Variation In Temperature Tolerance Research Articles

Molecular Mechanisms of Temperature Tolerance Plasticity in an Arthropod.

How species thrive in a wide range of environments is a major focus of evolutionary biology. For many species, limited genetic diversity or gene flow among habitats means that phenotypic plasticity must play an important role in their capacity to tolerate environmental heterogeneity and to colonize new habitats. However, we have a limited understanding of the molecular components that govern plasticity in ecologically relevant phenotypes. We examined this hypothesis in a spider species (Stegodyphus dumicola) with extremely low species-wide genetic diversity that nevertheless occupies a broad range of thermal environments. We determined phenotypic responses to temperature stress in individuals from four climatic zones using common garden acclimation experiments to disentangle phenotypic plasticity from genetic adaptations. Simultaneously, we created data sets on multiple molecular modalities: the genome, the transcriptome, the methylome, the metabolome, and the bacterial microbiome to determine associations with phenotypic responses. Analyses of phenotypic and molecular associations reveal that acclimation responses in the transcriptome and metabolome correlate with patterns of phenotypic plasticity in temperature tolerance. Surprisingly, genes whose expression seemed to be involved in plasticity in temperature tolerance were generally highly methylated contradicting the idea that DNA methylation stabilizes gene expression. This suggests that the function of DNA methylation in invertebrates varies not only among species but also among genes. The bacterial microbiome was stable across the acclimation period; combined with our previous demonstrations that the microbiome is temporally stable in wild populations, this is convincing evidence that the microbiome does not facilitate plasticity in temperature tolerance. Our results suggest that population-specific variation in temperature tolerance among acclimation temperatures appears to result from the evolution of plasticity in mainly gene expression.

Queen honey bees exhibit variable resilience to temperature stress.

Extreme temperature exposure can reduce stored sperm viability within queen honey bees; however, little is known about how thermal stress may directly impact queen performance or other maternal quality metrics. Here, in a blind field trial, we recorded laying pattern, queen mass, and average callow worker mass before and after exposing queens to a cold temperature (4°C, 2 h), hot temperature (42°C, 2 h), and hive temperature (33°C, control). We measured sperm viability at experiment termination, and investigated potential vertical effects of maternal temperature stress on embryos using proteomics. We found that cold stress, but not heat stress, reduced stored sperm viability; however, we found no significant effect of temperature stress on any other recorded metrics (queen mass, average callow worker mass, laying patterns, the egg proteome, and queen spermathecal fluid proteome). Previously determined candidate heat and cold stress biomarkers were not differentially expressed in stressed queens, indicating that these markers only have short-term post-stress diagnostic utility. Combined with variable sperm viability responses to temperature stress reported in different studies, these data also suggest that there is substantial variation in temperature tolerance, with respect to impacts on fertility, amongst queens. Future research should aim to quantify the variation and heritability of temperature tolerance, particularly heat, in different populations of queens in an effort to promote queen resilience.

Intraspecific individual variation of temperature tolerance associated with oxygen demand in the European sea bass (Dicentrarchus labrax).

The European sea bass (Dicentrarchus labrax) is an economically important fish native to the Mediterranean and Northern Atlantic. Its complex life cycle involves many migrations through temperature gradients that affect the energetic demands of swimming. Previous studies have shown large intraspecific variation in swimming performance and temperature tolerance, which could include deleterious and advantageous traits under the evolutionary pressure of climate change. However, little is known of the underlying determinants of this individual variation. We investigated individual variation in temperature tolerance in 30 sea bass by exposing them to a warm temperature challenge test. The eight most temperature-tolerant and eight most temperature-sensitive fish were then studied further to determine maximal swimming speed (U CAT), aerobic scope and post-exercise oxygen consumption. Finally, ventricular contractility in each group was determined using isometric muscle preparations. The temperature-tolerant fish showed lower resting oxygen consumption rates, possessed larger hearts and initially recovered from exhaustive exercise faster than the temperature-sensitive fish. Thus, whole-animal temperature tolerance was associated with important performance traits. However, the temperature-tolerant fish also demonstrated poorer maximal swimming capacity (i.e. lower U CAT) than their temperature-sensitive counterparts, which may indicate a trade-off between temperature tolerance and swimming performance. Interestingly, the larger relative ventricular mass of the temperature-tolerant fish did not equate to greater ventricular contractility, suggesting that larger stroke volumes, rather than greater contractile strength, may be associated with thermal tolerance in this species.

