It is known that repeated bouts of high-intensity interval training (HIIT) lead to enhanced levels of glycolysis, glycogenesis, and lactate transport proteins in skeletal muscle; however, little is known about the molecular mechanisms underlying these adaptations. To decipher the mechanism leading to improvement of skeletal muscle glycolytic capacity associated with HIIT, we examined the role of hypoxia-inducible factor-1α (Hif-1α), the major transcription factor regulating the expression of genes related to anaerobic metabolism, in the adaptation to HIIT. First, we induced Hif-1α accumulation using ethyl 3,4-dihydroxybenzoate (EDHB) to assess the potential role of Hif-1α in skeletal muscle. Treatment with EDHB significantly increased the protein levels of Hif-1α in gastrocnemius muscles, accompanied by elevated expression of genes related to glycolysis, glycogenesis, and lactate transport. Daily administration of EDHB for 1 wk resulted in elevated glycolytic enzyme activity in gastrocnemius muscles. Second, we examined whether a single bout of HIIT could induce Hif-1α protein accumulation and subsequent increase in the expression of genes related to anaerobic metabolism in skeletal muscle. We observed that the protein levels of Hif-1α and expression of the target genes were elevated 3 h after an acute bout of HIIT in gastrocnemius muscles. Last, we examined the effects of long-term HIIT. We found that long-term HIIT increased the basal levels of Hif-1α as well as the glycolytic capacity in gastrocnemius muscles. Our results suggest that Hif-1α is a key regulator in the metabolic adaptation to high-intensity training.

Narrow foraging specialization may increase the vulnerability of marine predators to climate change. The red-legged kittiwake (Rissa brevirostris) is endemic to the Bering Sea and has experienced drastic population fluctuations in recent decades, presumably due to climate-driven changes in food resources. Red-legged kittiwakes are presumed to be a nocturnal surface-foraging seabird that feed almost entirely on deep water Myctophidae fishes. However, there is little empirical evidence confirming their nocturnal foraging activity during the breeding season. This study investigated the foraging behavior of red-legged kittiwakes by combining GPS tracking, accelerometry, and dietary analyses at the world’s largest breeding colony of red-legged kittiwakes on St. George I. GPS tracking of 5 individuals revealed that 82.5% of non-flight behavior (including foraging and resting) occurred over the ocean basin (bottom depth >1,000 m). Acceleration data from 4 birds showed three types of behaviors during foraging trips: (1) flight, characterized by regular wing flapping, (2) resting on water, characterized by non-active behavior, and (3) foraging, when wing flapping was irregular. The proportions of both foraging and resting behaviors were higher at night (14.1 ± 7.1% and 20.8 ± 14.3%) compared to those during the day (6.5 ± 3.0% and 1.7 ± 2.7%). The mean duration of foraging (2.4 ± 2.9 min) was shorter than that of flight between prey patches (24.2 ± 53.1 min). Dietary analyses confirmed myctophids as the dominant prey (100% by occurrence and 98.4 ± 2.4% by wet-weight). Although the sample size was limited, these results suggest that breeding red-legged kittiwakes concentrated their foraging on myctophids available at the surface during nighttime in deep water regions. We propose that the diel patterns and ephemeral nature of their foraging activity reflected the availability of myctophids. Such foraging specialization may exacerbate the vulnerability of red-legged kittiwakes to climate change in the Bering Sea.

Changes in climate and anthropogenic pressures might affect the composition and abundance of forage fish in the world's oceans. The junk‐food hypothesis posits that dietary shifts that affect the quality (e.g., energy content) of food available to marine predators may impact their physiological state and consequently affect their fitness. Previously, we experimentally validated that deposition of the adrenocortical hormone, corticosterone, in feathers is a sensitive measure of nutritional stress in seabirds. Here, we use this method to examine how changes in diet composition and prey quality affect the nutritional status of free‐living rhinoceros auklets (Cerorhinca monocerata). Our study sites included the following: Teuri Is. Japan, Middleton Is. central Gulf of Alaska, and St. Lazaria Is. Southeast Alaska. In 2012 and 2013, we collected “bill loads” delivered by parents to feed their chicks (n = 758) to document dietary changes. We deployed time–depth–temperature recorders on breeding adults (n = 47) to evaluate whether changes in prey coincided with changes in foraging behavior. We measured concentrations of corticosterone in fledgling (n = 71) and adult breeders' (n = 82) feathers to determine how birds were affected by foraging conditions. We found that seasonal changes in diet composition occurred on each colony, adults dove deeper and engaged in longer foraging bouts when capturing larger prey and that chicks had higher concentrations of corticosterone in their feathers when adults brought back smaller and/or lower energy prey. Corticosterone levels in feathers of fledglings (grown during the breeding season) and those in feathers of adult breeders (grown during the postbreeding season) were positively correlated, indicating possible carryover effects. These results suggest that seabirds might experience increased levels of nutritional stress associated with moderate dietary changes and that physiological responses to changes in prey composition should be considered when evaluating the effect of prey quality on marine predators.

Penguins are adapted to underwater life and have excellent swimming abilities. Although previous motion analyses revealed their basic swimming characteristics, the details of the 3-D wing kinematics, wing deformation, and thrust generation mechanism of penguins are still largely unknown. In this study, we recorded the forward and horizontal swimming of gentoo penguins Pygoscelis papua at an aquarium with multiple underwater action cameras and then performed a 3-D motion analysis. We also conducted a series of water tunnel experiments with a 3-D printed rigid wing to obtain the lift and drag coefficients in the gliding configuration. Using these coefficients, the thrust force during flapping was calculated in a quasi-steady manner, where the following two wing models were considered: (1) an “original” wing model reconstructed from 3-D motion analysis including bending deformation and (2) a “flat” wing model obtained by flattening the original wing model. The resultant body trajectory showed that the penguin accelerated forward during both upstroke and downstroke. The motion analysis of the two wing models revealed that considerable bending occurred in the original wing, which reduced its angle of attack during upstroke in particular. Consequently, the calculated stroke-averaged thrust was larger for the original wing than for the flat wing during upstroke. In addition, the original wing required less work for flapping, indicating more efficient propulsion. Our results unveil a detailed mechanism of lift-based propulsion in penguins and underscore the importance of wing bending.

Alcids propel themselves by fl apping wings in air and water that have vastly diff erent densities. We hypothesized that alcids change wing kinematics and maintain Strouhal numbers ( St ϭ fA / U , where f is wingbeat frequency, A is the wingbeat amplitude, and U is forward speed) within a certain range, to achieve effi cient locomotion during both fl ying and swimming. We used acceleration and GPS loggers to measure the wingbeat frequency and forward speed of free-ranging rhinoceros auklets Cerorhinca monocerata during both fl ying and swimming. We also measured wingbeat amplitude from video footage taken in the wild. On average, wingbeat frequency, forward speed, and wingbeat amplitude were 8.9 Hz, 15.3 m s -1 , and 0.39 m, respectively, during fl ying, and 2.6 Hz, 1.3 m s -1 , and 0.18 m, respectively, during swimming. Th e smaller wingbeat amplitude during swimming was achieved by partially folding the wings, while maintaining the dorso-ventral wingbeat angle. Mean St was 0.23 during fl ying and 0.36 during swimming. Th e higher St value for swimming might be related to the higher thrust force required for propulsion in water. Our results suggest that rhinoceros auklets maintain St for both fl ying and swimming within the range (0.2 -0.4) that propulsive effi ciency is known to be high and St in both fl ying specialists and swimming specialists are known to converge.