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I've heard of claims that aphids can be born pregnant, like tribbles in ''Star Trek''.

However, doing a web search didn't provide very convincing evidence.

The Straight Dope refers to being pregnant before birth as paedogenesis. The Wikipedia article on paedogenesis has no citations on pregnancy before birth (it does, however, have a citation on male offspring eating its mother!). It also states that the term also refers to animals that get pregnant before they're fully sexually mature.

Wikipedia's article on Aphids refers to the phenomenon as Telescoping generations, which is a single paragraph stub article that has no citations.

Searching for paedogenesis in pubmed only got 8 hits. (Is pubmed an appropriate tool for such a search?)

Are animals being born pregnant well-established but little discussed, or is is yet to be well-established?

(Note: I'm referring to organisms being pregnant to their own offspring, rather than accidentally being pregnant with their own siblings)

  • en.wikipedia.org/wiki/Parthenogenesis Happens in quite a few organisms, vertebrates as well. Gynogenesis is similar, but I don't think it can occer in the womb/egg etc. – user7473 Jun 9 '12 at 11:40
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A good tool to use for this is Google Scholar. The first hit revealed this article which claims

Most aphids are born pregnant and beget females without wastrel males. ... Embryos complete development within the mother’s ovary one after another, in assembly line fashion. These developing embryos contain developing embryos of the third generation within them, like Russian dolls.

The second hit is an interesting set of slides on the subject.

2

In some gall midges, the larvae develop inside the mother even before she is mature (pupal paedogenesis). Stephen Jay Gould wrote about them in 'Ever Since Darwin,' which you can find from google books at this large link:

http://books.google.com/books?id=_VCnI02FwHAC&pg=PA91&lpg=PA91&dq=gall+midges+stephen+jay+gould&source=bl&ots=KOHnKuFWFt&sig=irJkYgdR23KARbO8MGXh-8Qe_f0&hl=en&ei=eySyTdi-Eojh0QHH_-SbBg&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CBgQ6AEwAA#v=onepage&q&f=false

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sexual reproduction would exclude the possibility (as there'd be no way to impregnate them prenatally, obviously, unless you want to have offspring impregnated by their own fathers by encapsulting some of their semen into their bodies during gestation), so you should limit your search to those creatures reproducing a-sexually.

The closest I could find quickly was the budding of jellyfish, but that's not really the same. Here a single polyp splits into multiple young jellyfish over time. This is asexual reproduction of a polyp which is itself the result of sexual reproduction.

Nice description (with a diagram) on wikipedia: http://en.wikipedia.org/wiki/Jellyfish More info confirming this on http://www.wildsingapore.com/wildfacts/cnidaria/others/jellyfish/jellyfish.htm http://www.nature.com/scitable/blog/creature-cast/more_budding_jelly_babies http://fusionanomaly.net/jellyfish.html

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    Sexual reproduction wouldn't be theoretically impossible - they could be impregnated by their siblings. (Weirder stuff has happened, such as embryos eating each other) – Andrew Grimm Apr 22 '11 at 13:45
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    you are excluding the possibility of parthenogenesis which can happen in either an adult or in utero, even if that particular species typically breeds by sexual reproduction. Parthenogenesis is documented in aphids and is mentioned in the citation provided by Esultanik. – Monkey Tuesday Apr 22 '11 at 19:57
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    impregnations by siblings might theoretically happen, but would have no benefit over asexual reproduction as there'd be no genetic mixing. Makes it evolving rather unlikely. – jwenting Apr 22 '11 at 20:22
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    Check @ESultanik's Aphid link - in the case they write about, sexual reproduction can take place once a year. The rest of the year the aphids are born pregnant with exact genetic clones of the mother. – FoleyIsGood Apr 23 '11 at 9:54
  • @jwenting There is a viviparous mite (Acarophenax tribolii) where the male siblings impregnate the female siblings in the mother's body (the males then die and the mother bursts open and dies). This is an interesting edge case for sex ratio theory as it's one of the few cases where you find a skewed sex ratio (fewer males because it's local mate competition it doesn't make sense to have the "excess" males). Here's a blogpost on the subject. – Ruben Jun 10 '12 at 16:05

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