Adaptive Landscape

∞ generated and posted on 2023.05.21 ∞

Means of visualizing the relationship between genotype and fitness.

Adaptive Landscapes are not actual, out-of-doors landscapes but instead are a form that especially three-dimensional graphs can take on, where the x and y axes represent 'genotype space' while the z axis represents fitness.

Adaptive landscapes are usually metaphorical rather than representing a mapping of actual fitness measurements onto actual genotypes. That is, adaptive landscapes are employed more as models than as actual representations of data, and this is in no small part due the difficulty associated with obtaining such data, where gathering fitness data for even a single genotype is often no small feat.

Within such representations, typically all variance in genotype is presented as a single two-dimensional plane, with genotypes displaying greater fitness rising above the plane as peaks and those displaying lower fitness falling below the plane or at least to the plane as valleys. In addition, for a given environment, the topography of fitness landscapes are fixed, and it is assumed that not all possible genotypes associated with the landscape are found in a population.

The following video provides a nice visualization of populations with their varied genotypes moving up and down adaptive peaks found within various adaptive landscapes.

An adaptive landscape thus is the totality of the impact that different alleles that are available to a population can have on the evolutionary fitness of the species (or subspecies) involved. Based on the height of 'peaks' in this landscape, we therefore can visualize especially how certain combinations of alleles can result in greater or lesser degrees of evolutionary success.

A primary question in considering adaptive landscapes is one of how populations might maximize their fitness, i.e., by possessing genotypes that are found higher above the genotype plane. This can be straightforward in terms of moving up a single adaptive peak, which may be accomplished via a series of single mutations along with associated natural selection. It is less obvious, however, how populations might move away from shorter adaptive peaks in order to scale adaptive peaks that possess greater heights, i.e., greater fitness potentials. A standard answer is that it is through random processes, such as genetic drift or random environmental changes, that such shifts to the vicinity of higher adaptive peaks may occur.

Note as an aside that the chemist in me has always struggled with the how adaptive landscapes are presented since higher fitness ought to coincide with the equivalent of energy lows, that is, with fitter genotypes falling to lower depths of evolutionary 'stability' rather than climbing up to ever more precarious heights. Still, greater fitness obviously should be a larger number than lesser fitness, explaining why natural selection would push populations upwards in terms of their fitness. It just kind of bothers me conceptually is all.

Note also that it is usually implicitly assumed that most possible genotypes will not be found within a population, i.e., sequence space will not have been fully explored by a population. Thus, adaptive landscapes are unlikely to be fully explored, as the above video nicely illustrates.