Anatomical self-efficacy of undergraduate students improves during a fully online biology course with at-home dissections.

Student enrollments in online college courses have grown steadily over the past decade, and college administrators expect this trend to continue or accelerate. Despite the growing popularity of online education, one major critique in the sciences is that students are not trained in the hands-on skills they may need for the workforce, graduate school, or professional school. For example, the Association of American Medical Colleges has recommended that medical schools evaluate applicants on their motor skills and observation skills, yet many online biology programs do not offer opportunities for students to develop these skills. In on-campus biology programs, students commonly develop these skills through hands-on animal dissections, but educators have struggled with how to teach dissections in an online environment. We designed a fully online undergraduate biology course that includes at-home, hands-on dissections of eight vertebrate specimens. Over three course offerings, we evaluated changes in four student outcomes: anatomical self-efficacy, confidence in laboratory skills, perceptions of support, and concerns about dissections. Here, we describe how we implemented at-home dissections in the online course and show that students taking the course gained anatomical self-efficacy and confidence in multiple laboratory skills. Based on open-ended responses, the students perceived that their experiences with the at-home dissections facilitated these gains. These results demonstrate that at-home, hands-on laboratories are a viable approach for teaching practical skills to students in fully online courses. We encourage science instructors to introduce at-home laboratories into their online courses, and we provide recommendations for instructors interested in implementing at-home laboratories.

Plant carbohydrate content limits performance and lipid accumulation of an outbreaking herbivore.

Locusts are major intermittent threats to food security and the ecological factors determining where and when these occur remain poorly understood. For many herbivores, obtaining adequate protein from plants is a key challenge. We tested how the dietary protein : non-structural carbohydrate ratio (p : c) affects the developmental and physiological performance of 4th-5th instar nymphs of the South American locust, Schistocerca cancellata, which has recently resurged in Argentina, Bolivia and Paraguay. Field marching locusts preferred to feed on high carbohydrate foods. Field-collected juveniles transferred to the laboratory selected artificial diets or local plants with low p : c. On single artificial diets, survival rate increased as foods became more carbohydrate-biased. On single local plants, growth only occurred on the plant with the lowest p : c. Most local plants had p : c ratios substantially higher than optimal, demonstrating that field marching locusts must search for adequate carbohydrate or their survival and growth will be carbohydrate-limited. Total body lipids increased as dietary p : c decreased on both artificial and plant diets, and the low lipid contents of field-collected nymphs suggest that obtaining adequate carbohydrate may pose a strong limitation on migration for S. cancellata. Anthropogenic influences such as conversions of forests to pastures, may increase carbohydrate availability and promote outbreaks and migration of some locusts.

Thermal acclimation of flies from three populations of Drosophila melanogaster fails to support the seasonality hypothesis.

In seasonal environments, natural selection should favor genotypes that acclimate to slow and predictable changes in temperature. Selective pressure for acclimation should be especially strong for animals that complete many generations per year, because seasonal warming or cooling causes offspring to experience different temperatures than their parents did. Here, we studied variation in acclimation capacity among three populations of Drosophila melanogaster. We used a reverse acclimation design to see whether developmental acclimation persisted throughout adulthood. Flies developed from fertilization to adulthood at either 16° or 26 °C. Then, flies either remained at the same temperature or moved to the other temperature for 7 days. We measured fecundity at seven temperatures ranging from 14° to 36°C. Genotypes from North Carolina and Vermont laid more eggs at 16 °C after spending the larval and adult stages at 16 °C, instead of 26 °C. In both populations, the benefit of acclimation to 16 °C during development was erased by acclimation to 26 °C during adulthood. In contrast to our prediction, genotypes from Indiana laid fewer eggs at 16 °C or 26 °C after developing at this temperature. Overall, these data provide only weak support for the models of optimal acclimation in seasonal environments.

A positive genetic correlation between hypoxia tolerance and heat tolerance supports a controversial theory of heat stress.

We used quantitative genetics to test a controversial theory of heat stress, in which animals overheat when the demand for oxygen exceeds the supply. This theory, referred to as oxygen- and capacity-limited thermal tolerance, predicts a positive genetic correlation between hypoxia tolerance and heat tolerance. We demonstrate the first genetic correlation of this kind in a model organism, Drosophila melanogaster Genotypes more likely to fly under hypoxic stress (12% O2) were also more likely to fly under heat stress (39°C). This finding prompts new questions about mechanisms and limits of adaptation to heat stress.

Vulnerability to climate change increases with trophic level in terrestrial organisms.

