Microbiome Fish Breeding

Abstract:

Artificial selection is the process where humans consciously choose which organisms to breed based on desirable traits. In this experiment, Endler’s Livebearers and Blue Diamond Shrimp were selectively bred to see how specific traits, like coloration, changed over time. It was originally hypothesized that individuals chosen for breeding would pass on desirable traits to their offspring and increase the frequency of those traits in a population. To test this, organisms that displayed the preferred characteristics were placed in a tank together and allowed to reproduce. Offsprings who did not show the target characteristics were removed so the next generation could produce the desired traits. Observations were made across multiple generations and changes in appearance and trait frequency were tracked. The data showed that the selected traits became increasingly more common, supporting the prediction that artificial selection can rapidly influence a population, however it also highlighted that selective breeding may reduce genetic variation.

Introduction:

Unlike natural selection, where environmental pressures determine survival and reproduction, artificial selection allows people to influence evolution by deciding which organisms reproduce based on desirable traits. Over time, this can produce desirable populations. For example, breeding larger chickens or fattier cows to feed populations is an example of artificial selection. This process can be done in two ways: either selective breeding, which encourages reproduction in certain individuals, and culling, which removes individuals from a population that do not exhibit favorable traits.

For Endler’s Livebearers, bright and vibrant coloration is important because it helps males attract mates and also depicts their overall health. Additionally, Blue Diamond Shrimp are known for their rich blue coloration, which are often associated with good health and increased attraction in breeding. The benefits these colorations provide increase the likelihood that the characteristics will be passed on to offspring. 

Methodology: 

The study took place in a freshwater aquarium that contained a filtration system, heater, gravel, artificial plants, and snails (to clean the tank) to provide a suitable habitat for the organisms. The heater maintained the tank’s temperature between 23-28 ºC and occasionally the temperature would be increased to promote the environment for breeding. Water conditions were tested weekly using an aquarium test kit that measured pH, alkalinity, carbonate harness, general hardness, nitrate, nitrite, and chlorine levels. If any of these measurements were not normal, additional chemicals would be added to the water in order to stabilize the aquarium and maintain an acceptable range for the health and survival of both the Endler’s Livebearers and Blue Diamond Shrimp. 

The aquarium was prepared through a personal selection of gravel, plants, and decorations. Our group chose to include black and white gravel and artificial plants to make up our aquarium. After the biome was prepared, a small group of 3-4 individuals displaying desirable characteristics was selected from the original population and moved to the experimental tank. The organisms were gradually acclimated to the water and eventually released into the aquarium. Over the course of a few months, the selected individuals then reproduced naturally over the course of the experiment, creating multiple generations.

As offspring were produced, their physical traits were monitored with particular attention given to coloration. Individuals who did not fall under the category of desirable traits were removed from the breeding population (culling). Data was collected on the frequency of desirable traits by comparing them across successive generations and measuring the effectiveness of selective breeding and culling. The results were then used to determine whether artificial selection increased the occurrence of the target characteristics and thus supported the original prediction.

Results:

Throughout this experiment, the desired traits were more frequent and intense over the successive generations. At the end of the study, a majority of the Blue Diamond Shrimp and Endler’s Livebearers were the desired trait of vibrant colors. In each generation, the frequency would continue to increase as the undesirable fish were culled and the rest were left to breed. The tank’s parameters were relatively consistent throughout the study, besides slightly increasing the temperature at times to encourage breeding. 

Figure 1: Graph of percent change of vibrancy of colors over time

Discussion:

The results supported the original hypothesis. By consistently selecting only individuals with the desired traits for reproduction, these traits became the most frequent in later generations. In the Blue Diamond Shrimp population, most individuals that remained in the breeding group were those with a strong, blue coloration, while shrimp with a pale and inconsistent complexion were culled. In the Endler's Livebearer population, individuals that were brightly colored remained, while individuals will less vibrant coloration were removed. 

The selective breeding process caused a noticeable shift in the overall coloration of the population, rapidly increasing the frequency of the targeted characteristics. Over time, the experimental population became more uniform with offsprings expressing traits similar to the parents. This demonstrates inheritance and trait selection, showing that alleles associated with bright coloration were passed down and became more concentrated in the population.

Environmental conditions also played an important role in the success of the study. Stable water temperature, pH, and mineral content were necessary for abundant reproduction in both species. Poor water quality or sudden environmental changes could discourage reproduction and cause stress, which all lead to reduced health. That is why it was crucial to consistently check the conditions of the tank and set the conditions according to the optimal environmental range. 

From an ethical standpoint, selective breeding and culling raise concerns about reduced genetic variation and diversity. This can cause potential long-term health issues such as inbreeding and inherited deformities. While culling was used to maintain genetic uniformity, it also eliminated genetic variation that could be essential for population health when adapting new environmental changes. For example, if a new predator that feeds on brightly colored organisms is introduced to this population, the entire population would die off since there is not enough genetic variation to favor a different set of traits. This highlights the importance of balancing scientific goals with the responsibility to maintain healthy and sustainable populations in artificial selection experiments.

Conclusion:

The findings support the hypothesis that artificial selection can significantly increase the prevalence of specific traits in a population. When only organisms with selective traits are allowed to reproduce, those characteristics become more prominent across successive generations. The results also show that human-driven selection can rapidly shape a population, both positively and negatively. The reduction in genetic variance can make a population more vulnerable to even small fluctuations in the environment. Overall, the experiment demonstrates that artificial selection is an effective way to alter trait distribution over time, while also highlighting the importance of maintaining genetic diversity in order to ensure a healthy population over a long period of time.

References:

Paine. (2025). Paine AP Bio Intro Slides 25-26 (Master Slide Set) (Paine, Ed.) [Review of Paine AP Bio Intro Slides 25-26 (Master Slide Set)]. https://docs.google.com/presentation/d/1-uqCtAdqkVpjjzdbKAUT6pZSHQ90Jfb9kdh3Ik9akIU/edit?slide=id.g37fbd91b925_1_0#slide=id.g37fbd91b925_1_0