Elemental stoichiometry and insect chill tolerance: evolved and plastic changes in organismal Na+ and K+ content in Drosophila.

Acclimation and evolutionary adaptation can produce phenotypic changes that allow organisms to cope with challenges. Determining the relative contributions and the underlying mechanisms driving phenotypic shifts from acclimation and adaptation is of central importance to understanding animal responses to change. Rates of evolution have traditionally been considered slow relative to ecological processes that shape biodiversity.

Measuring insect osmoregulation in vitro: A reference guide.

Osmoregulation is influenced by a wide variety of biotic and abiotic variables, and maintenance of systemic osmoregulatory homeostasis is critical to insect fitness. Because insects are so small, accurately quantifying renal organ function is technically challenging, and often requires specialized equipment. On top of this, nearly a century of toiling in the laboratory has led to a wide and still growing variety of methods that can be difficult for novice researchers to disentangle.

Dietary potassium and cold acclimation additively increase cold tolerance in Drosophila melanogaster.

In the cold, chill susceptible insects lose the ability to regulate ionic and osmotic gradients. This leads to hemolymph hyperkalemia that drives a debilitating loss of cell membrane polarization, triggering cell death pathways and causing organismal injury. Biotic and abiotic factors can modulate insect cold tolerance by impacting the ability to mitigate or prevent this cascade of events.

The freeze-avoiding mountain pine beetle (Dendroctonus ponderosae) survives prolonged exposure to stressful cold by mitigating ionoregulatory collapse.

Insect performance is linked to environmental temperature, and surviving through winter represents a key challenge for temperate, alpine and polar species. To overwinter, insects have adapted a range of strategies to become truly cold hardy. However, although the mechanisms underlying the ability to avoid or tolerate freezing have been well studied, little attention has been given to the challenge of maintaining ion homeostasis at frigid temperatures in these species, despite this limiting cold tolerance for insects susceptible to mild chilling.

A neurophysiological limit and its biogeographic correlations: cold-induced spreading depolarization in tropical butterflies.

The physiology of insects is directly influenced by environmental temperature, and thermal tolerance is therefore intrinsically linked to their thermal niche and distribution. Understanding the mechanisms that limit insect thermal tolerance is crucial to predicting biogeography and range shifts. Recent studies on locusts and flies suggest that the critical thermal minimum (CTmin) follows a loss of CNS function via a spreading depolarization.

A cold and quiet brain: mechanisms of insect CNS arrest at low temperatures.

Exposure to cold causes insects to enter a chill coma at species-specific temperatures and such temperature sensitivity contributes to geographic distribution and phenology. Coma results from abrupt spreading depolarization (SD) of neural tissue in the integrative centers of the central nervous system (CNS). SD abolishes neuronal signaling and the operation of neural circuits, like an off switch for the CNS.

Plasticity in Na+/K+-ATPase thermal kinetics drives variation in the temperature of cold-induced neural shutdown of adult Drosophila melanogaster.

Most insects can acclimate to changes in their thermal environment and counteract temperature effects on neuromuscular function. At the critical thermal minimum, a spreading depolarization (SD) event silences central neurons, but the temperature at which this event occurs can be altered through acclimation. SD is triggered by an inability to maintain ion homeostasis in the extracellular space in the brain and is characterized by a rapid surge in extracellular K+ concentration, implicating ion pump and channel function.

Acclimation, duration and intensity of cold exposure determine the rate of cold stress accumulation and mortality in Drosophila suzukii.

The spotted wing drosophila (SWD), Drosophila suzukii, is a major invasive fruit pest. There is strong consensus that low temperature is among the main drivers of SWD population distribution, and the invasion success of SWD is also linked to its thermal plasticity. Most studies on ectotherm cold tolerance focus on exposure to a single stressful temperature but here we investigated how cold stress intensity affected survival duration across a broad range of low temperatures (-7 to +3 °C).

Thermal acclimation alters Na/K-ATPase activity in a tissue-specific manner in Drosophila melanogaster.

