It's a two-way street between evolution and environmental change

The tale of the peppered moths remains one of the most powerful narratives of evolution’s relentless course. These moths faced a life-and-death struggle during the Industrial Revolution in England. The white-bodied moths, once plentiful, became easy pickings for predators as coal smoke blackened the tree bark in urban environments. On the flip side, black-bodied moths, initially a rare sight, prospered and became the dominant variant under the newfound conditions. 

This case has long served as a key illustration of how environmental change can guide species evolution. Recently, however, a role reversal has intrigued the scientific community. Could it be possible that species evolution, rather than just being influenced by, actually shapes environmental change? 

A new study from the University of Rhode Island lends credibility to this provocative notion, offering robust evidence of this reverse dynamic.

What the researchers learned

The study, published in the Proceedings of the National Academy of Sciences, exposes a fascinating connection between evolutionary change in lizards’ leg length and consequent impacts on vegetation growth and spider populations on a selection of small islands in the Bahamas. 

The researchers consider this as one of the first demonstrations of evolution-to-environment effects recorded in a real-world setting.

“The idea here is that, in addition to the environment shaping the traits of organisms through evolution, those trait changes should feed back and drive changes in predator-prey relationships and other ecological interactions between species,” explained study senior author Professor Jason Kolbe.

He emphasized the importance of understanding these dynamics for predicting species persistence and potential ecological changes.

For two decades, Professor Kolbe and his team have focused on the anole lizards inhabiting a chain of tiny islands in the Bahamas. These islands, numbering around 40, are small enough to allow for comprehensive monitoring of the resident lizards, and sufficiently isolated to prevent inter-island lizard migration, facilitating the formation of distinct populations.

Previous observations were used in the new study

Prior investigations have demonstrated that brown anoles are adept at adapting to the specific characteristics of their vegetative surroundings. In settings where tree and brush limbs are narrower, natural selection favors short-legged lizards, granting them greater agility in predator evasion or prey pursuit. 

However, in habitats where plant and tree limbs are thicker, lizards with longer limbs have the upper hand. Scientists have also found that this limb-length trait can evolve swiftly within a few generations in brown anoles.

Segregation by leg length

To explore how this evolved trait might reverberate through the ecosystems on these tiny Bahamian islands, the team decided to segregate short- and long-legged lizards on separate islands, then compare the ecological impacts.

Equipped with poles outfitted with tiny dental floss lassos, the team captured hundreds of brown anoles. They gauged the leg length of each lizard, selecting only those with exceptionally short or long limbs, and released the rest. They then populated lizard-free islands with these distinct groups.

The researchers hypothesized that the short-legged lizards, given the predominance of smaller diameter vegetation on the experimental islands, would prove more adept hunters in this environment. They then aimed to determine if the ecological impact of these efficient predators would be noticeable.

Eight months later, the team revisited the islands to observe any ecological disparities between those inhabited by short- and long-legged lizards. The differences were, indeed, striking. Islands with the shorter-legged lizards saw a 41% reduction in web spider populations – a primary food source for brown anoles – compared to the islands with the longer-legged lizards (see image here). 

The plant growth also varied significantly due to the short-legged lizards’ superior insect herbivore hunting prowess, which allowed plants to thrive. On such islands, buttonwood trees showed twice as much shoot growth as those on islands with the long-legged counterparts.

Full feedback loop between ecology and evolution

The results of the study bring the intricate interaction between ecology and evolution full circle. “These findings help us to close that feedback loop. We knew from previous research that ecological factors shape limb length, and now we show the reciprocal relationship of that evolutionary change on the environment,” said Professor Kolbe.

This study signifies a leap forward in understanding the full breadth of interactions between evolution and ecology. It provides invaluable insights into how morphological adaptations – like the limb length in lizards – can exert influence on broader ecological dynamics such as vegetation growth and spider populations. Moreover, it reveals how quick evolutionary changes can have immediate and measurable impacts on the surrounding ecosystem.

Study’s outcome is crucial to making future environmental predictions

It’s important to highlight the pivotal role that this understanding could play in predicting future ecological outcomes, especially at a time when human activities are rapidly accelerating both evolutionary and ecological changes globally. Understanding these feedback loops is crucial to anticipate and manage potential challenges and changes that ecosystems might encounter.

In essence, the narrative of evolution has come full circle with this research. It reinforces the fact that the relationship between evolution and ecology is not one-way, but rather a complex, intertwined interaction. 

Just like how the environment can impact species through natural selection and evolution, the evolution of species can, in turn, modify the environment, influencing the dynamics of other species and ecological processes.

As the story of the peppered moth once shed light on how environmental change fuels species evolution, this latest research might soon find its way into textbooks as an example of the reverse – how species evolution, in return, steers environmental change.

More about environmental change and evolution

Environmental change can significantly influence the evolution of species. This process, referred to as natural selection, is one of the cornerstones of evolutionary biology.

When the environment changes, it can alter the balance of ecosystems and the survival prospects of species. Such changes can include shifts in climate, alterations in landscape, or variations in the availability of resources, like food or water. These changes can make certain traits more beneficial, leading those individuals with these traits to have higher survival and reproduction rates.

For instance, let’s consider a hypothetical population of rabbits in an environment that suddenly experiences a colder, longer winter. In this scenario, rabbits with thicker fur will have a survival advantage over those with thinner fur. 

Over time, these warmer, thicker-furred rabbits are more likely to survive the harsh winters, and thus more likely to pass on their genes to subsequent generations. As a result, the rabbit population, as a whole, will gradually evolve to have thicker fur.

Similarly, in the case of the peppered moths during the Industrial Revolution, the darkening of tree bark due to soot made the black-bodied moths less visible to predators compared to the white-bodied moths. This camouflage gave the black-bodied moths a survival advantage, leading to their increase in population, while the white-bodied moths dwindled. This is an excellent example of how environmental changes can drive the evolution of a species.

Changes in the environment can also lead to speciation, the process through which new species evolve. For instance, when a population gets divided by a geographical barrier such as a mountain range or a river, different environmental conditions on either side can lead to the evolution of two distinct species from the original population. Over time, the separated populations may evolve unique traits in response to their specific environmental pressures, eventually becoming different species.

In summary, environmental changes can have a profound impact on the evolution of species, shaping their traits and even leading to the emergence of new species. This process of natural selection is a dynamic and ongoing part of life on Earth.

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