Respiratory Biology during Gravidity in Crotaphytus collarisand Gambelia wislizenii
During gravidity lizards experience a striking decrease in lung volume as a result of lung compression by eggs growing within the body cavity. In order to understand the effect of this decrease in lung volume on the respiratory biology of gravid egg-laying lizards, we measured changes in total lung volume, resting and postexercise expired volume, minute volume, respiratory frequency, and carbon dioxide production rate during reproduction in the Collared Lizard, Crotaphytus collaris, and the Leopard Lizard, Gambelia wislizenii. We found that compression of the lungs by shelled eggs resulted in an average 48% (range: 26–70%) decrease in total lung volume compared to the same postlaying C. collaris females, and an average 38% (range: 29–46%) decrease in G. wislizenii. CO2 production rates were altered significantly during reproduction in female C. collaris and were 58% higher in females carrying late-stage follicles, compared to after laying. Despite the remarkable reduction in lung volume in both of these species and the increase in CO2 production rates in C. collaris, no ventilation parameters changed over the course of reproduction. The highly distensible body cavities of C. collaris and G. wislizenii appear to be able to accommodate both growing eggs and adequate lung volumes for normal respiratory function during gravidity.Abstract
Images from computed-tomography (CT) scans of females of Crotaphytus collaris and Gambelia wislizenii. The four groups of images are lateral (left image) and dorsal–ventral (right image) views. Black areas within the body cavity are lungs (L) and gray areas at the mid to lower end of the body are eggs (E) in A and C. (A) Gravid female of C. collaris (relative clutch mass 28% with associated 70% reduction in lung volume). (B) The same female of C. collaris after laying. (C) Gravid female of G. wislizenii (relative clutch mass 44% with associated 46% reduction in lung volume). (D) The same female of G. wislizenii after laying. White 5-mm scale bars are located in the lower right area of each scan. Image depth is 0.2 mm.
CO2 production rate throughout the reproductive cycle in females, and males of Crotaphytus collaris and Gambelia wislizenii. Values are shown as mean and SE. The sample size for each category is shown at the base of each bar. There were significant changes in CO2 production rates during reproduction in females of C. collaris (P = 0.01). Stars denote the largest difference between groups (58%).
Breathing frequency, resting expired volume, and minute ventilation of individuals of Crotaphytus collaris and Gambelia wislizenii. Values are shown as mean and SE. Sample sizes for each category are shown at the base of each bar and are the same within each category for all respiratory parameters unless noted otherwise. There were no significant differences among different stages in females in either species, or between postreproductive female and male G. wislizenii. Postreproductive females had significantly higher breathing frequencies than males of C. collaris (P = 0.04).
Postexercise expired volume throughout the reproductive cycle in females, and males of Crotaphytus collaris and Gambelia wislizenii. Values are shown as mean and SE. The sample size for each category is shown at the base of each bar. There were no significant differences in postexercise expired volume among different stages in females and between postreproductive females and males, within a species.
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