Larval Diapause Research Articles

Has the currently warming climate affected populations of the mountain ringlet butterfly, Erebia epiphron (Lepidoptera: Nymphalidae), in low-elevation mountains?

Climate change scenarios predict losses of cold-adapted species from insular locations, such as middle high mountains at temperate latitudes, where alpine habitats extend for a few hundred meters above the timberline. However, there are very few studies following the fates of such species in the currently warming climate. We compared transect monitoring data on an alpine butterfly, Erebia epiphron (Nymphalidae: Satyrinae) from summit elevations of two such alpine islands (above 1300 m) in the Jesenik Mts and Krkonose Mts, Czech Republic. We asked if population density, relative total population abundance and phenology recorded in the late 1990s (past) differs that recorded early in 2010s (present) and if the patterns are consistent in the two areas, which are separated by 150 km. We found that butterfly numbers recorded per transect walk decreased between the past and the present, but relative population abundances remained unchanged. This contradictory observation is due to an extension in the adult flight period, which currently begins ca 10 days earlier and lasts for longer, resulting in the same total abundances with less prominent peaks in abundance. We interpret this development as desynchronization of annual cohort development, which might be caused by milder winters with less predictable snow cover and more variable timing of larval diapause termination. Although both the Jesenik and Krkonose populations of E. epiphron are abundant enough to withstand such desynchronization, decreased synchronicity of annual cohort development may be detrimental for innumerable small populations of relic species in mountains across the globe.

Diapause is associated with a change in the polarity of secretion of insulin-like peptides.

The insulin/IGF-1 signalling (IIS) pathway plays an important role in the regulation of larval diapause, the long-lived growth arrest state called dauer arrest, in Caenorhabditis elegans. In this nematode, 40 insulin-like peptides (ILPs) have been identified as putative ligands of the IIS pathway; however, it remains unknown how ILPs modulate larval diapause. Here we show that the secretory polarity of INS-35 and INS-7, which suppress larval diapause, is changed in the intestinal epithelial cells at larval diapause. These ILPs are secreted from the intestine into the body cavity during larval stages. In contrast, they are secreted into the intestinal lumen and degraded during dauer arrest, only to be secreted into the body cavity again when the worms return to developmental growth. The process that determines the secretory polarity of INS-35 and INS-7, thus, has an important role in the modulation of larval diapause.

The clock gene period is essential for the photoperiodic response in the jewel wasp Nasonia vitripennis (Hymenoptera: Pteromalidae)

The role of the clock gene period (per) in photoperiodism was investigated in the jewel wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae). Typically, females reared under long days lay eggs that develop to adulthood without developmental interruption, whereas those reared under short days lay eggs that enter larval diapause. We found that RNA interference (RNAi) of per disrupts the photoperiodic response; RNAi wasps failed to produce diapause-destined eggs in response to short days. This indicates that per is essential for the photoperiodic response in this species. Exposure to low temperature swiftly affects maternal physiology and prompts N. vitripennis females to lay diapause-destined eggs. Interestingly, per RNAi females also laid diapause-destined eggs in response to the low temperature treatment in the current study. This finding indicates that per RNAi did not disrupt the maternal physiology that was directly involved in production of diapause-destined eggs, but it did affect photoperiodic perception. We also investigated the expression patterns of several clock genes, per, mammalian-type cryptochrome (cry-m), cycle (cyc), PAR-domain protein 1 (Pdp1), and clockwork orange (cwo), to determine whether their expression patterns were affected by different photoperiods.

