepancy between the scaling of cross-sectional areas versus movements suggests changes in the energy storage and release mechanisms implicated in tongue projection.

Effects of rat visual, olfactory, or combined stimuli during cohousing on stress-related physiology and behavior in C57BL/6NCrl mice.

The Guide for the Care and Use of Laboratory Animals recommends housing rats and mice separately to reduce the potential for environmental stress to mice. The literature presents equivocal support for this practice, and housing practices vary widely. According to the existing literature, it is unclear whether visual, olfactory, or combined stimuli are responsible for stress-related changes in mouse physiology and behavior. To determine the extent to which exposure to visual, olfactory, or combined stimuli produce stress-related changes, measures of physiologic and behavioral stress were evaluated in mice after cohousing them in a room with rats. Adult, male C57BL/6NCrl mice (n = 8 per group) were randomly assigned to control, isolator cage, visual stimuli, olfactory stimuli, or visual+olfactory stimuli groups. After 15 d of exposure, body, and adrenal weights did not differ between groups. None of the groups of mice experienced significant increases in corticosterone or stress-related behavior in the open-field test after exposure to rat stimuli. These results suggest that the stress-related effects of cohousing with rats are negligible in mice and have implications for housing rats and mice in shared rooms, thereby al- lowing efficient use of research resources.