Researchers find a novel interaction between proteins during embryo development that allows adult water striders to jump and more efficiently avoid predation.
Water striders may seem an unlikely candidate for teaching us about evolutionary principles. However, this group of insects is actually quite diverse and many groups occupy different niches and have developed different life strategies for survival and reproduction. This makes them excellent candidates for studying evolution and selection based on environmental pressures.
For example, some groups of water striders live on open water and have long midlegs and short back legs, while others live closer to shore and have short midlegs and long back legs. The open water insects with long midlegs use these appendages to jump several body lengths into the air to avoid predation from fish below them.
The shore insects with short midlegs cannot jump and have other mechanisms such as wings to escape predation. This short-legged group is thought to be the ancestral population, while the more recently diverged long-midlegged group gained this trait and jumping behavior.
Importantly, a fish predator system has shown that jumping is much more efficient than flying for escaping predation from below. So how did this innovation arise?
A recent report published in Nature Communications has resolved the genetic cause of long midlegged water striders and, thus, the origin of the adaptation responsible for water striders’ ability to more efficiently escape predation from below.
Researchers found that a novel interaction between two proteins during water strider embryo development manifests long middle legs in adults. Specifically, a gene belonging to the Hox gene family (a group of genes highly conserved in animals) interacts with an enzyme called Gilt. Though Gilt itself is not a novel enzyme, its role in controlling embryo development has never been documented.
In water striders with long midlegs these two genes interact at the tips of the legs during early development of a water strider embryo. This interaction leads to the eventual growth of longer legs.
The ancestral group does not express these two proteins at the correct times or in the correct ratio for the interaction to be present – they develop short midlegs. However, genetically altering short midleg insects to have the correct expression pattern of these two proteins during development causes the adults to have long midlegs.
Therefore, the research team discovered a novel interaction between two proteins during water strider embryo development that has facilitated the success of insects living in the open water.
Their study did not attempt to show when this evolutionary adaptation arose and was fixed into the population. However, it does show that, in addition to mutations that produce novel enzymes, changes in the expression patterns of existing proteins can also create increased fitness in the environment (in this case, predator evasion).
Article image by Schnobby (Own work) [CC BY-SA 3.0], via Wikimedia Commons