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Sexual size dimorphism and body condition in the Australasian Gannet

Angel, Lauren P., Wells, Melanie R., Rodríguez-Malagón, Marlenne A., Tew, Emma, Speakman, John R. and Arnould, Johyn P. Y. 2015, Sexual size dimorphism and body condition in the Australasian Gannet, PLoS one, vol. 10, no. 12, Article number : e0142653, pp. 1-16, doi: 10.1371/journal.pone.0142653.

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Title Sexual size dimorphism and body condition in the Australasian Gannet
Author(s) Angel, Lauren P.ORCID iD for Angel, Lauren P. orcid.org/0000-0002-8696-3945
Wells, Melanie R.
Rodríguez-Malagón, Marlenne A.
Tew, Emma
Speakman, John R.
Arnould, Johyn P. Y.ORCID iD for Arnould, Johyn P. Y. orcid.org/0000-0003-1124-9330
Journal name PLoS one
Volume number 10
Issue number 12
Season Article number : e0142653
Start page 1
End page 16
Total pages 16
Publisher Public Library of Science
Place of publication San Francisco, Calif.
Publication date 2015-12-04
ISSN 1932-6203
Summary Sexual size dimorphism is widespread throughout seabird taxa and several drivers leading to its evolution have been hypothesised. While the Australasian Gannet (Morus serrator) has previously been considered nominally monomorphic, recent studies have documented sexual segregation in diet and foraging areas, traits often associated with size dimorphism. The present study investigated the sex differences in body mass and structural size of this species at two colonies (Pope's Eye, PE; Point Danger, PD) in northern Bass Strait, south-eastern Australia. Females were found to be 3.1% and 7.3% heavier (2.74 ± 0.03, n = 92; 2.67 ± 0.03 kg, n = 43) than males (2.66 ± 0.03, n = 92; 2.48 ± 0.03 kg, n = 43) at PE and PD, respectively. Females were also larger in wing ulna length (0.8% both colonies) but smaller in bill depth (PE: 2.2%; PD: 1.7%) than males. Despite this dimorphism, a discriminant function provided only mild accuracy in determining sex. A similar degree of dimorphism was also found within breeding pairs, however assortative mating was not apparent at either colony (R2 < 0.04). Using hydrogen isotope dilution, a body condition index was developed from morphometrics to estimate total body fat (TBF) stores, where TBF(%) = 24.43+1.94*(body mass/wing ulna length) - 0.58*tarsus length (r2 = 0.84, n = 15). This index was used to estimate body composition in all sampled individuals. There was no significant difference in TBF(%) between the sexes for any stage of breeding or in any year of the study at either colony suggesting that, despite a greater body mass, females were not in a better condition than males. While the driving mechanism for sexual dimorphism in this species is currently unknown, studies of other Sulids indicate segregation in foraging behaviour, habitat and diet may be a contributing factor.
Language eng
DOI 10.1371/journal.pone.0142653
Field of Research 060809 Vertebrate Biology
060205 Marine and Estuarine Ecology (incl Marine Ichthyology)
060308 Life Histories
Socio Economic Objective 970106 Expanding Knowledge in the Biological Sciences
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2015, The Authors
Free to Read? Yes
Use Rights Creative Commons Attribution licence
Persistent URL http://hdl.handle.net/10536/DRO/DU:30080520

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Every reasonable effort has been made to ensure that permission has been obtained for items included in DRO. If you believe that your rights have been infringed by this repository, please contact drosupport@deakin.edu.au.