Similar to many institutions, Reed College (Portland, OR) transitioned to a remote leaning environment in Spring 2020, with 5 weeks remaining in the semester. Historically, many of Reed's upper division courses in math and natural sciences-including Ecology (Biology 301) and an interdisciplinary Environmental Science (ES 300) Junior Seminar (both full credit, one semester courses)-culminate in students pursuing independent research projects (IPs), a type of course-based undergraduate research experience, CURE (Linn et al., 2015). In conducting IPs, students conceive of an original research question, design and implement an appropriate research plan, work individually or in small teams, and conclude by communicating their findings to an audience of their peers and faculty member. A remote version of these IPs was enacted in Spring 2020 in response to the novel academic setting initiated by the COVID-19 pandemic. Pursuing IPs amidst the challenges of living through the COVID-19 pandemic are apparent. At the onset of this endeavor, we identified the following (explicitly not exhaustive) primary challenges associated with students living and studying remotely: (1) no access existed to our typical teaching laboratories, limiting instrumentation and software access; (2) limited access to known field sites in the areas surrounding students-both due to geographic distance between students and our campus, geographic variation in the extent
Light fluctuations are ubiquitous, exist across multiple spatial and temporal scales, and directly affect the physiology and ecology of photoautotrophs. However, the indirect effects of light fluctuations on the sensitivity of organisms to other key environmental factors are unclear. Here, we evaluate how photoperiod regime (period of time each day where organisms receive light), a dynamic element of aquatic ecosystems, can influence the interactive effects of temperature and irradiance (intensity of light) on the growth rate of phytoplankton populations. We first completed a literature review and meta-analysis that suggests photoperiod alters the individual effects of temperature -but not irradiance -on algal growth rates and that highlights how few studies experimentally manipulate photoperiod, temperature and irradiance. To address this empirical gap, we conducted a set of laboratory experiments on three freshwater phytoplankton species (Chlamydomonas reinhardtii, Chlorella vulgaris and Cryptomonas ovata). We measured performance surfaces relating growth rate to irradiance and temperature gradients for each species in constant (24:0 h of light:dark) environments. We then evaluated whether analogous surfaces measured under different photoperiods (6:18, 12:12 and 16:8 h of light:dark) and scaled by the duration of light availability could be inferred from results under constant light. For a majority of the combinations of species and photoperiods examined, photoperiod meaningfully altered the intercept and shape of performance surfaces. These differences were most pronounced under the shortest photoperiod (6:18 h light:dark), where populations underperformed expectations. Alterations to performance surfaces were non-linear and mostly structured by temperature with higher temperatures yielding higher than anticipated growth rates. Collectively, these experiments and synthesis reveal the potential for photoperiod regime to influence the effects of temperature, irradiance and their interaction on phytoplankton growth. Beyond the environmental variables and organisms presently considered, this research highlights the capacity for dynamic, abiotic variables to exert direct effects while also influencing relationships among other environmental factors.
Environmental contamination of bisphenol A (BPA) is a widespread and multifaceted issue with vast ecological, social and economic consequences. Thus, understanding how local environmental conditions, such as temperature, interact with BPA to affect populations and community dynamics remain important areas of research. Here, we conduct laboratory experiments aimed at understanding how environmental gradients of both temperature and BPA concentration influence freshwater phytoplankton population growth and community structure. We exposed phytoplankton assemblages comprised of three common species of green algae (Chlorella vulgaris, Ankistrodesmus braunii and Scenedesmus quadricauda) as well as isolates of each individual species to three BPA concentrations (0, 2, 13 mg/L BPA) and three temperatures (18, 23, 27°C) monitoring population growth and community structure (via biovolume). We observed antagonistic interactions between BPA and warmer temperatures, such that when warmer temperatures decreased growth (observed with A. braunii), high concentrations of BPA elevated growth at these warm temperatures; however, when warmer temperatures increased growth (C. vulgaris, S. quadricauda), high BPA concentrations diminished these gains. Although BPA exposure inhibited the growth of most C. vulgaris populations, growth was not reduced in A. braunii or S. quadricauda populations exposed to 2 mg/L BPA. Phytoplankton assemblage evenness (Pielou evenness index) decreased as BPA concentration increased and was consistently lowest under 27°C. Community composition was similar in assemblages cultured under 0 and 2 mg/L BPA under 18 and 23°C but was most similar between assemblages cultured under 2 and 13 mg/L BPA under 27°C. These results indicate that local environmental temperatures can mediate the consequences of BPA for freshwater phytoplankton growth rates and community structure and that BPA can diminish potential gains of increased growth rate for warm-adapted phytoplankton species at high environmental temperatures.
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