Mammals diversified by colonizing drastically different environments, with each transition yielding numerous molecular changes, including losses of protein function. Though not initially deleterious, these losses could subsequently carry deleterious pleiotropic consequences. We have used phylogenetic methods to identify convergent functional losses across independent marine mammal lineages. In one extreme case, () accrued lesions in all marine lineages, while remaining intact in all terrestrial mammals. These lesions coincide with PON1 enzymatic activity loss in marine species' blood plasma. This convergent loss is likely explained by parallel shifts in marine ancestors' lipid metabolism and/or bloodstream oxidative environment affecting PON1's role in fatty acid oxidation. PON1 loss also eliminates marine mammals' main defense against neurotoxicity from specific man-made organophosphorus compounds, implying potential risks in modern environments.

SUMMARYThe purpose of this study was to compare underwater behavioral and auditory evoked potential (AEP) audiograms in a single captive adult loggerhead sea turtle (Caretta caretta). The behavioral audiogram was collected using a go/no-go response procedure and a modified staircase method of threshold determination. AEP thresholds were measured using subdermal electrodes placed beneath the frontoparietal scale, dorsal to the midbrain. Both methods showed the loggerhead sea turtle to have low frequency hearing with best sensitivity between 100 and 400Hz. AEP testing yielded thresholds from 100 to 1131Hz with best sensitivity at 200 and 400Hz (110dBre.1Pa). Behavioral testing using 2s tonal stimuli yielded underwater thresholds from 50 to 800Hz with best sensitivity at 100Hz (98dBre.1Pa). Behavioral thresholds averaged 8dB lower than AEP thresholds from 100 to 400Hz and 5dB higher at 800Hz. The results suggest that AEP testing can be a good alternative to measuring a behavioral audiogram with wild or untrained marine turtles and when time is a crucial factor.

This Corrigendum relates to J. Exp. Biol. 215, 1442-1447 The authors misunderstood JEB's policies on citing non-peer-reviewed literature, and failed to cite the dissertation of Gerstein (Gerstein, 1999), who also measured critical ratios in two captive manatees.Gerstein measured critical ratios using both pulsed and continuous (4s) tones in the presence of 1/3-octave wide masking noise using two different noise levels. The critical ratios were lower for the pulsed tones than the continuous tone. Although we did not test the same frequencies, our measurements of critical ratios in two other manatees were similar or lower for similar test frequencies for the continuous tone. For example, we measured critical ratios from two manatees at 4kHz of 30.8 and 29.9dB, while Gerstein measured critical ratios at 3kHz of 31 and 34dB. At 16kHz we measured critical ratios of 27.0 and 28.1dB, while Gerstein measured critical ratios of 38 and 42dB at 18kHz. The results Gerstein obtained for the pulsed tones were closer to the critical ratios we measured with the 1s tone.