Diapause In Species Research Articles

The Diapause Lipidomes of Three Closely Related Beetle Species Reveal Mechanisms for Tolerating Energetic and Cold Stress in High-Latitude Seasonal Environments.

During winter insects face energetic stress driven by lack of food, and thermal stress due to sub-optimal and even lethal temperatures. To survive, most insects living in seasonal environments such as high latitudes, enter diapause, a deep resting stage characterized by a cessation of development, metabolic suppression and increased stress tolerance. The current study explores physiological adaptations related to diapause in three beetle species at high latitudes in Europe. From an ecological perspective, the comparison is interesting since one species (Leptinotarsa decemlineata) is an invasive pest that has recently expanded its range into northern Europe, where a retardation in range expansion is seen. By comparing its physiological toolkit to that of two closely related native beetles (Agelastica alni and Chrysolina polita) with similar overwintering ecology and collected from similar latitude, we can study if harsh winters might be constraining further expansion. Our results suggest all species suppress metabolism during diapause and build large lipid stores before diapause, which then are used sparingly. In all species diapause is associated with temporal shifts in storage and membrane lipid profiles, mostly in accordance with the homeoviscous adaptation hypothesis, stating that low temperatures necessitate acclimation responses that increase fluidity of storage lipids, allowing their enzymatic hydrolysis, and ensure integral protein functions. Overall, the two native species had similar lipidomic profiles when compared to the invasive species, but all species showed specific shifts in their lipid profiles after entering diapause. Taken together, all three species show adaptations that improve energy saving and storage and membrane lipid fluidity during overwintering diapause. While the three species differed in the specific strategies used to increase lipid viscosity, the two native beetle species showed a more canalized lipidomic response, than the recent invader. Since close relatives with similar winter ecology can have different winter ecophysiology, extrapolations among species should be done with care. Still, range expansion of the recent invader into high latitude habitats might indeed be retarded by lack of physiological tools to manage especially thermal stress during winter, but conversely species adapted to long cold winters may face these stressors as a consequence of ongoing climate warming.

Diapause in a tropical oil-collecting bee: molecular basis unveiled by RNA-Seq

BackgroundDiapause is a natural phenomenon characterized by an arrest in development that ensures the survival of organisms under extreme environmental conditions. The process has been well documented in arthropods. However, its molecular basis has been mainly studied in species from temperate zones, leaving a knowledge gap of this phenomenon in tropical species. In the present study, the Neotropical and solitary bee Tetrapedia diversipes was employed as a model for investigating diapause in species from tropical zones. Being a bivoltine insect, Tetrapedia diversipes produce two generations of offspring per year. The first generation, normally born during the wet season, develops faster than individuals from the second generation, born after the dry season. Furthermore, it has been shown that the development of the progeny, of the second generation, is halted at the 5th larval instar, and remains in larval diapause during the dry season. Towards the goal of gaining a better understanding of the diapause phenomenon we compared the global gene expression pattern, in larvae, from both reproductive generations and during diapause. The results demonstrate that there are similarities in the observed gene expression patterns to those already described for temperate climate models, and also identify diapause-related genes that have not been previously reported in the literature.ResultsThe RNA-Seq analysis identified 2275 differentially expressed transcripts, of which 1167 were annotated. Of these genes, during diapause, 352 were upregulated and 815 were downregulated. According to their biological functions, these genes were categorized into the following groups: cellular detoxification, cytoskeleton, cuticle, sterol and lipid metabolism, cell cycle, heat shock proteins, immune response, circadian clock, and epigenetic control.ConclusionMany of the identified genes have already been described as being related to diapause; however, new genes were discovered, for the first time, in this study. Among those, we highlight: Niemann-Pick type C1, NPC2 and Acyl-CoA binding protein homolog (all involved in ecdysteroid synthesis); RhoBTB2 and SASH1 (associated with cell cycle regulation) and Histone acetyltransferase KAT7 (related to epigenetic transcriptional regulation). The results presented here add important findings to the understanding of diapause in tropical species, thus increasing the comprehension of diapause-related molecular mechanisms.

