The Temperature–Size Rule in Lecane inermis (Rotifera) is adaptive and driven by nuclei size adjustment to temperature and oxygen combinations

The evolutionary implications of the Temperature–Size Rule (TSR) in ectotherms is debatable; it is uncertain whether size decrease with temperature increase is an adaptation or a non-adaptive by-product of some temperature-dependent processes. We tested whether (i) the size of the rotifer Lecane inermis affects fecundity in a way that depends on the combination of low or high temperature and oxygen content and (ii) the proximate mechanism underlying TSR in this species is associated with nuclei size adjustment (a proxy of cell size).Small-type and large-type rotifers were obtained by culturing at different temperatures prior to the experiment and then exposed to combinations of two temperature and two oxygen conditions. Fecundity was estimated and used as a measure of fitness. Nuclei and body sizes were measured to examine the response to both environmental factors tested.The results show the following for L. inermis. (i) Body size affects fecundity in response to both temperature and oxygen, supporting a hypothesis regarding the contribution of oxygen in TSR. (ii) Large individuals are generally more fecund than small ones; however, under a combination of high temperature and poor oxygen conditions, small individuals are more fecund than large ones, in accordance with a hypothesis of the adaptive significance of TSR. (iii) The body size response to temperature is realised by nuclei size adjustment. (iv) Nuclei size changes in response to temperature and oxygen conditions, in agreement with hypotheses on the cellular mechanism underlying TSR and on a contribution of oxygen availability in TSR. These results serve as empirical evidence for the adaptive significance of TSR and validation of the cellular mechanism for the observed response.     

Life-history responses of the rice stem borer Chilo suppressalis to temperature change: Breaking the temperature–size rule

Temperature is a key environmental factor for ectotherms and affects a large number of life history traits. In the present study, development time from hatching to pupation and adult eclosion, pupal and adult weights of the rice stem borer, Chilo suppressalis were examined at 22, 25, 28 and 31 °C under L18:D 6. Larval and pupal times were significantly decreased with increasing rearing temperature and growth rate was positively correlated with temperature. Larval and pupal developmental times were not significantly different between females and males. The relationship between body weight and rearing temperature in C. suppressalis did not follow the temperature–size rule (TSR), both males and females gained the highest body weight at 31 °C. Females were significantly larger than males at all temperatures, showing a female biased sex size dimorphism (SSD). Contrary to Rensch's rule, SSD and body weight in C. suppressalis tended to increase with rising temperature. Male pupae lost significantly more weight at metamorphosis compared to females. We discuss the adaptive significance of the reverse-TSR in the moth's life history.     

Phenotypic plasticity of body size in a temperate population ofDrosophila melanogaster: When the temperature—size rule does not apply

A natural population ofDrosophila melanogaster in southern France was sampled in three different years and 10 isofemale lines were investigated from each sample. Two size-related traits, wing and thorax length, were measured and the wing/thorax ratio was also calculated. Phenotypic plasticity was analysed after development at seven different constant temperatures, ranging from 12‡C to 31‡C. The three year samples exhibited similar reaction norms, suggesting a stable genetic architecture in the natural population. The whole sample (30 lines) was used to determine precisely the shape of each reaction norm, using a derivative analysis. The practical conclusion was that polynomial adjustments could be used in all cases, but with different degrees: linear for the wing/thorax ratio, quadratic for thorax length, and cubic for wing length. Both wing and thorax length exhibited concave reaction norms, with a maximum within the viable thermal range. The temperatures of the maxima were, however, quite different, around 15‡C for the wing and 19.5‡C for the thorax. Assuming that thorax length is a better estimate of body size, it is not possible to state that increasing the temperature results in monotonically decreasing size (the temperature-size rule), although this is often seen to be the case for genetic variations in latitudinal clines. The variability of the traits was investigated at two levels—within and between lines—and expressed as a coefficient of variation. The within-line (environmental) variability revealed a regular, quadratic convex reaction norm for the three traits, with a minimum around 21‡C. This temperature of minimum variability may be considered as a physiological optimum, while extreme temperatures are stressful. The between-line (genetic) variability could also be adjusted to quadratic polynomials, but the curvature parameters were not significant. Our results show that the mean values of the traits and their variance are both plastic, but react in different ways along a temperature gradient. Extreme low or high temperatures decrease the size but increase the variability. These effects may be considered as a functional response to environmental stress.     

The effect of the entry and re-entry size in the aortic dissection: a two-way fluid–structure interaction simulation

Biomechanics and Modeling in Mechanobiology - Aortic dissection (AD) is one of the most catastrophic cardiovascular diseases. AD occurs when a layer inside the aorta is disrupted and gives rise to...     

