Timing Of Diapause Research Articles

Diapause: Circadian Clock Genes Are at It Again.

Understanding how insects synchronize their annual life cycle to local conditions remains poorly understood. A new study integrates a QTL investigation with population genomic analyses in a Lepidopteran to show that, yet again, allelic variation in circadian clock genes has a role in seasonal timing of diapause.

A Crude Awakening: Effects of Crude Oil on Lipid Metabolism in Calanoid Copepods Terminating Diapause.

Calanus finmarchicus and Calanus glacialis are keystone zooplankton species in North Atlantic and Arctic marine ecosystems because they form a link in the trophic transfer of nutritious lipids from phytoplankton to predators on higher trophic levels. These calanoid copepods spend several months of the year in deep waters in a dormant state called diapause, after which they emerge in surface waters to feed and reproduce during the spring phytoplankton bloom. Disruption of diapause timing could have dramatic consequences for marine ecosystems. In the present study, Calanus C5 copepodites were collected in a Norwegian fjord during diapause and were subsequently experimentally exposed to the water-soluble fraction of a naphthenic North Sea crude oil during diapause termination. The copepods were sampled repeatedly while progressing toward adulthood and were analyzed for utilization of lipid stores and for differential expression of genes involved in lipid metabolism. Our results indicate that water-soluble fraction exposure led to a temporary pause in lipid catabolism, suggested by (i) slower utilization of lipid stores in water-soluble fraction-exposed C5 copepodites and (ii) more genes in the β-oxidation pathway being downregulated in water-soluble fraction-exposed C5 copepodites than in the control C5 copepodites. Because lipid content and/or composition may be an important trigger for termination of diapause, our results imply that the timing of diapause termination and subsequent migration to the surface may be delayed if copepods are exposed to oil pollution during diapause or diapause termination. This delay could have detrimental effects on ecosystem dynamics.

The genetic architecture underlying diapause termination in a planktonic crustacean.

Diapause is a feature of the life cycle of many invertebrates by which unfavourable environmental conditions can be outlived. The seasonal timing of diapause allows organisms to adapt to seasonal changes in habitat suitability and thus is key to their fitness. In the planktonic crustacean Daphnia, various cues can induce the production of diapause stages that are resistant to heat, drought or freezing and contain one to two embryos in developmental arrest. Daphnia is a keystone species of many freshwater ecosystems, where it acts as the main link between phytoplankton and higher trophic levels. The correct seasonal timing of diapause termination is essential to maintain trophic interactions and is achieved via a genetically based interpretation of environmental cues like photoperiod and temperature. Field monitoring and modelling studies raised concerns on whether populations can advance their seasonal release from diapause to advances in spring phenology under global change, or if a failure to adapt will cause trophic mismatches negatively affecting ecosystem functioning. Our capacity to understand and predict the evolution of diapause timing requires information about the genetic architecture underlying this trait. In this study, we identified eight quantitative trait loci (QTLs) and four epistatic interactions that together explained 66.5% of the variation in diapause termination in Daphnia magna using QTL mapping. Our results suggest that the most significant QTL is modulating diapause termination dependent on photoperiod and is involved in three of the four detected epistatic interactions. Candidate genes at this QTL could be identified through the integration with genome data and included the presynaptic active zone protein bruchpilot. Our findings contribute to understanding the genomic control of seasonal diapause timing in an ecological relevant species.

Selection for reproduction under short photoperiods changes diapause-associated traits and induces widespread genomic divergence.

The incidence of reproductive diapause is a critical aspect of life history in overwintering insects from temperate regions. Much has been learned about the timing, physiology and genetics of diapause in a range of insects, but how the multiple changes involved in this and other photoperiodically regulated traits are inter-related is not well understood. We performed quasinatural selection on reproduction under short photoperiods in a northern fly species, Drosophila montana, to trace the effects of photoperiodic selection on traits regulated by the photoperiodic timer and/or by a circadian clock system. Selection changed several traits associated with reproductive diapause, including the critical day length for diapause (CDL), the frequency of diapausing females under photoperiods that deviate from daily 24 h cycles and cold tolerance, towards the phenotypes typical of lower latitudes. However, selection had no effect on the period of free-running locomotor activity rhythm regulated by the circadian clock in fly brain. At a genomic level, selection induced extensive divergence from the control line in 16 gene clusters involved in signal transduction, membrane properties, immunologlobulins and development. These changes resembled those detected between latitudinally divergent D. montana populations in the wild and involved SNP divergence associated with several genes linked with diapause induction. Overall, our study shows that photoperiodic selection for reproduction under short photoperiods affects diapause-associated traits without disrupting the central clock network generating circadian rhythms in fly locomotor activity.

