Increased Salinity’s Impact on Freshwater Insects Linked to Metabolic Responses, Study Finds
The impact of increased salinity on freshwater insects has been the subject of a new study conducted by researchers at North Carolina State University. The study found that the lack of metabolic responses to salinity may explain why some freshwater insects struggle in higher salinity, while other freshwater invertebrates thrive.
Freshwater habitats are becoming saltier due to a variety of factors, including road salt, agricultural runoff, and sea level rise. These ecosystems are home to a diverse range of organisms, and their health can be assessed by examining the insect population. When these systems become saltier, insect diversity tends to decrease, but the reason for this decline has not been well understood.
Aquatic animals, including insects and crustaceans, must maintain the right balance of water and salts within their bodies through a process called osmoregulation. Theoretically, the most favorable environment for these animals would be one where external salinity levels are similar to those inside their bodies, reducing the need for osmoregulation.
However, the study found that higher salinity levels are associated with increased rates of ion uptake in insects but are also linked to developmental delays or death. It was hypothesized that insects might expend so much energy on osmoregulation in saltier environments that they cannot grow or thrive.
To test this hypothesis, the researchers measured the metabolic rates of crustaceans and insects in dilute and saline environments. They found that the metabolic rates of crustaceans and a freshwater snail increased in dilute conditions, indicating that they were working harder to maintain osmoregulation. In contrast, the metabolic rates of insects remained constant regardless of salinity.
Further investigation revealed that the increased metabolism in non-insects was driven by the need to transport calcium ions, which were scarce in dilute environments. Insects, on the other hand, had a higher transport rate of calcium ions in the saline environment but had little demand for calcium. Excess calcium is potentially toxic to insects, so they seem to utilize their resources to maintain equilibrium in saltier environments, diverting energy away from growth and development.
The researchers speculate that the difference in physiological responses may be based on the organisms’ ancestry or their use of calcium in their exoskeletons or shells.
The findings of this study shed light on the complex relationship between salinity and freshwater insects. Contrary to expectations, insects do not thrive in environments with salinity levels similar to their internal conditions. Their low demand for calcium may allow them to dominate in very dilute environments. On the other hand, low calcium levels are stressful for crustaceans and snails.
This research highlights the critical role of osmoregulation in determining the survival and diversity of freshwater organisms. Future studies will further explore the factors influencing physiological differences among these organisms.
The study was published in the Journal of Experimental Biology and received support from the National Science Foundation. Jamie Cochran, a Ph.D. candidate, was the first author of the study.
