Real-time Evolution in Action !

This story of an Australian lizard is an interesting one. The lizard is in the transition stage of oviparous (egg laying ) to viviparous (giving birth to young ones) phase.This species are seen both in the mountain as well in the coastal regions. Those in the coastal regions are laying eggs and the population seen in the mountain are giving birth to young ones.

The species described is the three toed yellow-bellied skink (Saiphos equalis) and are seen in the New South Wales of Australia. The coastal areas are warmer and those live there lay eggs, while those live in the cooler areas like the mountain, give birth to live young one. It is estimated that, approximately a hundred of the reptilian lineage has independently moved from egg-laying to live birth.

Saiphos equalis thus provides the scientists to see the evolutionary process in action. One question that baffles the scientists is the problem of nourishment to live ones. In placental mammals the nourishment is received thorough the umbilical cord and after the birth through the milk. In the egg-laying species, yolk provides the immediate nourishment after hatching. In the oviparous, the egg develops while inside the body itself. In all these, the embryos get calcium  for the bones either from the yolk or through the placenta.

Now the scientists have discovered that in the Saiphos, the uterine walls secretes calcium which in-turn is absorbed by the embryo. This could be an evolutionary link of development of placenta in reptiles. The eggs run a risk of being eaten by predators, while the living birth gives the risk of pregnancy as well as exposure of young-ones to the inclement weather. Historically this type of transition is not uncommon in reptiles.

Now, nearly 20% of reptiles like snakes and lizards reproduce by live birth.

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