Changes in Energy Reserves and Gene Expression Elicited by Freezing and Supercooling in the Antarctic Midge, Belgica antarctica

Two-Fold ND5 Genes, Three-Fold Control Regions, lncRNA, and the "Missing" ATP8 Found in the Mitogenomes of Polypedates megacephalus (Rhacophridae: Polypedates)

In prior research on the mitochondrial genome (mitogenome) of Polypedates megacephalus, the one copy of ND5 gene was translocated to the control region (CR) and the ATP8 gene was not found. Gene loss is uncommon among vertebrates. However, in this study, we resequenced the mitogenomes of P. megacephalus from different regions using a "primer bridging" approach with Sanger sequencing technologies, which revealed the "missing" ATP8 gene in P. megacephalus as well as three other previously published Polypedates. The mitogenome of this species was found to contain two copies of the ND5 genes and three copies of the control regions. Furthermore, multiple tandem repeats were identified in the control regions. Notably, we observed that there was no correlation between genetic divergence and geographic distance. However, using the mitogenome, gene expression analysis was performed via RT-qPCR of liver samples and it was thus determined that COIII, ND2, ND4, and ND6 were reduced to 0.64 ± 0.24, 0.55 ± 0.34, 0.44 ± 0.21 and 0.65 ± 0.17, respectively, under low-temperature stress (8 °C) as compared with controls (p < 0.05). Remarkably, the transcript of long non-coding RNA (lncRNA) between positions 8029 and 8612 decreased significantly with exposure to low-temperature stress (8 °C). Antisense ND6 gene expression showed a downward trend, but this was not significant. These results reveal that modulations of protein-coding mitochondrial genes and lncRNAs of P. megacephalus play a crucial role in the molecular response to cold stress.

Mitochondrial metabolism and oxidative stress in the tropical cockroach under fluctuating thermal regimes

The cockroach Gromphadorhina coquereliana can survive at low temperatures under extensive periods of cold stress. To assess energy management and insect adaptation in response to cold, we measured mitochondrial activity and oxidative stress in muscle and fat body tissues from G. coquereliana under a fluctuating thermal regime (FTR; stressed at 4°C for 3 h on 3 consecutive days, with or without 24 h recovery). Compared with our earlier work showing that a single exposure to cold significantly affects mitochondrial parameters, here, repeated exposure to cold triggered an acclimatory response, resulting in unchanged mitochondrial bioenergetics. Immediately after cold exposure, we observed an increase in the overall pool of ATP and a decrease in typical antioxidant enzyme activity. We also observed decreased activity of uncoupling protein 4 in muscle mitochondria. After 24 h of recovery, we observed an increase in expression of antioxidant enzymes in muscles and the fat body and a significant increase in the expression of UCP4 and HSP70 in the latter. This indicates that processes related to energy conversion and disturbance under cold stress may trigger different protective mechanisms in these tissues, and that these mechanisms must be activated to restore insect homeostasis. The mitochondrial parameters and enzymatic assays suggest that mitochondria are not affected during FTR but oxidative stress markers are decreased, and a 24 h recovery period allows for the restoration of redox and energy homeostasis, especially in the fat body. This confirms the crucial role of the fat body in intermediary metabolism and energy management in insects and in the response to repeated thermal stress.

Thermal biology and overwintering behavior of the red sunflower seed weevil (Coleoptera: Curculionidae)

Most natural mortality of the red sunflower seed weevil, Smicronyx fulvus LeConte (Coleoptera: Curculionidae), occurs while larvae overwinter in the soil. To test the hypothesis that S. fulvus mortality is related to low temperatures, experiments were used to (i) evaluate the temperature at which larvae freeze (= supercooling point [SCP]), (ii) assess possible vertical movement between entry into the soil in fall and adult emergence in summer, and (iii) determine if realistic soil temperatures could explain patterns of overwintering mortality. Mean SCP for groups of S. fulvus larvae differed between years and months, but only ranged from -20.93 to -22.68 °C. Most overwintering larvae were found within 6 cm of the soil surface, but larvae appeared to move 1-2 cm deeper between pairs of successive sample dates (September to January, January to April). Significant larval mortality that occurred between January and April 2021 was tentatively attributed to a period in February where daily minimum soil temperatures ranged from -8 to -12 °C. When overwintering under control conditions (constant 4 °C) was interrupted with week-long exposure to -4, -8, or -12 °C in a cold bath, significant S. fulvus mortality was seen for temperatures at or below -8 °C. Combined results suggest that mortality of overwintering S. fulvus is likely caused by continuous exposure to low temperatures that may not be cold enough to freeze larvae. Additionally, the shallow overwintering by S. fulvus supports the idea that routine farm management, including tillage and herbicide incorporation, may help limit populations of this sunflower pest.

Gene family expansions in Antarctic winged midge as a strategy for adaptation to cold environments

Parochlus steinenii is the only flying insect native to Antarctica. To elucidate the molecular mechanisms underlying its adaptation to cold environments, we conducted comparative genomic analyses of P. steinenii and closely related lineages. In an analysis of gene family evolution, 68 rapidly evolving gene families, involved in the innate immune system, unfolded protein response, DNA packaging, protein folding, and unsaturated fatty acid biosynthesis were detected. Some gene families were P. steinenii-specific and showed phylogenetic instability. Acyl-CoA delta desaturase and heat shock cognate protein 70 (Hsc70) were representative gene families, showing signatures of positive selection with multiple gene duplication events. Acyl-CoA delta desaturases may play pivotal roles in membrane fluidity, and expanded Hsc70 genes may function as chaperones or thermal sensors in cold environments. These findings suggest that multiple gene family expansions contributed to the adaptation of P. steinenii to cold environments.

