Evolutionary walks through a land plant morphospace
1999
Niklas, K.J.
A model for mimicking land plant evolution is here expanded and re-evaluated. The model consists of (1) a morphospace containing on the order of 10(9) phenotypic variants, (2) 15 different fitness landscapes, each defined on the basis of performing one or more of four tasks (i.e. maximizing light interception, mechanical stability and reproduction, and minimizing total surface area), and (3) an algorithm driving a search through fitness landscapes for more fit variants. The model is used to predict the effects of the number of simultaneously performed tasks ('complexity'), abrupt changes in environmental conditions (mimicked by random replacement of one fitness landscape with another), and developmental barriers (mimicked by barring searches from entering specific subdomains in the morphospace) on number and accessibility of variants occupying fitness maxima. The model predicts that (1) the number and accessibility of fitness peaks will increase (while the difference between the relative fitness of peaks and valleys will decrease) in proportion to functional complexity, (2) abrupt shifts in landscapes will increase rather than decrease phenotypic diversity, and (3) obstructed searches have an equal or higher probability of reaching fitness peaks than unfettered searches. These results follow axiomatically from the way hypothetical variants are spatially ordered in the morphospace, the manner in which relative fitness is defined, and the protocol used to locate fitness peaks. A critique of the model's predictions and desiderata for future research are provided.
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