A skink species from conflict-ridden parts of Africa could help to explain some of the secrets of how the uterine systems of mammals developed.
Reptile expert and evolutionary biologist, Dr Alex Flemming of the Department of Botany and Zoology at Stellenbosch University, has just described the first ever finding of a reptile in which the embryo does not only develop in full in the uterus before it is born, but also draws nutrients from the uterine wall itself by attaching to the wall. The findings were published in the Journal of Morphology in an article written with Prof Daniel Blackburn of Trinity College (USA).
Previously, it was assumed that only mammal embryos could attach to the uterus, feed and develop in this way.
The importance of their research has also been published in popular scientific publications such as NewScientist and Bionieuws.
Explaining the importance of the phenomenon, Dr Flemming says “mammals are not as unique as we thought after all, and our study has highlighted a number of functional and evolutionary issues”.
The phenomenon was observed in Trachylepis ivensi, a particularly large semi-aquatic skink from the floodplains of rivers in Angola, Zambia and the Democratic Republic of the Congo.
“One does not find fossilised uteruses of the earliest mammals or their forebears, therefore it is difficult to speculate about their evolutionary development,” he says. “Even though Trachylepis ivensi is very far removed from mammal lineages, scientists can use this skink as an example to learn more about the development of mammal placentas.”
All reptiles (such as lizards and snakes) do not lay eggs from which their young hatch. Some reptiles bear live young. Their young develop in full in an egg full of nutrients inside the female’s body, and then are “hatched” from her when they are ready to be born.
In addition, reptile experts worldwide have already discovered four groups of lizards with an advanced placenta. They provide nutrients to their young through a process known as placentotrophy. The unborn animals are separated from their mother’s placentas by way of a very thin eggshell membrane, in which they partially feed on the yolk in the ovi-sac. The yolk alone is not sufficient for development, however, and is supplemented with nutrients from the uterus.
However, Trachylepis ivensi is the first reptile in relation to which scientists know that they have a placenta that permits the embryo to implant directly into the walls of the oviducts, the tubes that extend from the ovaries, and to attach directly to the uterine tissue of the female. Thanks to the imbedding process, the embryo withdraws 100% of the nutrients that are required for growth and development directly from the female’s bloodstream.
“It is similar to how the young of many mammals also develop,” explains Dr Flemming.
“By this we are in no way saying that this skink has a sort of ‘mammal placenta’,” he warns. “It rather remains a reptile placenta that functions very much like that of a mammal.”
Dr Flemming regards the phenomenon as a “wonderful example of convergent or independent evolution”, in which the same phenomenon developed separately in two different lineages.
The skinks that were studied form part of the reptile collection of Bayworld Museum in Port Elizabeth. The South African reptile collector, Gerald Haagner, collected them in Zambia in 1993.
Knowledge about their unique reproductive secrets only came to the fore after some ‘kinship detective work’.
Bayworld’s reptile expert, Prof William Branch, had noticed that another type of skink (Eumecia anchietae) in his collection had particularly small eggs with very little yolk.
Prof Branch and Dr Flemming then determined that Eumecia’s advanced placenta provided nearly all the nutrients to the young via uterine secretions.
“It was only the fourth time in the world that such placentotrophism had been recorded, and the first time ever in a specie from Africa,” says Dr Flemming about Eumecia, about which they published an article in 2001.
“We then started searching for closely related skinks that might display the same phenomenon,” relates Dr Flemming on how his path crossed that of the Bayworld Trachylepis ivensi collection.
And then he found an even more unique phenomenon than what he was hoping for!
“By the third female that I opened, I realised, ‘bingo’, here was something else,” he narrates.
Since 2006, Dr Flemming, along with reptile expert Prof Blackburn, has completed laboratory studies on 40 embryos that have been available to them.
Although they did find extremely small eggs in Trachylepis ivensi, at less than 1 mm in diameter they were as large as a human ovum. The eggshell membranes disappear early in the development process, which gives the foetus time to attach to the uterine tissue.
“The investigation of the complex structure and composition of the placenta, and how it is transformed in the course of pregnancy, was a challenging and time-consuming process, but at the same time it was worthwhile,” he says.
Thanks to Engela Duvenage in the Faculty of Science at Stellenbosch University for alerting us to this interesting finding and allowing MyPE to point out ONE MORE REASON why the Bayworld facility should be preserved.
Bayworld museum lizard a unique reptile find in Stellenbosch Univ research http://t.co/V67DGZ0x @StellenboschUni @PEwebsite @MyPE
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Dr Alex Flemming in his office at the Department of Botany and Zoology. Photo: Engela Duvenage
