Marine animals living high in the rocky intertidal zone experience long durations of aerial emersion, sometimes enduring rapid increases in temperature. To date, much of our understanding of the thermalphysiology of intertidal organisms comes from studies in which organisms are exposed to increasing temperatures when immersed, with the added effect of aerial emersion rarely considered. In this study, we examined the physiological response of the finger limpet, Lottia digitalis, to increases in temperature under both immersed and emersed conditions. We investigated the thermal sensitivity and upper temperature tolerance of limpets through assessment of cardiac performance, metabolic rate, glycogen depletion and maintenance of protein integrity. Cardiac performance in response to ecologically relevant increases in temperature was similar in emersed and immersed limpets from 15 to 35°C and showed multiple break patterns in heart rate as temperature was increased. Overall, emersed limpets had a greater upper thermal limit on cardiac performance, with the ability to maintain heart rate at a temperature 3–5°C higher than that for immersed limpets. Metabolism in limpets also differed significantly between emersion and immersion, where a significant depression in aerobic metabolic rate was observed under immersion with increasing temperature. Greater levels of ubiquitin-conjugated proteins were found under emersed conditions compared with immersed limpets. Maintaining cardiac performance and aerobic metabolism to higher temperatures under emersed conditions is likely reflective of physiological adaptations to live in an aerially exposed environment. Measured field temperatures where fingered limpets were collected demonstrated that limpets have a narrow thermal safety margin for aerobic performance, and currently experience multiple days where summer temperatures might exceed their threshold limits.
Department of Biology, National Changhua University of Education, Changhua 50058, Taiwan, R.O.C.
ABSTRACT—We compared the reproductive phenology and tadpole thermalphysiology of two populations of Buergeria japonica in Taiwan. The population in Jentse breeds in a geothermal hot spring whose water is a warm, over 35 ° C year-round, whereas the population in Chukou breeds in a stream whose water tempera- ture is closely correlated with fluctuations in air temperature and averages 23 ° C. The B. japonica population in Jentse breeds year-round, but the Chukou population breeds only from March to October. Tadpoles from Jentse that reared at 32 ° C attained larger sizes than tadpoles from Chukou that reared at 32 ° C, whereas tadpoles from both sites attained similar body size when reared at 22 ° C. Chukou tadpoles reared at 40 ° C died within 1–2 d, whereas Jentse tadpoles survived for 9 d at 40 ° C. All tadpoles tolerated heat well, but Jentse tadpoles had higher critical thermal maxima (CTMax) than Chukou tadpoles. Tadpoles from Jentse showed no metabolic compensation but those from Chukou showed an “inverse” metabolic compensation. Results suggest that B. japonica that breed in the geothermal hot spring has a prolonged breeding season, high growth rates and the reduction or absence of intra- and inter-specific competition. Evolution of a high level of heat tolerance and, possibly, behavioral temperature selection, enable tadpoles in the hotsprings to offset the thermal stress imposed by warm water.
Environmental complexity and, specifically, the repeated nature of aerial exposure and unpredictable magnitude of temperature increase are important aspects of the thermalphysiology of L. digitalis and modulate upper temperature tolerance. Studies that have not incorporated these aspects of the intertidal environment may not be accurately capturing the current sensitivity of intertidal organisms to projected changes in temperature under different climate change scenarios. Our study highlights the critical importance of repeated aerial exposure for increasing the upper temperature tolerance of L. digitalis. If aerial exposure is the predominant factor driving thermal tolerance of intertidal limpets, and perhaps intertidal organisms more broadly, it suggests that organisms inhabiting the low intertidal are likely sensitive to warming not only as a result of a thermal history of lower temperatures but also as a result of not predictably being exposed to air during low tide periods. We also provide evidence that thermal history from a few days prior may be important in fine-tuning upper temperature tolerance in unpredictable fluctuating environments. Timing of low tides (i.e. during midday versus early morning in summer months) has been predicted to be an important factor defining risk of thermal stress from extreme events in intertidal organisms (Helmuth et al., 2002). Therefore, opportunities exist to better understand the link between aerial exposure and heating in defining the thermalphysiology of organisms by examining populations of limpets along a latitudinal gradient, such as the west coast of the United States. Additional studies are needed to determine the cellular mechanisms conferring higher thermal tolerance from heating regimes that are unpredictable in nature. Moving forward, physiological studies should incorporate environmental unpredictability rather than just focusing on the magnitude of heat stress to fully understand the thermalphysiology of animals living in variable environments. More studies are needed to identify which aspects of environmental complexity are the key drivers of organisms ’ physiological responses. Identifying these key components of thermal variability will lead to more informed experimental designs that will improve our predictions regarding how intertidal organisms will respond to climate change (Helmuth et al., 2014).
