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Postfreeze reduction of locomotor endurance in the freeze-tolerant wood frog, Rana sylvatica.
Full text linkConsiderable study has focused on the physiological adaptations for freeze tolerance in the wood frog, Rana sylvatica, a northern species that overwinters within the frost zone, but little attention has been paid to the associated costs to organismal performance. Here we report that freezing causes transient impairment of locomotor endurance and adverse changes in exercise physiology that persist for at least 96 h. Wood frogs frozen at −2°C for 36 h exhibited normal behaviors and hydro‐osmotic status and near‐normal metabolite (glycogen, glucose, and lactate) levels within 24 h after thawing began. However, when exercised to exhaustion on a treadmill, these frogs showed a 40% reduction in endurance as compared to sham‐treated (unfrozen) controls, a reduction that persisted for at least 96 h. Previously frozen frogs exhibited higher rates of lactate accumulation during exercise than controls, suggesting that prior freezing forces greater reliance on the glycolytic pathways of energy production to support exercise. Given that this species breeds in late winter, when subzero temperatures are common, freezing may result in reduced fitness by hampering their ability to reach the pond, avoid predators, and successfully obtain mates
Full-Cycle Assessment of Critical Thinking in an Ethics and Science Course
Full text linkEnhancing critical thinking skills for undergraduate students is important across the curriculum and between disciplines. We report on a method of improving critical thinking skills, which was studied through an Ethics and Science First-Year Seminar course. We used full cycle assessment over a three-year period to assess students’ development and to modify the course teaching and assignments with the goal of increasing student development of critical thinking skills. Data were obtained from student writing throughout the semester during each offering. Modest, but significant, overall gains of ~0.7 on a 4 point scale are reported between early and midterm assignments in the course using a seven trait assessment rubric. Key factors that contribute to the increase in critical thinking skills are identified including peer review, scaffolded assignments, and the use of a grading rubric for each assignment
Cryoprotectants and extreme freeze tolerance in a subarctic population of the wood frog.
Full text linkWood frogs (Rana sylvatica) exhibit marked geographic variation in freeze tolerance, with subarctic populations tolerating experimental freezing to temperatures at least 10-13 degrees Celsius below the lethal limits for conspecifics from more temperate locales. We determined how seasonal responses enhance the cryoprotectant system in these northern frogs, and also investigated their physiological responses to somatic freezing at extreme temperatures. Alaskan frogs collected in late summer had plasma urea levels near 10 μmol ml-1, but this level rose during preparation for winter to 85.5 ± 2.9 μmol ml-1 (mean ± SEM) in frogs that remained fully hydrated, and to 186.9 ± 12.4 μmol ml-1 in frogs held under a restricted moisture regime. An osmolality gap indicated that the plasma of winter-conditioned frogs contained an as yet unidentified osmolyte(s) that contributed about 75 mOsmol kg-1 to total osmotic pressure. Experimental freezing to –8°C, either directly or following three cycles of freezing/thawing between –4 and 0°C, or –16°C increased the liver’s synthesis of glucose and, to a lesser extent, urea. Concomitantly, organs shed up to one-half (skeletal muscle) or two-thirds (liver) of their water, with cryoprotectant in the remaining fluid reaching concentrations as high as 0.2 and 2.1 M, respectively. Freeze/thaw cycling, which was readily survived by winter-conditioned frogs, greatly increased hepatic glycogenolysis and delivery of glucose (but not urea) to skeletal muscle. We conclude that cryoprotectant accrual in anticipation of and in response to freezing have been greatly enhanced and contribute to extreme freeze tolerance in northern R. sylvatica
Gun-Free Zones: A Second Look
No full textA study conducted over the course of the semester to see if there's a positive correlation to Gun-Free Zones and criminal gun violence within this zone