Spider Mites Collectively Avoid Cadmium-Contaminated Tomato Plants Regardless of Competitor Presence or Frequency of Contaminated Plants

Core Concepts

Spider mites collectively avoid tomato plants that have hyperaccumulated the toxic heavy metal cadmium, even when faced with the presence of a competitor species or varying frequencies of contaminated plants.

Abstract

The study investigated how the spider mite Tetranychus urticae responds to cadmium-contaminated tomato plants, both individually and collectively.
Key findings:

Individual spider mite females did not preferentially avoid leaf discs from cadmium-contaminated plants, despite a reduction in their performance on these leaves.
However, when given a collective choice between plants with and without cadmium, spider mites consistently avoided the contaminated plants, regardless of the frequency of contaminated plants in the environment.
Spider mites did not discriminate between plants infested with their competitor T. evansi and uncontaminated plants. However, they preferred plants with competitors when the alternative was a cadmium-contaminated plant.
Cadmium accumulation in plants appears to be a stronger selective pressure than interspecific competition with T. evansi for T. urticae.
The collective avoidance of metal-accumulating plants by spider mites is robust to environmental conditions and may have important consequences for species distribution and interactions in metal-contaminated sites.

Stats

"Feeding on cadmium-contaminated leaves resulted in a significant reduction in the oviposition rate of spider mites."
"Spider mites distributed themselves unevenly across cadmium-free plants, suggesting aggregation behavior."
"The presence of cadmium significantly reduced the number of spider mite offspring produced on plants, regardless of the frequency of contaminated plants in the environment."
"In cadmium-free environments, the presence of the competitor T. evansi significantly reduced the number of T. urticae offspring produced."

Quotes

"Our results show that aggregation may facilitate avoidance of contaminated plants."
"They also indicate that cadmium accumulation in plants is a stronger selective pressure than interspecific competition with T. evansi."
"Therefore, collective avoidance of metal-accumulating plants by herbivores is robust to environmental conditions and may have important consequences for species distribution and interactions in metal contaminated sites."

Key Insights Distilled From

Spider mites collectively avoid plants with cadmium irrespective of their frequency or the presence of competitors

by Godinho,D. P... at www.biorxiv.org 08-18-2023

https://www.biorxiv.org/content/10.1101/2023.08.17.553707v5

Deeper Inquiries

How might the collective avoidance of cadmium-contaminated plants by spider mites influence the long-term evolution of metal hyperaccumulation as a defense mechanism in plants?

The collective avoidance of cadmium-contaminated plants by spider mites can have significant implications for the long-term evolution of metal hyperaccumulation as a defense mechanism in plants. This avoidance behavior by herbivores can exert selective pressure on plants, favoring those that are able to hyperaccumulate metals as a defense strategy. Over time, this selective pressure may lead to the prevalence of plant species that have the ability to accumulate high levels of metals, such as cadmium, as a means of deterring herbivory.
Furthermore, the avoidance of cadmium-contaminated plants by spider mites can contribute to the maintenance of metal hyperaccumulation in plant populations. Plants that are successful in deterring herbivores through metal accumulation are likely to have higher fitness and reproductive success, leading to the persistence of this trait in the population. As a result, the evolution of metal hyperaccumulation as a defense mechanism may be reinforced by the collective avoidance behavior of herbivores like spider mites.

What other environmental cues or factors could modulate the relative importance of abiotic (e.g., heavy metal contamination) versus biotic (e.g., competition) pressures on herbivore host selection and performance?

Several environmental cues or factors can influence the relative importance of abiotic and biotic pressures on herbivore host selection and performance. One key factor is the availability of alternative food sources. In environments where suitable host plants are scarce, herbivores may prioritize host selection based on nutritional quality rather than abiotic factors like heavy metal contamination. Additionally, the presence of natural enemies or predators can also influence herbivore host selection, as the risk of predation may outweigh the benefits of feeding on a preferred host plant.
Seasonal variations in plant chemistry can also play a role in modulating herbivore host selection. For example, plants may vary in their metal accumulation levels throughout the growing season, leading to fluctuations in the attractiveness of different host plants to herbivores. Climate conditions, such as temperature and humidity, can also impact the performance of herbivores on metal-contaminated plants, potentially altering their host selection behavior.
Overall, the interplay between abiotic and biotic factors, along with the availability of alternative hosts and environmental conditions, can collectively influence the importance of heavy metal contamination versus competition in shaping herbivore host selection and performance.

Given the potential for metal contamination to alter species interactions, how might these changes in community dynamics impact ecosystem-level processes in metal-polluted environments?

Changes in species interactions resulting from metal contamination can have far-reaching effects on ecosystem-level processes in metal-polluted environments. One major impact is on trophic dynamics, where alterations in herbivore-plant interactions can cascade through the food web. For example, reduced herbivory on metal-hyperaccumulating plants can lead to changes in plant community composition and structure, ultimately affecting higher trophic levels.
Furthermore, shifts in species interactions due to metal contamination can influence nutrient cycling and energy flow within ecosystems. Changes in herbivore feeding behavior and plant defense mechanisms can impact nutrient availability and cycling, potentially altering ecosystem productivity and stability. In addition, alterations in species interactions may affect the resilience of ecosystems to environmental stressors and disturbances.
Moreover, changes in community dynamics driven by metal contamination can have implications for ecosystem services. For example, alterations in plant-herbivore interactions can impact pollination, seed dispersal, and other essential ecosystem functions. Overall, the disruption of species interactions in metal-polluted environments can have profound effects on ecosystem structure, function, and resilience, highlighting the importance of understanding and managing the impacts of metal contamination on biodiversity and ecosystem processes.