Insects, like the model species Drosophila melanogaster, lose neuromuscular function and enter a state of paralysis (chill coma) at a population- and species-specific low temperature threshold that is decreased by cold acclimation. Entry into this coma is related to a spreading depolarization in the central nervous system, while recovery involves restoration of electrochemical gradients across muscle cell membranes. The Na/K-ATPase helps maintain ion balance and membrane potential in both the brain and hemolymph (surrounding muscles), and changes in thermal tolerance traits have therefore been hypothesized to be closely linked to variation in the expression and/or activity of this pump in multiple tissues.

Osmoregulatory capacity at low temperature is critical for insect cold tolerance.

At low temperature many insects lose extracellular ion homeostasis and the capacity to mitigate homeostatic imbalance determines their cold tolerance. Extracellular homeostasis is ensured by the osmoregulatory organs and recent research has emphasized key roles for the Malpighian tubules and hindgut in modulating insect cold tolerance. Here, we review the effects of low temperature on transport capacity of osmoregulatory organs and outline physiological processes leading from cold exposure to disruption of ion homeostasis and cold-injury in insects.

Hyperkalaemia, not apoptosis, accurately predicts insect chilling injury.

There is a growing appreciation that insect distribution and abundance are associated with the limits of thermal tolerance, but the physiology underlying thermal tolerance remains poorly understood. Many insects, like the migratory locust (), suffer a loss of ion and water balance leading to hyperkalaemia (high extracellular [K]) in the cold that indirectly causes cell death. Cells can die in several ways under stress, and how they die is of critical importance to identifying and understanding the nature of thermal adaptation.

Maintenance of hindgut reabsorption during cold exposure is a key adaptation for cold tolerance.

Maintaining extracellular osmotic and ionic homeostasis is crucial for organismal function. In insects, hemolymph volume and ion content is regulated by the secretory Malpighian tubules and reabsorptive hindgut. When exposed to stressful cold, homeostasis is gradually disrupted, characterized by a debilitating increase in extracellular K concentration (hyperkalemia).

The central nervous system and muscular system play different roles for chill coma onset and recovery in insects.

When insects are cooled, they initially lose their ability to perform coordinated movements at their critical thermal minima (CT). At a slightly lower temperature, they enter a state of complete paralysis (chill coma onset temperature - CCO) and if they are returned to permissive temperatures they regain function after a recovery period which is termed chill coma recovery time (CCRT). These three phenotypes (CT, CCO, and CCRT) are all popular measures of insect cold tolerance and it is therefore important to characterize the physiological processes that are responsible for these phenotypes.

Fluctuating thermal regime preserves physiological homeostasis and reproductive capacity in Drosophila suzukii.

Drosophila suzukii, an invasive species recently introduced in Europe, lays eggs in thin-skinned fruits and causes huge financial losses to fruit growers. One potential way to control this pest is the sterile insect technique (SIT) which demands a large stock of reproductive females to produce millions of sterile males to be released on demand. Unfortunately, Drosophila stocks age quickly, show declining fecundity when maintained at warm temperatures and conversely, they die from chill injury if they are maintained at constant low temperature.

Cold exposure causes cell death by depolarization-mediated Ca overload in a chill-susceptible insect.

Cold tolerance of insects is arguably among the most important traits defining their geographical distribution. Even so, very little is known regarding the causes of cold injury in this species-rich group. In many insects it has been observed that cold injury coincides with a cellular depolarization caused by hypothermia and hyperkalemia that develop during chronic cold exposure.

Central nervous system shutdown underlies acute cold tolerance in tropical and temperate species.

When cooled, insects first lose their ability to perform coordinated movements (CT) after which they enter chill coma (chill coma onset, CCO). Both these behaviours are popular measures of cold tolerance that correlate remarkably well with species distribution. To identify and understand the neuromuscular impairment that causes CT and CCO we used inter- and intraspecific model systems of species that have varying cold tolerance as a consequence of adaptation or cold acclimation.

Paralytic hypo-energetic state facilitates anoxia tolerance despite ionic imbalance in adult .

