Take-off mechanics in hummingbirds (Trochilidae)

Initiating flight is challenging, and considerable effort has focused on understanding the energetics and aerodynamics of take-off for both machines and animals. For animal flight, the available evidence suggests that birds maximize their initial flight velocity using leg thrust rather than wing flapping. The smallest birds, hummingbirds (Order Apodiformes), are unique in their ability to perform sustained hovering but have proportionally small hindlimbs that could hinder generation of high leg thrust. Understanding the take-off flight of hummingbirds can provide novel insight into the take-off mechanics that will be required for micro-air vehicles. During take-off by hummingbirds, we measured hindlimb forces on a perch mounted with strain gauges and filmed wingbeat kinematics with high-speed video. Whereas other birds obtain 80–90% of their initial flight velocity using leg thrust, the leg contribution in hummingbirds was 59% during autonomous take-off. Unlike other species, hummingbirds beat their wings several times as they thrust using their hindlimbs. In a phylogenetic context, our results show that reduced body and hindlimb size in hummingbirds limits their peak acceleration during leg thrust and, ultimately, their take-off velocity. Previously, the influence of motivational state on take-off flight performance has not been investigated for any one organism. We studied the full range of motivational states by testing performance as the birds took off: (1) to initiate flight autonomously, (2) to escape a startling stimulus or (3) to aggressively chase a conspecific away from a feeder. Motivation affected performance. Escape and aggressive take-off featured decreased hindlimb contribution (46% and 47%, respectively) and increased flight velocity. When escaping, hummingbirds foreshortened their body movement prior to onset of leg thrust and began beating their wings earlier and at higher frequency. Thus, hummingbirds are capable of modulating their leg and wingbeat kinetics to increase take-off velocity

Escaping the Arrhenius Tyranny: Metabolic Compensation during exposure to high temperature in Daphnia

Poikilothermic organisms experience trade-offs by differential physiological demands generated by temperature extremes. Many such organisms exhibit acclimatory effects, adjusting their metabolism and physiology to recently experienced temperatures. One such acclimatory effect is metabolic compensation, the deceleration of biological rates below Arrhenius expectations. Daphnia magna is eurythermal, and if acclimated to mildly stressful temperatures first, survives longer in lethal temperatures. This study examined the effect of ambient temperature (5°C-37°C) and acclimation history (lifetime at 10°C or 25°C) on the oxygen consumption rates of 8 genotypes of Daphnia with high or low acute temperature tolerance. There were decelerations of respiratory rates across a temperature gradient when acclimated to 25°C or following short 8- hour acclimation to measurement temperatures. Daphnia exposed to a near-lethal temperature (35°C) with a 24-hour recovery period at 25°C-acclimation temperature showed no difference in respiratory control compared to unexposed 25°C-acclimated Daphnia. Genotypes showed no difference in potential compensatory ability

Effects of Antioxidants on Development of In Vitro Fertilized Bovine Embryos

Free radicals are short-lived molecules that can cause decreased embryonic development in vitro. Antioxidants are molecules that block free radical formation or guard against their harmful effects. Many studies have linked exposure of media to light and culturing of embryos in high (20%) oxygen concentrations to free radical production. Some of the antioxidants used in culture media are superoxide dismutase (SOD), catalase, zinc (II), ethylenedinitrilo tetraacetic acid (EDTA), mannitol, vitamin E, dimethyl sulfide, and taurine. Most research involving antioxidants and embryonic development has been conducted on non-farm animals, particularly mouse and rabbit. Studies have shown that antioxidants in vitro culture improved embryo development to the blastocyst stage. In this study, we evaluated the effects of SOD and catalase on bovine embryo development. Four concentrations of SOD (0, 1500, 3000, 6000 IU/ml) and catalase (0, 75, 100, 125 μg/ml) and combinations of the two antioxidants were evaluated through maturation, fertilization, and culture. SOD and catalase were first reconstituted in water and then diluted to their final concentrations. Oocytes were matured in M-199 plus 0.5 μg/ml LH, 5 μg/ml FSH, and 10% FBS at 39°C in 5% CO2 for 24 hours. They were then placed in fertilization-TALP with heparin and 1 x 106/ml sperm. Embryos were cultured in CR2 medium supplemented with alanine, glycine, and 3 mg/ml of fatty-acid free bovine serum albumin in modular incubators with 5% CO2, 5% O2, and 90% N2. Embryo development was evaluated on day 8. Three replicates with approximately 50 embryos per treatment were used to evaluate the effects of SOD and catalase. The control had better embryo development than all treatments. The treatment that was most similar to the control was treatment 2, which consisted of no SOD and 75 μg/ml catalase. Based on these observations, levels of both SOD and catalase were lowered to 0, 100, 250, and 500 IU/ml and 0, 10, 25, and 50 μg/ml, respectively. Although these levels appeared to improve embryo development, there were no statistical differences. Based on the culture system and media currently used along with the precautions against light and oxygen concentration, we did not find any beneficial effects of supplementing medium with SOD or catalase