Form Of Diapause Research Articles

Gene expression in diapausing rotifer eggs in response to divergent environmental predictability regimes

In unpredictable environments in which reliable cues for predicting environmental variation are lacking, a diversifying bet-hedging strategy for diapause exit is expected to evolve, whereby only a portion of diapausing forms will resume development at the first occurrence of suitable conditions. This study focused on diapause termination in the rotifer Brachionus plicatilis s.s., addressing the transcriptional profile of diapausing eggs from environments differing in the level of predictability and the relationship of such profiles with hatching patterns. RNA-Seq analyses revealed significant differences in gene expression between diapausing eggs produced in the laboratory under combinations of two contrasting selective regimes of environmental fluctuation (predictable vs unpredictable) and two different diapause conditions (passing or not passing through forced diapause). The results showed that the selective regime was more important than the diapause condition in driving differences in the transcriptome profile. Most of the differentially expressed genes were upregulated in the predictable regime and mostly associated with molecular functions involved in embryo morphological development and hatching readiness. This was in concordance with observations of earlier, higher, and more synchronous hatching in diapausing eggs produced under the predictable regime.

Trichodina diaptomi (Ciliophora: Peritrichia) from Two Calanoid Copepods from Botswana and South Africa, with Notes on its Life History

Members of the genus Trichodina are mostly found on fish, but have also been recorded from a variety of other aquatic organisms, including calanoid copepods. So far, it appears that all the trichodinid populations collected from calanoids in various parts of the world are the same species, i.e. Trichodina diaptomi Sramek-Husek, 1953. This paper reports on a new record of T. diaptomi from Metadiaptomus meridianus in a large reservoir in South Africa, as well as on a new host species, Metadiaptomus transvaalensis, and the first record of T. diaptomi from pools in an ephemeral river in northern Botswana, therefore adding a new country to the distribution of this species. We used the history of the discovery of T. diaptomi in different parts of the world and came to the conclusion that it is a cosmopolitan species, exclusively associated with copepods of the order Calanoida. Based on existing information, T. diaptomi does not appear to have a reservoir host. Against this background, we provide a discussion on the possibility that, although no dormant stage has been recorded for any trichodinid, it may be possible that T. diaptomi possesses some form of diapause and that this might be related to that of calanoid copepods.

Prevalence of kairomone-induced diapause in Daphnia magna from habitats with and without fish

The prevalence of the diapause response of the freshwater crustacean Daphnia magna to chemical cues on fish predation was evaluated in 35 clones originating from 14 European water bodies—inhabited or not inhabited by fish. Clonal lineages of experimental animals were cultured for 4 weeks in the presence or absence of water to which an extract of faeces of crucian carps (Carassius carassius), that were fed with Daphnia, was added. The proportion of females producing diapausing forms during the experimental period was used as a measure of the diapause response. A positive diapause response to fish predation cues was observed in 43% of investigated clones that originated from 71% of the water bodies tested. This indicated that the diapause response to fish scent is a common phenomenon in Daphnia magna from various locations in Europe. Surprisingly, no signs of a stronger diapause reaction to the tested cues were found in Daphnia originating from water bodies inhabited by fish compared with those from fish-free habitats.

Encystment Processes and the “Matrioshka-like Stage” in a Moss-dwelling and in a Limnic Species of Eutardigrades (Tardigrada)

Tardigrades have two forms of dormancy, namely cryptobiosis and encystment. The encystment is a form of diapause known for a limited number of species of tardigrades and still little studied. To increase the knowledge on encystment, two species of eutardigrades from Italy have been considered: the moss-dwelling Amphibolus volubilis (Eohypsibiidae), and the limnic Dactylobiotus parthenogeneticus (Murrayidae). Cysts have been collected in nature, or induced under laboratory conditions. In the latter case, it was possible to follow the several steps of encystment processes. Two different types of cyst (“type 1” and “type 2”) have been found in A. volubilis, while in D. parthenogeneticus only one type has been found. In general, the ovoid-shaped cysts are constituted by a series of cuticles surrounding the animals and resemble an onion or a Matrioshka Russian doll. In all three types of cyst, the encystment processes show both common and peculiar traits. Encystment begins with the discharging of the sclerified parts of the buccal-pharyngeal apparatus, as in the molting process, but without the loss of the old cuticle. Then, two or three new cuticles are serially synthesized, according to cyst type. In A. volubilis, the ultrastructure of these new cuticular involucra is similar to that of non-encysted animal cuticles, while in D. parthenogeneticus the ultrastructure of the new cuticular involucra differs from that of non-encysted animal cuticle. A modified buccal-pharyngeal apparatus has been observed both in “type 2” cyst of A. volubilis and in the D. parthenogeneticus cyst.