Effects of environmental factors on life cycle regulation in Lasius japonicus Santschi (Formicidae)

This study investigated environmental factors that regulate oviposition by queens and colony development in Lasius japonicus Santschi. Newly mated queens were collected from fields in Okayama, Japan. All queens died within 50 days at 30 °C, whereas all or most of the queens survived at lower temperatures. At 25 °C, many pupae were observed approximately 1 month after the onset of oviposition. Diapause in either queens or workers was not induced at 25 °C. At 20 °C, many larvae did not pupate, indicating that larval diapause was induced. At 15 °C, hatching was not recorded and eggs disappeared. Low temperatures may induce reproductive diapause in queens. There were no significant differences between long-day (LD 16:8 h) and short-day (LD 12:12 h) conditions at any temperature. Under outdoor conditions, when summer temperature was moderate in 2005, queens started their nuptial flights in June, and pupation was recorded three times. However, when summer temperature was high in 2006, pupation occurred 1–2 times before winter, with queens making their nuptial flights as late as mid-July. Eggs and pupae disappeared in most colonies before the arrival of winter. Only queens, adult workers, and larvae were observed during winter. The present study showed that queens of L. japonicus founded and developed their colonies for as long as environmental conditions remained favorable, by responding to changes in temperature.

Assessing phenological synchrony between the Chinese sawfly, Cephus fumipennis (Hymenoptera: Cephidae), its egg-larval parasitoid, Collyria catoptron (Hymenoptera: Ichneumonidae), and the North American sawfly, Cephus cinctus: implications for biological control

AbstractMany pest and beneficial insects overwinter as larvae in a state of diapause, with development resuming in the spring. In these cases, rates of post-diapause development of parasitoids must be synchronised with the vulnerable life stages of their hosts. Phenological asynchrony between introduced parasitoids and their targeted hosts has limited the success of some biological control efforts. Here, we assess the potential synchrony between Collyria catoptron Wahl (Hymenoptera: Ichneumonidae), a parasitoid of the Chinese wheat stem sawfly, Cephus fumipennis Eversmann (Hymenoptera: Cephidae), which is being considered as a biological control against a novel host species, Cephus cinctus Norton, in North America. We compared development timing and emergence patterns of both native and exotic species of sawflies with that of the parasitoid. We found that the mean number of days between termination of larval diapause and adult eclosion varied by less than one day across species, and patterns of emergence were also similar. The rate of development of this egg-larval parasitoid was within the range necessary to attack C. cinctus eggs. Furthermore, the development of C. cinctus from western Montana, United States of America most closely matched that of the parasitoid, suggesting western Montana as a possible release area.

Effects of thermoperiods on the reproductive activity of females and on the maternal induction of larval diapause in the blowfly, Calliphora vicina R.-D. (Diptera, Calliphoridae)

The interaction of thermoperiod and photoperiod in their influence on the reproductive maturation of females and on the induction of the maternal effect determining larval diapause of the progeny of the blowfly, Calliphora vicina, was first investigated under laboratory conditions. Under the combination of a day length of 12 h with a thermoperiod (the alternation of 12 h long periods with temperatures of 10 and 20°C) the reproductive maturation of females was faster than at the corresponding mean constant temperature of 15°C. Under the “natural” thermoperiod, when the period with a temperature of 10°C coincided with “night-time” (the dark phase of the diurnal light-dark cycle) the maturation of females was slower than that under the “inverted” thermoperiod, when the period with a temperature of 10°C coincided with “day-time” (the light phase of the diurnal light-dark cycle). The proportion of diapausing individuals was maximal in the progeny of females kept at 20°C and decreased with the increase in temperature. Under thermoperiods (the alternations of 12 h long periods with temperatures of 20 and 26°C) the proportion of diapausing progeny was lower than that under the corresponding mean constant temperature of 23°C, but under the inverted thermoperiod with a high night temperature this effect was much stronger. In combination with the results of our previous studies, these data support the hypothesis that the effects of “night” and “day” temperatures are substantially different only when the thermal response interacts with a strong photoperiodic response.

