Figure 1.

Hybrid fitness varies by genotype and by environment. (a) Individuals (represented by linkage groups; the different colored regions reflect genetic material from hybridizing species) may suffer from reduced fitness as the result of genetic incompatibilities regardless of the environment. These hybrid genotypes are then lost from the population (indicated by a red ‘X'). (b) The fitness of the remaining individuals can then be tested in different environmental conditions (such as wet and sunny versus dry and shady).