Blackstone, Neil W.
M.S. (Master of Science)
Department of Biological Sciences
Hydra--Illinois--Shabbona Lake--Reproduction; Reproduction--Seasonal variations; Hydrozoa--Illinois--Shabbona Lake--Reproduction
The possible effects of temperature on seasonality in the freshwater invertebrate hydra were studied utilizing laboratory experiments and a field study at Shabbona Lake, Illinois. Five hydra species were found at Shabbona Lake: in the oligactis group, H. canadensis and H. oligactis; in the braueri group, H. utahensis and H. hymanae; and in the viridissima group, H. viridissima. Of these, H. canadensis, H. oligactis and H. utahensis were chosen for laboratory experiments, and one clone representing each species was cultured. Combined effects of temperature and photoperiod on relative timing of initiation of gonad development in the three hydra species was investigated using a 56-day experiment with conditions of gradually diminishing temperature and photoperiod. Each of the three species initiated sexuality for the most part with a high degree of synchronicity, each at a different time during the experiment. H. utahensis developed gonads first, at the warmest temperature and longest photoperiod, followed by H. canadensis, and finally H. oligactis, at the lowest temperature and shortest photoperiod. Effects of temperature on asexual reproductive rate by budding was investigated using three experiments. The first two experiments examined temperature effects at 20°C and 25°C at two feeding levels. The third examined temperature effects at 15°C and 20°C at a single feeding level. H. canadensis individuals budded fastest at the coolest temperatures in all experiments. H. oligactis individuals budded fastest at 20° C at a feeding level of three times per week, and budded fastest at 25 °C at a feeding level of 5 times per week. H. utahensis individuals budded fastest at the warmest temperature in all experiments. Results of the experiments on timing of gonad development and budding rate led to the hypothesis that H. utahensis (braueri group) is best adapted for warm temperatures and has a shorter growing season relative to the other two species, and other related hypotheses. During field sampling at Shabbona Lake in the fall of 1994, braueri group hydra (H. hymanae) exhibited sexual reproduction earlier in the fall than oligactis group hydra (H. canadensis and H. oligactis). Further, numbers of both braueri group species were found to decrease earlier in the fall than the two oligactis group species. During field sampling in the spring of 1995, oligactis group hydra appeared in the samples earlier than braueri group hydra (H. hymanae). No H. utahensis or H. viridissima were found in spring 1995. Results of sampling at Shabbona Lake suggest that at least the braueri group species H. hymanae has a shorter growing season during the summer than the two oligactis group species.
Green, Joel Anson, "The influence of temperature on seasonal patterns of abundance of hydra at Shabbona Lake, Illinois" (1995). Graduate Research Theses & Dissertations. 5939.
ix, 73 pages
Northern Illinois University
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