Genetic resuscitation from extinction
Galapagos tortoises
Charles Darwin made a number of observations on his round the world voyage from 1831 to 1835.
One of his most famous accounts stem from the variety between the giant Galapagos tortoises found on different islands and different habitats. The saddle-shaped carapace of some tortoises (Chelonoidis elephantopus) at the right in the photo, Darwin surmised, allowed these reptiles to forage at higher levels on the drier areas where vegetation was scarce, thus allowing them to obtain more food and so energy to live longer and reproduce their type of offspring. Other tortoises (Geochelone nigra) have a lower anterior opening and a dome-shaped carapace as for the tortoise on the left in the photo. This second type is found predominantly in wetter habitats where vegetation is rather luxurious and it would seem that there was no selective advantage for the higher opening.
A recent article has described the work of Gisella Caccone at Yale University who has done a genetic analysis of tortoises on various islands. Her work has established that some previously thought extinct varieties are still extant but not where one would expect them to be. Hybrid tortoises, determined from this genetic analysis, could (theoretically) be used to re-establish a population by back crossing to produce the extinct forms. Of course with the reproductive rate of tortoises, this could take a long time.
Students could consider how the DNA profiles of the hybrid tortoises could be matched in their studies of Topic 4.4 Genetic engineering & biotechnology.
A discussion about the evolution of the carapace shapes would be a excellent example for natural selection in Topic 5.4 Evolution while the investigation of the names of the tortoises could be used in Topic 5.5 Classification. Questions such as
How did such a change arise in a population of tortoises?
What could have been the selective advantages for the each shape?
Why are the different shaped shells limited to different islands?
What could have happened since sailors may have moved tortoises from one island to another?