In a groundbreaking study that challenges foundational assumptions in evolutionary biology, researchers at Johannes Gutenberg University Mainz (JGU) have uncovered compelling evidence that species separated by different habitats and lacking any direct interaction can still exert significant evolutionary influence on one another. Published in the prestigious journal Proceedings of the National Academy of Sciences (PNAS) on August 21, 2025, the research sheds light on the powerful role of indirect ecological interactions, revealing how these unseen forces can shape the genetic trajectories of species in profound ways.
For decades, evolutionary biology has primarily focused on direct species interactions—such as predation, competition, and mutualism—as the main drivers of adaptation and genetic change. However, natural ecosystems are far more complex than these simple dyadic relationships imply. In fact, myriad species are connected through intricate, cascading networks that span multiple habitats and trophic levels, operating via indirect ecological effects mediated by shared environments and resource dynamics. Yet, direct empirical evidence demonstrating that such indirect interactions can catalyze rapid evolutionary change has remained elusive—until now.
Led by Professor Dr. Shuqing Xu, the international research team conducted a meticulous long-term experiment in the Experimental Ponds Facility at Eawag, Switzerland. These artificial ponds, each with a capacity of 15,000 liters, were used to simulate aquatic communities subject to varying terrestrial influences. The experiment ingeniously introduced aphids—small, plant-feeding insects that inhabit terrestrial ecosystems—onto duckweed, a small aquatic plant that floats on pond surfaces, thereby initiating a cascade of indirect environmental changes affecting aquatic species such as Daphnia, a genus of tiny, planktonic crustaceans commonly known as water fleas.
The presence of aphids feeding on duckweed led to a marked suppression of the duckweed population. This decline altered fundamental physical properties of the aquatic habitat; notably, it increased the amount of light penetrating the water, which in turn stimulated the growth of pond algae. This shift in primary producer abundance cascaded upward to affect Daphnia, which consume these algae. Despite the geographical separation and absence of any direct encounters between aphids and Daphnia, the aphids nonetheless created a domino effect influencing the latter’s ecological niche and evolutionary pressures—a phenomenon previously hypothesized but never empirically substantiated at this scale.
Over two years, the research team collected biweekly samples from the ponds, rigorously measuring environmental parameters including temperature, oxygen concentration, nutrient levels, and biological metrics such as aphid, duckweed, algae, and Daphnia densities. These granular temporal data allowed the scientists to construct a continuous ecological and evolutionary narrative. In the aphid-infested ponds, the Daphnia populations benefited from increased algal availability, translating into enhanced growth conditions and selective pressures distinct from those in control ponds without aphid presence.
To investigate genetic consequences, the team employed whole-genome sequencing of Daphnia populations from both aphid-treated and control ponds. Their analyses revealed pronounced genomic divergence between these groups, with multiple loci exhibiting significant allele frequency shifts. This genomic differentiation indicates that Daphnia populations evolved along separate trajectories contingent on the indirect effects initiated by the terrestrial aphids. The findings thus provide the first direct, genome-wide evidence that indirect interspecies interactions, even in the absence of physical contact, can drive rapid adaptive evolution.
Crucially, the study also explored the adaptive trade-offs underpinning these evolutionary responses. By reciprocally transplanting Daphnia individuals between control and aphid ponds, researchers demonstrated that Daphnia from aphid-affected ponds displayed reduced fitness in control environments, suggesting specialization and potential costs associated with adaptation to the altered algal community and environmental conditions. Conversely, Daphnia from control ponds performed adequately in aphid ponds, underscoring asymmetrical adaptation. These results underscore the nuanced and sometimes costly nature of evolutionary responses to indirect ecological factors.
Intriguingly, the indirect evolutionary feedback loop extended beyond the response of Daphnia. The environmental modifications induced by aphid herbivory—including increased nutrient concentrations and water temperature—positively influenced the aphid populations themselves, suggesting a reciprocal dynamic whereby terrestrial and aquatic species are entangled in complex, indirect evolutionary interactions mediated by ecosystem changes. This bidirectional influence calls for a reevaluation of how biodiversity and species interactions are conceptualized across ecosystem boundaries.
The implications of this research are far-reaching, challenging the compartmentalized view of terrestrial and aquatic ecosystems and urging scientists to appreciate the permeability of ecological and evolutionary processes across habitat borders. Professor Xu emphasized that neglecting indirect interactions risks oversimplifying ecological models and undermines the application of laboratory findings to nature’s multifaceted realities. The study advocates for an integrative approach to evolutionary biology, incorporating indirect ecological networks to better predict and understand adaptive dynamics in a changing world.
This pioneering work exemplifies the power of interdisciplinary collaboration. The conceptual framework originated from the duckweed expertise of the Mainz team, while colleagues at the University of Basel contributed their specialized knowledge on Daphnia ecology and genetics. Meanwhile, the Eawag researchers facilitated the sophisticated aquatic experimental setup and monitoring protocols. Such teamwork, spanning terrestrial botany, aquatic zoology, genomics, and ecosystem ecology, was indispensable to unraveling the complexity of indirect evolutionary influences.
Beyond expanding scientific understanding, these findings have vital practical ramifications for biodiversity conservation and ecosystem management. Anthropogenic disturbances often do not respect ecosystem boundaries; thus, recognizing how indirect effects traverse these boundaries is critical for predicting ecosystem responses to environmental change, invasive species, and habitat fragmentation. This study equips ecologists with a more holistic lens through which to evaluate the evolutionary and ecological consequences of global change in interconnected terrestrial-aquatic landscapes.
In conclusion, the demonstration that indirect ecological interactions can drive adaptive evolution across habitat divides marks a paradigm shift in evolutionary biology. This research not only fills a long-standing empirical gap but also inspires a new framework for studying species interactions that transcends direct contact assumptions. As Professor Xu remarked, accounting for indirect interactions is essential for accurately reflecting nature’s complexity and for advancing both theoretical and applied biological sciences in the 21st century.
Subject of Research: Animals
Article Title: Aphid herbivory on macrophytes drives adaptive evolution in an aquatic community via indirect effects
News Publication Date: 21-Aug-2025
Web References: https://doi.org/10.1073/pnas.2502742122
Image Credits: Illustrations by Shuqing Xu (icons from biorender.com)
Keywords: Indirect ecological interactions, adaptive evolution, Daphnia, aphids, duckweed, aquatic-terrestrial ecosystem linkages, evolutionary ecology, genome sequencing, environmental cascades, experimental ponds, trophic cascades
