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Relationships between underwater vocalizations and mating systems in phocid seals
Abstract: In this paper, we considered the number and diversity of underwater vocalizations given by aquaticbreeding phocids, and two species that copulate both in the water and on ice, in relation to what is known or hypothesized about their mating systems. Underwater recordings made throughout the year by both bearded (Erignathus barbatus) and Weddell (Leptonychotes weddellii) seals indicated that most of the vocalizations could be attributed to males and were given almost exclusively during the breeding season. Less extensive studies of other species indicated the same pattern. Thus, for this study, we considered only underwater vocalizations known, or suspected, to be given by adult males during intra-specific agonistic behaviour, defence of territories or access to females, or attraction of females. A one-way ANOVA and linear regression indicated a significant relationship between the numbers of underwater vocalizations given by individual species and their mating systems. A Pearson’s correlation analysis discerned the following: the mating system and the number of vocalizations were positively correlated; female gregariousness was positively correlated with the number of underwater vocalizations and geographic variation in vocalizations, but there was no correlation with the duration of lactation. The degree of predation was negatively correlated with the number of vocalizations, geographic variation in vocalizations, and the number of days of lactation. A principal component analysis showed that 66.1% of the variation in this data set was explained by Factor 1, a suite of variables that included mating system, number of underwater vocalizations, intensity of predation, female gregariousness, and geographic variation in vocalizations. The number of days of lactation explained an additional 19.5% of the variability. These results suggest that additional selection pressures, more specific to the ecological circumstances of individual species, also influence the size of the underwater repertoire. The development of a diverse underwater repertoire with geographic variations was consistently associated with the development of population genetic structure and geographic fidelity. Within each category of social system, the species with the greatest number of underwater vocalizations consistently occurred at higher densities during the breeding season than did the species with the lowest vocal diversity. The role of predators on the evolution of social systems is not well known, but could be significant for some species. Characteristics of the underwater vocalizations of walruses during the breeding season were found to share similar characteristics to phocids occurring at similar densities in similar habitats, suggesting that the most important selection factors influenced both phocids and odobenids similarly. On the basis of the available information from better-studied species, some testable hypotheses are proposed for further investigations of spotted (Phoca largha), Ross (Ommatophoca rossii), Hawaiian monk (Monachus schauinslandi), and ribbon (Phoca fasciata) seals.
Key Words: VOCALIZATION; PINNIPEDS; PHOCID; SOCIAL; BEHAVIOUR; GEOGRAPHIC VARIATION; MATING SYSTEMS; PREDATION.
Document Type: Research article