A common garden experiment is a method used in biology to study how an organism’s traits are affected by its genes and its environment. It involves collecting organisms from different geographical locations and growing them together in one place under the same conditions. These experiments are used in fields like ecology and evolutionary biology.
By creating a uniform environment for all subjects, scientists can observe whether the differences seen in their natural habitats persist. This allows for a direct comparison of their inherited characteristics without the confusing influence of varying environmental factors.
The Core Purpose of a Common Garden
The goal of a common garden experiment is to separate the influences of genetics from the environment on an organism’s observable traits, known as its phenotype. For instance, one plant population might be taller than another because of its genetic makeup or simply because it receives more rainfall.
By raising individuals from various populations in a single, controlled setting, scientists eliminate environmental variation as a cause for the differences among them. If the variations observed in the wild persist in the common garden, it provides evidence that those traits are genetically determined. This helps researchers understand the genetic basis of adaptation.
This experimental setup is also used to study phenotypic plasticity. Phenotypic plasticity is the ability of a single set of genes to produce different physical characteristics depending on the environment. A common garden experiment can reveal if the differences between populations are due to this plasticity. If individuals from different origins grow to be similar in the common garden, it suggests their differences in the wild were a plastic response to their distinct environments.
Designing the Experiment
The design of a common garden experiment is a systematic process to ensure the only significant variable is the genetic origin of the individuals. The first step involves collecting samples from multiple distinct populations. For plants, this could mean gathering seeds or taking cuttings from individuals in different locations, such as at high and low altitudes or in wet and dry climates.
Once collected, these individuals are transported to a single location—the common garden. This garden can be an outdoor plot, a greenhouse, or a laboratory growth chamber. The defining feature is that all individuals, regardless of their origin, are grown under identical conditions.
Every aspect of the environment is standardized. All plants receive the same type of soil, the same amount of water, and are exposed to the same sunlight, temperature, and day length. For animal studies, this would translate to identical housing, diet, and social environments.
Interpreting the Results
Scientists measure various traits, such as growth rate, size, reproductive output, or timing of life events like flowering. There are two main outcomes that provide clear insights. If the individuals from different populations maintain the same distinct traits they exhibited in their home environments, it suggests that these differences are genetically hardwired.
For example, if seeds from a mountaintop population consistently grow into shorter plants than seeds from a valley population, this points to genetic differentiation as the cause. Conversely, if all the individuals in the common garden grow to be very similar, and the differences seen in the wild disappear, the interpretation changes.
This outcome indicates that the original variations were not due to genetics but were instead a result of phenotypic plasticity. In this scenario, the valley plants were taller simply because their environment was more favorable for growth, and when placed in the same conditions as the mountain plants, that advantage vanished.