Shrinking body sizes in response to warming: explanations for the temperature–size rule with special emphasis on the role of oxygen

Body size is central to ecology at levels ranging from organismal fecundity to the functioning of communities and ecosystems. Understanding temperature-induced variations in body size is therefore of fundamental and applied interest, yet thermal responses of body size remain poorly understood. Temperature–size (T–S) responses tend to be negative (e.g. smaller body size at maturity when reared under warmer conditions), which has been termed the temperature–size rule (TSR). Explanations emphasize either physiological mechanisms (e.g. limitation of oxygen or other resources and temperature-dependent resource allocation) or the adaptive value of either a large body size (e.g. to increase fecundity) or a short development time (e.g. in response to increased mortality in warm conditions). Oxygen limitation could act as a proximate factor, but we suggest it more likely constitutes a selective pressure to reduce body size in the warm: risks of oxygen limitation will be reduced as a consequence of evolution eliminating genotypes more prone to oxygen limitation. Thus, T–S responses can be explained by the ‘Ghost of Oxygen-limitation Past’, whereby the resulting (evolved) T–S responses safeguard sufficient oxygen provisioning under warmer conditions, reflecting the balance between oxygen supply and demands experienced by ancestors. T–S responses vary considerably across species, but some of this variation is predictable. Body-size reductions with warming are stronger in aquatic taxa than in terrestrial taxa. We discuss whether larger aquatic taxa may especially face greater risks of oxygen limitation as they grow, which may be manifested at the cellular level, the level of the gills and the whole-organism level. In contrast to aquatic species, terrestrial ectotherms may be less prone to oxygen limitation and prioritize early maturity over large size, likely because overwintering is more challenging, with concomitant stronger end-of season time constraints. Mechanisms related to time constraints and oxygen limitation are not mutually exclusive explanations for the TSR. Rather, these and other mechanisms may operate in tandem. But their relative importance may vary depending on the ecology and physiology of the species in question, explaining not only the general tendency of negative T–S responses but also variation in T–S responses among animals differing in mode of respiration (e.g. water breathers versus air breathers), genome size, voltinism and thermally associated behaviour (e.g. heliotherms).     

Patterns of size variation in bees at a continental scale: does Bergmann's rule apply?

Body size latitudinal clines have been widley explained by the Bergmann's rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann's rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142 008 distribution records of 615 bee species at 50 × 50 km (CGRS) grids across the West Palearctic. We then applied generalized least squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann's rule. However, considering bee genera separately, four genera were consistent with Bergmann's rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann's cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a ‘season length effect’ (i.e. shorter foraging season) is a potential driver of the converse Bergmann's cline particularly in bumblebees.     

Nuclear size is regulated by importin α and Ntf2 in Xenopus

The size of the nucleus varies among different cell types, species, and disease states, but mechanisms of nuclear size regulation are poorly understood. We investigated nuclear scaling in the pseudotetraploid frog Xenopus laevis and its smaller diploid relative Xenopus tropicalis, which contains smaller cells and nuclei. Nuclear scaling was recapitulated in vitro using egg extracts, demonstrating that titratable cytoplasmic factors determine nuclear size to a greater extent than DNA content. Nuclear import rates correlated with nuclear size, and varying the concentrations of two transport factors, importin α and Ntf2, was sufficient to account for nuclear scaling between the two species. Both factors modulated lamin B3 import, with importin α increasing overall import rates and Ntf2 reducing import based on cargo size. Importin α also contributes to nuclear size changes during early X. laevis development. Thus, nuclear transport mechanisms are physiological regulators of both interspecies and developmental nuclear scaling.     

The synthesis of oligosaccharides by the reversed hydrolysis reaction of β-glucosidase at high substrate concentration and at high temperature

Summary In the presence of -glucosidase from almond, a 90% glucose solution gave four kind of -linked glucose-disaccharides. The yield increased as the concentration of glucose was increased and as the reaction temperature was raised. The maximum yield of disaccharides from 90% glucose solution was 40% at 55°C.     