Variation in temperature tolerance among families of Atlantic salmon (Salmo salar) is associated with hypoxia tolerance, ventricle size and myoglobin level

In fishes, performance failure at high temperature is thought to be due to a limitation on oxygen delivery (the theory of oxygen and capacity limited thermal tolerance, OCLTT), which suggests that thermal tolerance and hypoxia tolerance might be functionally associated. Here we examined variation in temperature and hypoxia tolerance among 41 families of Atlantic salmon (Salmo salar), which allowed us to evaluate the association between these two traits. Both temperature and hypoxia tolerance varied significantly among families and there was a significant positive correlation between critical maximum temperature (CTmax) and hypoxia tolerance, supporting the OCLTT concept. At the organ and cellular levels, we also discovered support for the OCLTT concept as relative ventricle mass (RVM) and cardiac myoglobin (Mb) levels both correlated positively with CTmax (R(2)=0.21, P<0.001 and R(2)=0.17, P=0.003, respectively). A large RVM has previously been shown to be associated with high cardiac output, which might facilitate tissue oxygen supply during elevated oxygen demand at high temperatures, while Mb facilitates the oxygen transfer from the blood to tissues, especially during hypoxia. The data presented here demonstrate for the first time that RVM and Mb are correlated with increased upper temperature tolerance in fish. High phenotypic variation between families and greater similarity among full- and half-siblings suggests that there is substantial standing genetic variation in thermal and hypoxia tolerance, which could respond to selection either in aquaculture or in response to anthropogenic stressors such as global climate change.

Geographic variation in temperature tolerance as an indicator of potential population responses to climate change

The temperature tolerances of individuals in geographically separated populations of a single species can be used as indicators of each population's potential to persist or become extinct in response to climate change. We evaluated the population-level variation in temperature tolerance in populations of several marine invertebrate taxa, including bryozoans, tunicates, bivalves, and gastropods, separated by distances of < 200 km to > 5000 km. We then combined physiological thermotolerance data with current temperature data and climate change predictions to predict which of these populations may be most vulnerable to future changes. In a trans-continental comparison of four subtidal epibenthic species, we show that populations on the east coast of the United States, which experienced higher habitat temperatures than those on the west coast, had higher thermal tolerances but lived closer to individuals' tolerance limits. Similarly, temperature tolerances varied between western and eastern Atlantic populations of the mussel Mytilus edulis; however, these differences only emerged after repeated exposures to high temperatures. Furthermore, the less thermotolerant M. edulis population in the western Atlantic was more susceptible to temperature increases, as evidenced by a recent range contraction. Thus, for both the subtidal epibenthic and intertidal mussel species, we identified the western Atlantic as a ‘hot spot’ of populations susceptible to climate change compared to those in the eastern Pacific and eastern Atlantic, respectively. Finally, because current tolerances are not the sole indicators of individuals' abilities to cope with temperature increases, we also assessed the possibility for acclimatization to facilitate the persistence of populations via the buffering of temperature effects. We show that, for four populations of intertidal Littorina snail species in the northwest Atlantic, most populations were able to overcome geographic differences in temperature tolerance via acclimation. When acclimation capacity is low, the potential for “rescue” may depend on the particular species' life-history strategy and dispersal ability. For example, although individuals from the coldest-adapted population of Littorina littorea were unable to acclimate as quickly as those from more southern populations, this species has a pelagic larval stage and, thus, the greatest dispersal potential of these littorines. Together, these studies highlight the importance of considering variation in temperature tolerance between populations within species to improve the forecasting of changes in the abundances and distributions of species in response to climate warming.

