Answer up to two questions to have reserve credit for the quizzes later in the semester. To get credit, write your answer in a paragraph IN YOUR OWN WORDS. You MUST CITE RELIABLE REFERENCES! You may add to existing comments with new information for credit, but once someone has answered (with properly cited sources), you won't get credit for repeating the information.
Please add comments & discussion to any question at any time, even if you are not answering the questions for credit.
2. Did bones evolve from cartilage? How did bones develop?
3. Are tadpoles born with lungs? When and how do lungs develop? Is it related to what happens with the gills? (note: salamanders have tadpole stages too)
5. Brittle stars – What are their natural predators? How can they exist in such large populations without being eaten? Do they have a special type of defense?
6. What do scientists know about the adhesive of the starfish (or other animals with tube
feet that have adhesive)? Are material engineers studying this?
A brittle star uses defense mechanisms to save itself from becoming a predator’s snack. It can illuminate and flash green light to scare off the predator. Also, to save its entire body from being consumed, the brittle star will allow the predator to take its arm, because it will eventually regenerate. Additionally, the brittle star’s dropped arm may still wiggle because the ossicles are connected by mutable connective tissue, which distracts the predator, giving the brittle star a chance to escape. Brittle stars also hide under rocks and even in sponges for protection. Being the fastest echinoderm, the brittle star can attempt to run from a predator should it find him hiding. Because of their many predators including fish, crabs, mantis shrimp, and sea stars, the brittle stars are nocturnal.
ReplyDeleteIf attacked near shelter, the brittle star will try to take a few steps back into safety. In a study, when pinched by forceps, the brittle star had a rapid escape response. There was an even greater rapid response when the brittle star’s arm was amputated.
Skold, M., (1998). Escape responses in four epibenthic brittle stars (Ophiuroidea: Echinodermata). Ophelia Publications, 49(3), 163-179.
Cartilage and bone appear to have evolved independent of each other in order for different functions to be served. The cartilage was thought to have a primary role as an internal material used for support. Bone, on the other hand, was not used as an internal support until only recently. Bone started out as a "chemical store" and then was used for protection. Cartilage needs phosphate to form collagen and so the distinction between the formation of catrilage and bone is thought to be dependent on the prescence of phosphate acting on the cells. If phosphate is present, cartilage forms. If the phosphate is not present, the bone forms because phosphate acts as a barrier for calification.
ReplyDeleteHalstead-Tarlo, L.B. (1968). Bone versus Cartilage- A study in Evolution. Calcified Tissue International, Volume 2, Supplement 1. Retrieved July 21, 2009, from http://www.springerlink.com/content/j30818950852kv23/