Molecular plasticity to ocean warming and habitat loss in a coral reef fish.

Sea surface temperatures are rising at unprecedented rates, leading to a progressive degradation of complex habitats formed by coral reefs. In parallel, acute thermal stress can lead to physiological challenges for ectotherms that inhabit coral reefs, including fishes. Warming and habitat simplification could push marine fishes beyond their physiological limits in the near future. Specifically, questions remain on how warming and habitat structure influence the brain of marine fishes. Here we evaluated how thermal stress and habitat loss are acting independently and synergistically as stressors in a damselfish of the Western Atlantic, Abudefduf saxatilis. For this experiment, 40 individuals were exposed to different combinations of temperature (27°C or 31°C) and habitat complexity (complex vs simple) for 10 days, and changes in brain gene expression and oxidative stress of liver and muscle were evaluated. The results indicate that warming resulted in increased oxidative damage in the liver (p=0.007) and changes in gene expression of the brain including genes associated with neurotransmission, immune function, and tissue repair. Individuals from simplified habitats showed higher numbers of differentially expressed genes, and changes for genes associated with synaptic plasticity and spatial memory. In addition, a reference transcriptome of A. saxatilis is presented here for the first time, serving as a resource for future molecular studies. This project enhances our understanding of how fishes are responding to the combination of coral reef degradation and thermal stress, while elucidating the plastic mechanisms that will enable generalists to persist in a changing world.

Effects of developmental exposure to neurotoxic algal metabolites on predator-prey interactions in larval Pimephales promelas.

Harmful algal blooms are a growing environmental concern in aquatic systems. Although it is known that some of the secondary metabolites produced by cyanobacteria can alter predator-prey dynamics in aquatic communities by reducing foraging and/or predator evasion success, the mechanisms underpinning such responses are largely unknown. In this study, we examined the effects of a potent algal neurotoxin, ß-N-methylamino-L-alanine (BMAA), on the development and behavior of larval Fathead Minnows, Pimephales promelas, during predator-prey interactions. We exposed eggs and larvae to environmentally relevant concentrations of BMAA for 21 days, then tested subjects in prey-capture and predator-evasion assays designed to isolate the effects of exposure at sequential points of the stimulus-response pathway. Exposure was associated with changes in the ability of larvae to detect and respond to environmental stimuli (i.e., a live prey item and a simulated vibrational predator), as well as changes in behavior and locomotor performance during the response. Our findings suggest that chronic exposure to neurodegenerative cyanotoxins could alter the outcomes of predator-prey interactions in natural systems by impairing an animal's ability to perceive, process, and respond to relevant biotic stimuli.

Do microplastics impair male dominance interactions in fish? A test of the vector hypothesis.

Microplastics (MPs) are widespread in aquatic environments and have become a critical environmental issue in recent years due to their adverse impacts on the physiology, reproduction, and survival of aquatic animals. Exposure to MPs also has the potential to induce sub-lethal behavioral changes that can affect individual fitness, but these effects are understudied. Many plastic additives introduced during the manufacture of MPs are known endocrine-disrupting chemicals (EDCs) that mimic the action of natural hormones, alter sexual and competitive behavior, and impair reproductive success in fish. In addition, EDCs and other aquatic contaminants may adhere to MPs in the environment, the latter of which may serve as transport vectors for these compounds (i.e., the vector hypothesis). In this study, we staged territorial contests between control males, and males exposed to virgin MP particles or to MPs previously immersed in one of two environmentally relevant concentrations of 17-alpha ethinyl estradiol (EE2; 5 ng/L and 25 ng/L) to evaluate the independent and synergistic effects of exposure to MPs and a common environmental estrogen on male-male aggression and competitive territory acquisition in a freshwater fish, Pimephales promelas. Short-term (30 days) dietary exposure to MPs did not impair the ability of males to successfully compete for and obtain a breeding territory. Overall levels of aggression in control and exposed males were also similar across trial series. These results help to fill a critical knowledge gap regarding the direct and indirect (vector-borne) effects of MPs on the reproductive behavior of aquatic vertebrates in freshwater systems.

Multigenerational effects of a complex urban contaminant mixture on the behavior of larval and adult fish in multiple fitness contexts.

Agricultural and urban storm water runoffs can introduce chemicals of emerging concern (CECs) into waterways. These chemicals can be continually released, persist, or even accumulate over time, with adverse effects on the physiology and behavior of aquatic species. Most studies aimed at evaluating the intergenerational effects of CECs have focused exclusively on single chemicals. By comparison, little is known about the effects of complex CEC mixtures on the behavior of organisms, or how these effects might manifest in subsequent generations. In this study, we exposed three generations of fathead minnows (Pimephales promelas) to environmentally relevant concentrations of a complex CEC mixture representative of urban-impacted waterways and assessed the growth and behavior of larval and adult fish in life-stage-relevant fitness contexts (foraging, boldness, courtship). We found that (i) multigenerational exposure to a complex mixture of CECs altered the behavior of both larvae and adults in different fitness contexts; (ii) concentration-dependent patterns of behavioral impairment were consistent across fitness contexts and life stages; and (iii) the effects of exposure were magnified in the F1 and F2 generations. These results highlight the need for long-term, multigenerational assessments of CECs in affected waterways to robustly inform conservation practices aimed at managing aquatic systems.