Oxygen limitation plays a key role in many pathologies; yet, we still lack a fundamental understanding of the mechanisms responsible for variation in anoxia tolerance. Most vertebrate studies suggest that anoxia tolerance involves the ability to maintain cellular ATP despite the loss of aerobic metabolism. However, insects such as adult are able to survive long periods of anoxia (LT: ∼8 h) in a hypo-energetic state characterized by low [ATP].

Cold tolerance of species is tightly linked to the epithelial K transport capacity of the Malpighian tubules and rectal pads.

Insect chill tolerance is strongly associated with the ability to maintain ion and water homeostasis during cold exposure. Maintenance of K balance is particularly important due to its role in setting the cell membrane potential that is involved in many aspects of cellular function and viability. In most insects, K balance is maintained through secretion at the Malpighian tubules, which balances reabsorption from the hindgut and passive leak arising from the gut lumen.

Physiological correlates of chill susceptibility in Lepidoptera.

The majority of insects enter a state of reversible coma if temperature is lowered sufficiently. If the cold treatment is not too severe these insects recover gradually when returned to benign temperatures in a time-dependent manner that often depends on the duration and intensity of the cold exposure. Previous studies have associated these phenotypes to changes in membrane potential (V) and ion balance, and especially hemolymph [K] is known to be of importance for the recovery time.

Cold acclimation improves chill tolerance in the migratory locust through preservation of ion balance and membrane potential.

Most insects have the ability to alter their cold tolerance in response to temporal temperature fluctuations, and recent studies have shown that insect cold tolerance is closely tied to the ability to maintain transmembrane ion gradients that are important for the maintenance of cell membrane potential (V). Several studies have therefore suggested a link between preservation of V and cellular survival after cold stress, but none has measured V in this context. We tested this hypothesis by acclimating locusts (Locusta migratoria) to high (31°C) and low temperature (11°C) for 4 days before exposing them to cold stress (0°C) for up to 48 h and subsequently measuring ion balance, cell survival, muscle V, and whole animal performance.

Ambient CO2, fish behaviour and altered GABAergic neurotransmission: exploring the mechanism of CO2-altered behaviour by taking a hypercapnia dweller down to low CO2 levels.

Recent studies suggest that projected rises of aquatic CO2 levels cause acid-base regulatory responses in fishes that lead to altered GABAergic neurotransmission and disrupted behaviour, threatening fitness and population survival. It is thought that changes in Cl(-) and HCO3 (-) gradients across neural membranes interfere with the function of GABA-gated anion channels (GABAA receptors). So far, such alterations have been revealed experimentally by exposing species living in low-CO2 environments, like many oceanic habitats, to high levels of CO2 (hypercapnia).

Lymphotropism and host responses during acute wild-type canine distemper virus infections in a highly susceptible natural host.

The mechanisms behind the in vivo virulence of immunosuppressive wild-type morbillivirus infections are still not fully understood. To investigate lymphotropism and host responses, we have selected the natural host model of canine distemper virus (CDV) infection in mink. This model displays multisystemic infection, similar to measles virus and rinderpest virus infections in their susceptible natural hosts.

Immunization with plasmid DNA encoding the hemagglutinin and the nucleoprotein confers robust protection against a lethal canine distemper virus challenge.

We have investigated the protective effect of immunization of a highly susceptible natural host of canine distemper virus (CDV) with DNA plasmids encoding the viral nucleoprotein (N) and hemagglutinin (H). The combined intradermal and intramuscular routes of immunization elicited high virus-neutralizing serum antibody titres in mink (Mustela vison). To mimic natural exposure, we also conducted challenge infection by horizontal transmission from infected contact animals.

Changes in the receptorbinding haemagglutinin protein of wild-type morbilliviruses are not required for adaptation to Vero cells.

We examined the consequences of isolation and adaptation to Vero cells for the receptorbinding haemagglutinin (H) gene of four syncytia-forming isolates of canine distemper virus (CDV) and of a dolphin morbillivirus isolate. A Vero-adapted CDV isolate exhibited biased hypermutation, since 11 out of 12 nucleotide differences to other isolates from the same epidemic were U-C transitions. Most of these transitions appeared to have taken place during in vitro cultivation.