Thermal tolerance and cold hardiness strategy of the sub-Antarctic psocid <Emphasis Type="Italic">Antarctopsocus jeanneli</Emphasis> Badonnel

Despite considerable work on the upper and lower lethal limits of insects, several major taxa have received little attention. We investigated the lower and upper thermal tolerances and cold hardiness strategy of Antarctopsocus jeanneli Badonnel (Psocoptera: Elipsocidae) from sub-Antarctic Marion Island. A. jeanneli is freeze intolerant and, more specifically, moderately chill tolerant. Field fresh A. jeanneli had a mean supercooling point (SCP) of –11.1°C, whereas LT50 was –7.7°C, indicating pre-freeze mortality. A. jeanneli responds to acclimation: mean SCP increased from –15.8°C at a treatment temperature of 0 to –7.3°C at 15°C, as a result of a shift in the proportion of individuals in the high and low groups of the bimodal SCP distribution. A. jeanneli has upper thermal tolerances that are lower than those of other insect species on Marion Island, but within the range of expected microhabitat temperatures. Further study will establish whether freeze intolerance is characteristic of Psocoptera.     

Differential responses of thermal tolerance to acclimation in the sub-Antarctic rove beetle Halmaeusa atriceps

Abstract. Investigations of the responses to acclimation of upper and lower lethal limits and limits to activity in insects have focused primarily on Drosophila. In the present study, Halmaeusa atriceps (Staphylinidae) is examined for thermal tolerance responses to acclimation, and seasonal acclimatization. In summer and winter, lower lethal temperatures of adults and larvae are approximately −7.6 ± 0.03 and −11.1 ± 0.06 °C, respectively. Supercooling points (SCPs) are more variable, with winter SCPs of −5.4 ± 0.4 °C in larvae and −6.3 ± 0.8 °C in adults. The species appears to be chill susceptible in summer and moderately freeze tolerant in winter, thus showing seasonal acclimatization. Similar changes cannot be induced solely by acclimation to low temperatures in the laboratory. Upper lethal temperatures show a weaker response to acclimation. There are also significant responses to acclimation of critical thermal limits. Critical thermal minima vary between −3.6 ± 0.2 and −0.6 ± 0.2 °C in larvae, and from −4.1 ± 0.1 to −0.8 ± 0.2 °C in adults. By contrast, critical thermal maxima vary much less within adults and larvae. These findings are in keeping with the general pattern found in insects, although this species differs in several respects from others found on Marion Island.     

Colonisation of sub-Antarctic Marion Island by a non-indigenous aphid parasitoid <Emphasis Type="Italic">Aphidius matricariae</Emphasis> (Hymenoptera,Braconidae)

Over the past two decades seven non-indigenous vascular plant or arthropod species have established reproducing populations at sub-Antarctic Marion Island (46°54′S, 37°55′E). Here we record the eighth establishment, a braconid wasp Aphidius matricariae Haliday, which uses the aphid Rhopalosiphum padi (Linnaeus) as its only host on the island. Molecular markers (18S rDNA and mtCOI) support the conventional taxonomic identification and indicate that all individuals are characterized by a single haplotype. Surveys around the island show that adult abundance and the frequency of aphid parasitism are highest at Macaroni Bay on the east coast, and decline away from this region to low or zero values elsewhere on the coast. The South African research and supply vessel, the SA Agulhas, regularly anchors at Macaroni Bay, and Aphidius sp. have been collected from its galley hold. Current abundance structure, low haplotype diversity, and the operating procedures of the SA Agulhas all suggest that the parasitoid was introduced to the island by humans. Regular surveys indicate that this introduction took place between April 2001 and April 2003, the latter being the first month when this species was detected. The wasp’s establishment has significantly added to trophic complexity on the island. Low haplotype diversity suggests that propagule pressure is of little consequence for insect introductions. Rather, single or just a few individuals are probably sufficient for successful establishment.     

Acclimation effects on thermal tolerances of springtails from sub-Antarctic Marion Island: indigenous and invasive species

Collembola are abundant and functionally significant arthropods in sub-Antarctic terrestrial ecosystems, and their importance has increased as a consequence of the many invasive alien species that have been introduced to the region. It has also been predicted that current and future climate change will favour alien over indigenous species as a consequence of more favourable responses to warming in the former. It is therefore surprising that little is known about the environmental physiology of sub-Antarctic springtails and that few studies have explicitly tested the hypothesis that invasive species will outperform indigenous ones under warmer conditions. Here we present thermal tolerance data on three invasive (Pogonognathellus flavescens, Isotomurus cf. palustris, Ceratophysella denticulata) and two indigenous (Cryptopygus antarcticus, Tullbergia bisetosa) species of springtails from Marion Island, explicitly testing the idea that consistent differences exist between the indigenous and invasive species both in their absolute limits and the ways in which they respond to acclimation (at temperatures from 0 to 20 degrees C). Phenotypic plasticity is the first in a series of ways in which organisms might respond to altered environments. Using a poorly explored, but highly appropriate technique, we demonstrate that in these species the crystallization temperature (Tc) is equal to the lower lethal temperature. We also show that cooling rate (1 degree C min(-1); 0.1 degrees C min(-1); 0.5 degrees C h(-1) from 5 to -1 degrees C followed by 0.1 degrees C min(-1)) has little effect on Tc. The indigenous species typically have low Tcs (c. -20 to -13 degrees C depending on the acclimation temperature), whilst those of the invasive species tend to be higher (c. -12 to -6 degrees C) at the lower acclimation temperatures. However, Ceratophysella denticulata is an exception with a low Tc (c. -20 to -18 degrees C), and in P. flavescens acclimation to 20 degrees C results in a pronounced decline in Tc. In general, the invasive and alien species do not differ substantially in acclimation effects on Tc (with the exception of the strong response in P. flavescens). Upper lethal temperatures (ULT50) are typically higher in the invasive (33-37 degrees C) than in the indigenous (30-33 degrees C) species and the response to acclimation differs among the two groups. The indigenous species show either a weak response to acclimation or ULT50 declines with increasing acclimation temperature, whereas in the invasive species ULT50 increases with acclimation temperature. These findings support the hypothesis that many invasive species will be favoured by climate change (warming and drying) at Marion Island. Moreover, manipulative field experiments have shown abundance changes in the indigenous and invasive springtail species in the direction predicted by the physiological data.     