Lipids and fatty acids of the benthic marine harpacticoid copepod Heteropsyllus nunni Coull during diapause: a contrast to pelagic copepods

Many free-living copepods produce and store lipids prior to entering diapause (long-term dormancy). Heteropsyllus nunni Coull is the only marine harpacticoid copepod known to undergo any form of diapause. This study presents the first information on the types of lipids and fatty acids produced for long-term diapause in this benthic species. Sexually immature adults of H. nunni undergo diapause within a pliable self-made cyst. Prior to entering diapause (which lasts 3–4 months), they produce and store large amounts of orange lipid. The lipids apparently are utilized during diapause. Although some residual lipids remain, chiefly around the gonads, after the copepods emerge from their cysts, the lipid stores are visibly reduced. Typically, the copepods mate and produce eggs within 48 h after diapause is terminated. Light level and confocal laser scanning microscopy revealed that the lipid stores are distributed throughout the body in numerous oil droplets and not as a single oil sac, as seen in many marine calanoid copepods prior to overwintering (winter diapause). Transmission electron microscopy showed lipid spheres within the gut epithelium and large droplets of lipids stored extracellularly. Confocal laser scanning microscopy of copepods in pre-diapause, during diapause (encysted), post-diapause (recently excysted), and in reproductive condition, revealed that lipid stores are reduced following diapause, but are not totally absent. Analysis of lipid classes showed that H. nunni store predominantly wax esters/sterol esters (83% of total lipids) during diapause. The predominant lipid is most likely wax esters, as sterol esters typically are found only in small amounts in copepods. Fatty acid (FA) profiles of the copepods in diapause showed 16:0 to be most abundant followed by 16:1n-7 and 18:0; other FA occurred at concentrations <10% of total FA. Three polyunsaturated fatty acids (PUFA), 20:5n-3, 18:2n-6 and 20:4n-6, were found at concentrations <2% of total FA. These PUFA are "essential fatty acids" in H. nunni, obtained through dietary sources. The lipid classes and fatty acids present in H. nunni during diapause are compared to those of other copepods, some in a state of diapause and others not. It appears that lipid class and FA profiles are indicative of genetic makeup, type of diet or amount of food consumed prior to dormancy. Some classic paradigms of lipids and their association with copepod diapause are re-evaluated.

Insect photoperiodism and circadian clocks: models and mechanisms.

Photoperiodic clocks allow organisms to predict the coming season. In insects, the seasonal adaptive response mainly takes the form of diapause. The extensively studied photoperiodic clock in insects was primarily characterized by a "black-box" approach, resulting in numerous cybernetic models. This is in contrast with the circadian clock, which has been dissected pragmatically at the molecular level, particularly in Drosophila. Unfortunately, Drosophila melanogaster, the favorite model organism for circadian studies, does not demonstrate a pronounced seasonal response, and consequently molecular analysis has not progressed in this area. In the current article, the authors explore different ways in which identified molecular components of the circadian pacemaker may play a role in photoperiodism. Future progress in understanding the Drosophila circadian pacemaker, particularly as further output components are identified, may provide a direct link between the clock and photoperiodism. In addition, with improved molecular tools, it is now possible to turn to other insects that have a more dramatic photoperiodic response.

Food Threshold for Diapause in Daphnia under the Threat of Fish Predation

The chances of prey to survive and leave viable offspring may be determined by many environmental constraints, of which food conditions may be of key importance. When food is not limited, the high reproductive effort of a well-fed prey individual dis- playing various defensive responses may assure successful reproduction, whereas low food supplies may prevent it by limiting energy gains and expenditures on defense and procre- ation. Under low chances for survival of active forms in a local environment, production of diapausing forms of enhanced resistance to unfavorable conditions or dispersion to more favorable places may assure persistence. The laboratory batch-cultured experiments detailed here sought to test whether food concentration may influence probability of producing resting eggs by Daphnia when under chemically simulated predation pressure. In fish-free conditions, no production of resting eggs was observed with either the tested low (0.4 mg C/L) or high (1.6 mg C/L) food concentrations, whereas in fish treatments, resting eggs were produced by various proportions of females according to food concentration. With the limited food (0.4 mg C/ L) there was production of ephippial (dormant) eggs in the early broods of almost all females in the fish treatment. Where food concentrations were higher, proportions of ephippial females were progressively lower, with females postponing the formation of resting eggs until later broods. At the highest food concentration (1.6 mg C/L), only about 17% of females produced ephippia when exposed to cues. These results are considered to indicate an adaptive response of prey individuals to a simulated danger of predation in various food conditions, determining relative gains of producing active vs. dormant off- spring. It seems that D. magna may assess their chances of survival and successful reproduction in accordance with the anticipated danger of predation and food conditions, and enter diapause when the expected gains from diapause exceed those of active life. A graphical model explaining observed production of active vs. dormant offspring by D. magna under predation pressure at various food concentration is proposed.