The resilience of ecosystem function under global climate change is governed by individual species vulnerabilities and the functional groups they contribute to (e.g. decomposition, primary production, pollination, primary, secondary and tertiary consumption). Yet it remains unclear whether species that contribute to different functional groups, which underpin ecosystem function, differ in their vulnerability to climate change. We used existing upper thermal limit data across a range of terrestrial species (N = 1701) to calculate species warming margins (degrees distance between a species upper thermal limit and the maximum environmental temperature they inhabit), as a metric of climate change vulnerability. We examined whether species that comprise different functional groups exhibit differential vulnerability to climate change, and if vulnerability trends change across geographic space while considering evolutionary history. Primary producers had the broadest warming margins across the globe (µ = 18.72 °C) and tertiary consumers had the narrowest warming margins (µ = 9.64 °C), where vulnerability tended to increase with trophic level. Warming margins had a nonlinear relationship (second-degree polynomial) with absolute latitude, where warming margins were narrowest at about 33°, and were broader at lower and higher absolute latitudes. Evolutionary history explained significant variation in species warming margins, as did the methodology used to estimate species upper thermal limits. We investigated if variation in body mass across the trophic levels could explain why higher trophic level organisms had narrower warming margins than lower trophic level organisms, however, we did not find support for this hypothesis. This study provides a critical first step in linking individual species vulnerabilities with whole ecosystem responses to climate change.

Oxygen supply limits the chronic heat tolerance of locusts during the first instar only.

Although scientists know that overheating kills many organisms, they do not agree on the mechanism. According to one theory, referred to as oxygen- and capacity-limitation of thermal tolerance, overheating occurs when a warming organism's demand for oxygen exceeds its supply, reducing the organism's supply of ATP. This model predicts that an organism's heat tolerance should decrease under hypoxia, yet most terrestrial organisms tolerate the same amount of warming across a wide range of oxygen concentrations. This point is especially true for adult insects, who deliver oxygen through highly efficient respiratory systems. However, oxygen limitation at high temperatures may be more common during immature life stages, which have less developed respiratory systems. To test this hypothesis, we measured the effects of heat and hypoxia on the survival of South American locusts (Schistocerca cancellata) throughout development and during specific instars. We demonstrate that the heat tolerance of locusts depends on oxygen supply during the first instar but not during later instars. This finding provides further support for the idea that oxygen limitation of thermal tolerance depends on respiratory performance, especially during immature life stages.

Oxygen Limitation Does Not Drive the Decreasing Heat Tolerance of Grasshoppers during Development.

Thermal physiology changes as organisms grow and develop, but we do not understand what causes these ontogenetic shifts. According to the theory of oxygen- and capacity-limited thermal tolerance, an organism's heat tolerance should change throughout ontogeny as its ability to deliver oxygen varies. As insects grow during an instar, their metabolic demand increases without a proportional increase in the size of tracheae that supply oxygen to the tissues. If oxygen delivery limits heat tolerance, the mismatch between supply and demand should make insects more susceptible to heat and hypoxia as they progress through an instar. We tested this hypothesis by measuring the heat tolerance of grasshoppers (Schistocerca americana) on the second and seventh days of the sixth instar, in either a normoxic or a hypoxic atmosphere (21% or 10% O2, respectively). As expected, heat tolerance decreased as grasshoppers grew larger. Yet contrary to expectation, hypoxia had no effect on heat tolerance across all stages and sizes. Although heat tolerance declines as grasshoppers grow, this pattern must stem from a mechanism other than oxygen limitation.

The neuroscience of adaptive thermoregulation.

The nervous system acts as a biological thermostat by controlling behaviors that regulate the warming and cooling of animals. We review the structures responsible for thermoregulation in three model species: roundworms (Caenorhabditis elegans), flies (Drosophila melanogaster), and rats (Rattus novegicus). We then consider additional features of the nervous system required to explain adaptive plasticity of the set-point temperature and the precision of thermoregulation. Because animals use resources such as energy, water, and oxygen to thermoregulate, the nervous system monitors the abundance of these resources and adjusts the strategy of thermoregulation accordingly. Starvation, dehydration, or hypoxemia alter the activity of temperature-sensitive neurons in the pre-optic area of the hypothalamus. Other regions of the brain work in conjunction with the hypothalamus to promote adaptive plasticity of thermoregulation. For example, the amygdala likely inhibits neurons of the pre-optic area, overriding thermoregulation when a risk of predation or a threat of aggression exists. Moreover, the hippocampus enables an animal to remember microhabitats that enable safe and effective thermoregulation. In ectothermic animals, such as C. elegans and D. melanogaster, the nervous system can alter set-point temperatures as the environmental temperatures change. To build on this knowledge, neuroscientists can use experimental evolution to study adaptation of neural phenotypes in controlled thermal environments. A microevolutionary perspective would leverage our understanding of ecological processes to predict the origin and maintenance of neural phenotypes by natural selection.

Fundamental Flaws with the Fundamental Niche.

For more than 70 years, Hutchinson's concept of the fundamental niche has guided ecological research. Hutchinson envisioned the niche as a multidimensional hypervolume relating the fitness of an organism to relevant environmental factors. Here, we challenge the utility of the concept to modern ecologists, based on its inability to account for environmental variation and phenotypic plasticity. We have ample evidence that the frequency, duration, and sequence of abiotic stress influence the survivorship and performance of organisms. Recent work shows that organisms also respond to the spatial configuration of abiotic conditions. Spatiotemporal variation of the environment interacts with the genotype to generate a unique phenotype at each life stage. These dynamics cannot be captured adequately by a multidimensional hypervolume. Therefore, we recommend that ecologists abandon the niche as a tool for predicting the persistence of species and embrace mechanistic models of population growth that incorporate spatiotemporal dynamics.