Developmental constraints versus flexibility in morphological evolution

Abstract

Evolutionary developmental biology has encouraged a change of research emphasis from the sorting of phenotypic variation by natural selection to the production of that variation through development. Some morphologies are more readily generated than others, and developmental mechanisms can limit or channel evolutionary change. Such biases determine how readily populations are able to respond to selection, and have been postulated to explain stasis in morphological evolution and unexplored morphologies. There has been much discussion about evolutionary constraints but empirical data testing them directly are sparse. The spectacular diversity in butterfly wing patterns is suggestive of how little constrained morphological evolution can be. However, for wing patterns involving serial repeats of the same element, developmental properties suggest that some directions of evolutionary change might be restricted. Here we show that despite the developmental coupling between different eyespots in the butterfly Bicyclus anynana, there is great potential for independent changes. This flexibility is consistent with the diversity of wing patterns across species and argues for a dominant role of natural selection, rather than internal constraints, in shaping existing variation.

A strong response to selection on mass-independent maximal metabolic rate without a correlated response in basal metabolic rate

“…The reported correlations range from 0.15 to 0.72 (Dohm et al, 2001;Nespolo et al, 2005b;Sadowska et al, 2008;Wone et al, 2009). Even the highest of these values indicates that the genetic constraint between BMR and MMR is not absolute, and hence that some measure of independent evolution of each of the traits is possible (Beldade et al, 2002). However, evolutionary constraints depend not only on genetic correlations/ covariances but also on genetic variances and the relative strength of selection acting on correlated traits.…”

The interaction between developmental bias and natural selection: from centipede segments to a general hypothesis

“…This point is particularly important, given the recent work of Beldade et al (2002) on butterfly wing pigmentation patterns. These authors use as the basis for an artificial selection experiment positive co-variation in the size of anterior and posterior eyespots on the forewing of the African species Bicyclus anynana, which corresponds well to the abstract picture shown in Figure 3.…”

The extended evolutionary synthesis: its structure, assumptions and predictions

“…Of particular interest is the observation that phenotypic variation can be biased by the processes of development, with some forms more probable than others [12,17,[25][26][27][28]. Bias is manifest, for example, in the nonrandom numbers of limbs, digits, segments and vertebrae across a variety of taxa [25,26,29,30], correlated responses to artificial selection resulting from shared developmental regulation [31], and in the repeated, differential re-use of developmental modules, which enables novel phenotypes to arise by developmental rearrangements of ancestral elements, as in the parallel evolution of animal eyes [32].…”