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Having a big nose: structure, ontogeny, and function of the elephant seal proboscis

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The proboscis of male elephant seals (Mirounga Gray, 1827) has been suggested as an example of a secondary sexual trait since Darwin. There has been much speculation about its social function (e.g., optical signal of breeding status, amplification of vocalizations, cue for female choice). However, it has never been studied in detail, probably because its fleshy nature makes measurement difficult. In this paper, we employ photogrammetry to measure the proboscis and facial morphology of a large sample of wild, unrestrained, displaying male southern elephant seals (Mirounga leonina (L., 1758)). We describe ontogeny and allometry of the proboscis and analyze current phenotypic selection pressures on proboscis traits. We discuss the potential role of the proboscis in optical and acoustic signaling of male resource-holding potential and status. We demonstrate that proboscis size is positively correlated with age and body size independently, and that it is currently under a positive sexual selection pressure when the effect of selection on body size is removed. We suggest that selection on proboscis size is functionally related to the emission of agonistic vocalizations.

À la suite de Darwin, on considère le proboscis des éléphants de mer (Mirounga Gray, 1827) comme un exemple de caractère sexuel secondaire. On a beaucoup spéculé sur la fonction sociale de cet organe (par exemple, comme signal optique du statut reproductif, amplificateur des vocalises, signal pour le choix des femelles). On ne l’a cependant jamais étudié en détail, probablement parce que sa nature charnue rend les mesures difficiles. Dans notre étude, nous utilisons la photogrammétrie pour mesurer le proboscis et la morphologie faciale chez un grand échantillon d’éléphants de mer du Sud (Mirounga leonina (L., 1758)) mâles, sauvages et libres au moment de leurs parades reproductives. Nous décrivons l’ontogénie et l’allométrie du proboscis et nous analysons les pressions phénotypes actuelles de sélection sur les caractères du proboscis. Nous discutons du rôle potentiel du proboscis dans la signalisation optique et acoustique du statut du mâle et de son potentiel de possession de ressources. Nous démontrons l’existence d’une corrélation positive indépendante entre la taille du proboscis, d’une part, et l’âge et la taille corporelle, d’autre part; la taille du proboscis est l’objet d’une sélection sexuelle positive, une fois retiré l’effet de la sélection sur la taille corporelle. Nous croyons que la sélection de la taille du proboscis est reliée fonctionnellement à l’émission de vocalises agonistes.

Document Type: Research Article

Publication date: 2007-02-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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