Adaptive plasticity in thermal tolerance traits may buffer organisms against changing temperatures, making such responses of particular interest in the face of global climate change. Although population variation is integral to the evolvability of this trait, many studies inferring proxies of physiological vulnerability from thermal tolerance traits extrapolate data from one or a few populations to represent the species. Estimates of physiological vulnerability can be further complicated by methodological effects associated with experimental design. We evaluated how populations varied in their acclimation capacity (i.e., the magnitude of plasticity) for critical thermal maximum (CTmax) in two species of tailed frogs (Ascaphidae), cold‐stream specialists. We used the estimates of acclimation capacity to infer physiological vulnerability to future warming. We performed CTmax experiments on tadpoles from 14 populations using a fully factorial experimental design of two holding temperatures (8 and 15°C) and two experimental starting temperatures (8 and 15°C). This design allowed us to investigate the acute effects of transferring organisms from one holding temperature to a different experimental starting temperature, as well as fully acclimated responses by using the same holding and starting temperature. We found that most populations exhibited beneficial acclimation, where CTmax was higher in tadpoles held at a warmer temperature, but populations varied markedly in the magnitude of the response and the inferred physiological vulnerability to future warming. We also found that the response of transferring organisms to different starting temperatures varied substantially among populations, although accounting for acute effects did not greatly alter estimates of physiological vulnerability at the species level or for most populations. These results underscore the importance of sampling widely among populations when inferring physiological vulnerability, as population variation in acclimation capacity and thermal sensitivity may be critical when assessing vulnerability to future warming.
Understanding how altered temperature regimes affect harmful cyanobacterial bloom formation is essential for managing aquatic ecosystems amidst ongoing climate warming. This is difficult because algal performance can depend on both current and past environments, as plastic physiological changes (acclimation) may lag behind environmental change. Here, we investigate how temperature variation on sub‐weekly timescales affects population growth and toxin production given acclimation. We studied four ecologically important freshwater cyanobacterial strains under low‐ and high‐nutrient conditions, measuring population growth rate after acclimation and new exposure to a range of temperatures. Cold‐acclimated populations (15.7°C) outperformed fully acclimated populations (held in constant conditions) across 65% of thermal environments, while hot‐acclimated populations (35.7–42.6°C) underperformed across 75% of thermal environments. Over a 5‐day period, cold‐acclimated
- Award ID(s):
- 1856415
- NSF-PAR ID:
- 10361248
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography Letters
- Volume:
- 7
- Issue:
- 1
- ISSN:
- 2378-2242
- Page Range / eLocation ID:
- p. 34-42
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Temperature is a major driver of phytoplankton growth and physiology, but despite decades of study on temperature effects, the influence of temperature fluctuations on the growth acclimation of marine phytoplankton is largely unknown. To address this knowledge gap, we subjected a coastal phytoplankton species,
Heterosigma akashiwo , to ecologically relevant temperature shifts of 2–3°C, cumulatively totaling 3–16°C across a range from 6°C to 31°C over a 3‐week period. Using a symmetric design, we show time dependent differences between growth rates and that these changes were related to the magnitude of the temperature shift, but not the direction. Cell size scaled inversely with temperature at a rate of −1.9 to −3.3%°C−1at all except the highest temperature treatments > 25°C. Intraspecific variability in growth rates increased exponentially with cumulative thermal shifts, suggesting thermal variability may be a driver of intraspecific variation. The observed acclimation effects on phytoplankton growth rates suggest that ignoring acclimation effects could systematically under or overestimate temperature‐dependent primary production. Empirical results, contextualized with in situ coastal ocean temperature record, demonstrated that daily primary production could differ from current model assumptions utilizing acclimated rates by −33% to +36%. If broadly applicable to diverse phytoplankton species, these results have ramifications for predicting the ecology and production of phytoplankton in present day dynamic ecosystems and in future climate scenarios where thermal variability is expected to increase. -
