Micro RNAs control how DNA codes are expressed, and they help work out evolutionary relationships.
Micro RNAs
DNA codes for proteins, and RNA is the way the code is translated. The recently discovered 'micro RNAs' are the way that the genes (DNA) are turned on and off. Subtle alterations in the sequences of 'on-off' can affect the way the animal develops. It has been found that these micro RNAs are good indicators of relatedness in animals. Animals sharing the same micro RNAs are closely related.
Lizards and Turtles
Lyson et al. (Biology Letters) have reported that Lizards and the Painted Turtle share four micro DNAs, out of 77 identified in the study. This seems to be conclusive proof of relatedness, and maybe answers the long-standing question about how turtles and tortoises fit in to the reptile landscape.
Turtles, Tortoises, Birds and Dinosaurs
The whole 'Turtle/Tortoise' group (Chelonia) have been problematic for many years. Their body plan is unique, and skull details have made them seem to be closely related to the crocodiles. Different specialists (at different times) have argued for them being most closely allied with a variety of different reptile types, living and extinct. Some have thought them very ancient, others have thought them to be quite close to the birds – their morphology (body plan and particularly skull details) has proved to be very difficult to interpret.
Current Research
The research findings of Lyson et al. suggest that the Painted Turtle (at least) is quite closely related to the lizards. This would suggest that the 'ancient' skull design of the turtles could have been a recent adaptation – confusing because it hinted at their relationship with much older ancestors. Recent inclusion of micro RNA analysis suggests that the modern turtles evolved along with the lizards and snakes, and then 're-developed' the old skull architecture later.
Molecular Biology and Morphology
Looking at the structure of an animal can lead to an understanding of what it is and where it came from, but a study of the detailed mechanisms of how that body-plan was arrived at can often tell more. Details of the proteins, DNA, RNA (etc.), can hint at unexpected relationships – look, for example, at the way the 'Simplest Animal on Earth' might be related to the much more complex sponges.
Does it really matter?
Exactly how the turtles and tortoises came to be the way they are might seem to be of little importance, but an understanding of the way they changed might be useful. If a few little 'switches' (micro RNAs) can alter the way animals develop, then these micro RNAs need to be studied very carefully.
Maybe we have a tool for working out how animals might change in the future – possibly a way of understanding how animals might adapt to the changes humans are imposing on the environment?
Sources:
- 'Turtles emerge from their evolutionary shell - Genetic data show turtles and lizards had a close common ancestor.' Chloe McIvor, Nature, July 2011.
- Lyson et al., Biology Letters, Royal Society Publishing, 2011 (abstract).
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