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Thermal performance curves enable physiological constraints to be incorporated in predictions of biological responses to shifts in mean temperature. But do thermal performance curves adequately capture the biological impacts of thermal extremes? Organisms incur physiological damage during exposure to extremes, and also mount active compensatory responses leading to acclimatization, both of which alter thermal performance curves and determine the impact that current and future extremes have on organismal performance and fitness. Thus, these sub-lethal responses to extreme temperatures potentially shape evolution of thermal performance curves. We applied a quantitative genetic model and found that beneficial acclimatization and cumulative damage alter the extent to which thermal performance curves evolve in response to thermal extremes. The impacts of extremes on the evolution of thermal performance curves are reduced if extremes cause substantial mortality or otherwise reduce fitness differences among individuals. Further empirical research will be required to understand how responses to extremes aggregate through time and vary across life stages and processes. Such research will enable incorporating passive and active responses to sub-lethal stress when predicting the impacts of thermal extremes.

The morphology of the rectal gland was examined in spiny dogfish (Squalus acanthias L, 1758) sharks fasted (1 week) or 6 and 20 h postfeeding. The morphology of the fasted gland showed a pattern reflecting a dormant physiology, with thick gland capsule, thick stratified epithelium, and secretory parenchyma with tubules of small diameter and lumen. The secretory cells of the tubular epithelium were enlarged and irregularly shaped with abnormally condensed or highly vacuolized cytoplasm containing numerous lysosomes. Early-stage apoptotic cells were not uncommon. Secretory cells showed signs of low activity, e.g., mitochondria with weakly stained matrix and small cristae, poorly branched infoldings of basolateral membranes, and microvesicle-free subapical cytoplasm. All characteristics examined changed significantly upon feeding, consistent with increased salt and fluid secretion: the outer capsule muscle layer and the stratified epithelium decreased in diameter; the tubules enlarged; the secretory cells showed extensive development of the basolateral membrane, more mitochondria, and abundant apical microvesicles. Secretory cell apical surface was increased. The minor differences between morphology in 6 and 20 h postfeeding indicated that changes took place rapidly and were complete by 6 h. Our results are discussed in the context of prior studies of metabolism, proteomics, and cellular pathways of gland activation Nous avons examine la morphologie de la glande rectale chez des aiguillats communs (Squalus acanthias L., 1758) apres un jeune (1 semaine) ou alors 6 et 20 h apres un repas. La morphologie de la glande apres le jeune presente un patron de physiologie de repos, avec une capsule glandulaire epaisse, un epithelium stratifie important et un parenchyme secreteur avec des tubules a diametre et a lumiere de petite taille. Les cellules secretrices de l'epithelium tubulaire sont agrandies et de forme irreguliere avec un cytoplasme anormalement condense ou fortement vacuole contenant de nombreux lysosomes. Les cellules au premier stade de l'apoptose ne sont pas rares. Les cellules secretrices montrent des signes d'activite reduite, par ex., des mitochondries a matrice peu coloree et a cretes petites, des membranes basolaterales avec des replis peu ramifies et un cytoplasme subapical sans microvesicules. Toutes les caracteristiques examinees changent apres l'alimentation, ce qui correspond a une secretion accrue de sels et de fluides : la couche musculaire externe de la capsule et l'epithelium stratifie diminuent en diametre, les tubules s'agrandissent, les cellules secretrices affichent un developpement considerable de leur membrane basolaterale et elles possedent plus de mitochondries et des microvesicules apicales plus abondantes. La surface apicale des cellules secretrices augmente. Les differences mineures entre la morphologie 6 et 20 h apres un repas indiquent que les changements se produisent rapidement et sont completes au bout de 6 h. Nous discutons de nos resultats dans le contexte des etudes anterieures sur le metabolisme, de la proteomique et des voies cellulaires de l'activation de la glande. [Traduit par la Redaction], Introduction The elasmobranch rectal gland has been an organ of experimental interest for decades. This small, digitiform organ, located as an outpocketing of the posterior intestine, is responsible for salt [...]

Abstract--Using a bioenergetics model, we estimated daily ration and seasonal prey consumption rates for six age classes of juvenile sandbar sharks (Carcharhinus plumbeus) in the lower Chesapeake Bay summer nursery [...]

Abstract--Standard and routine metabolic rates (SMRs and RMRs, respectively) of juvenile sandbar sharks (Carcharhinus plumbeus) were measured over a range of body sizes (n=34) and temperatures normally associated with western [...]