Aspects of life history ofPlatycnemis subdilatata(Zygoptera: Platycnemididae) in Northeast Algeria

The determination of seasonal regulation is important to understand how species have adapted to their local environmental conditions. In this study, we investigate the life history of a North African endemic damselfly, Platycnemis subdilatata, in a northeast Algerian population. We combined field and laboratory investigations to assess the embryonic development, larval growth, emergence pattern and adult flight season. The embryonic development was direct and asynchronous, with 50% of all eggs hatching after three weeks of egg laying and a hatching period ranging from 13 to 51 days. Hatching success was 48.8%, and the causes of hatching failure were infertility and unhatchability. Larval population structure was quite asynchronous during the winter and less so before emergence. The occurrence of larval diapause is improbable due to the increase of the proportion of the last larval stadium in late winter. Emergence was asynchronous with half of the larval population (EM50) emerging after 44 days within an ...

Seasonal adaptations of the scarce silver-lines Bena bicolorana (Fuessly, 1775) (Lepidoptera, Noctuidae)

The influence of photoperiod and temperature on the growth and development of the scarce silver-lines Bena bicolorana (Fuessly, 1775) (Lepidoptera, Noctuidae) was studied in Belgorod Province, Russia (50°N, 36°E). At temperatures of 21 and 24°C, all photoperiodic regimes with 12 to 17 h of light per day induced diapause in the IV instar larvae. At 24°C, under long-day conditions with a photophase of 18 h, both diapausing and nondiapausing (i.e., directly developing) IV instar larvae were recorded in almost equal proportions; this photoperiodic regime may thus be considered as the threshold one. Diapause induction in B. bicolorana was associated with the larvae changing color from light green to brick-red. The larval growth rates, their weight dynamics, and timing of diapause induction are under photoperiodic control. Thus, seasonal development of B. bicolorana is controlled by two photoperiodic responses: the qualitative one that controls larval diapause induction, and the quantitative one that regulates larval growth parameters before diapause induction. In Belgorod Province B. bicolorana annually produces only one generation, what agrees well with the parameters of both of its photoperiodic responses. The results of the experimental eco-physiological studies support the separation of the monotypic genus Bena because it includes the only species in the subfamily Chloephorinae (B. bicolorana) that overwinters at the larval stage.

Molecular cloning, developmental expression and tissue distribution of diapause hormone and pheromone biosynthesis activating neuropeptide in the bamboo borer Omphisa fuscidentalis

AbstractDiapause, an arrested period of post‐embryonic development in insects, is under the control of hormonal interactions. In the bamboo borer Omphisa fuscidentalis Hampson (Lepidoptera: Crambidae), larvae remain in diapause for as long as 9 months during the dry season, from September to the following June, although the factors that regulate larval diapause are poorly understood. The present study describes the cloning and expression analysis of the diapause hormone and pheromone biosynthesis activating neuropeptide (DH‐PBAN) precursor of O. fuscidentalis (Ompfu‐DH‐PBAN cDNA), aiming to reveal how it may be involved regulating larval diapause in this species in combination with environmental factors. The open reading frame (ORF) of the cDNA encodes a 199‐amino acid precursor protein that contains DH, PBAN and three other neuropeptides, all of which share a conservative C‐terminal pentapeptide motif FXPR/KL (X = G, T or S). The Ompfu‐DH‐PBAN is highly similar (74%) to the DH‐PBAN of the legume pod borer (Maruca vitrata). A quantitative real‐time polymerase chain reaction reveals that Ompfu‐DH‐PBAN mRNA is expressed only in neural tissues and that expression is highest in the suboesophageal ganglion. In addition, the expression level of Ompfu‐DH‐PBAN mRNA in the suboesophageal ganglion is consistently high during the fifth larval instar, increasing moderately in early diapause before reaching a peak during late diapause. After pupation, expression of the Ompfu‐DH‐PBAN precursor decreases to a low level. In addition to endocrine factors, the results demonstrate that photoperiod increases the expression level of Ompfu‐DH‐PBAN mRNA in larval diapause. These results also suggest that the expression of the Ompfu‐DH‐PBAN gene correlates with larval diapause development and may be activated by photoperiod in O. fuscidentalis.