Adult reproductive diapause in Drosophila suzukii females

Drosophila suzukii (Diptera: Drosophilidae) is an emerging pest of soft fruits, but in this species diapause has not been thoroughly explored. We examined the effects of different temperatures and photoperiods on diapause induction and termination under laboratory conditions. There was variation in the ovarian development and oviposition rate under different photoperiods at 10 ± 1 °C, and the percentage of adults with immature ovaries was higher during the short photoperiod (8L:16D) than other photoperiods at 10 ± 1 °C. Adults were most sensitive to photoperiod within 3 days of eclosion. The optimal combination of photoperiod and temperature for diapause termination was a long photoperiod (16L:8D) at 25 ± 1 °C. The supercooling point was significantly reduced in reproductive diapause females, and trehalase, pyruvate kinase, sorbitol dehydrogenase, hexokinase and phosphofructokinase enzyme activities were significantly reduced (36.46, 57.85, 32.64, 54.68 and 24.59 %, respectively); glycogen and triglyceride levels were significantly increased (42.17 and 120.36 %). We conclude that D. suzukii is typical of short-day diapause species within a certain photoperiod range. This information might contribute to a more fundamental understanding of adult reproductive diapause for this important pest.

Drosophila americana Diapausing Females Show Features Typical of Young Flies.

Diapause is a period of arrested development which is controlled physiologically, preprogrammed environmentally and characterized by metabolic depression that can occur during any stage of insect development. Nevertheless, in the genus Drosophila, diapause is almost always associated with the cessation of ovarian development and reproductive activity in adult females. In this work, we show that, in D. americana (a temperate species of the virilis group), diapause is a genetically determined delay in ovarian development that is triggered by temperature and/or photoperiod. Moreover, we show that in this species diapause incidence increases with latitude, ranging from 13% in the southernmost to 91% in the northernmost range of the distribution. When exposed to diapause inducing conditions, both diapausing and non-diapausing females show a 10% increase in lifespan, that is further increased by 18.6% in diapausing females, although senescence is far from being negligible. ActinD1 expression levels suggest that diapausing females are biologically much younger than their chronological age, and that the fly as a whole, rather than the ovarian development alone, which is phenotypically more evident, is delayed by diapause. Therefore, diapause candidate genes that show expression levels that are compatible with flies younger than their chronological age may not necessarily play a role in reproductive diapause and in adaptation to seasonally varying environmental conditions.

Ecological and evolutionary aspects of photothermal regulation of diapause in trichogrammatidae

Facultative winter diapause in species of the genus Trichogramma Westw. (Hymenoptera, Trichogrammatidae) is regulated, like in the majority of other insects, by photoperiod and temperature. In trichograms, prepupae are diapausing, but sensitivity to length of the light day and to temperature as to the cue factors inducing diapause is characteristic of all stages of development from embryo to the egg-laying female. The action of the cue factors affects not only the current, but also the subsequent generations. Under natural conditions the photothermal regulation provides the timely induction of the diapause coordinated both with astronomical year time (the photoperiodic reaction) and with specificity of this season (the temperature reaction). In the course of special experiments in trichograms there are also revealed the "rudimentary" reactions that have lost their adaptive role. Results of these studies prove once more that specificity of photoperiodic and temperature reactions inducing diapause and their relative importance and confinement to certain sensitive stages are determined not only by peculiarities of ecology of different insect taxa, but also by the course of their previous evolution.

