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Research Article

Ovulation Order Mediates a Trade-Off between Pre-Hatching and Post-Hatching Viability in an Altricial Bird

  • Keith W. Sockman mail

    To whom correspondence should be addressed. E-mail: kws@unc.edu

    Affiliation: Department of Biology, University of North Carolina, Chapel Hill, North Carolina, United States of America

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  • Published: March 12, 2008
  • DOI: 10.1371/journal.pone.0001785

Reader Comments (6)

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Why does hatching failure occur?

Posted by er12 on 23 Jun 2008 at 17:40 GMT

I found this paper quite thought provoking with respect to why hatching failure occurred at all, and why it occurred more in first-laid eggs. It will be important to find out whether these hatching failures are due to failure of those eggs to be fertilized or to embryonic death. Early embryonic death due to suboptimal temperature would be the most supportive of the author’s argument for a trade-off between pre-hatching and post-hatching viability. Fertilization failure, on the other hand, could be due to either the female or her male mate, for example, if he had not yet transferred a sufficient number of sperm when the first ovum was ovulated. Male sources of failure would have different implications for female solutions to the trade-offs they face.

Looking at birds more generally, there is interesting variation both between and within avian species in the incidence of hatching failure, only some of which has been explained [1]. It is seldom known whether the cause is lack of fertilization or embryonic death. Given that female birds can store viable sperm, often mate with more than one male, and produce only one relatively large egg per day, why should any egg ever be unfertilized and therefore wasted? What percentage of eggs that fail to hatch are truly unfertilized? Simply breaking open an egg that has failed to hatch may not always be enough to tell the difference between fertilization failure and early embryonic death. Fortunately, effective methods have now been published to distinguish between these outcomes that can be used with eggs of wild species [2]. For future research along the lines of the Sockman study, the cause of hatching failure should be identified if possible.

References:

1. Spottiswoode C, Møller AP (2004) Genetic similarity and hatching success in birds. Proceedings of the Royal Society B 271: 267-272. DOI: 10.1098/rspb.2003.2605
2. Birkhead TR, Hall J, Schut E, Hemmings N (2008) Unhatched eggs: methods for discriminating between infertility and early embryo mortality. Ibis, published online 11-Mar-2008. DOI: 10.1111/j.1474-919X.2008.00813.x


RE: Why does hatching failure occur?

kwsockman replied to er12 on 04 Jul 2008 at 21:42 GMT

It is not clear to me why lack of fertilization as the source of mortality in early-laid eggs would be less supportive of my argument for a trade-off than early embryonic death would be. Indeed, the failure to fertilize an egg may reflect a problem with the male, but its occurrence more frequently in first than later-laid eggs still supports this argument, I think. I do agree that male failure to fertilize would have different implications for the resolutions to the trade-off, but it seems that the trade-off would still exist.

I also agree that it would seem surprising for fertilization failure to occur often, but it at least seems plausible, so I included it in the paper as a possibility. Note that I give this possibility very little discussion compared to the other possibility of early embryonic death due to exposure to ambient conditions. In a previous, unpublished version of this manuscript, I had written, "Although first laid eggs may be more susceptible to infertility than later laid eggs in some situations (e.g., Potti & Merino 1996; Codero et al. 1999; Cabezas-Diaz & Virgos 2007), it would seem that infertility is not highly probable for any eggs of the Lincoln's sparrow, regardless of laying order, simply due to the presumed production costs of energy-rich eggs and the limited opportunities parents have for breeding." Perhaps I should have retained this sentence in the final publication.

I appreciate your pointing out the papers that discuss this issue and how to determine when eggs are infertile.

Thank you again for your comments.

Cabezas-Diaz, S. & Virgos, E. 2007. Adaptive and non-adaptive explanations for hatching failure in eggs of the red-legged partridge Alectoris rufa. Ardea, 95, 55-63.
Codero, P. J., Wetton, J. H. & Parkin, D. T. 1999. Within-clutch patterns of egg viability and paternity in the house sparrow. Journal of Avian Biology, 30, 103-107.
Potti, J. & Merino, S. 1996. Causes of hatching failure in the pied flycatcher. Condor, 98, 328-336.