Spiracular air breathing in polypterid fishes and its implications for aerial respiration in stem tetrapods.
The polypterids (bichirs and ropefish) are extant basal actinopterygian (ray-finned) fishes that breathe air and share similarities with extant lobe-finned sarcopterygians (lungfishes and tetrapods) in lung structure. They are also similar to some fossil sarcopterygians, including stem tetrapods, in having large paired openings (spiracles) on top of their head. The role of spiracles in polypterid respiration has been unclear, with early reports suggesting that polypterids could inhale air through the spiracles, while later reports have largely dismissed such observations. Here we resolve the 100-year-old mystery by presenting structural, behavioural, video, kinematic and pressure data that show spiracle-mediated aspiration accounts for up to 93% of all air breaths in four species of Polypterus. Similarity in the size and position of polypterid spiracles with those of some stem tetrapods suggests that spiracular air breathing may have been an important respiratory strategy during the fish-tetrapod transition from water to land.
Marine Biology Research Division, Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA.
Jeffrey B
JB
Graham
1] Marine Biology Research Division, Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA [2] Fisheries Resource Division, Southwest Fisheries Science Center, NOAA Fisheries, La Jolla, California 92037, USA.
Nicholas C
NC
Wegner
Marine Biology Research Division, Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA.
Lauren A
LA
Miller
Marine Biology Research Division, Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA.
Corey J
CJ
Jew
1] Marine Biology Research Division, Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA [2] VA San Diego Healthcare System, San Diego, California 92161, USA.
N Chin
NC
Lai
Department of Radiology, Center for Scientific Computation in Imaging, University of California San Diego, La Jolla, California 92037, USA.
Rachel M
RM
Berquist
Department of Radiology, Center for Scientific Computation in Imaging, University of California San Diego, La Jolla, California 92037, USA.
Lawrence R
LR
Frank
1] School of Biological Sciences, Flinders University, Adelaide, South Australia 5001, Australia [2] Natural History Museum of Los Angeles County, Los Angeles, California 90007, USA.
John A
JA
Long
D000818:Animals; D005075:Biological Evolution; D005399:Fishes; D005580:Fossils; D012119:Respiration