Search

AbstractOxygen bioavailability is declining in aquatic systems worldwide as a result of climate change and other anthropogenic stressors. For aquatic organisms, the consequences are poorly known but are likely to reflect both direct effects of declining oxygen bioavailability and interactions between oxygen and other stressors, including two-warming and acidification-that have received substantial attention in recent decades and that typically accompany oxygen changes. Drawing on the collected papers in this symposium volume ("An Oxygen Perspective on Climate Change"), we outline the causes and consequences of declining oxygen bioavailability. First, we discuss the scope of natural and predicted anthropogenic changes in aquatic oxygen levels. Although modern organisms are the result of long evolutionary histories during which they were exposed to natural oxygen regimes, anthropogenic change is now exposing them to more extreme conditions and novel combinations of low oxygen with other stressors. Second, we identify behavioral and physiological mechanisms that underlie the interactive effects of oxygen with other stressors, and we assess the range of potential organismal responses to oxygen limitation that occur across levels of biological organization and over multiple timescales. We argue that metabolism and energetics provide a powerful and unifying framework for understanding organism-oxygen interactions. Third, we conclude by outlining a set of approaches for maximizing the effectiveness of future work, including focusing on long-term experiments using biologically realistic variation in experimental factors and taking truly cross-disciplinary and integrative approaches to understanding and predicting future effects.

A growing body of evidence has shown that active learning has a considerable advantage over traditional lecture for student learning in undergraduate STEM classes, but there have been few large-scale studies to identify the specific types of activities that have the greatest impact on learning. We therefore undertook a large-scale, curriculum-wide study to investigate the effects of time spent on a variety of classroom activities on learning gains. We quantified classroom practices and related these to student learning, assessed using diagnostic tests written by over 3700 students, across 31 undergraduate biology classes at a research-intensive university in the Pacific Northwest. The most significant positive predictor of learning gains was the use of group work, supporting the findings of previous studies. Strikingly, we found that the addition of worksheets as an active learning tool for in-class group activities had the strongest impact on diagnostic test scores. This particular low-tech activity promotes student collaboration, develops problem solving skills, and can be used to inform the instructor about what students are struggling with, thus providing opportunities for valuable and timely feedback. Overall, our results indicate that group activities with low barriers to entry, such as worksheets, can result in significant learning gains in undergraduate science.

To determine the factors that may contribute to the poor survival of triploid (3n) rainbow trout (Oncorhynchus mykiss) in lake stocking programs, we compared the physiology and responses to environmental challenges of four wild strains and one domestic strain of diploid (2n) and 3n juvenile rainbow trout. Over four successive years, wild trout were caught from nature, spawned, and progeny were reared in a hatchery along with hatchery-bred domestic trout. Offspring of each strain were raised for up to 12 months as both 2n and 3n, and growth rate, critical swimming speed, routine oxygen consumption rate, critical oxygen tensions, thermal tolerance, and hypoxia tolerance were assessed in a laboratory setting. Cohorts of the 2008, 2009, and 2010 wild strains were also stocked into two experimental lakes and recaptured as adults using traps and fyke nets in 2011 for laboratory analysis. In the juvenile trout, the only measure of performance to show a consistent difference between 2n and 3n individuals across all strains was hypoxia tolerance, where 3n trout had a shorter time to loss of equilibrium (LOE) at 16 Torr than their 2n counterparts, but this effect was not seen in adult, lake-reared trout. Strain had a significant effect on specific growth rate, critical swimming speed (Ucrit), and time to LOE in hypoxia, although the effects of strain on these variables was not consistent from year to year. Overall, this study suggests that poorer hypoxia tolerance in 3n trout compared with 2n trout may be a contributing factor to the higher lake stocking mortalities in 3n trout. Afin de cerner les facteurs qui pourraient expliquer la faible survie des truites arc-en-ciel (Oncorhynchus mykiss) triploides (3n) dans le cadre de programmes d'empoissonnement de lacs, nous avons compare la physiologie et les reactions a des defis ambiants de quatre lignees sauvages et d'une lignee domestique de truites arc-en-ciel diploides (2n) et 3n juveniles. Durant quatre annees consecutives, des truites sauvages ont ete capturees en milieu naturel et reproduites, et leur progeniture a ete elevee en aleviniere avec des truites domestiques issues d'aleviniere. La progeniture de chaque lignee a ete elevee pendant une periode allant jusqu'il 12 mois sous forme tant de 2n que de 3n, et le taux de croissance, la vitesse critique de nage (Ucrit), le taux de consommation d'oxygene courant, les tensions d'oxygene critiques, la tolerance a la chaleur et la tolerance a l'hypoxie ont ete evalues en laboratoire. Des cohortes des lignees sauvages de 2008, 2009 et 2010 ont egalement ete empoissonnees dans deux lacs experimentaux et recapturees une fois adultes a l'aide de pieges et de verveux en 2011, pour analyse en laboratoire. Chez les truites juveniles, la seule mesure de la performance qui montre une difference coherente entre les individus 2n et 3n pour toutes les lignees est la tolerance a l'hypoxie, les truites 3n etant caracterisees par une plus courte periode avant la perte d'equilibre a 16 torr que leurs homologues 2n. Cet effet n'est toutefois pas observe chez les truites adultes elevees en lac. La lignee avait une incidence significative sur le taux de croissance specifique, l'Ucrit et la periode avant la perte d'equilibre en hypoxie, bien que les effets de la lignee sur ces variables ne fussent pas uniformes d'une annee a l'autre. Globalement, l'etude indiquerait que la plus faible tolerance a l'hypoxie des truites 3n comparativement aux truites 2n pourrait etre un facteur qui participe aux taux de mortalite plus eleves des truites 3n empoissonnees dans des lacs. [Traduit par la Redaction], Introduction Since the discovery of triploid (3n) trout in nature (Cuellar and Uyeno 1972) and the subsequent development of technologies to induce triploidy in hatcheries, 3n rainbow trout have been [...]