Changes in gene expression linked with adult reproductive diapause in a northern malt fly species: a candidate gene microarray study

BackgroundInsect diapause is an important biological process which involves many life-history parameters important for survival and reproductive fitness at both individual and population level. Drosophila montana, a species of D. virilis group, has a profound photoperiodic reproductive diapause that enables the adult flies to survive through the harsh winter conditions of high latitudes and altitudes. We created a custom-made microarray for D. montana with 101 genes known to affect traits important in diapause, photoperiodism, reproductive behaviour, circadian clock and stress tolerance in model Drosophila species. This array gave us a chance to filter out genes showing expression changes during photoperiodic reproductive diapause in a species adapted to live in northern latitudes with high seasonal changes in environmental conditions.ResultsComparisons among diapausing, reproducing and young D. montana females revealed expression changes in 24 genes on microarray; for example in comparison between diapausing and reproducing females one gene (Drosophila cold acclimation gene, Dca) showed up-regulation and 15 genes showed down-regulation in diapausing females. Down-regulation of seven of these genes was specific to diapause state while in five genes the expression changes were linked with the age of the females rather than with their reproductive status. Also, qRT-PCR experiments confirmed couch potato (cpo) gene to be involved in diapause of D. montana.ConclusionsA candidate gene microarray proved to offer a practical and cost-effective way to trace genes that are likely to play an important role in photoperiodic reproductive diapause and further in adaptation to seasonally varying environmental conditions. The present study revealed two genes, Dca and cpo, whose role in photoperiodic diapause in D. montana is worth of studying in more details. Also, further studies using the candidate gene microarray with more specific experimental designs and target tissues may reveal additional genes with more restricted expression patterns.

Up-regulation of heat shock proteins is essential for cold survival during insect diapause

Diapause, the dormancy common to overwintering insects, evokes a unique pattern of gene expression. In the flesh fly, most, but not all, of the fly's heat shock proteins (Hsps) are up-regulated. The diapause up-regulated Hsps include two members of the Hsp70 family, one member of the Hsp60 family (TCP-1), at least four members of the small Hsp family, and a small Hsp pseudogene. Expression of an Hsp70 cognate, Hsc70, is uninfluenced by diapause, and Hsp90 is actually down-regulated during diapause, thus diapause differs from common stress responses that elicit synchronous up-regulation of all Hsps. Up-regulation of the Hsps begins at the onset of diapause, persists throughout the overwintering period, and ceases within hours after the fly receives the signal to reinitiate development. The up-regulation of Hsps appears to be common to diapause in species representing diverse insect orders including Diptera, Lepidoptera, Coleoptera, and Hymenoptera as well as in diapauses that occur in different developmental stages (embryo, larva, pupa, adult). Suppressing expression of Hsp23 and Hsp70 in flies by using RNAi did not alter the decision to enter diapause or the duration of diapause, but it had a profound effect on the pupa's ability to survive low temperatures. We thus propose that up-regulation of Hsps during diapause is a major factor contributing to cold-hardiness of overwintering insects.

Predictions of summer diapause in the redlegged earth mite, Halotydeus destructor (Acari: Penthaleidae), in Australia

A prediction for the onset of a summer diapause in the eggs of the redlegged earth mite, Halotydeus destructor, was developed for Australia. In this species diapause eggs pass the summer in the cadavers of adult female mites. Adult female mites were collected for several weeks from pastures in spring at 18 sites in south-western Australia and dissected to determine the timing of the production of diapause eggs. Some sites were sampled for several years between 1990 and 1997. A model was developed to predict the time for onset of diapause. The week at which 90% of eggs were in diapause was predicted best by daylength (80.1% of the variability), then by duration of the long-term plant growing season (10.4%, of variability), leaving 9.5% due to other factors. A single chemical spray in spring 2 weeks before the production of 90% diapause eggs resulted in 99% fewer mites present in autumn 7–8 months later at three sites. The timing of the spring spray was the factor leading to successful control. This model was tested at 17 sites across the whole geographical distribution of the redlegged earth mite in Australia between 1998 and 2001. The observed week of 90% diapause was within 1 week of the predicted week on 81% of occasions, and 2 weeks earlier on 15% of occasions. A database was created for the predicted date of onset of 90% diapause for the whole distribution of the redlegged earth mite in southern Australia on a 10 km 2 grid. Australian farmers are using this for timing a spring spray to control mites in the following autumn.

