title: Sex-Based Differences in Adélie Penguin (Pygoscelis adeliae) Chick Growth Rates and Diet.
abstract: Sexually size-dimorphic species must show some difference between the sexes in growth rate and/or length of growing period. Such differences in growth parameters can cause the sexes to be impacted by environmental variability in different ways, and understanding these differences allows a better understanding of patterns in productivity between individuals and populations. We investigated differences in growth rate and diet between male and female Adélie Penguin (Pygoscelis adeliae) chicks during two breeding seasons at Cape Crozier, Ross Island, Antarctica. Adélie Penguins are a slightly dimorphic species, with adult males averaging larger than adult females in mass (~11%) as well as bill (~8%) and flipper length (~3%). We measured mass and length of flipper, bill, tibiotarsus, and foot at 5-day intervals for 45 male and 40 female individually-marked chicks. Chick sex was molecularly determined from feathers. We used linear mixed effects models to estimate daily growth rate as a function of chick sex, while controlling for hatching order, brood size, year, and potential variation in breeding quality between pairs of parents. Accounting for season and hatching order, male chicks gained mass an average of 15.6 g d(-1) faster than females. Similarly, growth in bill length was faster for males, and the calculated bill size difference at fledging was similar to that observed in adults. There was no evidence for sex-based differences in growth of other morphological features. Adélie diet at Ross Island is composed almost entirely of two species--one krill (Euphausia crystallorophias) and one fish (Pleuragramma antarctica), with fish having a higher caloric value. Using isotopic analyses of feather samples, we also determined that male chicks were fed a higher proportion of fish than female chicks. The related differences in provisioning and growth rates of male and female offspring provides a greater understanding of the ways in which ecological factors may impact the two sexes differently.
authors.affiliation: Oregon Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR, United States of America.
authors.forename: Scott
authors.initials: S
authors.lastname: Jennings
authors.affiliation: School of Biological Sciences and Biomolecular Interaction Centre, University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand.|Electron Microscope Unit, Division of Medical Biochemistry, Department of Clinical Laboratory Sciences, University of Cape Town, Observatory, 7700, South Africa.|Department of Plant Pathology and Emerging Pathogens Institute, University of Florida, Gainesville, FL 32611, United States of America.
authors.forename: Arvind
authors.initials: A
authors.lastname: Varsani
authors.affiliation: U.S. Geological Survey, Oregon Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR, United States of America.
authors.forename: Katie M
authors.initials: KM
authors.lastname: Dugger
authors.affiliation: Point Blue Conservation Science, Petaluma, CA, United States of America.
authors.forename: Grant
authors.initials: G
authors.lastname: Ballard
authors.affiliation: H.T. Harvey and Associates, Los Gatos, CA, United States of America.
authors.forename: David G
authors.initials: DG
authors.lastname: Ainley
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000864:Antarctic Regions; D004032:Diet; D005260:Female; D008297:Male; D008954:Models, Biological; D012621:Seasons; D012727:Sex Characteristics; D046429:Spheniscidae / Q000254:growth & development* / Q000502:physiology