FOOD THRESHOLD FOR DIAPAUSE INDAPHNIAUNDER THE THREAT OF FISH PREDATION

The chances of prey to survive and leave viable offspring may be determined by many environmental constraints, of which food conditions may be of key importance. When food is not limited, the high reproductive effort of a well-fed prey individual displaying various defensive responses may assure successful reproduction, whereas low food supplies may prevent it by limiting energy gains and expenditures on defense and procreation. Under low chances for survival of active forms in a local environment, production of diapausing forms of enhanced resistance to unfavorable conditions or dispersion to more favorable places may assure persistence. The laboratory batch-cultured experiments detailed here sought to test whether food concentration may influence probability of producing resting eggs by Daphnia when under chemically simulated fish predation pressure. In “fish-free” conditions, no production of resting eggs was observed with either the tested low (0.4 mg C/L) or high (1.6 mg C/L) food concentrations, whereas in “fish” treatments, resting eggs were produced by various proportions of females according to food concentration. With the limited food (0.4 mg C/L) there was production of ephippial (dormant) eggs in the early broods of almost all females in the “fish” treatment. Where food concentrations were higher, proportions of ephippial females were progressively lower, with females postponing the formation of resting eggs until later broods. At the highest food concentration (1.6 mg C/L), only about 17% of females produced ephippia when exposed to fish cues. These results are considered to indicate an adaptive response of prey individuals to a simulated danger of predation in various food conditions, determining relative gains of producing active vs. dormant offspring. It seems that D. magna may “assess” their chances of survival and successful reproduction in accordance with the anticipated danger of predation and food conditions, and enter diapause when the expected gains from diapause exceed those of active life. A graphical model explaining observed production of active vs. dormant offspring by D. magna under predation pressure at various food concentration is proposed.

Postcocooning Temperatures and Diapause in the Alfalfa Pollinator &lt;I&gt;Megachile rotundata&lt;/I&gt; (Hymenoptera: Megachilidae)

Megachile rotundata (F.), an adventive, gregarious, cavity-nesting, leaf cutting bee, is used throughout North America for the pollination of alfalfa, Medicago sativa L., seed crops. We examined the influence of various postcocooning (prewintering) temperature regimes on development, survival, emergence time, and longevity in both nondiapausing and diapausing forms of this species. Diapausing male and female M. rotundata required 27–30 d and 29–32 d, respectively, to develop from prepupae to emergence after incubation at constant 29°C, regardless of postcocooning treatments to which they were exposed. Likewise, longevity after emergence was not related to postcocooning temperatures and ranged from 5 to 6 d and 4 to 6 d for males and females, respectively. Elevated postcocooning temperatures were associated with a higher prevalence of nondiapausing individuals, those completing development from eggs through emergence as adults in the same summer season. Relevance of our results to the commercial production of alfalfa leafcutting bees is discussed.

Development and Emergence of the Alfalfa Pollinator &lt;I&gt;Megachile rotundata&lt;/I&gt; (Hymenoptera: Megachilidae)

Megachile rotundata (F.), a gregarious, cavity-nesting, leaf-cutting bee, is used throughout North America for the pollination of alfalfa, Medicago sativa L., seed crops. We examined the influence of various temperature regimes on development, survival, emergence, and longevity in both nondiapausing and diapausing forms of this species. In general, development rates increased with increasing constant temperatures used in this study (18, 22, 26, and 29°C), but the 26 and 29°C treatments were clearly superior as rearing temperatures for immatures. In diapausing individuals, a variable temperature treatment 14:27°C (8:16 h daily cycle, mean 22°C) reduced the length of prepupal and pupal development stages following incubation in the early summer when compared with individuals reared under the constant 22°C treatment. We discuss the importance of differing temperature regimes on M. rotundata development, survival, and longevity over the entire life cycle. We also discuss the importance of making a connection between immature development and sufficient wintering conditions to postdiapause development, a topic that has received much more attention in the literature.

