The genome sequence of a spider mite,Tetranychustruncatus, provides insights into interspecific host rangevariation and the genetic basis of adaptation to a low-qualityhost plant

The phytophagous miteTetranychus truncatusis a serious pest in East Asiabut has a relatively narrower host range than the pest miteTetranychus urticae,which canfeed on over 1200 plant species.Here,we generated a high-quality chromosomal levelgenome ofT.truncatusand compared it with that ofT.urticae,with an emphasis on thegenes related to detoxification and chemoreception,to explore the genomic basis under-lying the evolution of host range.We also conducted population genetics analyses(in 86females from 10 populations)and host transfer experiments(in 4 populations)to investi-gate transcription changes following transfer to a low-quality host(Solanum melongena,eggplant),and we established possible connections between fitness on eggplant and genesrelated to detoxification and chemoreception.We found thatT.truncatushas fewer genesrelated to detoxification,transport,and chemoreception thanT.urticae,with a particularlystrong reduction in gustatory receptor(GR)genes.We also found widespread transcrip-tional variation amongT.truncatuspopulations,which varied in fitness on eggplant.Wecharacterized selection on detoxification-related genes throughωvalues and found a nega-tive correlation between expression levels andωvalues.Based on the transcription results,as well as the fitness and genetic differences among populations,we identified genes po-tentially involved in adaptation to eggplant inT.truncatus.Our work provides a genomicresource for this pest mite and new insights into mechanisms underlying the adaptation ofherbivorous mites to host plants.

Summer egg diapause in a matchstick grasshopper synchronizes the life cycle and buffers thermal extremes

The phenological response is among the most important traits affecting a species’sensitivity to climate.In insects,strongly seasonal environments often select for a univoltine life cycle such that one seasonal extreme is avoided as an inactive stage.Through understanding the underlying mechanisms for univoltinism,and the consequences of its failure,we can better predict insect responses to climate change.Here we combine empirical data and simulation studies to investigate the consequences of an unusual diapause mechanism in a parthenogenetic matchstick grasshopper,Warramaba virgo,from arid southern Australia.Our field body temperature measurements indicate that this species is a thermoconformer and our laboratory studies of the thermal response of feeding rate imply strong constraints on winter activity.However,the species exhibits no obligate winter diapause,and eggs can develop in 1 month under constant temperatures approximating the mean soil temperature at the time of oviposition(summer).We show that diurnal temperature cycles exceeding a peak of 36℃ inhibit egg development in summer,and that this is sufficient to prevent autumnal hatching of eggs.Development is also strongly retarded below 24℃.Microclimate-driven simulation studies of egg development show that these thermal responses provide robust maintenance of a univoltine life cycle,thereby resulting in survival of heat stress as an egg(due to limited developmental state)and avoidance of cold stress as a nymph and adult(due to overwintering in the soil as an egg).

Comparative studies of critical physiological limits and vulnerability to environmental extremes in small ectotherms:How much environmental control is needed?

Researchers and practitioners are increasingly using comparative assessments of critical thermal and physiological limits to assess the relative vulnerability of ectothermic species to extreme thermal and aridity conditions occurring under climate change.In most assessments of vulnerability,critical limits are compared across taxa exposed to different environmental and developmental conditions.However,many aspects of vulnerability should ideally be compared when species are exposed to the same environmental conditions,allowing a partitioning of sources of variation such as used in quantitative genetics.This is particularly important when assessing the importance of different types of plasticity to critical limits,using phylogenetic analyses to test for evolutionary constraints,isolating genetic variants that contribute to limits,characterizing evolutionary interactions among traits limiting adaptive responses,and when assessing the role of cross generation effects.However,vulnerability assessments based on critical thermal/physiological limits also need to take place within a context that is relevant to field conditions,which is not easily provided under controlled environmental conditions where behavior,microhabitat,stress exposure rates and other factors will differ from field conditions.There are ways of reconciling these requirements,such as by taking organisms from controlled environments and then testing their performance under field conditions(or vice versa).While comparisons under controlled environments are challenging for many taxa,assessments of critical thermal limits and vulnerability will always be incomplete unless environmental effects within and across generations are considered,and where the ecological relevance of assays measuring critical limits can be established.

Characterization of the first Wolbachia from the genus Scaptodrosophila,a male-killer from the rainforest species S.claytoni

The Scaptodrosophila genus represents a large group of drosophilids with a worldwide distribution and a predominance of species in Australia,but there is little information on the presence and impacts of Wolbachia endosymbionts in this group.Here we describe the first Wolbachia infection from this group,wClay isolated from Scaptodrosophila claytoni(van Klinken),a species from the east coast of Australia.The infection is polymorphic in natural populations,occurring at a frequency of around 6%–10%.wClay causes male killing,producing female-biased lines;most lines showed 100%male killing,though in 1 line it was<80%.The lines need to be maintained through the introduction of males unless the infection is removed by tetracycline treatment.wClay is transmitted at a high fidelity(98.6%)through the maternal lineage and has been stable in 2 laboratory lines across 24 generations,suggesting it is likely to persist in populations.The infection has not been previously described but is closely related to the male-killing Wolbachia recently described from Drosophila pandora based on multilocus sequence typing and the wsp gene.Male-killing Wolbachia are likely to be common in drosophilids but remain difficult to detect because the infections can often be at a low frequency.

Mortality of Australian alpine grasses (Poa spp.) after drought: species differences and ecological patterns

Aims Australian alpine ecosystems currently experience high precipitation in the snow-free season,but they are predicted to experience drier conditions under climate change.We observed high mortality of the dominant alpine grasses following drought in 2007.Our aims were as follows:to test the involvement of plant-available water(PAW)and other environmental variables in grass mortality in the field;to detect possible species differences in drought response and to link soil moisture to precipitation using soil properties and climate data.Methods The dominant tussock grasses of the Australian alpine zone,Poa hothamensis var.hothamensis N.G.Walsh,Poa hiemata Vickery and Poa phillipsiana Vickery(Poaceae),all exhibited mortality following drought in the Bogong High Plains,Victoria,Australia in 2007.PAW was calculated using soil water potential measurements,and past drought occurrence was modelled using climate data.We then tested the effects of PAW and soil depth on grass survival both at a large spatial scale spanning the elevational range of the alpine zone and at a smaller scale.Poa hothamensis and P.phillipsiana were compared in a common-garden experiment to test drought tolerance.Important Findings Poa hothamensis survival was predicted by dry-season PAW at the small spatial scale;at the large scale,soil depth and elevation were more important predictors of P.hothamensis survival,but dry-season PAW predicted P.hiemata survival.Common-garden experiments supported field observations that P.hothamensis is more droughtsensitive than is P.phillipsiana.We also present a simple polynomial relationship between rainfall and field soil moisture,which predicts that the alpine soils dry below wilting point several times a year.We suggest the timing of long rain-free periods may be more important than their duration.