Control and Co-Ordination of Gas Exchange in Bimodal Breathers

Abstract

DOI https://doi.org/10.1007/978-3-642-75380-0 Copyright Information Springer-Verlag Berlin Heidelberg 1990 Publisher Name Springer, Berlin, Heidelberg chapter 9 The ability to exchange respiratory gases effectively in either air or water has been exploited by a wide variety of amphibious vertebrates. The partitioning of O2 and CO2 transfer between aerial and aquatic exchange sites is a function of the exchange organs’ surface area, blood-to-medium diffusion distances and ventilation-perfusion ratios (see Piiper, this Vol.). In addition, the physical properties of water and air place different demands on the respiratory organs (Dejours 1981; Piiper 1982), and this is thought to have had important consequences, during evolution, on the design and performance of gas exchange organs in bimodal breathers (Johansen 1970; Randall et al. 1981; Shelton and Boutilier 1982; Shelton et al. 1986). It is generally accepted that a major selective force in the evolution of the air-breathing habit was aquatic hypoxia (Packard 1974), enabling those animals with air-breathing organs to remain in the warm, O2-deficient waters that are thought to have existed in the Upper Devonian (Inger 1957). Indeed, the intermittent use of air-breathing organs by extant vertebrates is indicative of this, where constraints on aquatic gas exchange lead to a periodic need for supplemental forms of gas exchange.