Meeting Abstract
S3-1.7 Saturday, Jan. 5 Physiology in deep time: Using extant vertebrates to model behavioral and functional aspects of the Devonian land transition JEW, C.J.*; WEGNER, N.C.; GRAHAM, J.B.; University of California, San Diego, Scripps Institution of Oceanography; University of California, San Diego, Scripps Institution of Oceanography; University of California, San Diego, Scripps Institution of Oceanography cjew@ucsd.edu
Extant air-breathing fishes can be used to infer the physiological and behavioral changes that occurred during the fish-tetrapod land invasion (early Middle to Late Devionian) that otherwise could not be studied due to the lack of living stem tetrapods. Here we describe two such projects from the laboratory of the late Jeffrey B. Graham. Mudskippers (Teleostei: Gobiidae), which possess many respiratory and locomotive specializations for amphibious life, were used to study how changing atmospheric O2 concentrations in the late Paleozoic may have influenced the emergence and subsequent radiation of the first tetrapods. Japanese mudskippers (Periophthalmus modestus) exercised on a treadmill under 7, 21, and 35% atmospheric O2 revealed that hyperoxia increased both terrestrial endurance and aerial O2 uptake efficiency in the buccopharyngeal chamber following exercise. Extrapolated to early tetrapods, this suggests higher lung efficiency in hyperoxia that may have allowed for increased aerobic performance on land and a decreased reliance on skin respiration, permitting the skin to become more resistant to water loss and allowing for prolonged excursions farther from water. In a second study, we examined bimodal (lung and gill) breathing in Polypterus, a basal ray-fin fish. Structural, behavioral, video, and pressure data show that under unstressed conditions Polypterus uses it spiracles (dorsally located openings on the skull) for up to 93% of its air breaths. Similarities in size and position of polypterid spiracles with those of some stem tetrapods suggest the use of spiracles for breathing air during the fish-tetrapod land transition.
