Researchers have discovered two genes underlying the evolution of a water striding insect fan used for locomotion, which they say were essential for survival in fast-flowing stream environments. Their results highlight a central role for taxon-restricted genes (or genes unique to a particular organism) in the adaptation of the fan. Changes in species-specific traits that lead to expanded functions - including the evolution of plant flowers, insect wings and bird feathers - are critical triggers of diversification and are thought to help organisms adapt to different surroundings. Such changes are suspected to stem from either the use of existing genes for a new purpose or the emergence of taxon-restricted genes. The majority of available evidence supports the former, and clear examples of the latter remain scarce. What's more, adaptations associated with the potential for organisms to occupy novel environments are poorly documented. In search of a better understanding, Maria Emília Santos and colleagues carefully examined the genetic mechanisms and environmental pressures underlying the evolution of the propelling fan, a structure found exclusively on the middle leg in the water strider genus Rhagovelia. The scientists combined gene expression with functional and behavioral assays, finding that two taxon-restricted genes, which they named geisha and mother-of-geisha, controlled fan development. Santos et al. report that geisha originated through a duplication event at the base of the Rhagovelia lineage and both duplicates gained expression in a specific cell population prefiguring fan development. These gene duplicates played a central role in the insects' adaptation to unexpected environments, further hinting that the evolution of taxon-restricted genes can enable access to unexploited ecological niches.
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Science