Phylogenetic relationships among the true porpoises (Cetacea:Phocoenidae).

Portions of the cytochrome b gene and control region of the mitochondrial DNA molecule were sequenced to investigate systematic relationships among the six extant species of true porpoises, (Cetacea: Phocoenidae). Phylogenetic analyses of mitochondrial cytochrome b sequences support a close relationship between Burmeister's porpoise, Phocoena spinipinnis, and the vaquita, Phocoena sinus, and the association of these two species with the spectacled porpoise, Australophocaena dioptrica. The latter result is not in concordance with a recent morphological reclassification which groups A. dioptrica with Dall's porpoise, Phocoenoides dalli, in the subfamily Phocoenoidinae. The molecular analysis found no support for this grouping. A. dioptrica was originally described as a member of the genus Phocoena, and our results support returning it to that genus at this time. Finally, the data suggest that the tropical species Neophocaena phocaenoides, the finless porpoise, may represent the most basal member of the family. The control region sequences corroborated the relationships among the closely related taxa P. sinus, P. spinipinnis, and A. dioptrica, but were unable to resolve the deeper branches of the tree, probably as a result of a high level of saturation of these sequences.

Hypoxia and auditory thresholds.

This paper reports the effects of hypoxia on hearing. Pure tone hearing and speech discrimination were tested at ground level and during hypoxic states at simulated altitudes of 4,600 m (15,000 ft) and 6,100 m (20,000 ft) in a high-altitude chamber. Pure tone hearing was not significantly altered during hypoxia produced by this method. Speech discrimination showed alterations, possibly due to central nervous system hypoxia. It was concluded that hypoxia does not cause significant deterioration of hearing for pure tones.