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?

For one thing, nature revolves around the fat that those organisms that are more successful than others will live longer. As for both hagfishes and lampreys, they are the most well adapted species of the class Agnatha, since they are still living today. It’s simply when you place natural selection into play – only the best survive. Hagfishes and lampreys may have not been the “top” predator when before, but in the overall outcome, they are the most successful ones since they are “living fossils.”

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 development characteristics of this species?

· A factor which makes this question very broad is the fact that there is little to no information for this scenario. And although hypothesis may be assumed, giving that it has been studied in detail and has an empty stomach, one can derive the answer to be that the shark is a filter feeder, or in such cases that it has a slow metabolic rate because of its lifestyle, which therefore means that the food that has been consumed prior to its capture has moved from the shark’s stomach and into it’s intestine.

· Out of the three types of shark egg development – viviparous, oviparous, and ovoviviparous, as well as the factor that it has not been observed in a contained or wild environment, there would be no way of proving the type of developmental characteristics of the newly found species yet.

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?
• The advantage for maintaining more males than females is that it would ensure that the most dominant male(s) would be able to mate to pass on their traits making their offspring genetically advantageous in comparison to other offsprings whose parents may have not been the dominant of the group; however, due to the amount of females, there would be less offspring.
• An advantage that more females than males offers is that that certain species would produce more offspring; but, because of that, the survival rate of the offspring would be low.
• As for the equal amount of males and females, for one, there would be a higher amount of offspring > to the scenario where there would be more males then females; yet, there would be an average survival rate, as for the factors dealing with genetics, well; it would quite hard to determine this factor since juvenile fishes are exposed to a vast amount of danger when they are maturing.