Subject index

The response of ‘Hayward’ kiwifruit [Actinidia deliciosa (A. Chev.) C.-F. Liang et A.R. Ferguson var. deliciosa] to high-temperature controlled atmosphere (CA) treatments for control of two-spotted spider mite (Tetranychus urticae Koch) was investigated. Mean LT99 values for two-spotted spider mite inoculated onto kiwifruit and exposed to 0.4% O2, 20% CO2 (CA) at 40 °C, were 5.4 ± 0.1 h and 8.1 ± 0.3 h for the non-diapausing and diapausing forms, respectively. ‘Hayward’ kiwifruit were subjected to 40 °C for 7 or 10 h in CA (treatments identified as giving 100% mortality for non-diapausing and diapausing two-spotted spider mites, respectively) or in air. Following treatment, fruit were cooled in ambient water or ambient air, stored at 0 °C in air for eight weeks, then held at 20 °C overnight and assessed for quality. Relative to non-treated controls, no significant damage was observed with fruit subjected to 40 °C air treatments. With CA treatments, no significant damage was observed with fruit treated for 7 h followed by hydrocooling. The 7 h CA treatment without hydrocooling and 10 h CA treatments with hydrocooling showed only slight damage, while the 10 h CA without hydrocooling had moderate fruit damage. The main disorders found were vascular browning and rots. Following storage, flesh firmness of fruit treated at 40 °C in air for 10 h or in CA for 7 and 10 h, with and without hydrocooling, was lower than that of non-treated controls.

Response of ‘Hayward’ kiwifruit to high-temperature controlled atmosphere treatments for control of two-spotted spider mite (Tetranychus urticae)

Abstract The response of ‘Hayward’ kiwifruit [ Actinidia deliciosa (A. Chev.) C.-F. Liang et A.R. Ferguson var. deliciosa ] to high-temperature controlled atmosphere (CA) treatments for control of two-spotted spider mite ( Tetranychus urticae Koch) was investigated. Mean LT 99 values for two-spotted spider mite inoculated onto kiwifruit and exposed to 0.4% O 2 , 20% CO 2 (CA) at 40 °C, were 5.4 ± 0.1 h and 8.1 ± 0.3 h for the non-diapausing and diapausing forms, respectively. ‘Hayward’ kiwifruit were subjected to 40 °C for 7 or 10 h in CA (treatments identified as giving 100% mortality for non-diapausing and diapausing two-spotted spider mites, respectively) or in air. Following treatment, fruit were cooled in ambient water or ambient air, stored at 0 °C in air for eight weeks, then held at 20 °C overnight and assessed for quality. Relative to non-treated controls, no significant damage was observed with fruit subjected to 40 °C air treatments. With CA treatments, no significant damage was observed with fruit treated for 7 h followed by hydrocooling. The 7 h CA treatment without hydrocooling and 10 h CA treatments with hydrocooling showed only slight damage, while the 10 h CA without hydrocooling had moderate fruit damage. The main disorders found were vascular browning and rots. Following storage, flesh firmness of fruit treated at 40 °C in air for 10 h or in CA for 7 and 10 h, with and without hydrocooling, was lower than that of non-treated controls.

Abundance and Diversity of Adult Carabidae in Insecticide-Treated and Untreated Alfalfa Fields

Forty-nine species of Carabidae were collected from 10 alfalfa fields in Rockbridge County, Va. Species composition and diversity of carabid populations were affected by insecticides applied to control the alfalfa weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae) Harpalus pensylvanicus DeGeer (Coleoptera: Carabidae), a species known to feed on diapausing forms of the alfalfa weevil parasite, Bathyplectes curculionis (Thomson) (Hymenoptera: Ichneumonidae), and on adult alfalfa weevils was more abundant in untreated alfalfa fields than in fields treated with insecticides. A positive relationship was found between densities of adult H. pensylvanicus and damaged Bathyplectes spp. cocoons.

The life history of Dicosmoecus atripes (Hagen) (Limnephilidae: Trichoptera) in a Rocky Mountain stream of Alberta, Canada

Dicosmoecus atripes (Hagen) has a 2-year life cycle in Dyson Creek, Alberta, a second order foothills stream of the eastern Canadian Rockies. Emergence and oviposition occur from August to mid-October. The first winter is spent as first instar larvae, the second as inactive fifth (final) instars in a form of diapause. No growth was observed in overwintering first instar larvae, and a significant (P &lt; 0.05) weight loss was recorded in overwintering fifth instar larvae. Temperature seems to be the most important factor responsible for the 2-year life cycle. Annual production was estimated at 91.4 mg∙m−2∙year−1, with an annual production and biomass turnover (P/B) ratio of 4.97. Larval diet and microhabitat changed between instars. The proportion of diatoms in the diet of early instar larvae was significantly (P &lt; 0.001) greater than that of third and later instars. Early instar larvae inhabit stream margins, while larvae of third and later instars were mainly found in midstream reaches. Larvae of all instars preferred pools to riffles. Abiotic factors important in microhabitat selection seemed to differ between larval instars.

