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Does a female animal that lays eggs experience a pregnancy-like period of time, where she will feel and behave differently as if she were fertilized and her body is prepared to lay a fertile egg, not a sterile egg (like the chicken eggs we eat)?

For example,

  • does the egg takes more time to be formed?
  • is it different in size?
  • maybe the animal will feel hormonal changes that cause it to increase body heat to help her sit on the egg, etc.?
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Can you elaborate on what you mean by "fill deferentially", as it's not very clear what you are trying to say there. – jonsca Jul 30 '12 at 2:03
And can you also clarify what "pregnancy-like period" refers to? A "period" can refer to two things :P And the short answer is yes, but I don't fully understand the question. – jello Jul 30 '12 at 3:05
@jonsca, jello, "deferentially" was a typo, the hour was late and I was tired. "Pregnancy like period" - a period of time, when the animal will fill/act differently than every-day, or have changes to her body that are do not happen unless she is going to lay a fertile egg. – Ilya Melamed Jul 30 '12 at 5:49
@IlyaMelamed See if that's closer to what you were aiming for. – jonsca Jul 30 '12 at 5:54
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@shigeta, in guess that this means that a full answer will need to touch on both types. For example what happens to a sparrow or a salmon that doesn't mate on its season, and as asked before is there a difference between laying a fertile and an infertile egg from the POV of the chicken/ant. – Ilya Melamed Aug 8 '12 at 21:43
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1 Answer

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In oviparous animals the egg retention phase in the uterus is brief. After fertilization eggshell mineralization is triggered but it seems the initial triggers of the pathway is not understood. The uterine fluid is rich in calcium and bicarbonates and calcium carbonate, in the form of calcite, precipitates around the egg. Shell mineralization is quite a rapid process and there are some specific proteins involved in this pathway. Have a look at these:

http://www.ncbi.nlm.nih.gov/pubmed/22201802

http://hera.ugr.es/doi/15773115

In ovo-viviparous animals the egg is retained in the uterus for a longer time and embryo is quite developed when the egg is laid (happens in boas). You can call it a sort of "pregnancy".

However progesterone pathway exists in birds and is involved in oocyte maturation

Oxytocin pathways also exist in birds, acting through oxytocin homolog Mesotocin, and perhaps they cause development of maternal care as they do in mammals.

This article talks about effects of oxytocin on birds but not exactly about its role in maternal care.

However i believe that the shell size and mineralization time shouldn't differ much between unfertilized and fertilized eggs in oviparous animals.

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So your answer is that the animal doesn't feel any serious change between laying a fertilized and an unfertilized egg? – Ilya Melamed Apr 6 at 21:22
i dont know in what sense you are talking about.. parthenogenesis or what they do with chicken in poultry.. i think the behavioral response will be the same but observations in poultry chicken can be misleading.. there is a practice called forced-molting which poultry industry adopts in order to increase the egg yield.. during molting the reproductive tract of the hen again becomes capable of egg-laying.. So definitely there is some endocrine response after egg laying and perhaps the hen doesn't "know" if its a viable egg or not – WYSIWYG Apr 7 at 5:17

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