Abstract
Polyphenisms, the production of two or more discrete phenotypes from a single genome, are a remarkable reflection of the flexibility of developmental mechanisms. Examples of polyphenisms include castes in eusocial insects, and winged versus wingless forms of aphids. How the signals that drive these alternate forms are received and interpreted, and how they trigger different developmental trajectories remains unknown. While different polyphenisms have evolved independently with different signals and outcomes, there are some commonalities that may help us understand the way development can be remodelled. In this Review, I discuss the relationship between plasticity and polyphenisms, and the role of neuro-endocrine signalling and epigenetic pathways. I focus on developmental polyphenisms, outlining current knowledge and unanswered questions regarding the underlying developmental mechanisms. To understand polyphenism mechanisms, we need functional experiments; I lay out a framework for interpreting such experiments. I hope to convince you that polyphenisms are an important topic of study for developmental biologists and that functional experiments may unlock a better understanding of the interplay between the environment and development, shedding light on how morphology evolves.