The rigour with which comparisons can be made between the different studies, however, is constrained by variations in practices between laboratories and changes that have occurred to luminescence dating procedures over the years.
Even so, the future evolution of migration time will eventually be constrained by eroding genetic variation and conflicting demands.
However, their ability to adapt may be constrained by available genetic variation and genetic correlations between traits.
Adaptation can be constrained by available genetic variation [ 1, 2], and developmental [ 3], biomechanical-chemical [ 4- 6], and functional [ 1, 7] factors.
Similarly, sexual signals may be constrained by ecology and environmental variation if, for example, diet affects the expression of the trait [ 6], or if ecological factors constrain the transmission of signals [ 7].
Overall, the evolution of these traits might be constrained by a lack of genetic variation in some environments, but not by negative genetic correlations between the different traits.
It is important to note, however, our ability to increase genetic variation will be constrained by the actual number of fish in the lake.
In contrast, evolution of laying-date plasticity towards new trait optima may be constrained by a lack of among-individual variation.
