Adaptation and diversification
When considering the adaptations of these two living organisms (rattus norvegicus & amoeba proteus) it’s important to look at their habitats, how they have adapted for the best chance of survival of the species and then look at the past evolutions of the organisms and how they have changed from their ancestors.
Habitat of Rattus norvegicus (brown rat): In the past this animal was known to mainly occupy forests. However, with the expanding of the human race and how much living space we occupy and what we have made, these rats are now more commonly found in sewers in buildings than forests. (Smithsonian national zoo & conservation biology institute, 2019). As I’m sure most people have seen a rat lurking around bins and drains at some point. These can be found in any climates excluding desert areas, tundra and icy polar areas of the world. (elifesciences.org, 2019). Most of the resources that these rats use to live nowadays are leftover from human waste in things like bins or badly kept buildings. The challenges that these rats are most likely to encounter are competition for resources from other rodents or even the same species or animals and humans who try to exterminate and catch traps and poison. (PubMed central, 2001)
Habitat of the amoeba proteus: This organism is found in different water environments. Mainly freshwater, or in places like lakes and ponds. In these areas it can usually be found lurking in the bottom layer of thick mud in these areas. These amoeba like to live in environments which are very moist, and this organism tries to avoid light as much as possible and will usually be found in shady areas of the ponds, lakes etc. (Microbe Notes, 2023). These amoebae eat other organisms in these areas such as other smaller amoebae and the algae in the lakes and ponds, or even protozoa and bacteria. (gbif.org, 2025) They can face challenges in their habitats mainly being: extreme environments, whereas they are adapted to live in many extreme environments some environment can pose a great threat because they are to violent or baron for these amoebae, but they can survive in most by forming cysts to defend themselves. They also face the challenge that some bacteria which they do eat are becoming better at defending themselves from being consumed. (PubMed central, 2004)
So how have they adapted for their environments?
Brown rat adaptations: The brown rat has developed a keen sense of smell and touch over time which helps them to forage for food, they are also omnivores and can go for either meat from other animals or human waste etc. This gives them a greater variety of food that they can eat in order to survive as there is more options for them to consume. These rats are also very good at burrowing and can create a labyrinth of tunnels, including this they can also memorize mazes to explore and return and know their location. This allows for protection from many predators as they are in small, secluded areas. They also live with other rats in larger colonies in these secluded areas which means they are not only hidden from many predators but also have high numbers to defend if any predators do try, it also allows them to be more efficient at building and gathering together. This is also further helped by the fact that these rats can mimic each other’s actions and copy what the others are doing for more efficiency and ease. (Animal Diversity Web, 2019) This all allows them to be hidden and efficiently get food and build habitats to thrive in. They can reproduce in these secluded areas and have protection whilst doing so.
Amoeba Proteus adaptations: The main adaptation of this amoebae is their pseudopodia. This is what allows them to move and is also how they feed. It is a temporary extension of cells of the organism. (Microworld, 2023). Here is an image of this. Without this the organism would not be able to feed and would not be nearly as mobile so this is paramount to the survival of this species. Another very important adaptation is their ability to undergo encsystment. This is when the amoeba creates a layer of tough and strong material that is like chitin like that of many exoskeletons of other living creatures. This tough layer helps them withstand extreme environment temperatures and conditions. This then allows them to reproduce many times in this created safe environment. (Microworld, 2023).
Evolutionary Background:
Brown rat: The brown rat spans back millions of years with the last common ancestors being M. musculus as far back as 11 million years ago and R. rattus with a closer 2-3 million years ago. The species traces its lineage to southeast Asia and later spread throughout Asia, Australia and then continued to spread around the globe. The original habitats of these rats is unclear because from when history recorded them they have been living mostly in human-made areas. However, differing from other rats these trace back to more colder climates than we would typically see rats. The earliest dated fossils of this species are found in China and Japan so there is not a lot of evidence to go off to trace them back very detailed. (Science | AAAS, 2024). The spread of these rats to the other places of the world is most likely linked to humans and mainly the industrial revolution and they were carried in ships and large cargos almost unnoticed much of the time. (The Wildlife Trusts, 2019). They are now widespread around the globe and will have adapted to the introduction of their new environments after being carried to other parts of the globe and reproducing.
Amoeba proteus: All amoeba including this one trace their earliest lineage to eukaryotic ancestors. Single celled amoebae were a very early lifeform that evolved in the oceans. Fossils found in Scotland in rock formations found amoebae dated as far back as 400 million years old. These fossils support the theory that over a large span of time these amoebae made it from marine environments into freshwater in which they colonized the soils of lakes and ponds and other formations of freshwater. This is though to be at about the same time as many vascular plants were first starting to appear. So it is thought that these early plants and these amoeba had a symbiotic relationship and were necessary for both to evolve. (Natural History Museum, 2019). Because of their long spanning habitation of an unchanging environment being that of the bottom of freshwater not much evolution has occurred throughout their time as amoebae. (sciencedirect.com ,2019).
Overall these 2 organisms are very different in both habitats, one being freshwater and unchanged for millions of years and the brown rat spreading from a select few countries to the entire world over a short period of history. Their diets are very different also as their sizes vastly differ as the amoeba eat other microscopic bacteria and algae in comparison to the rats diet of waste meat from humans. Due to the changing environment of the rats they also have different ways of making their habitats as the rats burrow to create safe environments whereas the amoeba give themselves a protective layer and do not collaborate with other amoebae unlike the rats colonies. The brown rat faces threats from humans and predators whereas the amoeba proteus is an environment with minimal predators and this environment is unchanging. However, this has lead to some of their common prey to start defending themselves. Because the amoeba proteus lives alone it differs in behavior to the rats which will work together and move and mimic each other in order to create burrows and forage together to reproduce and survive whereas the amoeba lives alone and reproduces by itself. The lineage of amoeba proteus can be dated to much farther back than the brown rat by hundreds of millions of years and remains a noncomplex organism that hasn’t undergone many great evolutionary changes over time compared to the rats.