Answer:
In order to propose a hypothesis, there is a need to first see the function of gills in fishes. The gills of fishes comprise blood vessels that exhibit inherited tendencies of getting oxygen out of the water, which was consumed by fishes from their mouths. These gills also comprise thin walls, and when water moves over these walls of blood vessels, the oxygen from water moves into the blood, and then this oxygen-enriched blood goes to various organs.
Thus, one of the hypotheses in the given case, can be the number of blood vessels, which are found in the gills of the mentioned freshwater fish to be higher in comparison to the blood vessels found in the normal fishes, and apart from this, the surface area of the thin walls, which are found in the gills is also more in the new species of freshwater fish.
I think it'd be change in allele frequencies & microevolution.
The classification of organism
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<u>mechanism:</u> the process of evoluton .
Evolution is the process by which veriety of modern organisms have descended from ancient ancestors. Evolution is responsible for both the remarkable similarities of all 0rganisms and the amazing diversity of that organisms but exactly how does it work? Fundamental of the process of evolution is genetic variation upon which selective forces can act in order for evolution to occur.
Examines the mechanisms of evolution focusing on:
•<u>Decent </u>: the genetic differences that are heritable and passed on to the next generation successfully.
• <u>mechanisms of change</u>: Mutation, migration (gene flow), genetic drift, and natural selection are act as mechanism of change .
• The random nature of genetic drift and their effects .
• How variation, differential reproduction, and heredity result in evolution natural selection
.
• How different species can affect each other's evolution through co-evolution.
All of these mechanisms can cause changes in the frequencies of genes produce change in in populations, and so all of them are mechanisms of evolutionary change. However, natural selection and genetic drift (genetic flow) cannot operate unless there is genetic variation among organisms.