![]() While most of our examples arise through insights from the widely studied Drosophila melanogaster, we also provide examples from other animals, as well as from plants. Finally, we will highlight evidence that shows the extent to which the mechanisms that give rise to body and organ shape overlap, with views to future avenues of research. In this review, we will first outline the different methods used to characterize body and organ shape, before delving into the recent literature that describes genetic pathways regulating each. In parallel, studies in plants and animals have begun to determine the molecular mechanisms resulting in organ shape. These studies have provided new insight into the molecular mechanisms that underlie the differences in growth across organs that are responsible for generating allometric patterns. Studies over the past twenty years, primarily from insects, have highlighted key genetic pathways required for regulating body size and relative organ size. 2b).Ĭountless examples describe how organ shape changes as organs increase in size, demonstrating that shape and size are likely to share developmental regulators. Describing the geometry of organs in this way – known as geometric morphometrics – provides a sophisticated measure of organ shape (Fig. The geometric properties of organ shape are commonly described using the relative position of morphological features that can be readily identified across specimens, known as landmarks, while accounting for size, orientation, and position (Fig. The second way of thinking about body shape is to consider all geometric properties of a body part, but to exclude its size. However, we will return to how organ shape varies with organ size when discussing how and when the mechanisms regulating each might overlap. This review will define allometry in terms of how traits differ in their relative size (Huxley-Jolicoeur definition). In contrast, the Gould-Mosimann school conceptually distinguishes shape from size and measures the difference in shape as the variation of proportions independent of size. The Huxley-Jolicoeur school describes allometry as variation among traits resulting from differences in their size. Practitioners differ in how they define allometry, and these differences are divided into two main schools of thought. ![]() ![]() In this review, we discuss the methods of characterizing body and organ shape, the developmental programs thought to underlie each, highlight when and how the mechanisms regulating body and organ shape might overlap, and provide our perspective on future avenues of research. These descriptions fall into the domain of geometric morphometrics. Characterization of organ shape is frequently described by the relative position of homologous features, known as landmarks, distributed throughout the organ. Organ shape, on the other hand, is defined as the geometric features of an organ’s component parts excluding its size. The patterns of relative organ size are characterized using allometry. Body shape results from the extent to which organs, or parts of organs, grow relative to each other. Main textĬonceptually, body and organ shape can be separated in two categories, although in practice these categories need not be mutually exclusive. Achieving these specific shapes involves coordinating the many processes that transform single cells into complex organs, and regulating their growth so that they can function within a fully-formed body. Organisms show an incredibly diverse array of body and organ shapes that are both unique to their taxon and important for adapting to their environment.
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