Belgica antarctica (Diptera: Chironomidae): A natural model organism for extreme environments

Belgica antarctica (Diptera: Chironomidae), a brachypterous midge endemic to the maritime Antarctic, was first described in 1900. Over more than a century of study, a vast amount of information has been compiled on the species (3 750 000 Google search results as of January 10, 2021), encompassing its ecology and biology, life cycle and reproduction, polytene chromosomes, physiology, biochemistry and, increasingly, omics. In 2014, B. antarctica's genome was sequenced, further boosting research. Certain developmental stages can be cultured successfully in the laboratory. Taken together, this wealth of information allows the species to be viewed as a natural model organism for studies of adaptation and function in extreme environments.

Mitochondria as a target and central hub of energy division during cold stress in insects

Temperature stress is one of the crucial factors determining geographical distribution of insect species. Most of them are active in moderate temperatures, however some are capable of surviving in extremely high as well as low temperatures, including freezing. The tolerance of cold stress is a result of various adaptation strategies, among others the mitochondria are an important player. They supply cells with the most prominent energy carrier—ATP, needed for their life processes, but also take part in many other processes like growth, aging, protection against stress injuries or cell death. Under cold stress, the mitochondria activity changes in various manner, partially to minimize the damages caused by the cold stress, partially because of the decline in mitochondrial homeostasis by chill injuries. In the response to low temperature, modifications in mitochondrial gene expression, mtDNA amount or phosphorylation efficiency can be observed. So far study also showed an increase or decrease in mitochondria number, their shape and mitochondrial membrane permeability. Some of the changes are a trigger for apoptosis induced via mitochondrial pathway, that protects the whole organism against chill injuries occurring on the cellular level. In many cases, the observed modifications are not unequivocal and depend strongly on many factors including cold acclimation, duration and severity of cold stress or environmental conditions. In the presented article, we summarize the current knowledge about insect response to cold stress focusing on the role of mitochondria in that process considering differences in results obtained in different experimental conditions, as well as depending on insect species. These differentiated observations clearly indicate that it is still much to explore.

External Morphology of Larvae of Belgica antarctica Jacobs, 1900 (Diptera, Chironomidae) Obtained from Two Locations in Maritime Antarctica

Simple Summary

The chironomid midge Belgica antarctica Jacobs is endemic to the western Antarctic Peninsula and South Shetland Islands. We provide the first detailed photomicrographic images of the fourth-instar larval head capsule and posterior parapods. We assessed variation in the morphology of larvae from two different collection locations off the coast of the western Antarctic Peninsula and compared it with that available in the literature. A number of differences were identified relating to the size of the larvae, the number of teeth on the mandibles, the number of antennal segments and the length of the antennal blade. Malformations of the mandible and mentum are reported for the first time in this species.

Abstract

The external morphology of the fourth-instar larva of the Antarctic endemic chironomid midge Belgica antarctica is described. Larvae were collected from Jougla Point (Wiencke Island) and an un-named island close to Enterprise Island, off the coast of the western Antarctic Peninsula. Light microscopy was used to examine and document photographically the structures of the mouthparts (mandible, mentum, premandible, labrum), antennae, pecten epipharyngis, clypeus, frontal apotome and posterior parapods. Measurements of the mouthparts are presented. The data obtained are compared with that available in the literature. A number of differences were identified relating to the size of the larvae, the number of teeth on the mandibles, the number of antennal segments and the length of the antennal blade. Malformations of the mandible and mentum are reported for the first time in this species. Features of larvae of taxonomic value that can be used to determine the species in larval stages are presented. These are of utility in using the larvae to reveal relationships with other species. Larvae are also important in ecological and genotoxicological studies, which require accurate species level identification.

Surviving the Antarctic winter-Life Stage Cold Tolerance and Ice Entrapment Survival in The Invasive Chironomid Midge Eretmoptera murphyi

An insect’s ability to tolerate winter conditions is a critical determinant of its success. This is true for both native and invasive species, and especially so in harsh polar environments. The midge Eretmoptera murphyi (Diptera, Chironomidae) is invasive to maritime Antarctic Signy Island, and the ability of fourth instar larvae to tolerate freezing is hypothesized to allow the species to extend its range further south. However, no detailed assessment of stress tolerance in any other life stage has yet been conducted. Here, we report that, although larvae, pupae and adults all have supercooling points (SCPs) of around −5 °C, only the larvae are freeze-tolerant, and that cold-hardiness increases with larval maturity. Eggs are freeze-avoiding and have an SCP of around −17 °C. At −3.34 °C, the CT_min activity thresholds of adults are close to their SCP of −5 °C, and they are likely chill-susceptible. Larvae could not withstand the anoxic conditions of ice entrapment or submergence in water beyond 28 d. The data obtained here indicate that the cold-tolerance characteristics of this invasive midge would permit it to colonize areas further south, including much of the western coast of the Antarctic Peninsula.