Development & Trait (Micro) Evolution
Development affects the evolution of morphology by (i) determining the portion of quantitative genetic variation available to selection during trait ontogeny through (ii) structuring the relationships among allelic, quantitative genetic, and phenotypic variation, and (iii) integrating the ontogeny of different morphological elements, producing covaring trait suites or modules. Working primarily with Jason Wolf and Aneil Agrawal, I have been involved in a few projects aimed at explicitly incorporating different kinds of developmental interactions into quantitative genetic models of trait evolution. These models use a ‘phenotype landscape’ approach to visualize interactions among developmental modules that determine trait values. I am particularly intrigued by our findings that the effects of genetic correlations on the independent evolution of trait values depends on the nature of the developmental interactions among them (e.g., additive by additive, additive by epistatic) and that, together, population variance and location in the phenotype landscape affects the response to selection. Moreover, these models indicate that environmental changes that affect developmental processes can produce new phenotypic variation and lead to rapid evolution without requiring changes in the selective environment.
Although the insights reveled by such theoretical treatments are potentially great, the predictions of these models need to be interpreted with caution because they remain largely untested empirically. However, several avenues of investigation would lend themselves to testing these predictions with living systems. For example, artificial selection can be applied to morphological traits which are well understood developmentally, and then the proximate bases of the responses to selection can be compared across lineages. Such work could be used to generate the full ‘phenotype landscape’ the models call for, which in turn would allow testing of the model predictions. An alternative approach involves using existing phenotypic, developmental, and genetic variation among lineages to define a landscape and test predictions about how these affect the correlational structure among traits in the short and long term. We are currently using these approaches using morphological scaling, which really describes the relative growth plasticity of traits, as a model system.
Lineages that show adaptive phenotypic plasticity in morphological traits can also be used to test predictions of the models. In particular, systems that exhibit polyphenisms in morphological traits can be investigated to better understand how development builds covarying trait suites within and across alternative morphotypes. Such data could test predictions regarding how varying contributions of developmental modules affect trait expression. Studying the proximate basis of trait expression in polyphenic systems, especially when studies are done in a comparative context, can also inform our understanding of how development shapes the evolution of morphology in general, and of adaptive plastic responses in particular.
Relevant publications
Dreyer, A.P., O. Saleh Ziabari, E.M. Swanson, A. Chawla, W.A. Frankino, A.W. Shingleton. 2016 Cryptic individual scaling relationships and the evolution of morphological scaling. Evolution 70:1703-1716.
Mirth, C.K., W. A. Frankino and A.W. Shingleton. 2016. Allometry and Size Control. invited submission. Current Opinion in Insect Science 13:93-98.
Shingleton, A.W. and W. A. Frankino. 2013. New perspectives on the evolution of exaggerated traits. BioEssays 35:100-107.
Shingleton, A., W. A. Frankino, T. Flatt, F. Nijhout, and D. Emlen. 2007. Size and Shape: The regulation of static allometry in insects.
Wolf, J. B., C. E. Allen, and W. A. Frankino. 2004. Multivariate phenotypic evolution in developmental hyperspace in M. Pigliucci and K. Preston, eds. The Evolutionary Biology of Complex Phenotypes. Oxford University Press.
Wolf, J. B., W. A. Frankino, A. F. Agrawal, E. D. Brodie III, and A. J. Moore. 2001. Developmental interactions and the constituents of quantitative variation. Evolution 55:232-245.
Suggested research programs for testing the models and exploring the role of development in morphological evolution:
Shingleton, A.W. and W. A. Frankino. 2013. New perspectives on the evolution of exaggerated traits. BioEssays 35:100-107.
Frankino, W. A., A. Shingleton, D. Emlen. 2009. Experimental approaches to studying the evolution of morphological allometries: The shape of things to come. in: Experimental Evolution: Concepts, Methods, and Applications, T. Garland and M. Rose, eds. University of California Press.
P.M. Brakefield and W. A. Frankino. 2009. Polyphenisms in Lepidoptera: Multidisciplinary approaches to studies of evolution and development. in: Phenotypic Plasticity in Insects: Mechanisms and Consequences. Ananthakrishnan, TN and D. W. Whitman (Eds.). Oxford University Press.
Frankino, W. A., and R. A. Raff. 2004. Evolutionary importance and pattern of phenotypic plasticity: Insights gained from development. Pp. 64-81 in T. J. DeWitt and S. M. Scheiner, eds. Phenotypic Plasticity, Functional and Conceptual Approaches. Oxford Press.