Insect pests and postharvest problems in the tropics

Tropical environments provide optimum conditions for insect growth and multiplication in the ideal medium of food stored by humans. Some insects begin infestation in the field and continue attack in storage. Other species diapause and remain in cracks and crevices in granaries or feed on grain residues while awaiting the new harvest. Since most of the tropical produce is for subsistence, the losses resulting from severe insect attack contribute to malnutrition and famine. In central stores and warehouses commodity management is poor and large amounts are lost to insects. In countries where heavy insecticide and fumigant pressure is maintained to preserve food stocks, insects rapidly build up resistance. The solutions for the future are to reduce dependence on pesticides and utilize in an integrated way the cultural, biological and physical techniques developed in recent years for safer storage and the successful preservation of strategic reserves for food security.

Dormancy in tropical insects.

Diapause is frequently viewed as a developmental strategy unique to insects of the temperate zone. My primary objective in this review is to dispell this myth by presenting evidence for the widespread existence of diapause among tropical species. Although the environmental regulators are still poorly defined, I attempt to identify factors implicated in regulation and some of the special problems of diapause in the tropics. For purposes of this review I restrict my discussion to insects living within 200 of the equator, but clearly this is an arbitrary line. Winter in temperate zones presents a conspicuous obstacle, and a wealth of studies examine diapause as an adaptation to circumvent this inimical period. Reviews have focused on diapause physiology (72), endocrinology (19,31, 129), ecology (22, 24, 25, 115, 116), genetics (55), evolution (12, 33), thermoperiodism (6), clock mechanisms (5, 102), and cold tolerance (37, 101). Masaki's review on summer diapause (76) is especially relevant to this review because the warm summer of the temperate zone is much akin to the tropical environment. Although there are many definitions of diapause, I use the term to refer to an arrest in development that occurs at a specific stage. Egg, larval, pupal, and adult diapauses are all well documented, but for most species diapause can be expressed in only one stage of the life cycle. Diapause is programmed far in advance of the actual developmental arrest and thus differs from a simple quiescence that is an immediate response to adverse conditions. For some tropical species the information available is too sketchy to allow adequate

Population structure, life histories and abundance of copepods in Tjeukemeer, the Netherlands

SUMMARY. The copepod zooplankton of Tjeukemeer was sampled at weekly intervals for 3 years (1969–1971), and ten species were recorded. Five species contributed more than 99% of all individuals collected. Acanthocyclops robustus is the most abundant species (66%), followed by Mesocyclops leuckarti (13%), Cyclops vicinus (11%), Eurytemora affinis (9%) and Diacyclops bicuspidatus (1%).The ecology of the A. robustus population in Tjeukemeer differs from other A. robustus populations in that it dominates the open water zone. This is an additional argument for a taxonomic revision of the A. vernalis‐robustus complex.Seasonal periodicity in abundance of each species was very similar in 3 successive years.All cyclopoid species went into diapause, A. robustus and M. leuckarti during winter, D. bicuspidatus and C. v. vicinus during summer. Most species diapause in a particular copepodite stage.The seasonal variation in the population structure, the fecundity and the sex ratio are described. Both population structure and sex ratio were influenced by diapause and size‐dependent mortality. The fecundity was more influenced by the water temperature and the age structure of the female population than by food situation or size of the females.

Factors Governing the Induction of Diapause in the Oriental Fruit Moth1

Diapause is a physiological state of arrested development which enables an organism to survive more easily a period of unfavorable conditions. Once an organism has entered diapause it usually has to remain in that state for a certain period, regardless of the conditions of the environment. In some species diapause is broken by exposure to particular conditions, notably cold. A few species may remain in diapause more than one year.