Funding: The research was financially supported by the Holsworth Wildlife Research Endowment. Acknowledgments We thank the Victorian Marine Science Consortium, Sea All Dolphin Swim, Parks Victoria, and the Point Danger Management Committee for logistical support. We are grateful for the assistance of the many field volunteers involved in the study.Peer reviewedPublisher PD

A Bunce

A Kato

A Velando

AD Ewing

AI Bijleveld

AI Schulte-Hostedde

AJ Hobday

AJ Mata

AV Hedrick

C Barbraud

C Daniel

C Moseley

C Stauss

CB Zavalaga

CL Hull

D Halliday

DJ Fairbairn

DR Evans

EJ Wingham

Emma Tew

EN Flint

F Dechaume-Moncharmont

GH Golet

GM Rishworth

H Lormee

H Weimerskirch

HN Layton

IR Cleasby

J Fairbairn

J Navarro

J Schultner

J Warham

JA Amat

JA Castillo-Guerrero

JA Green

JB Nelson

JC Coulson

JC Hennicke

JD Gilardi

JD Rising

JE Lovich

JL Schamber

JM Lough

John P. Y. Arnould

John R. Speakman

JP Croxall

JPY Arnould

KE Erikstad

KH Elliott

Lauren P. Angel

LB Spear

LD Einoder

M Bosch

M Guerra

M Renner

MA Serrano-Meneses

Marlenne A. Rodríguez-Malagón

Melanie R. Wells

MG Forero

MK Labocha

NC Stenseth

O Chastel

P Monaghan

R Gales

R Shine

RHE Mullers

Roberto Ambrosini

S Barker

S Choudhury

S Guggenheimer

S Lewis

SA Patterson

SA Shaffer

SMH Ismar

TM Pyk

TW O'Dwyer

VA Viblanc

Y Ropert-Coudert

PLoS ONE

English

PubMed

Crossref

Sexual Size Dimorphism and Body Condition in the Australasian Gannet

Funding: The research was financially supported by the Holsworth Wildlife Research Endowment. Acknowledgments We thank the Victorian Marine Science Consortium, Sea All Dolphin Swim, Parks Victoria, and the Point Danger Management Committee for logistical support. We are grateful for the assistance of the many field volunteers involved in the study.Peer reviewe

Angel, Lauren P

Wells, Melanie R

Rodríguez-Malagón, Marlenne A

Tew, Emma

Speakman, John R

Arnould, John P Y

Aberdeen University Research

<div>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.</div

Lauren P. Angel (803806)

Melanie R. Wells (833825)

Marlenne A. Rodríguez-Malagón (833826)

Emma Tew (833827)

John R. Speakman (380055)

John P. Y. Arnould (254857)

The Francis Crick Institute

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

Sexual Size Dimorphism and Body Condition in the Australasian Gannet

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