Chapter 8 Critical Thinking
1.) Hagfishes and lampreys are the only living representatives of a very ancient group. Why do you suppose there are still some of these jawless fishes around?
--> Jawless fishes are know to be the most primitive fishes living today. I suppose they have exsited this long due to their feeding habits. They feed mostly on dead or dying fishes. This resource is simply impossible to run out off.
2.) A deep-water shark, new to science, is collected for the first time. The specimen is studied in detail, but its stomach is empty. How could you get a rough idea of its feeding habits? The specimen is a female, and its reproductive tract is found to contain 20 eggs. Can you tell the type of developement characteristic of this species?-->
In order to determine the feeding habits of this new specimen, you can study the jaws. Not all of the nearly 350 living species of sharks conform the same body plan, but the majority are known to contain rows of numerous sharp, often triangular teeth. This feature helps since sharks are known to be adapted for predatory feeding. Also to keep in mind, that there are sharks (whale sharks) that are filter feeders. This is could very well help explain an empty stomach. Because this specimen is yet to be unknown, it is hard to study the type of developement characteristic of the 20 eggs found. There are two different types of sharks that may very well affect the developement. One is oviparous and the other is viviparous. In an oviparous shark, the yolk is needed to provide energy for at least several months of development. Without this amount of time, the eggs won't be fully developed. And in a vivparous shark, nutrition is provided by direct contact with the reproductive tract of the female.
3.) Individuals of some species of bony fishes change sex, some to maintain more males than females, others more females than males. What are the advantages and disadvantages of each situation? Are there any advantages and disadvantages in having an equal number of males and females?
-->One advantage of maintaining more males than females is that there will be more chances of having a dominant male. Since a dominant male is needed to triger these changes (protandry and protogyny). A disadvantage of this situation will be that with less female, there will be less chances of reproduction. Whereas, this would be an advantage of having more females than males. And as for having an equal number of males and females, I think that there will be no advantages or disadvantages, since everything will turn out to be average.