Temperature is an important factor determining distribution and abundance of organisms. Predicting the impact of warming climate on ectotherm populations requires information about species ’ thermal requirements, i.e. their so-called ‘ thermal niche ’ . The characterization of thermal niche remains a complicated task. We compared the applicability of two indirect approaches, based on reaction norm (aerobic scope curve) and optimality ( preferred body temperature) concepts, for indirect estimation of thermal niche while using newts, Ichthyosaura alpestris, as a study system. If the two approaches are linked, then digesting newts should keep their body temperatures close to values maximizing aerobic scope for digestion. After feeding, newts maintained their body temperatures within a narrower range than did hungry individuals. The range of preferred body temperatures was well below the temperature maximizing aerobic scope for digestion. Optimal temperatures for factorial aerobic scope fell within the preferred body temperature range of digesting individuals. We conclude that digesting newts prefer body temperatures that are optimal for the maximum aerobic performance but relative to the maintenance costs. What might be termed the ‘ economic ’ thermoregulatory response explains the mismatch between thermalphysiology and behaviour in this system.
Analysing thermal images, especially videos from conscious and active animals is a laborious process. Unlike many of the applications for which IRT was developed (physics, engineering), animals are rarely stationary with respect to the captured image frame, so any time-based analyses are plagued with changes in shape, perspective, and distance, and existing thermographic software packages appear to lack automation features that include object tracking along with temperature analysis. To date, the author is not aware of software packages that incorporate thermal analysis with motion sensing or object tracking, although customized solutions could be achieved with sufficient computation skills and access to existing analytical platforms (Abramoff et al., 2004; MATLAB, 2015). Typically, users are required to draw a region of interest (ROI) over the surface they wish to examine and simple mean, minimum, maximum and standard deviation of the pixels within the ROI is possible. The most powerful programs allow for ROI data to be examined over time. With respect to physiological data, movement artifacts typically make these impossible to use. One of the limiting factors in infrared thermal imaging is the file format. Image files are not always saved in a publically accessible format and require commercial software for analysis. Although normally provided at the time of purchase, unless the user has computer programming skills, they are at the whim of the company supplying the software. Open source alternatives to these commercial software packages are not available at present (Minkina and Dudzik, 2009), however, customized approaches could be employed (see supplementary
contemporary thermal capacity. Identifying these variables could aid in understanding a species ability to respond to climate change.
