The evolution of morphogenetic fitness landscapes: conceptualising the interplay between the developmental and ecological drivers of morphological innovation

Here I show how fitness landscapes can be used to understand the relative importance of developmental and ecological change in initiating morphological innovation. Key is the use of morphogenetic ‘rules’ as the axes of the landscape, which enables explicit incorporation of the contribution that specific morphologies make to fitness. Four modes of fitness landscape evolution are identified: (1) change in the density of peaks on the landscape, driven by an increase in the number of selective pressures encountered; (2) change in the dimensionality of the landscape through the addition of morphogenetic rules; (3) change in the size of one or more dimensions of the landscape through elaboration of already existing morphogenetic rules; and, (4) shifting the position of peaks in the landscape. Morphological innovation is initiated by ecological change in Mode (1), for example the Cambrian explosion of animals, and Mode (4), for example, when taxa such as sticklebacks make a shift in environment, or during coevolutionary escalation. Morphological change is initiated by developmental innovation for Mode (2), typified by some macroevolutionary innovations, such as the emergence of jaws, and in Mode (3), for example, in the differentiation of flower morphology facilitated by gene duplication of the B-class developmental genes