Ecoclinal variation in Ectocarpus siliculosus (Phaeophyceae) with respect to temperature growth optima and survival limits

The optimal temperature ranges for growth and the maximum temperatures for long-term survival have been ascertained for isolates of Ectocarpus siliculosus (Dillw.) Lyngb. collected at sites with prevailing temperature regimes ranging from Aretic to warm temperate. Although these had been maintained under constant temperature conditions for a number of years, differences in both growth and survival temperature ranges were demonstrated, which can be correlated with the temperature regimes at the original collection sites. Many of these strains have been previously shown to be genetically compatible and thus, although all isolates tested can be described as eurythemic, the extremely wide geographic and ecological range of the species has been achieved to an extent by the evolution of genetic variation in temperature tolerance between populations. Gradual variation is associated with similar rates of change in ambient temperature regime, and is best described as an ecocline.

GENETIC AND NON-GENETIC VARIABILITY IN TEMPERATURE TOLERANCE OF THE COPEPODEURYTEMORA AFFINISIN FIVE TEMPERATURE REGIMES

Genetic and nongenetic variation in temperature tolerance was measured in populations of copepods grown in two environments varying between 10° and 23°C on 26 day (SW) and 26 week (LW) cycles and in three constant environments at 10°C, 15°C, and 23°C.Genetic variation was maintained and expressed in both sexes in the cycling environments, but declined in males in the 23°C constant environment, perhaps indicating constant directional selection.Physiological variation was similar in males and females, in contrast to earlier results, again suggesting an effect of selection. There was evidence of selection for physiological flexibility in males in the 23°C and 15°C environments.A question arising was why sexual dimorphism in genetic variation and in physiological variation was maintained in nature but reduced, reversed, or even eliminated in the laboratory environment. Random drift was not a plausible explanation.

A Relationship of Genetic Variation Within and among Populations: An Extension of the Kluge-kerfoot Phenomenon

Pierce, B. A. and J. B. Mitton (Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, Colorado 80309) 1979. A Relationship of Genetic Variation Within and Among Populations: An Extension of the Kluge-Kerfoot Phenomenon. Syst. Zool. 28:63-70.-A positive correlation between intrapopulation variation and among population diversity has been demonstrated for morphometric characters (the Kluge-Kerfoot phenomemon). This study extends the relationship to allozyme variation. Four sets of statistics are utilized to partition genetic variation into within and among population components of diversity and the strength of association between these components is assessed by means of rank order correlation. All but one of the seven species tested demonstrate significant, positive correlation coefficients for all four of the diversity measures. Although both selective and stochastic mechanisms may generate such a relationship, it appears that stochastic forces do not totally account for the correlations seen in the data sets analyzed here. [Kluge-Kerfoot phenomenon; intrapopulation variation; among population diversity; allozyme variation.] Fundamental to evolutionary biology is an understanding of the nature of morphological variation and its underlying genetic diversity. Those factors responsible for the maintenance of variation within a population are not well understood and are currently the subject of much debate. A complementary and equally important topic of evolutionary theory concerns the basis of interpopulation diversity. The relationship between variation within populations and variation among populations was the focus of a seminal paper by Kluge and Kerfoot in 1973. In an analysis of seven vertebrate morphometric data sets, Kluge and Kerfoot (1973) were able to demonstrate a strong, significant correlation between within population variation and a measure of differentiation among populations. Sokal (1976) reexamined their methods and suggested some modifications in their technique. Sokal's calculations, however, also yielded a similar pattern of within and among population variation both in the original data sets of Kluge and Kerfoot and in additional data sets on invertebrates. An example of the relationship between variation within and among populations may be found in an analysis of seven meristic variables of the killifish, Fundulus heteroclitus, from four populations (Fig. 1). The Kluge-Kerfoot phenomenon of a positive relationship between within and among population variation is of potential importance to biologists studying the nature of character divergence. It may also prove to be a valuable predictive tool to those interested in the ecological divergence of populations. By examining levels of intrapopulation variation, one may be capable of statistically predicting the types of niches and environments a species is capable of occupying. For example, if one observes low intrapopulation variability in temperature tolerance, one could predict from the Kluge-Kerfoot relationship that interpopulation variation in temperature tolerance will also be low, and the organism will be limited in its range of thermal environments. In spite of its potential importance to evolutionary biology, the mechanisms responsible for the Kluge-Kerfoot phenomenon remain obscure. Kluge and Kerfoot (1973) explained the relationship by proposing that normalizing selection limits intrapopulation variability, and they suggested that divergence of characters among populations is a function of selection acting upon the levels of within pop-