Ammonia Effects on Social Hierarchy Formation

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Ammonia Effects on Social Hierarchy Formation

Project Abstract:

The interactions of species in an ecosystem rely on the stability of the keystone species within the system. Crayfish are keystone species with populations decreasing plant density by grazing and acting as a limited food source for predators, like the small-mouth bass. Crayfish as a keystone species of an ecosystem can be impacted by background chemicals. Ammonia as a background chemical in an ecosystem affects many different species. Low concentrations of ammonia are known to be toxic after only 96 hours to several aquatic species, including Rainbow trout, walleye, and Channel catfish. Behavioral changes can result from exposure to ammonia. Crayfish fighting behavior is impacted by ammonia in two ways. When exposed to a low amount of ammonia (0.9 mg/L), the chemosensory system of the crayfish is impaired and the fights between individuals lengthen in time. If the crayfish are exposed to high levels of ammonia (9.0 mg/L), fighting pairs are physiologically impaired and the duration of fights decrease. Ammonia is hypothesized to not only affect fighting between crayfish pairs, but to manipulate the hierarchy formation of populations as well. The social hierarchy of crayfish could be affected by the sensory impairment of low levels of ammonia and by physiological impairment from high levels of ammonia. Subordinate individuals can recognize dominant crayfish by chemical signals. It is predicted that exposure to low levels of ammonia will increase the fighting within the social hierarchy by decreasing recognition of dominant and subordinate individuals. High levels of ammonia will decrease fighting because of physiological impairment of the crayfish. It is hypothesized that the social hierarchy will not form as steadily because of decrease in fighting behavior.

Years Active:

2011

Methods:

Animals Male, form I crayfish, Orconectes propinquus, will be collected from Grapevine Point on Douglas Lake on University of Michigan Biological Station. Crayfish will be placed in isolated containers in a flow-through holding tank with a constant temperature (23 °C) at least one week before the experiment. The animals will be retained in a light:dark cycle (12:12 h) and one rabbit pellet will be provided three times a week. One hundred and fifty crayfish will be sorted into groups of five and marked with White-Out® to distinguish individuals. Animals will be returned to the lake after one week of recovery following the experiment. Experimental Habitats Experiments will be performed in meter by meter, non-flow through enclosures. The habitats will consist of tarps formed around cement blocks with gravel covered bottoms. Water from Maple River will be filled into the habitats up to twenty-five centimeters (approximately sixty-seven gallons of water). Five shelters will be provided in the habitat as a resource for competition. Treatment Exposures A. Control; exposed to artificial lake water; N=10 B. Low concentration of ammonia; 0.9 mg/L NH3 in artificial lake water (vol/vol); N=10 C. High concentration of ammonia; 9.0 mg/L NH3 in artificial lake water (vol/vol); N=10 The low concentration of 0.9 mg/L NH3 is determined by level determined to cause sensory impairment (unpublished data). The high concentration of 9.0 mg/L NH3 is established because previous studies have found that the level causes physiological impairment to crayfish (unpublished data). Behavioral Tests Two trials will be completed for every behavioral test. The first trial will be completed with water from Maple River as the control treatment exposure. Ten minutes after the habitat enclosure is set-up, five animals will be introduced into the habitat within containment shelters to prevent interaction. After an acclimation period of ten minutes, containment shelters will be removed. The trials will be video-taped for four hours. After the first trial, crayfish will be removed from the habitat and isolated for a period of one week to prevent chemical recognition of individuals. The second trial will begin after the isolation period. Water and the ammonia from the correlating treatment exposure will be added into the enclosure. After ten minutes, the five individuals that were grouped previously in the first trial will be reintroduced into the habitat in containment shelters. After ten minutes of habituation, the containment shelters will be removed and the interactions of the five crayfish will be video-taped for four hours. Data Analysis Both trials of the behavioral tests will be analyzed for hierarchy formation, linearity, and speed of hierarchy formation. To complete these analyses, the time spent fighting (from initiation of the fight to the point of retreat of at least one crayfish) and the winner/loser for each fight will be recorded.