Effects of photoperiod and temperature on the development and diapause of the endangered butterfly Zizina emelina (Lepidoptera: Lycaenidae)

We investigated the effects of photoperiod and temperature on the development of the endangered butterfly Zizina emelina under laboratory conditions, and its seasonal occurrence in Osaka Prefecture, central Japan in 2009. At 20 °C most individuals reared under conditions of <13 h of light/day entered diapause during the larval stage, whereas those reared under ≥14 h of light/day developed into adults without any developmental arrest. At 25 °C, none of the individuals entered larval diapause irrespective of the photoperiod. The critical photoperiod for diapause induction at 20 °C was 12 h 40 min. Almost all larvae that had been in diapause for 2 months (with or without chilling at 10 °C) developed into adults, and the mean pupation period after transfer to 25 °C under 16 h of light/day differed little between the two groups, suggesting that chilling is not necessary to terminate larval diapause in Z. emelina. Adults were continuously found from late April to late October, with a low population density during spring. We estimate that this species has 5–6 generations in Osaka, according to the developmental threshold, effective accumulated temperature, and critical photoperiod data obtained from the rearing experiment. The estimated seasonal life cycle was similar to the seasonal prevalence observed in the field.

Photothermal control of larval diapause in the blowfly, Calliphora vicina R.-D. (Diptera, Calliphoridae) from the Lofoten Islands (Northern Norway)

Photothermal control of the rate of development and of larval diapause in the arctic population of Calliphora vicina from the Lofoten Islands (Northern Norway) was studied under the laboratory conditions. In the temperature range from 8 to 23°C, the rate of development of the studied population from egg to puparium can be well (r = 0.95) approximated by linear regression. The sum of effective temperatures was about 160 degree-days with the lower development threshold of 4.5 ± 0.6°C. The maternal photoperiodic response induced the larval diapause in a significant fraction of individuals only when larvae developed at temperatures of 4–10°C; relatively high proportion of diapausing larvae was recorded even in the progeny of females that were kept under long day conditions. The intensity of the larval diapause was very variable, which was manifested in the separation of diapausing larvae into two fractions differing in the time of pupariation during both spontaneous and induced reactivation.

Shifts in metabolomic profiles of the parasitoid Nasonia vitripennis associated with elevated cold tolerance induced by the parasitoid's diapause, host diapause and host diet augmented with proline

The ectoparasitoid wasp, Nasonia vitripennis can enhance its cold tolerance by exploiting a maternally-induced larval diapause. A simple manipulation of the fly host diapause status and supplementation of the host diet with proline also dramatically increase cold tolerance in the parasitoid. In this study, we used a metabolomics approach to define alterations in metabolite profiles of N. vitripennis caused by diapause in the parasitoid, diapause of the host, and augmentation of the host's diet with proline. Metabolic profiles of diapausing and nondiapausing parasitoid were significantly differentiated, with pronounced distinctions in levels of multiple cryoprotectants, amino acids, and carbohydrates. The dynamic nature of diapause was underscored by a shift in the wasp's metabolomic profile as the duration of diapause increased, a feature especially evident for increased concentrations of a suite of cryoprotectants. Metabolic pathways involved in amino acid and carbohydrate metabolism were distinctly enriched during diapause in the parasitoid. Host diapause status also elicited a pronounced effect on metabolic signatures of the parasitoid, noted by higher cryoprotectants and elevated compounds derived from glycolysis. Proline supplementation of the host diet did not translate directly into elevated proline in the parasitoid but resulted in an alteration in the abundance of many other metabolites, including elevated concentrations of essential amino acids, and reduction in metabolites linked to energy utilization, lipid and amino acid metabolism. Thus, the enhanced cold tolerance of N. vitripennis associated with proline augmentation of the host diet appears to be an indirect effect caused by the metabolic perturbations associated with diet supplementation.

Insect diapause of very variable duration: the case of the palm nut bruchid Pachymerus nucleorum (Coleoptera: Chrysomelidae)

SummaryData are provided here showing that larval diapause in the tropical palm nut bruchid Pachymerus nucleorum (Fabricius) can extend up to a maximum of about five years, although for most individuals the duration ranges from 15 to 48 months. The data were obtained for insects originating from one source only that were held under one set of temperature and photoperiod conditions only so the wide variation in duration is attributed to maternal control. Staggering the adult emergence times of a parent’s progeny can be regarded as an evolutionary strategy that increases the chance that some at least encounter favourable biotic or abiotic conditions. It is believed that extended diapause may be quite widespread amongst insects, including those of temperate climates.