In complex habitats, environmental variation over small spatial scales can equal or exceed larger-scale gradients. This small-scale variation may allow motile organisms to mitigate stressful conditions by choosing benign microhabitats, whereas sessile organisms may rely on other behaviors to cope with environmental stresses in these variable environments. We developed a monitoring system to track body temperature, valve gaping behavior and posture of individual mussels (Mytilus californianus) in field conditions in the rocky intertidal zone. Neighboring mussels' body temperatures varied by up to 14°C during low tides. Valve gaping during low tide and postural adjustments, which could theoretically lower body temperature, were not commonly observed. Rather, gaping behavior followed a tidal rhythm at a warm, high intertidal site; this rhythm shifted to a circadian period at a low intertidal site and for mussels continuously submerged in a tidepool. However, individuals within a site varied considerably in time spent gaping when submerged. This behavioral variation could be attributed in part to persistent effects of the mussels' developmental environment. Mussels originating from a waveprotected, warm site gaped more widely, and remained open for longer periods during high tide than mussels from a wave-exposed, cool site. Variation in behavior was modulated further by recent wave heights and body temperatures during the preceding low tide. These large ranges in body temperatures and durations of valve closure events - which coincide with anaerobic metabolism - support the conclusion that individuals experience 'homogeneous' aggregations such as mussel beds in dramatically different fashion, ultimately contributing to physiological variation among neighbors. [ABSTRACT FROM AUTHOR]

Coping with environmental stress may involve combinations of behavioral and physiological responses. We examined potential interactions between adult mussels' simple behavioral repertoire – opening/closing of the shell valves – and thermal stress physiology in common-gardened individuals of three Mytilus congeners found on the West Coast of North America: two native species (M. californianus and M. trossulus) and one invasive species from the Mediterranean (M. galloprovincialis). We first continuously monitored valve behavior over three consecutive days on which body temperatures were gradually increased, either in air or in seawater. A temperature threshold effect was evident between 25 and 33°C in several behavioral measures. Mussels tended to spend much less time with the valves in a sealed position following exposure to 33°C body temperature, especially when exposed in air. This behavior could not be explained by decreases in adductor muscle glycogen (stores of this metabolic fuel actually increased in some scenarios), impacts of forced valve sealing on long-term survival (none observed in a second experiment), or loss of contractile function in the adductor muscles (individuals exhibited as many or more valve adduction movements following elevated body temperature compared with controls). We hypothesize that this reduced propensity to seal the valves following thermal extremes represents avoidance of hypoxia–reoxygenation cycles and concomitant oxidative stress. We further conjecture that prolonged valve gaping following episodes of elevated body temperature may have important ecological consequences by affecting species interactions. We then examined survival over a 90 day period following exposure to elevated body temperature and/or emersion, observing ongoing mortality throughout this monitoring period. Survival varied significantly among species (M. trossulus had the lowest survival) and among experimental contexts (survival was lowest after experiencing elevated body temperature in seawater). Surprisingly, we observed no cumulative impact on survival of 3 days relative to 1 day of exposure to elevated body temperature. The delayed mortality and context-specific outcomes we observed have important implications for the design of future experiments and for interpretation of field distribution patterns of these species. Ultimately, variation in the catalog of physiological and behavioral capacities among closely related or sympatric species is likely to complicate prediction of the ecological consequences of global change and species invasions. [ABSTRACT FROM AUTHOR]

Stenothermal Antarctic notothenioid fishes are noteworthy for their history of isolation in extreme cold and their corresponding lack of the canonical heat shock response. Despite extensive transcriptomic studies, the mechanistic basis for stenothermy has not been fully elucidated. Given that the proteome better represents an organism's physiology, the possibility exists that some aspects of stenothermy arise post-transcriptionally. Here, Antarctic emerald rockcod ( Trematomus bernacchii ) were sampled after exposure to chronic and/or acute high temperatures, followed by thorough assessment of proteomic responses in brain, gill, and kidney. Few cellular stress response proteins were induced, and overall responses were modest in terms of numbers of differentially expressed proteins and their fold changes. Inconsistencies in protein induction across treatments and tissues are suggestive of dysregulation, rather than an adaptive response. Changes in regulation of the translational machinery in Antarctic notothenioids could explain these patterns. Some components of translational regulatory pathways are highly conserved (e.g., Ser-52 of eIF2α), but proteins comprising the cellular "integrative stress response" - specifically, the eIF2α kinases GCN2 and PERK - may have evolved along different trajectories in Antarctic fishes. Taken together, these observations suggest a novel hypothesis for stenothermy and the absence of a coordinated cellular stress response in Antarctic fishes.