# Percentages/Dart Eggs



## crb_22601 (Jan 12, 2006)

Just thought about this on the toilet the other day. :wink: When dart frogs lay eggs does each egg have a 50/50 percent change of being a male or a female? Or Do some frogs have a higher male to female ratio or visa versa? 


Also does anybody think temperature might have an effect as to how many eggs turn out to be female? I think (but I am not sure) when crocodiles incubate eggs if it is a certian temp in the nest all the eggs are one gender, could something similar be along the lines of dendrobates?

Just a curious question.


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## kyle1745 (Feb 15, 2004)

I am not sure there is a clear answer to this. I do seem to remember some old tests with temperature being able to swing the sex, but I am sure this is different for every species. In my experience some species lean one way or the other but that is not to say there isn't an environmental cause to it either.


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## Ben_C (Jun 25, 2004)

Hi crb_22601,
All amphibians have their gender determined genetically. That is, 50% at conception will [on average] be male and 50% female.
However, temperature may have an affect of killing off a particular gender at a higher rate (although I haven't seen any good evidence of this in the literature).

I hope this helps,
B

P.S. You are correct about crocodilians in that they all undergo temperature sex determination.


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## Matt Mirabello (Aug 29, 2004)

Ben_C said:


> All amphibians have their gender determined genetically. That is, 50% at conception will [on average] be male and 50% female.


I would modify this to read:
All amphibians have their gender determined genetically. 
That is, 50% of the sex determining gametes produced will make males during fertilization and the other 50% of the sex determining gametes produced will make females during fertilization.

however other factors may influence the survivorship of these gametes prior to the fertilization process. One may be selected for by environmental conditions. Similar to preferential survivorship of male or female sperm in humans.

In poison frogs I lean more toward the males (sperm) being acted upon and not the eggs. I have heard instances of people having skewed sex ratios where unfertilized eggs and tadpole mortality were not enough to account for it.

The females may have a way of skewing the sex ratio. It has been shown to occur in Rana rugosa:
" Maternal control of sex ratio in Rana rugosa: evidence from DNA sexing"

will do some more research and post more information


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## Ed (Sep 19, 2004)

maternal sexual determination appears to be pretty widespread with multiple factors in play. 

For example, in zebra finches a high quality diet skews the sex toward males and a low quality diet skews the ratio towards females... 

This can even affect reptiles with TSD see http://humrep.oxfordjournals.org/cgi/co ... 11/11/2371 

there has been similar evidence collected in hoofstock... 

Ed


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## zombiefish (Sep 22, 2006)

*ratio*

Most of the groups I have experienced usally run a tad bit female, however there are exceptions.


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