LE3 .A278 2023

2023

Currie, Suzie

Acadia University

Bachelor of Science

Honours

Biology

Biology

A significant increase in unpredictable thermal fluctuations in aquatic ecosystems are predicted in current climate change scenarios. Ectothermic animals, like most fishes, will be particularly vulnerable to temperature change given their body temperatures fluctuate with the environment. Despite this vulnerability, we know relatively little about how fish will respond to warm, unpredictable fluctuating temperatures. Fish gills are highly plastic and in warm temperature s with high metabolic demand, there are morphological remodeling changes to increase surface area. This gill remodeling allows the fish to take up more oxygen in order to meet increased metabolic demand. By examining gill morphology using the hermaphroditic, amphibious mangrove rivulus fish (Kryptolebias marmoratus), I asked if there is a difference in how fish acclimate to unpredictable, warm thermal fluctuations compared to warm, stable conditions. As self-fertilizing hermaphrodites, mangrove rivulus can independently produce highly homozygous, genetically isolated lineages allowing us to disentangle environmental and genetic interactions on phenotype. I acclimated two isogenic lineages of mangrove rivulus to four different thermal regimes – two unpredictably fluctuating temperatures, a low cycle: 24°C-29°C and a high cycle: 29°C -34°C; and the stable mean of each cycle: low mean: 26.5°C, and high mean: 31.5°C. One mechanism many fishes use to remodel their gills and alter surface area is proliferatio n or regression of the interlamellar cell mass (ILCM). I predicted that at higher temperatures, regardless of cycling, gill surface area would increase by decreasing ILCM because of increased metabolic oxygen demand. I was interested if there would be a difference in gill surface area/ILCM coverage between the stable and cycling temperature conditions, as this has not been investigated in fishes. Growth rate was significantly reduced at high temperatures, and fecundity was highest in unpredictable cycles. I observed modest differences in gill remodeling between stable and unpredictable cycling temperatures in the low temperature groups. In contrast to my prediction and previous studies, I observed an overall increase in ILCM coverage (i.e., decrease in gill surface area) at higher temperatures, regardless of cycling. Furthermore, I detected significant differences in the two lineages suggesting a genetic component to the effects of temperature and thermal fluctuation on gill remodelling. My data suggest that high temperature environments may decrease functional gill surface area in this fish, possibly as an energetic saving and/or as structural support in preparation for air exposure/emersion. My research also points to subtle differences in gill remodeling in unpredictable cycling temperatures compared to stable temperatures, but at more extreme warming, these differences disappear. This finding suggests that in predicted climate warming scenarios, these fish are likely acclimating to their mean temperature, at least in terms of gill remodeling.

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https://scholar.acadiau.ca/islandora/object/theses:4005