DOUGLAS III, H.D.; Univ. of Alaska Fairbanks: Interspecific differences in Aethia auklet odorants and evidence for chemical signaling and chemical defense

Crested and whiskered auklets are closely related plankton-feeding seabirds of the North Pacific. Both species produce volatile citrus-like odorants. I show that the odorants differ in chemical composition. I suggest that these odorants could function in chemical signaling to conspecifics and in chemical defense against ectoparasites. The Crested Auklet Aethia cristatella emits an odorant dominated by saturated and mono-unsaturated aldehdyes, ranging in size from 6 to 12 carbons. Chemical composition of this odorant is similar across populations. By contrast the Whiskered Auklet Aethia pygmaea emits an odorant dominated by two odd-numbered aldehydes (heptanal and nonanal) with no unsaturated aldehydes. This is evidence of species-specific acquisition or biosynthetic pathways. The contrast in odor chemistry mirrors similar divergent patterns in plumage ornaments, courtship vocalizations, and courtship behavior. Crested Auklets acquire their odorant in spring and stop emitting the odor during chick rearing. Crested Auklets favor models scented with synthetic analogues of their odorant, and experiments with captive birds suggest a heightened response prior to copulation. Bioassays with synthetic analogs of the crested auklet odorant killed or repelled ectoparasites with an efficacy similar to commercial arthropod repellents. However, the evidence for chemical defense is not so clear-cut in nature. Crested Auklets have higher abundances of ectoparasites than a closely related species. Also mortality trials with pigeon lice suspended above plumage showed no effect for the crested auklet treatment. Nevertheless, auklet lice were killed when exposed to nicks in the skin of Crested Auklets, while the control treatment had no effect. In nature the Crested Auklet�s odorant may cause sublethal interference with ectoparasites such as paralysis or impairment.