Even though they don’t look like one, whales are mammals. They have a tail fluke, no hind limb and no body hair. Most whales don’t have teeth and those that do, like killer whales, have only a row of simple peg-like teeth, which looks the same. On the other hand, most mammals have four types of teeth, each shaped for specific task. A multidisciplinary team of researchers investigated how whales got its teeth using fossil records and the embryonic development process.
In this study, Brooke Armfield and her colleagues investigated the developmental processes of dolphins, which are whales' smaller cousins, and tracked the evolutionary progression of their dentition throughout the fossil records. Fossil records show that, 48 million years ago, whales had the same four types of teeth just like other mammals. Eventually, as they started adapting to life in the water, 30 million years ago, their teeth became simpler and transformed into their peg-like appearance.
The next step was to search how teeth are shaped during development. There are two proteins – FGF8 and BMP4 – in the embryo, which cause the developing teeth to grow into a certain shape. FGF8 expression occurs in the back of the jaw leading to development of molar teeth in mammals. BMP4 expression occurs near the tip of the jaws. Studies in pig embryos – relatives of whales and dolphins – have shown that these two proteins are distributed in the same way as they are in other mammals. This proves that whales' ancestors might have this distribution of gene expression as well.
However, studies on dolphin embryos show a different pattern. FGF8 is still present in the back part of the jaw, but BMP4 is present along the entire length of the jaw, overlapping with the presence of FGF8. The new hypothesis was that the overlapping presence of BMP4 in these new areas causes the teeth all along the jaw to be simple in shape and similar to each other.
It is interesting to see only a simple shift in the location of proteins would influence the shape of teeth in whales. This demonstrates that major changes to the design of an animal can result from small changes in early development by simply shifting the region where an already existing protein occurs.
Posted by Setareh Sepasi (3)
It is difficult to imagine what kind of diet an animal as large as a blue whale would have to eat to maintain that size without being able to harvest krill. Also a violent predator of that size would be very imposing, although likely impossible.
ReplyDeletePosted by Hunter Alexander (3)
Blue whale is the largest animal and consumes about 40 million krill in a single day. That is roughly about 8000 lb of food in each day. Blue whales eat using a technique known as filter feeding in which they swim around with their mouths open and filter food through their baleen plates (which often resemble teeth on a comb). However, toothed whales such as killer whale eat fish, squid, marine mammals, birds and even other whales.
DeletePosted by Setareh Sepasi
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ReplyDeleteTo build off the previous comment, killer whales do in fact predate on small animals if i'm not mistaken, and as a result do maintain regular peg like teeth. It is interesting to me that killer whales would have evolved simpler teeth when they already had more specialized teeth adapted for the kind of prey that they eat. Any thoughts as to why more specialized teeth were selected against in the case of killer whales?
ReplyDeletePosted by Sean McDougall
Well, it is surprising to know that killer whale diets include fish, marine mammals such as sea lions, seals, walruses, and even large whales. However the feeding habits of Killer whales depend on the place they are inhabiting at a particular time. whales in the coastal waters of the northeast Pacific eat fish and squids. Those that live along the coast of southern Alaska and California consume marine mammals. And those killer whales that travel far from shore feed primarily on schooling fish.
DeletePosted by Setareh Sepasi
This article shows how fascinating developmental biology can be and how the expression of proteins in certain areas of an embryo can have such a monumental impact on the morphology of the organism.
ReplyDeletePosted by Poya Jafari
That's pretty interesting. A simple mutation like that is thought to have aided turtles in having their scapulae form inside of their rib cage. I believe it was FGF10.
ReplyDeleteMichael Ball (1)