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Constraints on maternal ability to adjust sex ratios in mammals


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Edwards, AM 2016 , 'Constraints on maternal ability to adjust sex ratios in mammals', PhD thesis, University of Tasmania.

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Sex allocation theory predicts that mothers would benefit from sex-biased
differential investment into offspring in relation to their current local condition when
it maximizes their lifetime reproductive return. In mammals, however, the extent of
the sex bias at birth is often unpredictable, suggesting that mothers may be
constrained in their ability to adjust sex ratios. None of the current hypothesized
mechanisms of peri-conceptual mammalian maternal sex allocation fully explain the
amount of variation observed, and as such I suggested three possible physiological
constraints on maternal sex allocation. Firstly, mothers may be constrained by
variation in physiological traits, particularly mediated during their own early
development through in utero effects, such as testosterone levels and responsiveness
to stress. I tested the effects of physiological changes caused by down-regulated
stress during in utero development, and showed significant physiological changes in
females, as a result of mismatching pre- and post-natal environments, that skewed
sex ratios in the next generation. However, artificially lowering the stress of these
females at conception will cause the sex ratio to return to parity, as the pre- and postnatal
environments match again. Secondly, their physiology may be influenced more
proximally, by not only their current condition or ability to invest, but by clinically
asymptomatic disease and parasitic infection, particularly manipulative parasites.
Lastly, paternal influences such as sperm sex ratios and seminal plasma constituents
have been largely overlooked but may influence and constrain maternal ability to
adjust sex ratios. I showed evidence of variations in sperm sex ratios, both in the
literature and through observational studies where we would expect parity as a result
of meiosis during sperm production. I also presented the first evidence of paternal
sex allocation, through changes in sperm sex ratios and seminal plasma constituents
in relation to coital rate, as a proxy of male attractiveness. The possibility of
complementary or antagonistic interactions between maternal and paternal sex
allocation should now be accounted for in future research. Overall, my thesis has
provided explanations into previously unexplained variation in sex allocation
research, and may assist with improvements to conservation breeding and livestock
industries, as well as human health developments.

Item Type: Thesis - PhD
Authors/Creators:Edwards, AM
Keywords: Sex allocation, sex ratio, maternal investment, paternal investment, sperm, differential allocation
Copyright Information:

Copyright 2016 the Author

Additional Information:

Chapter 2 has been published as: Edwards, A.M., Cameron, E.Z., Pereira, J.C., Wapstra, E., Ferguson-Smith, M.A., Horton, S.R., Thomasson, K., (2016), Gestational experience alters sex allocation in the subsequent generation. Royal society open science, 3, 1-8, under the terms of the Creative Commons Attribution License, which permits unrestricted use, provided the original author and source are credited.

Chapter 3 appears to be the equivalent of an author's original version. This article has been accepted for publication in Behavioral ecology, published by Oxford University Press.

Chapter 6 appears to be the equivalent of a post print version of an article published as: Edwards, A.M., Cameron, E.Z., (2016), Cryptic male choice: experimental evidence of sperm sex ratio and seminal fluid adjustment in relation to coital rate, Reproduction, fertility and development, published online: 30 May 2016

Chapters 1, 4 and 5 have been removed for copyright or proprietary reasons.

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