ABSTRACT Physiology defines individual responses to global climate change and species distributions across environments. Physiological responses are driven by temperature on three time scales: acute, acclimatory and evolutionary. Acutely, passive temperature effects often dictate an expected 2-fold increase in metabolic processes for every 10°C change in temperature (Q10). Yet, these acute responses often are mitigated through acclimation within an individual or evolutionary adaptation within populations over time. Natural selection can influence both responses and often reduces interindividual variation towards an optimum. However, this interindividual physiological variation is not well characterized. Here, we quantified responses to a 16°C temperature difference in six physiological traits across nine thermally distinct Fundulus heteroclitus populations. These traits included whole-animal metabolism (WAM), critical thermal maximum (CTmax) and substrate-specific cardiac metabolism measured in approximately 350 individuals. These traits exhibited high variation among both individuals and populations. Thermal sensitivity (Q10) was determined, specifically as the acclimated Q10, in which individuals were both acclimated and assayed at each temperature. The interindividual variation in Q10 was unexpectedly large: ranging from 0.6 to 5.4 for WAM. Thus, with a 16°C difference, metabolic rates were unchanged in some individuals, while in others they were 15-fold higher. Furthermore, a significant portion of variation was related to habitat temperature. Warmer populations had a significantly lower Q10 for WAM and CTmax after acclimation. These data suggest that individual variation in thermal sensitivity reflects different physiological strategies to respond to temperature variation, providing many different adaptive responses to changing environments.more » « less
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Abstract 1. Critical thermal limits represent an important component of an organism's capacity to cope with future temperature changes. Understanding the drivers of variation in these traits may uncover patterns in physiological vulnerability to climate change. Local temperature extremes have emerged as a major driver of thermal limits, although their effects can be mediated by the exploitation of fine‐scale spatial variation in temperature through behavioural thermoregulation.
2. Here, we investigated thermal limits along elevation gradients within and between two cold‐water frog species (
Ascaphus spp.), one with a coastal distribution (A. truei ) and the other with a continental range (A. montanus ). We quantified thermal limits for over 700 tadpoles, representing multiple populations from each species. We combined local temporal and fine‐scale spatial temperature data to quantify local thermal landscapes (i.e., thermalscapes), including the opportunity for behavioural thermoregulation.3. Lower thermal limits for either species could not be reached experimentally without the water freezing, suggesting that cold tolerance is <0.3°C. By contrast, upper thermal limits varied among populations, but this variation only reflected local temperature extremes in
A .montanus , perhaps as a consequence of the greater variation in stream temperatures across its range. Lastly, we found minimal fine‐scale spatial variability in temperature, suggesting limited opportunity for behavioural thermoregulation and thus increased vulnerability to warming for all populations.4. By quantifying local thermalscapes, we uncovered different trends in the relative vulnerability of populations across elevation for each species. In
A .truei , physiological vulnerability decreased with elevation, whereas inA .montanus , all populations were equally physiologically vulnerable. These results highlight how similar environments can differentially shape physiological tolerance and patterns of vulnerability of species, and in turn impact their vulnerability to future warming. -
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Premise Cold tolerance is an important factor limiting the geographic distribution and growing season for many plant species, yet few studies have examined variation in cold tolerance extensively within and among closely related species and compared that to their geographic distribution.
Methods This study examines cold tolerance within and among species in the genus
Arabidopsis . We assessed cold tolerance by measuring electrolyte leakage from detached leaves in multiple populations of fiveArabidopsis taxa. The temperature at which 50% of cells were lysed was considered the lethal temperature (LT 50).Results We found variability within and among taxa in cold tolerance. There was no significant within‐species relationship between latitude and cold tolerance. However, the northern taxa,
A. kamchatica ,A. lyrata subsp.petraea , andA. lyrata subsp.lyrata , were more cold tolerant thanA. thaliana andA. halleri subsp.gemmifera both before and after cold acclimation. Cold tolerance increased after cold acclimation (exposure to low, but nonfreezing temperatures) for all taxa, although the difference was not significant forA. halleri subsp.gemmifera . For all taxa exceptA. lyrata subsp.lyrata , theLT 50values for cold‐acclimated plants were higher than the January mean daily minimum temperature (Tmin), indicating that if plants were not insulated by snow cover, they would not likely survive winter at the northern edge of their range.Conclusions Arabidopsis lyrata andA. kamchatica were far more cold tolerant thanA. thaliana . These extremely cold‐tolerant taxa are excellent candidates for studying both the molecular and ecological aspects of cold tolerance.