Taxonomic revision of the Taractrocera ilia (Waterhouse) complex (Lepidoptera : Hesperiidae) from north-western Australia and mainland New Guinea based on morphological and molecular data

The taxonomy of the Taractrocera ilia complex is revised based on evidence from multiple sources, including phenotypic characters (wing colour pattern elements, morphology of adult and immature stages), ecology and molecular data. Three species are recognised in the complex: T. psammopetra Braby, sp. nov. is restricted to north-western Australia where it has a disjunct distribution (Kimberley and the central Arnhem Land plateau); T. ilia (Waterhouse, 1932) sensu stricto is endemic to the central Arnhem Land plateau where it is narrowly sympatric with T. psammopetra; while T. beta Evans, 1934, stat. nov. is allopatric and endemic to mainland New Guinea. Each species is illustrated and diagnosed based on comparative morphology of the adult stage, including androconia and male and female genitalia, and information on type material, biology, distribution and habitat is summarised and discussed. A phylogenetic hypothesis of the Australian species of Taractrocera based on combined analysis of molecular data (2.6 kb: mitochondrial COI and nuclear CAD, MDH, wingless) revealed that T. psammopetra is monophyletic and sister to T. ilia, with an overall mean divergence of 3.4% between the two species; the genus Taractrocera, however, emerged as polyphyletic. For T. psammopetra and T. ilia, the life history, including details of larval food plant specialisation and morphology of the immature stages, is described for the first time. Larvae of T. psammopetra and T. ilia specialise on ‘resurrection’ grasses, Micraira spp. (Poaceae), which typically grow as moss-like, mat-forming pioneer plants on shallow rock surfaces comprising open sandstone pavements or on rock ledges and under rock overhangs of sandstone cliffs. These food plants, together with the butterflies that they support, are a characteristic element of the sandstone plateaux of the Kimberley and central Arnhem Land, and they exemplify patterns of diversification, endemism and adaptation to these unique environments within the Australian monsoon tropics. Facultative larval diapause is recorded for both T. psammopetra and T. ilia in which larvae (all instars, but particularly the final instar) may suspend feeding for up to six months during the dry season when the food plants typically dehydrate. It is hypothesised that larval diapause may be the most flexible strategy to ameliorate seasonal adversity of the dry season and the onset, duration and inter-annual cycle of monsoon rainfall during the wet season, which is highly variable and unpredictable, given that Micraira can revive rapidly from a desiccated state after rainfall. http://zoobank.org/urn:lsid:zoobank.org:pub:51438A5E-048C-4C72-AD22-3FD176ECBA55

Transcriptome profiling reveals mechanisms for the evolution of insect seasonality.

Rapid evolutionary change in seasonal timing can facilitate ecological speciation and resilience to climate warming. However, the molecular mechanisms behind shifts in animal seasonality are still unclear. Evolved differences in seasonality occur in the European corn borer moth (Ostrinia nubilalis), in which early summer emergence in E-strain adults and later summer emergence in Z-strain adults is explained by a shift in the length of the termination phase of larval diapause. Here, we sample from the developmental time course of diapause in both strains and use transcriptome sequencing to profile regulatory and amino acid changes associated with timing divergence. Within a previously defined quantitative trait locus (QTL), we nominate 48 candidate genes, including several in the insulin signaling and circadian rhythm pathways. Genome-wide transcriptional activity is negligible during the extended Z-strain termination, whereas shorter E-strain termination is characterized by a rapid burst of regulatory changes involved in resumption of the cell cycle, hormone production and stress response. Although gene expression during diapause termination in Ostrinia is similar to that found previously in flies, nominated genes for shifts in timing are species specific. Hence, across distant relatives the evolution of insect seasonality appears to involve unique genetic switches that direct organisms into distinct phases of the diapause pathway through wholesale restructuring of conserved gene regulatory networks.

