What was the investigation? But from my best guess I'm assuming it's the second option. This may be incorrect.
The basic unit of life is a cell. Have a great day!
The answer is no, high biological fitness in one environment doesn’t have to be high in another environment.
Biological fitness is a term used in evolutionary biology and it is the quantitative representation of how a genotype (or phenotype) is successful (reproductively) in a certain environment. Fitness depends on environment so it changes if the environment changes. The fitness of a genotype is manifested through its phenotype, which is affected by the environment.