Straight from the nematode’s mouth
The speed of roundworm evolution can be determined from whether a species can develop two different mouth shapes.
Every animal and plant grows to a body plan that is defined by its genes. However, the body plan must be flexible enough to allow the organism to respond to whatever the world throws at it. This flexibility — known as developmental plasticity — allows an organism to change certain characteristics in order to survive in varying environmental conditions. For example, nerve cells in the brain need to be able to remodel to form memories.
It has been suggested that developmental plasticity can affect evolution because the ability of an organism to grow in different ways opens a diverse treasure trove of options from which to generate new forms and ways to exploit the environment. However, this potential had not previously been tested.
Vladislav Susoy and co-workers looked at 90 species of roundworm that look different from one another, particularly in their mouths. Some of the worms have moveable teeth while others are simple and streamlined. Furthermore, of those examined, 23 species were found to be ‘dimorphic’ and have the ability to develop one of two types of mouth: either narrow or wide, depending on their prey.
Susoy and co-workers looked at how similar the sequences of 14 genes were across all 90 species and used this information to build a family tree of how the roundworms are related to one another. Tracking which animals have dimorphic mouths on this tree produced an intriguing result: the strategy arose once in a single ancestor of the worms. Although this ability has been lost at least 10 times in the species that retained teeth, it has persisted in others through long periods of evolutionary time.
Next, Susoy and co-workers estimated the speed of evolution in these worms based on how quickly the characteristics of the worms’ mouths had changed over evolutionary time. The gain of a dimorphic trait was associated with an increased rate of evolution and the appearance of many new species with diverse and more complex mouthparts. However, evolution was even faster where a dimorphism had been lost, even though the mouthparts generally became less complex.
Together, these findings demonstrate how developmental plasticity can introduce genetic diversity that can promote the evolution of new forms and species. The next challenges will be to find out how this genetic diversity is stored and released in the worms and to provide examples of the impact of environmental changes on developmental plasticity and shape.
To find out more
Read the eLife research paper on which this eLife digest is based:“Rapid diversification associated with a macroevolutionary pulse of developmental plasticity” (February 4, 2015).
Read a commentary on this research paper: “Evolution: To plasticity and back again”
