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.

Synchrotron imaging of the grasshopper tracheal system: morphological and physiological components of tracheal hypermetry.

As grasshoppers increase in size during ontogeny, they have mass specifically greater whole body tracheal and tidal volumes and ventilation than predicted by an isometric relationship with body mass and body volume. However, the morphological and physiological bases to this respiratory hypermetry are unknown. In this study, we use synchrotron imaging to demonstrate that tracheal hypermetry in developing grasshoppers (Schistocerca americana) is due to increases in air sacs and tracheae and occurs in all three body segments, providing evidence against the hypothesis that hypermetry is due to gaining flight ability. We also assessed the scaling of air sac structure and function by assessing volume changes of focal abdominal air sacs. Ventilatory frequencies increased in larger animals during hypoxia (5% O(2)) but did not scale in normoxia. For grasshoppers in normoxia, inflated and deflated air sac volumes and ventilation scaled hypermetrically. During hypoxia (5% O(2)), many grasshoppers compressed air sacs nearly completely regardless of body size, and air sac volumes scaled isometrically. Together, these results demonstrate that whole body tracheal hypermetry and enhanced ventilation in larger/older grasshoppers are primarily due to proportionally larger air sacs and higher ventilation frequencies in larger animals during hypoxia. Prior studies showed reduced whole body tracheal volumes and tidal volume in late-stage grasshoppers, suggesting that tissue growth compresses air sacs. In contrast, we found that inflated volumes, percent volume changes, and ventilation were identical in abdominal air sacs of late-stage fifth instar and early-stage animals, suggesting that decreasing volume of the tracheal system later in the instar occurs in other body regions that have harder exoskeleton.

Responses of terrestrial insects to hypoxia or hyperoxia.

Oxygen is critically important for catabolic ATP generation but is also a dangerous source of reactive oxygen species. Insects respond to short-term exposure to hypoxia or hyperoxia with compensatory changes in spiracular opening and ventilation that reduce variation in internal Po2. Below critical Po2 values (Pc), nitric oxide and hypoxia inducible factor (HIF)-mediated pathways induce long-term responses such as compensatory tracheal growth, suppressed development, and acclimation of ventilation. Pc values are strongly affected by activity and ontogeny, due to changes in the ratio of tracheal conductance to metabolic rate. Although growth rates and development are suppressed by significant hypoxia in all species studied to date, adult body size is only affected in some species. Severe hyperoxia causes major oxidative stress and reduces survival, while moderate hyperoxia increases development times and body sizes in some species by unknown mechanisms.

Plastic and evolved responses of larval tracheae and mass to varying atmospheric oxygen content in Drosophila melanogaster.

Structural changes in the tracheal system during development have the potential to allow insects to compensate for varying oxygen availability. Despite possible compensation, oxygen level during development may also affect insect body size. We investigated how atmospheric oxygen level affects the dimensions of the main dorsal tracheae (DT) and masses of larval Drosophila melanogaster (Meigen) reared for up to six generations in 10%, 21% or 40% O2 at 25 degrees C. Wandering-stage third-instar larvae were weighed every other generation, and the dimensions of the DT were measured. Hypoxia produced significantly lighter larvae after one generation of exposure, while hyperoxia did not affect larval mass. Atmospheric oxygen content did not significantly change the diameters of the anterior portions of the main tracheae; however, the posterior diameters were strongly affected. During the first generation of exposure, tracheal diameters were inversely proportional to rearing oxygen levels, demonstrating that developmental plasticity in DT diameters can partially (8-15%) compensate for variation in atmospheric oxygen level. After multiple generations in differing atmospheres and two further generations in 21% O2, larvae had tracheal diameters inversely related to their historical oxygen exposure, suggesting that atmospheric oxygen can produce heritable changes in insect tracheal morphology.