160 likes | 316 Views
Evolution of Whales: Hind Limbs and Inner Ear. By Megan Beaton, Laura Buennemeyer, and Catherine Romano. Evolution. Maiacetus inuus - 49-40 million years ago. Exploring the evolution of hind limbs to a vestigial structure. Exploring the evolution of the inner ear.
E N D
Evolution of Whales: Hind Limbs and Inner Ear By Megan Beaton, Laura Buennemeyer, and Catherine Romano
Evolution Maiacetus inuus- 49-40 million years ago • Exploring the evolution of hind limbs to a vestigial structure • Exploring the evolution of the inner ear Dorudon atrox- 41-33 million years ago
Key Terms • Vestigial Structure-homologous characters in an organism that has lost all or most of their original function • Vertigo- extreme dizziness, which can be caused by the ear • Myosin- motor proteins found in eukaryotic tissues that are responsible for motility • Myoblasts- a type of stem cell that exists in muscles • Somiticmyoblasts-causes the stem cells that develop in vertebrates to migrate • Cetacean- mammals adapted to aquatic life, including whales, dolphins, and porpoises • Echolocation- the ability to sense objects in the environments by hearing echoes from those objects
of Whales Evolution
Why would whales adapt to an aquatic lifestyle? • Approximately 50 million years ago, the ancestors of modern day whales were four legged terrestrial mammals about the size of a raccoon • Thick bone density made it easier escape predators in the water • The inner ear adapted to allow the whales to move quickly under water and avoid vertigo Zygorhiza kochii Late Eocene (39-37) million years ago
Overall Evolutionary Process On land- 50 million years ago (Packistis) Aquatic- 34 million years ago (Dorudon) Total evolutionary process- approximately 15 million years total Hind limbs- started 41 million years ago; finished 34 million years ago (Gaviocetus) Inner ear- started 47 million years ago (Dalanistes)
Hind Limb Development • In the 5th week of gestation, the genes responsible for hind limb development are no longer expressed • Initial limb outgrowth requires… • Apical ectodermal ridge (AER)- signaling center for the hind limb bud regulated by Fgf8 protein • Distal margin of limb bud • Zone of polarizing activity (ZPA)- signaling center that maintains initial limb outgrowth • Posterior connective tissue
Hand2 gene- a regulator of Sonic Hedgehog (Shh) transcription and required for cell survival • Hand2 is not expressed in the hind limb developing embryo after the 5th week of development • Shh- mediates the signaling activity of ZPA • Fgf8- protein that is coupled with AER and is not detectable or functional in the hind limb development
Gene expression In the embryo
Normal Hind Limb Developement • Muscles are formed when myosin evades limb buds • Myogenetic cells attracted to limb bud by signals sent out by the AER and ZPA • Hind limb bud induces somitic myoblasts to migrate • Myogenic cells are found in both the fore limbs and hind limbs
The Inner Ear • The inner ear canal of whales is 3 times smaller than that of the human ear • The evolution of the inner ear was a key point of no return • Today, with the size of their ear canal, a terrestrial whale would only be able to crawl at a slow pace • The ear is extremely specialized for the aquatic lifestyle
…Future Research… • Examine the relationship between size of hind limbs and whale length • Explore differences with balance, feeding techniques, swimming depth, life span, speed, and location in the ocean. • Study carried out by examination of different whales and different pods of whales • Examine other species with similar vestigial structures, and see if the evolutionary paths are similar
Video of evolution of Whales from land to marine life http://www.youtube.com/watch?v=8cn0kf8mhS4&feature=related