Trade-offs between storage and survival affect diapause timing in capital breeders

Many organisms spend the unfavourable part of the year, such as the winter season, in diapause or dormancy and reproduce in spring shortly after emergence. Reserves are acquired prior to diapause to cover metabolic costs and in some species also reproduction (capital breeding) directly after diapause. Storage is then a component of future reproduction, and capital breeders consequently pay a pre-breeding cost of reproduction as they risk dying while obtaining and carrying the reserves. How large should the reserves be, and to what extent should optimal storage, and thereby timing of diapause, depend on predation risk and reproductive strategy? We present a general and simplistic life history model of an arthropod (e.g. crustaceans or insects) that is exposed to background mortality risk when it accumulates reserves before diapause. The model optimizes diapause timing and resultant reserves for income, mixed and capital breeders, and predicts how mortality risk affects the degree of capital breeding. For income breeders, timing of diapause is insensitive to the risk while obtaining reserves as they, regardless of risk, acquire the minimum amount needed to survive the winter. For capital breeders, the higher the risk the earlier the diapause and less is consequently stored. Mixed breeders diapause late and store as much as pure capital breeders when exposed to low risk, but behave as income breeders and diapause early when mortality is high. Our model shows that the degree of capital breeding impacts phenology of diapause in a risk-dependent manner. This prediction should impact how diapause timing is thought of across a wide range of taxa, including the much studied marine copepods. Timing of diapause, including triggers and cues, can only be understood when the diversity of reproductive strategies and the adaptive value of storage is taken into account.

Calanus finmarchicus seasonal cycle and diapause in relation to gene expression, physiology, and endogenous clocks

AbstractThe copepod Calanus finmarchicus plays a crucial role in the north Atlantic food web. Its seasonal life cycle involves reproduction and development in surface waters before overwintering in diapause at depth. Although diapause has been studied for more than a century, the factors responsible for the initiation and termination of it are still unclear. Endogenous clocks have been identified as potent tools for photoperiod measurement and seasonal rhythmicity in many terrestrial species, but knowledge of these remains scarce in the marine realm. Focusing on the dominant CV copepodid stage, we sampled a population of C. finmarchicus from a Scottish sea loch to characterize population dynamics, several physiological parameters, and diel and seasonal expression rhythms of 35 genes representing different metabolic pathways, including the circadian clock machinery. This generated a detailed overview of the seasonal cycle of C. finmarchicus including the most extensive field dataset on circadian clock gene expression in a marine species to date. Gene expression patterns revealed distinct gene clusters upregulated at different phases of the copepod's seasonal cycle. While diel clock cycling was restricted to the active spring/summer phase, many clock genes exhibited the highest expression during diapause. Our results provide new insights into diapause on physiological and genetic levels. We suggest that photoperiod, in interaction with internal and external factors (lipid content, temperature, food availability) and the endogenous clock mechanism, plays an important role in the timing of diapause in C. finmarchicus.

Divergence in larval diapause induction between the rice and water-oat populations of the striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Crambidae).

Differences in diapause traits can result in the seasonal reproductive isolation of host plant-associated insect populations and thereby facilitate the population divergence. The striped stem borer, Chilo suppressalis, has two host plant-associated populations: rice population and water-oat population. Several studies have found evidence that seasonal reproductive isolation between these populations is at least partially due to interpopulation differences in diapause. However, there still lack unambiguous evidence comparing characteristics of diapause induction for both populations. We compared the photoperiodic response and the age of peak photoperiod sensitivity of these populations and used RNA-Seq to compare the molecular response of diapause induction between populations. The photoperiodic response of the two populations differed at 25°C; the critical night length of larvae from the rice population was 11h and 20min, whereas no obvious critical night length was in those from the water-oat population. In rice population, larvae were most sensitive to photoperiod at 9-12days of age, whereas in water-oat population, larvae were the most sensitive to photoperiod at 9-10days of age. The RNA-Seq results indicated that there were several differences in the molecular response of diapause induction and small overlap in differentially expressed genes (DEGs) between populations. Furthermore, GO analysis indicated that both rice and water-oat population's DEGs were significantly enriched in heme and iron binding. Besides, water-oat population's DEGs were significantly enriched in metabolizing nutrients but rice population's DEGs do not. Thus, our results described differences in diapause induction between rice and water-oat populations of C. suppressalis which could affect the timing of diapause and thereby contribute to the seasonal reproductive isolation of these host plant-associated populations. In conclusion, this work suggests that difference in diapause induction could promote the population divergence in insects associated with different host plants.

