Placenta question

[Bluish]

Blue tongues apparently have a fairly advanced placenta. Are nutrients passed from the mother to fetus or are the ova self sufficient in terms of nutrients. How different is the blue tongue gestation from a standard ovo-viviparous species in this regard?

[Jeff]

I'm not good at explaining the medical type stuff (probably because I don't have a very good understanding of much of it), but if I could figure out how to scan page 53 of the Bluey Bible, I think it would answer your question, and more, very thoroughly. If someone else knows a way to post that page, or at least the part of it titled: "Viviparity and placentation", that would be great. Just be sure to give proper credit to where it came from.

[Scotts1au]

I don't know how much this helps but I think the answer can be summarised as "facultative", that is, functionally yes for the exchange of blood gases and to a degree food but they also develop a large yolk. I think you will find that effectively the simplified placenta (cotyledon)/ umbilical cord feeds the yolk, the yolk then feeds the baby. This way the development of the foetus is buffered against nutritional needs of the mother. i.e mother feeds the yolk when it gets a good meal, but the yolk sustains the baby for example in periods of bad weather when the mother can't feed herself for some time, rather than relying on continuous eating. It also explains how they can still throw out reasonably well developed babies if they haven't eaten for a month or so before birth. Particularly given that the mass of babies and foetal matter is around 1/3 of the total body weight.

You can do a google on the subject this might help out a little.

http://www.jstor.org/discover/10.2307/3 ... 1441505511

[Bluish]

Thanks for the replies guys and the link Scott.
I did google before posting but there wasn't much mentioned about blue tongues specifically. Apparently there are 3 types /stages of reptile placenta. The best paper I read was on Mayuba skinks. It stated that most of the nutrients are in the yolk and only certain minerals and water are passed to the embryo through the placenta.
One thing I found interesting that was mentioned in your link and elsewhere s that viviparity has developed in 100 different reptile lineages.

[Scotts1au]

Having another look at this, I found this article which helps to understand where Tiliqua fit in. I don't think they are as "advanced" in terms of convergence with mammalian placentas as the Mayuba skinks but somewhere between, mainly because they have not done away with a seperate yolk sac. It would be interesting to look at other forms of tropical skinks other than Mayubas to see whether they also have done away with yolks, but then they evolved in idealistic tropical conditions. Looking into this in more detail might help to answer an age old question about the evolution and radiation of Tiliqua - I suspect that large yolk retention is an indicator of their temperate roots, lending more weight to the argument that Tiliqua evolved in temperate Aus, not tropical Indonesia. That, and the fact that fossils date them back at least 16 million years in Aus temperate zones.

http://www.mapoflife.org/topics/topic_3 ... d-mammals/

[Jos]

Mayuba = Mabuya??

Finally, in the most advanced, Type IV placentation morphotype, famously found in the South American genus Mabuya, complex adaptations converge in intricate detail upon the derived placentation of eutherian mammals. Placental features shared between mabuyids and eutherians include a placentome of densely folded fetal-maternal epithelia, and a surrounding chorioallantoic placenta (paraplacentome) covered in clusters of cells (chorionic areolae) specialised to absorb products secreted from complementary uterine glands, and giant, binucleate chorion cells covered in microvilli. Adding to the list of remarkable convergences, both Mabuya and eutherians also ovulate minuscule (~1mm) yolk-free ova, provide >99% of embryonic nourishment by placentotrophy, and do so over a protracted gestation period (8-12 months).

[Scotts1au]

yada yada was typing while taking a break from working at home. :-)

[Bluish]

Mayuba = Mabuya??.

Should have previewed my post.