The lost generation hypothesis: could climate change drive ectotherms into a developmental trap?

Climate warming affects the rate and timing of the development in ectothermic organisms. Short‐living, ectothermic organisms (including many insects) showing thermal plasticity in life‐cycle regulation could, for example, increase the number of generations per year under warmer conditions. However, changed phenology may challenge the way organisms in temperate climates deal with the available thermal time window at the end of summer. Although adaptive plasticity is widely assumed in multivoltine organisms, rapid environmental change could distort the quality of information given by environmental cues that organisms use to make developmental decisions. Developmental traps are scenarios in which rapid environmental change triggers organisms to pursue maladaptive developmental pathways. This occurs because organisms must rely upon current environmental cues to predict future environmental conditions and corresponds to a novel case of ecological or evolutionary traps. Examples of introduced, invasive species are congruent with this hypothesis. Based on preliminary experiments, we argue that the dramatic declines of the wall brown Lasiommata megera in northwestern Europe may be an example of a developmental trap. This formerly widespread, bivoltine (or even multivoltine) butterfly has become a conundrum to conservationist biologists. A split‐brood field experiment with L. megera indeed suggests issues with life‐cycle regulation decisions at the end of summer. In areas where the species went extinct recently, 100% of the individuals developed directly into a third generation without larval diapause, whereas only 42.5% did so in the areas where the species still occurs. Under unfavourable autumn conditions, the attempted third generation will result in high mortality and eventually a lost or ‘suicidal’ third generation in this insect with non‐overlapping, discrete generations. We discuss the idea of a developmental trap within an integrated framework for assessing the vulnerability of species to climate change.

The life cycle and production of three common stonefly species (Insecta, Plecoptera) in the Kedrovaya River (the south of Primorskii Territory)

The life cycles and production parameters of three common detritivorous stonefly species (Paracapnia khorensis, Amphinemura verrucosa, and Taenionema japonicum) from the Kedrovaya River at the Kedrovaya Pad Reserve (the south of Primorskii Territory, Russian Far East) were studied. Judging from the body size histograms, all these species are univoltine and have no winter diapause. Eggs develop directly; larval growth is slow, takes about 282–295 days, and proceeds even at low water temperatures in winter. The P. khorensis population is characterized by synchronous adult emergence and recruitment, as well as by slow continuous increase in larval linear size and body mass from June to March. Amphinemura verrucosa adults have a prolonged flight period from June to August, and their recruitment takes place for two months, till the end of November. Larvae grow during autumn and winter, but the most rapid growth is recorded in spring, when the water temperature rises, just before adult emergence in June and July. The development of T. japonicum is characterized by larval diapause in August and September when the water temperature is high. In October, larval growth is resumed and remains rapid through autumn and winter, up to adult emergence in May. The species studied had similar values of instantaneous growth rate (0.021–0.022 day−1), cohort production efficiency P/Bcohort (6.01–6.55), and annual efficiency of population production P/Bannual (7.78–8.11). More variable throughout the growing period was the mean biomass, and this accounted for the differences in secondary production values which ranged from 13.2 to 130.7 mg dry mass/m2.

Host diapause status and host diets augmented with cryoprotectants enhance cold hardiness in the parasitoid Nasonia vitripennis

Boosting cold hardiness in parasitoids is a goal that is particularly attractive for increasing shelf life and shipment of biological control agents. In the experiments reported here we use the parasitoid Nasonia vitripennis as a model to evaluate manipulations that may be capable of enhancing the wasp’s cold tolerance. We altered the parasitoid’s cold tolerance by manipulating the wasp’s diapause status, the diapause status of the host fly (Sarcophaga crassipalpis), and the diet of the host. Larval diapause in N. vitripennis dramatically increased cold tolerance and the diapause status of the host also exerted a positive, although less dramatic, effect. Augmenting the host fly’s diet with supplements of putative cryoprotectants (alanine, proline and glycerol) enhanced cold tolerance in parasitoids that fed on the flies, thus indicating a tri-trophic effect on parasitoid cold tolerance. The most pronounced improvement in cold tolerance was noted in parasitoids fed on fly hosts that had received a diet augmented with proline. These results suggest mechanisms that could be exploited for enhancement of cold tolerance in parasitoids of commercial interest.