The Asian tiger mosquito, Aedes (Stegomyia) albopictus (Skuse), a vector of dengue, chikungunya and zika viruses, reaches Portugal (Diptera: Culicidae).

The Asian tiger mosquito, Aedes (Stegomyia) albopictus (Skuse), is a tropical species originally from south-eastern Asia (Hawley, 1988). It has experienced a rampant human-mediated range expansion since the 1970s to now occupy almost the whole of the tropical and subtropical areas of the world. As an eclectic haematophagous species, it attacks humans and is able to use a number of man-made and natural structures where stagnant water is present (Estrada-Franco Craig, 1995). Eggs are able to survive for extended periods of time in complete dryness and diapause over unsuitable cold season, making it an especially resilient species (Hawley, 1988).

Keeping time without a spine: what can the insect clock teach us about seasonal adaptation?

Seasonal change in daylength (photoperiod) is widely used by insects to regulate temporal patterns of development and behaviour, including the timing of diapause (dormancy) and migration. Flexibility of the photoperiodic response is critical for rapid shifts to new hosts, survival in the face of global climate change and to reproductive isolation. At the same time, the daily circadian clock is also essential for development, diapause and multiple behaviours, including correct flight orientation during long-distance migration. Although studied for decades, how these two critical biological timing mechanisms are integrated is poorly understood, in part because the core circadian clock genes are all transcription factors or regulators that are able to exert multiple effects throughout the genome. In this chapter, we discuss clocks in the wild from the perspective of diverse insect groups across eco-geographic contexts from the Antarctic to the tropical regions of Earth. Application of the expanding tool box of molecular techniques will lead us to distinguish universal from unique mechanisms underlying the evolution of circadian and photoperiodic timing, and their interaction across taxonomic and ecological contexts represented by insects.This article is part of the themed issue 'Wild clocks: integrating chronobiology and ecology to understand timekeeping in free-living animals'.

Idiosyncratic development of sensory structures in brains of diapausing butterfly pupae: implications for information processing.

Diapause is an important escape mechanism from seasonal stress in many insects. A certain minimum amount of time in diapause is generally needed in order for it to terminate. The mechanisms of time-keeping in diapause are poorly understood, but it can be hypothesized that a well-developed neural system is required. However, because neural tissue is metabolically costly to maintain, there might exist conflicting selective pressures on overall brain development during diapause, on the one hand to save energy and on the other hand to provide reliable information processing during diapause. We performed the first ever investigation of neural development during diapause and non-diapause (direct) development in pupae of the butterfly Pieris napi from a population whose diapause duration is known. The brain grew in size similarly in pupae of both pathways up to 3 days after pupation, when development in the diapause brain was arrested. While development in the brain of direct pupae continued steadily after this point, no further development occurred during diapause until temperatures increased far after diapause termination. Interestingly, sensory structures related to vision were remarkably well developed in pupae from both pathways, in contrast with neuropils related to olfaction, which only developed in direct pupae. The results suggest that a well-developed visual system might be important for normal diapause development.

A year-round study on metabolic enzymes and body composition of the Arctic copepod Calanus glacialis: implications for the timing and intensity of diapause

Knowledge on the capability of zooplankton to adapt to the rapidly changing environmental conditions in the Arctic is crucial to predict future ecosystem processes. The key species on the Arctic shelf, the calanoid copepod Calanus glacialis, grows and accumulates lipid reserves in spring and summer in surface waters. The winter is spent in dormancy in deeper water layers with low metabolic activity. As timing and intensity of metabolic changes have been poorly investigated, our study aims to characterize the physiology of C. glacialis over an entire year, from July 2012 to July 2013. We followed anabolic and catabolic enzyme activities and the biochemical composition of this species, taking depth-stratified samples once a month in Billefjorden, a high-Arctic sill fjord. A large part of the population had migrated to depths >100 m by July 2012. Only thereafter, anabolic activities decreased slowly, suggesting that low metabolism is related to ceased feeding rather than to endogenous regulation. During overwintering, anabolic enzyme activities were reduced by half as compared to peak activities in spring. The biochemical composition of the copepods changed little from July to December. Then, the lipid catabolic activity increased and the lipid content decreased, likely fuelling moulting and gonad maturation. The protein content did not change significantly during winter, suggesting that proteins are not much catabolized during that time. The relatively high metabolic activity in C. glacialis in winter suggests that this species is not entering a true diapause and should thus be able to respond flexible to changing environmental conditions.

