Abstract
Southern Rockhopper Penguins Eudyptes chrysocome chrysocome exhibit marked intra-clutch egg size dimorphism and engage in obligate brood reduction of the first and smaller laid egg, with the rearing of the two nestlings occurring only on rare occasions. Studying the sex ratio of hatchlings within a brood in this species, under this breeding strategy context, is essential to understanding population dynamics. The objectives of this study were to analyze egg size dimorphism within the broods, determine the offspring sex ratio, and investigate if the hatchling sex ratio was determined by hatching order and egg volume to discuss potential biases in the context of brood reduction. We molecularly assessed hatchlings’ sex ratio according to the hatching order at Isla Pingüino, Argentina (3 years, n = 68 broods). Sex ratio was not different from the expected 50:50 proportion in all the studied years. In this sense, we found a balanced sex ratio in the first hatchlings, typically the survivors of the brood reduction process. Although not significant, we found a bias toward females in the second hatchlings. Assuming less energy is required to raise a female compared to a male, because of its smaller size; this strategy might enhance the chances of raising two nestlings if conditions are optimal. Southern Rockhopper Penguins at Isla Pingüino appear to exhibit a strategic sex allocation evident in the second but not in the first hatchlings, which might be consistent with its out-of-the-norm exponential growth population.
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Acknowledgements
We thank Javier Fernández from Darwin Expeditions for their help in the field. This study was financially supported by the Wildlife Conservation Society, Universidad Nacional de la Patagonia Austral, Consejo Nacional de Investigaciones Científicas, and Pan American Energy. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.
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MB contributed to Conceptualization (equal), Field work, Data curation, Formal analysis, and Writing of the original draft; VF contributed to Molecular analysis; AMo contributed to Field work and Reviewing of the final draft; NM contributed to Field work; AM contributed to Field work and Reviewing of the final draft; EF contributed to Conceptualization (equal); Field work; Writing, reviewing, and editing of the manuscript; and Funding acquisition (lead). All authors read and approved the manuscript.
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Ethical permission for this work was authorized by the Agrarian Council of Santa Cruz, Argentina (permit no. 491756/16).
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Barrionuevo, M., Morgenthaler, A., Ferretti, V. et al. Evaluating strategic offspring sex allocation in the Southern Rockhopper Penguins Eudyptes chrysocome chrysocome, a species with obligate brood reduction. Polar Biol 47, 305–308 (2024). https://doi.org/10.1007/s00300-024-03226-z
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DOI: https://doi.org/10.1007/s00300-024-03226-z