The transport of class I major histocompatibility complex antigens is determined by sequences in the α1 and α2 protein domains

The transport of human-mouse hybrid class I histocompatibility antigens has been studied in a mutant human cell line, 174 × CEM.T2 (T2). T2, a somatic cell hybrid of human B- and T-lymphoblastoid cell lines (B-LCL and T-LCL, respectively), synthesizes HLA-A2 and HLA-B5 glycoproteins, but expresses only low levels of A2 and undetectable levels of B5 at the cell surface. We have previously shown that the products of human class I genes introduced into T2 by transfection behave like the endogenous HLA-B5 glycoproteins, while the products of mouse class I alleles similarly introduced are transported normally to the cell surface. We have now determined that the surface expression of class I glycoproteins in T2 depends on the origin of the ₁ and ₂ domains. Human (HLA-B7) and mouse (H-2D ^p ) hybrid class I genes, encoding the leader, ₁, and ₂ sequences of one species fused to the ₃, transmembrane, and cytoplasmic domains of the other, were transfected into T2. Normal surface expression of the hybrid class I molecule was observed in T2 only when the leader, ₁, and ₂-encoding exons were derived from the mouse gene. The reciprocal construct, encoding human leader, ₁, and ₂ domains fused to the mouse ₃, transmembrane, and cytoplasmic regions, resulted in biosynthesis of a hybrid glycoprotein which was not transported to the cell surface. The products of both constructs were expressed normally in control cells. The effects of glycosylation on class I antigen transport were also studied using mutant class I constructs with altered glycosylation sites. Two mutant B7 genes encoding either an extra glycosylation site at position 176 or no glycosylation sites were transfected into T2. These mutant products were expressed at the cell surface in control cells, but were synthesized and not surface-expressed in T2. These data demonstrate that the HLA/H-2 transport dichotomy in T2 is a function of the origin of the ₁ and/or ₂ domains of the class I glycoprotein, and is not a reflection of glycosylation differences between the human and mouse molecules. Offprint requests to: P. Cresswell.     

Nitrogen translocation between clonal mother and daughter trees at a grassland–forest boundary

There is abundant evidence from short-term experiments using herbs that nutrients can be translocated from mother ramets to daughter ramets, but there is little long-term evidence from woody plants. Here, we examine translocation in field populations of a clonal tree over two growing seasons. We applied ¹⁵N to mothers or daughters in clones of Populus tremuloides at the northern edge of the North American Great Plains, where mother ramets form closed-canopy stands on relatively nutrient-rich soils, and daughter ramets occur nearby in relatively nutrient-poor grasslands. Unlabeled daughters in clones with labeled mothers had δ¹⁵N values significantly greater than those in unlabeled clones, confirming translocation from mothers to daughters. However, unlabeled mothers in clones with labeled daughters also had δ¹⁵N values significantly greater than those in unlabeled clones, indicating translocation from daughters to mothers. Further, the total foliage accumulation of added ¹⁵N was significantly (c. 10×) greater in mothers than in daughters, suggesting that more N was translocated from daughters to mothers, than from mothers to daughters. Thus, ¹⁵N moved both from mothers to daughters and from daughters to mothers, with net flow toward mothers. Because long-lived woody ramets in the field face nutrient competition from other ramets, interspecific neighbors, and soil microbes, the environmental availability of nutrients for uptake may be low for both mother and daughter ramets, causing translocation within a clone to be toward larger ramets with greater demand.     

High temperature tolerance and thermal-adaptability plasticity of Asian corn borer (Ostrinia furnacalis Guenée) after a single extreme heat wave at the egg stage

Due to ongoing climate change, short-term extreme heat waves in the summer are expected to be more frequent. Insect eggs are sensitive to thermal stress. This raises the question of whether herbivore insects' thermal adaptability would be changed after a single extreme heat wave at the egg stage. In this study, we examined the developmental performance of Ostrinia furnacalis Guenée at 25?°C, 27?°C, 29?°C or 31?°C after a single extreme heat wave (42?°C) for 0?h (control), 1?h, 2?h, or 3?h at the egg stage. The results showed that O. furnacalis at the egg or larval stage was more sensitive to a single heat wave than it was at the pupae or adult stage. After a single heat wave, O. furnacalis showed a reduced egg-hatching rate or reduced larval survival rate, but the optimum temperature for egg hatching and larval survival was higher than that in the control. The upper temperature threshold and optimum temperature for larval development in the control were higher than that after a single extreme heat wave. Both male and female pupal weight decreased with increasing temperature, and pupal weight decreased faster in females than in males. The Cox proportional hazard model showed that when O. furnacalis developed at 25?°C, the instantaneous death risk of adults with a 3?h heat wave at the egg stage was higher than that of the control, but when O. furnacalis developed at 29?°C and 31?°C, the instantaneous death risk of adults after a heat wave was significantly lower than that of the control. Our study highlights the effect of a single heat wave on O. furnacalis eggs and the subsequent development of survival individuals.     

