Evaluation of sub-lethal effects of neurodegenerative cyanotoxins on predator-prey interactions in a freshwater fish
A research project funded by the Indiana Water Resources Research Center through the U.S. Geological Survey’s 104B annual base grants (section 104 of the Water Resources Research Act of 1984, as amended).
Start Date: 2018-03-01 End Date: 2019-02-28
Total Federal Funds: $15,000 Total Non-Federal Funds: $30,030
Cyanobacteria are prevalent blue-green algae that impact Midwestern freshwater systems, important environmental and economic resources. Emerging evidence suggests that exposure to neurotoxic compounds can induce sub-lethal behavioral and central nervous system (CNS) changes that have the potential to affect individual fitness. Because behaviors are regulated though the CNS and proper neuronal function is essential to organismal responses to relevant ecological stimuli (e.g., predators, prey, or abiotic environmental cues), neurodevelopmental disturbances could (i) reduce larval recruitment to adult stocks, resulting in declines in native population densities and altered community function, and/or (ii) accelerate the rate of transfer through the food chain through increased predation risk. The long-term goal of this research is to evaluate the significance of emerging algal neurotoxins for fish populations and aquatic communities.
Figure 1. Fish larvae used in a behavioral trial.
- Establish behavioral lowest observed effect concentrations (LOECs) for cyanotoxins, β-N-methylamino-L-alanine (BMAA) and its isomer 2,4-diaminobutyric acid dihydrochloride (DABA). A range-finding study was conducted to evaluate whether or not sub-lethal behavioral alterations are evident at cyanotoxin concentrations below those commonly reported in Harmful Algal Bloom-affected waters.
- Evaluate the extent and mechanisms of behavioral impairment in larval fish exposed to algal neurotoxins. A series of behavioral assays were conducted to evaluate if changes in sensorimotor function directly increase predation risk by impairing escape performance, and indirectly increase predation risk by reducing foraging success and affecting body condition.
- Determine the long-term consequences of exposure. Fish larvae exposed to cyanotoxins were reared in freshwater until maturity and subjected to a suite of performance assays to evaluate if there are changes in motor function associated with developmental exposure to algal neurotoxins persist into the later life stages.
Major Conclusions & Significance
- Exposure to two neurodegenerative cyanotoxins (DABA and BMAA) significantly reduces foraging success of larval fish (fathead minnows). Analysis of prey-strike behavior indicates that this outcome may be due to changes in the ability to detect or recognize prey.
- Exposure to DABA (and likely BMAA) is associated with impaired anti-predator escape behavior, and impaired locomotor function.
- Effects of exposure are evident during the embryonic stage (5 days after being laid), manifested as decreased activity.
- The lowest observed effects concentration for both DABA and BMAA was a nominal exposure concentration of 5 ug/L.
- Long-term deficits due to developmental exposure (i.e., at 6 months of age) are more pronounced in perceptual ability (processing sensory information) than locomotor performance; fish show some recovery of locomotor impairment (i.e., swimming performance) ~2 months after exposure.
What Does This Mean For Indiana?
This research is significant because it is the first study to evaluate the potential effects of toxin-induced behavioral and CNS alterations on fish in real-world ecological contexts. β-N-methylamino-L-alanine (BMAA) and its isomer 2,4-diaminobutyric acid dihydrochloride (DABA) are potent neurotoxic cyanotoxins that have recently been reported in freshwater systems in the Midwestern United States. In addition to potentially compromising the ecological and economic integrity of Indiana’s freshwater resources, these toxic metabolites are transferred and accumulated up the food chain and are a risk factor for neurodegenerative diseases in humans.
Evidence from this study indicates that some secondary metabolites produced by cyanobacteria disrupt central nervous system function, and reduce growth, survival, and reproduction of affected aquatic organisms. Broadly, this study enhances current knowledge of the effects of Harmful Algal Blooms by providing key information important to both ecosystem management and assessments of human exposure.
Training The Next Generation
One of the missions of the Indiana Water Resources Research Center, and all Water Centers, is to train the next generation of water scientists. This project successfully funded research for one Masters student within Dr. Ward’s lab and trained six undergraduate researchers.