Phenotypic plasticity mediates climate change responses among invasive and indigenous arthropods

Synergies between global change and biological invasion have been identified as a major potential threat to global biodiversity and human welfare. The global change-type drought characteristic of many temperate terrestrial ecosystems is especially significant because it will apparently favour invasive over indigenous species, adding to the burden of conservation and compromising ecosystem service delivery. However, the nature of and mechanisms underlying this synergy remain poorly explored. Here we show that in a temperate terrestrial ecosystem, invasive and indigenous springtail species differ in the form of their phenotypic plasticity such that warmer conditions promote survival of desiccation in the invasive species and reduce it in the indigenous ones. These differences are consistent with significant declines in the densities of indigenous species and little change in those of invasive species in a manipulative field experiment that mimicked climate change trends. We suggest that it is not so much the extent of phenotypic plasticity that distinguishes climate change responses among these invasive and indigenous species, as the form that this plasticity takes. Nonetheless, this differential physiological response provides support for the idea that in temperate terrestrial systems experiencing global change-type drought, invasive species may well be at an advantage relative to their indigenous counterparts.     

Dietary choline intake is necessary to prevent systems-wide organ pathology and reduce Alzheimer's disease hallmarks

There is an urgent need to identify modifiable environmental risk factors that reduce the incidence of Alzheimer's disease (AD). The B-like vitamin choline plays key roles in body- and brain-related functions. Choline produced endogenously by the phosphatidylethanolamine N-methyltransferase protein in the liver is not sufficient for adequate physiological functions, necessitating daily dietary intake. ~90% of Americans do not reach the recommended daily intake of dietary choline. Thus, it's imperative to determine whether dietary choline deficiency increases disease outcomes. Here, we placed 3xTg-AD, a model of AD, and non-transgenic (NonTg) control mice on either a standard laboratory diet with sufficient choline (ChN; 2.0 g/kg choline bitartrate) or a choline-deficient diet (Ch-; 0.0 g/kg choline bitartrate) from 3 to 12 (early to late adulthood) months of age. A Ch- diet reduced blood plasma choline levels, increased weight, and impaired both motor function and glucose metabolism in NonTg mice, with 3xTg-AD mice showing greater deficits. Tissue analyses showed cardiac and liver pathology, elevated soluble and insoluble Amyloid-β and Thioflavin S structures, and tau hyperphosphorylation at various pathological epitopes in the hippocampus and cortex of 3xTg-AD Ch- mice. To gain mechanistic insight, we performed unbiased proteomics of hippocampal and blood plasma samples. Dietary choline deficiency altered hippocampal networks associated with microtubule function and postsynaptic membrane regulation. In plasma, dietary choline deficiency altered protein networks associated with insulin metabolism, mitochondrial function, inflammation, and fructose metabolic processing. Our data highlight that dietary choline intake is necessary to prevent systems-wide organ pathology and reduce hallmark AD pathologies.     

The RNA helicase DHX9 establishes nucleolar heterochromatin,and this activity is required for embryonic stem cell differentiation

Long non‐coding RNAs (lncRNAs) have been implicated in the regulation of chromatin conformation and epigenetic patterns. lncRNA expression levels are widely taken as an indicator for functional properties. However, the role of RNA processing in modulating distinct features of the same lncRNA is less understood. The establishment of heterochromatin at rRNA genes depends on the processing of IGS‐rRNA into pRNA, a reaction that is impaired in embryonic stem cells (ESCs) and activated only upon differentiation. The production of mature pRNA is essential since it guides the repressor TIP5 to rRNA genes, and IGS‐rRNA abolishes this process. Through screening for IGS‐rRNA‐binding proteins, we here identify the RNA helicase DHX9 as a regulator of pRNA processing. DHX9 binds to rRNA genes only upon ESC differentiation and its activity guides TIP5 to rRNA genes and establishes heterochromatin. Remarkably, ESCs depleted of DHX9 are unable to differentiate and this phenotype is reverted by the addition of pRNA, whereas providing IGS‐rRNA and pRNA mutants deficient for TIP5 binding are not sufficient. Our results reveal insights into lncRNA biogenesis during development and support a model in which the state of rRNA gene chromatin is part of the regulatory network that controls exit from pluripotency and initiation of differentiation pathways.