On the evolutionary and ecological significance of ornamental traits: the function and variability of the visual and acoustic displays of auklets (Aethiini, Alcidae, Charadriiformes)

Seneviratne, Sampath Sumedha (2008) On the evolutionary and ecological significance of ornamental traits: the function and variability of the visual and acoustic displays of auklets (Aethiini, Alcidae, Charadriiformes). Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The occurrence of extravagant display traits in animals can be explained by their phylogenetic history, and adaptations to the physical and social environment. None of these processes are mutually exclusive, however. The primary objective of my study was to elucidate the roles of such processes on evolution of ornamental and vocal traits in a monophyletic group of North Pacific seabirds - the auklets (Alcidae, Aethiini). Sexual selection has been the main explanation for the evolution of feather ornaments such as the elongated facial plumes of auklets. My experimental evidence pointed towards a mechanosensory use for the long facial plumes of Whiskered Auklet (Aethia pygmaea), a crevice dwelling and nocturnal seabird. While navigating inside a lightproof maze simulating the conditions of breeding crevices, Whiskered Auklets had more than double the frequency of head bumps (275%) in the absence of the protruding feathers. Tracing the hylogenetic pattern in several closely related auklet species (Aethia) revealed that only the ornamented younger species that breed in deep crevices have the mechanosensory ability. A pairwise analysis across all non-passerine bird families suggested a greater frequency of long facial plumes in species that live in complex habitats or active in low light conditions. Birds inhabiting cluttered environments would benefit from projecting long facial plumage that mechanically detects obstacles. Thus, once the primordial mechanosensory feather structures evolved through the selective pressure enforced by the habitat, sexual and other selection processes may have acted on these traits and led towards further elaboration. Vocal repertoires of breeding auklets were categorized and quantified to provide a baseline for a comparative study of the evolution of vocalization. Similar to their visual display, auklet vocal repertoires were complex and large (~25 display types across species) with 3-5 vocal display types for each species. There were vocal homologies in the frequency modulation of notes, and arrangement and composition of note types in display. Unlearned vocalizations of non-oscine birds such as auklets' are likely to be informative as to phylogenetic affinities. To test the hypothesis that phylogenetic relationships are the major determinant of vocal evolution in auklets, large number of vocal and syringeal characters were mapped onto a molecular phylogeny based on a combination of mitochondrial and nuclear DNA characters. Low Consistency and Retention Indices (CI = 0.70, Rl = 0.10) indicated a poor fit between molecular and vocal phylogeny. Temporal and syringeal attributes showed a greater congruence with molecular trees than do frequency attributes. A combination of factors including phylogenetic relatedness, visual ornaments, and the acoustic properties of the breeding habitat may have played roles in vocal divergence in auklets. Taken together, these results indicated a complex evolutionary pattern in visual and vocal display in Aethiini, suggesting that although visual and vocal display have evolved in close association with species divergence, natural and sexual selection have created patterns across species that are at odds with phylogeny.

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