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Sex-ratio of Little Penguin (Eudyptula minor) on Penguin Island and Garden Island, Western Australia

Povah, Ryan S. (2021) Sex-ratio of Little Penguin (Eudyptula minor) on Penguin Island and Garden Island, Western Australia. Honours thesis, Murdoch University.

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Abstract

Sex-ratio is an important demographic parameter, however, the literature surrounding bird and mammal sex-ratio is incredibly inconsistent. Some bird and mammal species provide strong evidence for sex-ratio adjustment because observed sex-ratio results match the predictions of sex manipulation hypotheses. However, some bird and mammal species exhibit sex-ratio results that conflict with the predictions of sex manipulation hypotheses. The need to rectify bird and mammal sex-ratio inconsistencies is paramount when considering many conserved populations face demographic collapse in the presence of climate change. Therefore, this study has reviewed all known bird and mammal sex manipulation hypotheses, and chosen to examine a species that theoretically displays few sex manipulation hypotheses for a simple study design. Displaying two sex manipulation hypotheses, Little Penguins (Eudyptula minor) were predicted to exhibit an even sex-ratio; whether they possessed the means to adjust sex-ratio or not.

To test the above prediction, Little Penguin blood samples were retrieved from chicks nesting on Penguin Island and Garden Island and sexed via the CHDI genetic sexing technique, using the established PL/PR primer pair. Little Penguin chick weight and foot length data were also recorded and examined via the logistic growth curve to determine whether the study’s assumption of ‘equal net costs associated with raising either offspring sex’ was true. The sex-ratio for Little Penguin populations on Penguin Island and Garden Island was marginally female-biased, (P = 0.092 and 0.096 respectively). Possible reasons why the predicted sex-ratio of 1:1 was not observed are;(1) the prediction was based on inaccurate species knowledge as the assumption of ‘equal net costs associated with raising either offspring sex’ was determined false, (2) a small sample size for both Penguin Island and Garden Island (41 and 19 respectively), or (3) aspects beyond those covered in sex manipulation hypotheses influenced what the most adaptive brood sex-ratio is for the species, such as sex manipulation constraints, a lagged processes, or cryptic benefits.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Environmental and Conservation Sciences
Supervisor(s): Chaplin, Jennifer and Cannell, Belinda
URI: http://researchrepository.murdoch.edu.au/id/eprint/61632
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