In the present study, the southern African endemic lacertid lizard, Meroles knoxii was used to investigate the genetic and physiological potential of a temperate west coast lizard to adapt to climate change. The South African west coast comprises two of the threatened biomes mentioned before, the Succulent Karoo and Fynbos biomes, both limited by the winter-rainfall zone with centres of high endemism (Rutherford et al., 1999). The entire coastal region is associated with steep thermal and rainfall gradients, with temperatures decreasing and rainfall increasing on north- south axes (Fig. 1.2). These gradients are likely affected by the cold north flowing Benguela Current and the winter rainfall zone (Lutjeharms, 1998; Schumann, 1998; Tyson & Preston-Whyte, 2000; Chase & Meadows, 2007). Changes in future climate could potentially affect these gradients as ocean circulation disruptions predict cascading effects for marine environments (IPCC, 2014). If these gradients affect M. knoxii, climate change could impact this temperate species. Climate warming of 3-6°C (IPCC, 2014), could potentially curb activity periods for this cold-adapted lizard. The west coastal region is associated with high incidence of fog and cloud cover (Janse van Rensburg et al., 2009). The direction and magnitude of future changes in rainfall in South Africa are uncertain (Ziervogel, 2014). However, it is conceivable that changes in fog and cloud cover could also occur. If, for instance, the incidence of fog and cloud cover increases, potential activity of lizards could be further restrained. As reptiles in the western region of South Africa are likely to face a challenging environment with thermal landscape changes and their habitats threatened with potential biome shifts and losses, M. knoxii could prove a model ectotherm to study a reptile‟s possible response to climate change.
convective conditions (reviewed in Dzialowski 2005). One live adult male Anolis armouri lizard and one copper lizard model were tethered to a cardboard panel using dental floss and a thermocouple (Type T, Omega) was inserted into the cloaca of each and secured using medical tape. The panel was exposed to different thermal conditions in fifteen minute intervals including: in the sun and shade on a sunny day (air temperature [T A ] = 31.1°C), outdoors on a breezy overcast day (T A = 22°C), indoors in an air-
Hyperspectral and thermal sensors installed on field robots-, aircraft-, and satellite-based platforms are an increasingly common approach used to characterize plant physiology [14–17]. In hyperspectral remote sensing, sensors measure radiative properties of plants with hundreds to thousands of continuous narrow bands in the optical domain (0.35–2.5 µm). This abundant spectral information increases the chance of detecting subtle physiological changes compared to multispectral data, which have a small number of bands averaged over a wide spectral region and are insensitive to narrow spectral signatures [18–20]. Photochemical reflectance index (PRI) and sun-induced fluorescence (SIF) retrieved from hyperspectral remote sensing are the most widely used indicators in the remote assessment of plant photosynthetic activity [21–24]. The PRI was formed to track the xanthophyll cycle, which relates to plant oxidative stress associated with photosynthesis, using changes in green reflectance centered at 531 nm . SIF is a direct proxy of photosynthesis, because it detects reemitted excess light energy at 600–800 nm, from photosystems I and II, to minimize photosystem damage as a part of the plant photo-protective mechanism [26–29].
nipulated mice has taken on an equally important role in de- veloping murine models of human disease, determining the role of single genes in complex physiological traits, and in as- cribing the lack of a phenotype to gene redundancy. Com- pounding the difficulty, the investigators having the skills re- quired to generate transgenic or gene-targeted mice often do not have the expertise necessary to quantitatively monitor a complex physiological phenotype, that encompasses changes in diastolic or systolic function, neural control of integrative cardiovascular function, exercise-induced cardiorespiratory endpoints, or other complex parameters. Given the diminutive size of the mouse heart and associated vessels (the diameter of the adult mouse aorta is 1 mm in its widest distribution), a heart rate in excess of 450 beats per minute, the dearth of base- line parameters describing murine cardiovascular function and physiology, and the lack of widely available miniaturized tech- nology to assess in vivo physiological phenotypes, until re- cently, most of the analysis of potential cardiovascular pheno- types in mice have been confined to simple histological assessments. Needless to say, since the usual classifications of many clinical diseases are not based on such parameters, the potential for making the wrong “diagnosis,” missing a major phenotype, or wrongly concluding the absence of a phenotype are substantial. In the latter case, it may be premature to con- clude that a lack of a phenotype in a gene-targeted animal is a true reflection of the functional redundancy of members of a given gene family, as this may simply reflect the inability to Address correspondence to Kenneth R. Chien, MD, PhD, Depart-