A Study of the Relationships of Diapause Phenomena and Other Life History Characters in Temperate Butterflies

A correlation coefficient matrix and two-way contingency tables reveal multiple associations among the life history characteristics of diapause, voltinism, phagism, and distribution. Diapause is at the hub of numerous intercorrelations, a position shared by voltinism. Diapause and voltinism are significantly correlated with phagism and frost-free day (FFD) numbers and range, each of which, in turn, is correlated with one or more of the other characters. When these data are treated to a PC analysis, the latent principal components of the intercorrelations become apparent. The major influence on the variations in the patterns of the characters in this study is a result of thermal habitat differences (measured by number of FFD). The niche width or resource diversity of the species (measured by breadth of the thermal range of distribution and diversity of acceptable host plants) and foodplant growth forms (the factor least implicated by simple univariate methods) are also principal components of the patterns of variation of these characters. Discernible patterns emerge with respect to thermal habitats and foodplant growth form and the stage at which diapause occurs. Species which fail to undergo any form of diapause during their life cycle are confined to warm habitats and are most frequently associated with herbaceous host plants. Associations with warmer habitats and woody host plants are apparent for species which undergo reproductive diapause as adults. The species which undergo diapause as pupae are relatively diverse with respect to these factors, but show definite clustering associated with woody host-plant species and relatively warm habitats. Species that undergo diapause as larvae are relatively diverse in relation to the three principal components, although a large number of these species are associated with colder habitats and herbaceous host-plant species. In contrast to species which undergo diapause as larvae or pupae, those species which undergo egg diapause are narrowly defined in both thermal habitat and foodplant-type and are associated with cooler habitats and woody host-plant species.

Seasonal Variation in Pheromone-Associated Behavior and Physiology of Ips pini1, 2

Both sexes of Ips pini showed marked seasonal variation in laboratory responses to male frass and to standard extracts of frass, and in their respiratory levels. The results indicate a change in the physiological state of overwintering beetles that may be a form of diapause.

Observations on Winter Survival and Diapausing Behaviour of Red Spider Mite (Tetranychus urticae) on Glasshouse Roses

SUMMARYObservations on the diapausing behaviour of red spider mite (Tetranychus urticae (Koch)) on glasshouse roses were made during the winters of 1969–70, 1970–71 and 1971–72 in a total of 11 glasshouses on six nurseries in Kent and Sussex. In one glasshouse no diapausing forms occurred but in another nearly all mites went into diapause. In the other glasshouses different proportions of diapausing and non‐diapausing forms occurred. On the three nurseries where tests were made diapausing mites were resistant to demeton‐S‐methyl. Diapausing behaviour was not apparently affected by different methods of growing roses.

Changes in the free amino acids of the haemolymph of Antheraea pernyi during induction and termination of diapause

Changes in the levels of haemolymph free amino acids were studied during the metamorphosis of a non-diapausing form and during the induction, maintenance, and termination of pupal diapause in a diapausing form of Antheraea pernyi. The levels of arginine, lysine, proline, and threonine increased gradually during metamorphosis; alanine and glutamine concentrations increased in the pupal stage before decrease during adult development, while glutamic acid decreased at the larval-pupal transformation before rising during adult development. The intervention of diapause resulted in increased levels of these amino acids (except glutamic acid) and histidine. Except for proline and histidine, the patterns of changes during metamorphosis in the levels of the affected amino acids were almost identical in both the non-diapausing and diapausing forms of the silkworm. Alanine and proline showed abnormal accumulation throughout the induction and maintenance of diapause before being depleted during post-diapause development. The increases in the levels of these amino acids appear to be secondary in nature, associated with physiological and biochemical adjustments during induction of diapause and cold-hardiness in A. pernyi.

The Culture of the Tick Rhipicephalus Sanguineus (Latreille) (Ixodidae) in the Laboratory

The tick, Rhipicephalus Sanguineus (Latr.), was cultured through 4 generations in the laboratory using techniques described in this paper. Larvae were fed on suckling rats and nymphs and adults on guinea pigs and rabbits. Older larvae took longer to feed and drop off than younger larvae. Adult ♀♀ engorged and dropped off only after ♂♂ had mated with them. At 25°C, the life cycle was completed in 86–123 days and at 29°C in 65–90 days. This relatively short life cycle, the ease with which the different stages could be fed on the common laboratory animals, and the absence of any form of diapause, make it an ideal species for screening acaricidal substances and for disease transmission experiments.