Environmental induction of larval diapause and life-history consequences of post-diapause development in the Large Copper butterfly, Lycaena dispar (Lepidoptera: Lycaenidae)

Many insects in temperate zones withstand the adverse conditions of winter through entering diapause and the two most important environmental stimuli that induce diapause are photoperiod and ambient temperature. The Large Copper butterfly, Lycaena dispar Haworth (Lepidoptera: Lycaenidae), is a Palearctic butterfly that hibernates as larvae. Since this butterfly is a near threatened species in some regions, there has been a growing need for a standardized protocol for mass rearing of this butterfly based on the adequate knowledge of its ecology. In the present study, we first identified that L. dispar larvae were sensitive to the photoperiodic induction of diapause during their first larval instar. We then investigated to what extent the diapause-inducing effects of photoperiod could be modified by ambient temperatures in L. dispar larvae by exposing them to the range of day-lengths (L:D 14:10, 12:12, 10:14 and 8:16) at three different temperatures (15, 20 and 25 °C). All larvae were induced to enter diapause at low ambient temperature (15 °C) regardless of photoperiod, whereas most of them (86 %) exhibited direct development when temperature was high (25 °C). The photoperiodic induction of diapause was evident when day-length was shorter than 14 h at intermediate temperature (20 °C). Pre-diapause development was prolonged at low temperatures. Finally, we found that post-diapause development of L. dispar larvae was determined by both the chilling temperature experienced by diapausing larvae and the duration of larval diapause. Adult emergence was enhanced when larvae were chilled at 8 °C and when they had been under the state of diapause for 20 days before they were treated to terminate diapause.

Hc-fau, a novel gene regulating diapause in the nematode parasite Haemonchus contortus

Diapause induced in the early fourth stage of Haemonchus contortus is a strategy to adapt this nematode to hostile environmental conditions. In this study, we identified a new gene, Hc-fau, a homologue of human fau and Caenorhabditis elegans Ce-rps30. Hc-fau encodes two proteins through alternative RNA splicing, Hc-FAUA and Hc-FAUB, consisting of 130 and 107 amino acids, respectively. Hc-FAU possesses a diverged ubiquitin-like (UBiL) protein domain and a conserved ribosome protein S30 domain. The protein is ubiquitously expressed, except in the gonad. However Hc-fau transcripts decrease significantly in diapausing L4s of H. contortus. In C. elegans, knockdown of Ce-rps30 confers an extended lifespan, increased lipid storage in the intestine and shortened body length. These morphological characteristics are comparable with dauer larvae of C. elegans, in which the gonad is condensed considerably. In contrast, a shortened lifespan is observed in C. elegans over-expressing Hc-faua, and especially Hc-faub, with hatching failure detected. The genes of insulin/IGF-1 signalling (IIS), TGF-β, cGMP, dafachronic acid (DA), apoptosis (AP) and fatty acids (FA) metabolism are all down-regulated in Ce-rps30RNAi (RNA interference) worms, except for akt-1 and daf-16. However, daf-16 up-regulation is inconsistent with its target gene down-regulation and the result from a heat stress assay in these worms. Daf-16 RNAi conducted in Ce-rps30 (tm6034/nt1) mutants failed to rescue the worms. The S30 domain stays in the nucleus, while UBiL accumulates in the cytoplasm. Compared with Hc-FAUA, results of UBiL domain and S30 domain over-expression indicate synergism between UBiL and S30 in regulating lifespan and reproduction. These results suggest the potential functions of Hc-fau in regulating larval diapause in H.contortus.