Is juvenile hormone involved in the maternal regulation of egg size and progeny characteristics in the desert locust?

The role of juvenile hormone (JH) in the maternal regulation of progeny characteristics was examined in the desert locust, Schistocerca gregaria. Female adults of this species are known to produce smaller but more eggs when reared in isolation than do those reared in a group. Eggs laid by isolated females develop green hatchlings typical of solitarious forms, whereas those laid by the latter produce black hatchlings typical of gregarious forms. Topical application of a juvenile hormone analog (JHA), fenoxycarb, or implantation of corpora allata (CA) taken from the migratory locust, Locusta migratoria, caused crowded S. gregaria females to deposit smaller eggs, but did not have a significant effect on the number of eggs per egg pod except at high doses of JHA. The production of smaller eggs by treated and untreated crowded females was closely associated with earlier deposition of the egg pods and shorter oviposition intervals. However, neither JHA application nor CA implantation influenced the progeny characteristics in actively reproducing aged females under crowded conditions, while untreated control females started producing smaller and more eggs upon transfer to isolated conditions. These results may suggest that JH is not directly involved in the maternal regulation of phase-dependent progeny characteristics.     

The Equilibria of Sphingolipid-Cholesterol and Sphingolipid–Sphingolipid in Monolayers at the Air–Water Interface

Monolayers of sphingomyelin (SM), ceramide (Cer) and cholesterol (Ch) and binary mixtures SM–Ch, SM–Cer and Cer–Ch were investigated at the air–water interface. SM, Cer and Ch were used in the experiment. The surface tension values of pure and mixed monolayers were used to calculate π-A isotherms. Surface tension measurements were carried out at 22 °C using a Teflon trough and a Nima 9000 tensiometer. Interactions between sphingolipid and Ch as well as sphingolipid and another sphingolipid result in significant deviations from the additivity rule. An equilibrium theory to describe the behavior of monolayer components at the air–water interface was developed in order to obtain the stability constants and Gibbs free energy values of SM–Ch, SM–Cer and Cer–Ch complexes. We considered the equilibrium between the individual components and the complex and established that sphingolipid and Ch as well as sphingolipid and another sphingolipid formed highly stable 1:1 complexes.     

The relationship between larval size and fitness in the tapeworm Schistocephalus solidus: bigger is better?

In organisms with complex life cycles, fitness often increases with body size at the transition from larva to adult. The translation of larval size into fitness, however, can depend on the source of size variation, with size, per se, not always increasing adult success. In parasitic worms, many factors influence larval growth, but little is known about the consequences of this growth variation. We examined how the size of the tapeworm Schistocephalus solidus in its copepod first intermediate host affects infection success and growth in the stickleback second host. Moreover, we assessed whether the conspicuous growth variation caused by copepod size is fitness‐relevant. Using larvae of the same age, we found that larger worms had a substantially higher infection probability and they tended to still be slightly larger after several months of growth in fish. However, big larvae from bigger copepods did not have higher fitness, suggesting that being large relative to the host, but not necessarily large in general, is important. These findings clarify some aspects of the life history strategy of S. solidus (e.g. why there is a flat ontogenetic reaction norm across copepod stages), but also raise questions (e.g. why growth costs have been hard to document). More generally, our results indicate that larval size can correlate with fitness in helminths, but that not all size variation is predictive of success in the next host.     

Exceptions to the temperature–size rule: no Lilliput Effect in end-Permian ostracods (Crustacea) from Aras Valley (northwest Iran)

The body size of marine ectotherms is often negatively correlated with ambient water temperature, as seen in many clades during the hyperthermal crisis of the end-Permian mass extinction (c. 252 Ma). However, in the case of ostracods, size changes during ancient hyperthermal events are rarely quantified. In this study, we evaluate the body size changes of ostracods in the Aras Valley section (northwest Iran) in response to the drastic warming during the end-Permian mass extinction at three taxonomic levels: class, order, species. At the assemblage level, the warming triggers a complete species turnover in the Aras Valley section, with larger, newly emerging species dominating the immediate post-extinction assemblage for a short time. Individual ostracod species and instars do not show dwarfing or a change in body size as an adaptation to the temperature stress during the end-Permian crisis. This may indicate that the ostracods in the Aras Valley section might have been exceptions to the temperature–size rule (TSR), using an adaptation mechanism that does not involve a decrease in body size. This adaptation might be similar to the accelerated development despite constant instar body sizes that can be observed in some recent experimental studies of ostracod responses to thermal stress.