In Defense of Chemical Defense: Quantification of Volatile Chemicals in Feathers is Challenging
[摘要] I believe that the methods employed by (
Hagelin et al. 2003) did not ensure accurate quantitative or qualitative measurements of the Crested Auklet odorant as it occurs in nature, and I suggested this to Hagelin in September 2002. My concern, then and now, is that feather samples stored in vials, in air, at temperatures well above 0°C, would be subject to oxidation. Aliphatic aldehydes like those that constitute the Crested Auklet's odorant are inherently unstable and readily oxidize in the presence of air (
Mann 1994,
Loudon 2002). The large surface area of bird feathers provides ample reaction sites for oxidation of feather lipids. As a result, constituents of the Crested Auklet odorant could diminish or disappear, and other chemical compounds could arise. Some differences in results can be expected because of differences in methods (
Raguso and Pellmyr 1998) or natural variability; however, the common and widespread problem of lipid oxidation is a more parsimonious explanation in this case. Until Hagelin and Jones produce estimates of sample degradation for their storage methods, they cannot make meaningful quantitative extrapolations from their data to other studies. Furthermore, to evaluate hypotheses regarding odorant function, it is important to have an accurate qualitative characterization of its composition as it occurs in nature. The point here is not to disparage previous work that went forward when less was known but to update and clarify the literature and point out a potential pitfall. Scientists researching avian odorants must be cognizant of problems with lipid oxidation, and they can increase confidence in their results by giving attention to methods development and validation.
