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Accueil du site → Doctorat → États-Unis → 1973 → THE ECOLOGY AND THERMAL PHYSIOLOGY OF GAMBUSIA AFFINIS FROM A HOT SPRING IN SOUTHERN ARIZONA

University of Arizona (1973)

THE ECOLOGY AND THERMAL PHYSIOLOGY OF GAMBUSIA AFFINIS FROM A HOT SPRING IN SOUTHERN ARIZONA

Winkler, Paul

Titre : THE ECOLOGY AND THERMAL PHYSIOLOGY OF GAMBUSIA AFFINIS FROM A HOT SPRING IN SOUTHERN ARIZONA

Auteur : Winkler, Paul

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1973

Résumé
Mammoth Hot Spring is a 750 ft. permanent stream with a winter temperature range of 41° to 0°C. Aquatic organisms show a gradual re placement of species and increase in the number of individuals as cooler water is reached. Gambusia a. affinis, the western mosquito fish, is the only fish in the spring and ranges throughout the stream. In the warmer re gions the female:male sex ratio was higher and individuals were smaller than shown by fish in the cooler areas. In the cooler waters the diet of G_. _a. af finis changes from a strictly herbivorous to a wholly carni vorous one. The field temperature preferendum of C5. _a. af finis was deter mined in two ways : first by observing the reaction of the entire popu lation to temperature change along the stream, and secondly by an analy sis of the time marked individuals spent at various temperatures in the warmest part of the stream. A laboratory temperature gradient was con structed and the field temperature preferendum of 31°C was corroborated under laboratory conditions. A field method for measuring thermal tolerance was developed in which the resistance time (survival time) of fish to constant high lethal temperatures was recorded. With subsequent modification, this method proved to be quite sensitive and reproducible. A critique of other methods is offered. Under cyclic thermal conditions in the field, the thermal tol erance of fish fluctuates with time and varies directly with the amount of time fish spent in warmer water. _G„ a. affinis behaviorally thermo regulates only during the daylight hours and such behavior has a .signif icant effect on the physiology of the fish. Therefore,, these fish acclimate to a behaviorally modal temperature in the field and not the maximum temperature they experience. Fish display a short term, possi bly metabolic, acclimation to maximum habitat temperatures within a few hours ; whereas long term, possibly enzymatic, acclimation from winter to summer maximal temperatures may take about seven days. Both size and sex significantly affect the thermal physiology of Gambusia. Thermal tolerance may be drastically depressed by transport unless quite sensitive measures are taken to avoid vibration and water movement. General laboratory conditions also appear to depress thermal tolerance within the first ten days of acclimation. Sensitive and re producible laboratory data may only be gathered when fish are acclimated in water transported from the collection site. Full acclimation to con stant higher temperatures (31°C) continued after thirty days of acclima tion in the laboratory even when this constant temperature was equal to the maximum habitat temperature from which the fish were collected. The thermal history of fish continued to significantly affect the results of thermal tolerance testing after seven day exposures to cyclic tempera tures in the field and 35 to 60 day acclimation to 31°C in the labora tory, The significance of these results are applied to the assumptions underlying most other thermal tolerance investigations.

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