Species can evolve together without ever making contact

Evolution does not only respond to rivals, predators, or mates that bump into each other. It can also respond and evolve when ripples move through the environment and reach species that never cross paths, as shown in a new study.

Researchers tracked a simple question with big consequences: Could one species change the evolution of another without ever meeting it face to face?

The team studied indirect ecological effects, where one species influences another through a third species or by altering the environment rather than through direct contact. These effects can even cross habitat boundaries – as when land insects shape aquatic grazers – and, unlike obvious interactions such as predation or competition, they often go unnoticed.

The study was led by Shuqing Xu at Johannes Gutenberg University Mainz and follows a long tradition of testing evolution in near-natural settings rather than only in small lab containers.

Experimental ponds track evolution

The researchers set up large outdoor mesocosms, which are controlled experimental ponds that mimic nature while allowing careful measurements. These systems were large enough to include many natural processes but controlled enough for clear tests.

Each pond held about 4,000 gallons of water, plus aquatic plants, algae, and the tiny crustacean Daphnia. The researchers added aphids that feed on duckweed to some ponds and kept other ponds as controls without aphids.

That created two worlds that never connected directly, since the aphids lived on floating macrophytes (larger aquatic plants like duckweed) while zooplankton and Daphnia (small drifting animals) as well as phytoplankton (microscopic algae) swam below.

“We showed that land-based aphids influenced the evolution of Daphnia, a tiny aquatic crustacean, even though the two species never come into contact,” said Xu.

The researchers carefully tracked environmental change and genetic change at the same time. The ponds allowed the team to connect cause to effect without guessing.

Nutrients and heat shift

When aphids heavily consumed duckweed, the floating plant thinned out. With less cover, more light penetrated the water, and pond phytoplankton flourished – providing extra food for Daphnia.

The result was a sustained increase in Daphnia numbers in aphid ponds compared to controls, along with measurable shifts in nutrients and water temperature.

For example, there was a roughly 71.5 percent jump in total phosphorus, plus higher underwater light and a small temperature rise.

Species evolve under pressure

Evolution leaves fingerprints in DNA. Whole genome sequencing showed that Daphnia in aphid ponds and Daphnia in control ponds diverged at many genomic sites, and the fraction of significantly different SNPs grew from one year to the next.

Population divergence increased across the experiment, and the team identified more than one hundred variants with strong treatment differences.

These genome-wide signals track with well-known resistance loci in Daphnia and support adaptive change in response to the altered environment.

Adaptation came with a cost

Transplant tests provided the decisive check on whether the observed genetic change was beneficial or just random drift.

Daphnia that evolved in aphid ponds performed better back in aphid ponds than in control ponds.

There was a trade-off: the same aphid-pond lineages performed worse when moved into control conditions, a classic cost of specialization that often follows rapid adaptation.

Species shifts spark ripples

The quality of algal food matters as much as the quantity. Some cyanobacteria provide poor nutrition – or are even harmful – for Daphnia, and their abundance shifted during the experiment.

Independent studies explain why this matters: cyanobacteria are difficult for Daphnia to process and lack the key lipids the crustaceans need.

These changes in the water column did not stop with Daphnia. They rippled outward, altering duckweed and boosting the growth of aphids, which thrived in ponds shaped by earlier herbivory.

Such two-step echoes match ecological theory and show how evolutionary shifts in one part of an ecosystem can reverberate through others without direct contact.

Species evolve across communities

Ecologists have long suspected that networks of interaction, not just pairwise encounters, shape evolution.

Past research shows that even species that do not interact directly can drive traits to evolve across mutualistic networks.

Experiments with guppies offered early proof that adaptation changes whole ecosystems, not only the fish themselves – locally adapted fish altered nutrient cycling, algae, and other organisms around them.

Daphnia add another layer to this picture. Far from being slow, they can respond to environmental change within just a few generations, and their genetic shifts ripple through communities.

Modern genomics reveal how quickly Daphnia adapt to strong pressures, confirming that rapid evolution is not rare noise but a common feature of freshwater systems.

The study is published in Proceedings of the National Academy of Sciences.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–