Variation in pulmonary compliance and lung volume is associated with lymph mobilization capabilities in anuran amphibians

Abstract

Lymph movement to dorsally-located lymph hearts in anurans is accomplished by specific skeletal muscles, lymph sac compliance and lung ventilation. We hypothesize that species with increased pulmonary compliance (Cpul) and lung volume (Vlung) will be more effective at changing lymph sac compliance and lymph mobilization. Thus, terrestrial species should have greater Cpul and Vlung compared with aquatic species. This study examined the variation in Cpul and Vlung in 18 anuran species representing 7 families that span a large range of body mass (M) and ecomorph types. Maximal lung compliance (Cmax) scaled to M0.77 (r2 = 48%) while Vlung scaled to M0.66 (r2 = 37%). Body shape did not explain the variation in Cmax and Vlung because there was a strong correlation between M and snout-vent length (r2 = 94%). Lymph flux rates, measured in a previous study, were highest in a terrestrial bufonid (Rhinella marina) compared with a semi-aquatic ranid (Lithobates catesbeianus) and an aquatic pipid (Xenopus laevis). Cmax and Vlung were significantly different between these three species with R. marina > L. catesbeianus > X. laevis; thus, there is a strong correlation between lymph flux rate and Cmax and Vlung. We suggest that the considerable variation in Cpul and Vlung is primarily explained by species' ecomorphology and related to lymph flux requirements in different environments. Supported by NSF-IOS 0843082.