Hydra: A Powerful Biological Model

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Hydra: A Powerful Biological Model∗ Surendra Ghaskadbi

Hydra, a freshwater diploblast, with a simple but deﬁned body plan, an organized nervous system, and the presence of stem cells, is one of the oldest model organisms used in biology. It exhibits many embryonic features even as an adult, a spectacular ability of regeneration, and lack of organismal aging. Hydra can provide insights into how complex animal forms evolved and is waiting to be better utilized in teaching. To understand biological processes, scientists often choose and use a small number of species based on the speciﬁc advantages each one of them oﬀers. Such studies not only allow us to understand how biological systems arose and function, but also provide insights into similar processes occurring in other species, sometimes even humans. Hydra, one of the oldest animals to have been used as a model system in biology, is a diploblast, i.e., with a body made up of only two layers of cells, outer ectoderm and inner endoderm, which lives in freshwater bodies. It is a Cnidarian with a simple but deﬁned body plan. It is structurally more complex than sponges, which do not exhibit a deﬁned body axis. Unlike us, who have three major body axes (dorsal-ventral, anterior-posterior, and left-right) and bilateral symmetry, hydra has an oral-aboral axis and radial symmetry. Way back, at the beginning of the eighteenth century, attempts were being made to study marine organisms, such as corals and mollusks, by simulating natural conditions [1]. The breakthrough, however, came, when in the year 1740, Abraham Trembley, who had a PhD in mathematical inﬁnity, began studying aquatic insects and ended up ﬁnding some strange and mobile tubes in water [1]. In the following few years, Trembley studied these strange mobile tubes closely and succeeded not only in keeping these alive in glass jars

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Surendra Ghaskadbi is a developmental biologist particularly interested in cell signaling during pattern formation and evolution of developmental mechanisms. Over the past two decades he has reintroduced hydra as a model system for teaching and research in India.

Keywords Hydra, regeneration, pattern formation, model system, teaching tool.

Vol.25, No.9, DOI: https://doi.org/10.1007/s12045-020-1039-2

RESONANCE | September 2020

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GENERAL ARTICLE

ﬁlled with water but also in transporting them over several miles through the postal system. Trembley carried out a large number of experiments with them; these included regeneration of whole polyps from cut pieces and production of the multiheaded hydra. Hydra derives its name from the multiheaded monster in Greek mythology. This is rather unfortunate since there seems to be nothing monstrous about this animal except perhaps to its prey. If one comes across a live hydra, one will immediately appreciate how beautiful, delicate, and lovable it is. Trembley’s work, published in 1744, led to what is widely known as the ‘Trembley’ eﬀect in marine biology [1]. Although hydra itself is a freshwater organism, Trembley’s work encouraged

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