The seasonal development cycle of Aphantopus hyperantus (L.) (Lepidoptera, Nymphalidae: Satyrinae) in Leningrad Province

The simultaneous influence of the photoperiodic and temperature conditions on pre-diapause and postdiapause larval development of the ringlet Aphantopus hyperantus was studied. At the short day (12 h of light a day) all larvae reached the III instar and entered diapause at all the temperatures tested (18–24°C). At the long day (22 h) the number of diapausing larvae increased with decreasing temperature, and the larvae diapaused at the III and IV instars. The I and II instar larvae (before winter) developed and grew faster under short-day, and the hibernated larvae, under long-day conditions. At the short day the growth rate of the I and II instar larvae did not depend on the temperature, and at the long day it decreased as the temperature increased. After hibernation the growth rate of the IV instar larvae increased with the temperature under long-day conditions, and did not depend on the temperature under short-day ones. Thus, acceleration or deceleration of development, depending on the photoperiodic and temperature conditions, regulated the timing of diapause in the overwintering stage (the III instar larva) and maintained the univoltine seasonal cycle. The males of A. hyperantus developed and grew faster than females while their weight at the larval and pupal stages was smaller. The thermal reaction norms for development (the lower temperature threshold and the coefficient of thermal sensitivity of development) were calculated for the eggs, IV and V instar larvae, and pupae. The coefficient of thermal sensitivity of development for the IV and V instar larvae taken together was lower, and the threshold was higher than the corresponding values for eggs and pupae. The thermal reaction norms for development of the latter stages were the same. The larvae of A. hyperantus retained their sensitivity to the photoperiod after hibernation. Resumption of development after cold reactivation occurred only under long-day conditions, whereas under short-day ones the overwintered larvae entered a repeated diapause. The possibility of photoperiodic reactivation and the absence of spontaneous resumption of development in these larvae were demonstrated.

Seasonal gene expression kinetics between diapause phases in Drosophila virilis group species and overwintering differences between diapausing and non-diapausing females.

Most northern insect species experience a period of developmental arrest, diapause, which enables them to survive over the winter and postpone reproduction until favorable conditions. We studied the timing of reproductive diapause and its long-term effects on the cold tolerance of Drosophila montana, D. littoralis and D. ezoana females in seasonally varying environmental conditions. At the same time we traced expression levels of 219 genes in D. montana using a custom-made microarray. We show that the seasonal switch to reproductive diapause occurs over a short time period, and that overwintering in reproductive diapause has long-lasting effects on cold tolerance. Some genes, such as Hsc70, Jon25Bi and period, were upregulated throughout the diapause, while others, including regucalcin, couch potato and Thor, were upregulated only at its specific phases. Some of the expression patterns induced during the sensitive stage, when the females either enter diapause or not, remained induced regardless of the later conditions. qPCR analyses confirmed the findings of the microarray analysis in D. montana and revealed similar gene expression changes in D. littoralis and D. ezoana. The present study helps to achieve a better understanding of the genetic regulation of diapause and of the plasticity of seasonal responses in general.

Distribution, host plant affiliation, phenology, and phylogeny of walnut-infestingRhagoletisflies (Diptera: Tephritidae) in Mexico

Many taxa of Nearctic origin have diversified in the subtropical highlands of Mexico. In particular, flies in the genus Rhagoletis have undergone episodes of isolation and gene flow during Pleistocene glaciations and post-glacial times that have produced lineage differentiation and reproductive isolation. To reach a better understanding of the phylogeography of the genus Rhagoletis, a host plant survey of the walnut-infesting Rhagoletis suavis species group was conducted across sixteen states comprising 34 different collecting sites in Mexico over a 9-year period. Five species of Juglans were found to be infested by three species of walnut-attacking Rhagoletis flies. Several species of parasitoids were also recovered from collections, but in contrast to their walnut fly hosts, they revealed little evidence for host or geographic subdivision. There was no consistent difference in mean eclosion time between walnut fly species or populations associated with different host walnuts in Mexico, unlike the case for other Rhagoletis species, in which allochronic isolation arising from variation in diapause timing is a major ecological adaptation, reproductively isolating flies. We compare the distribution of R. suavis flies in Mexico with those of other Rhagoletis species attacking hawthorns and cherries, and discuss its implications for population divergence and speciation.

One phase of the dormancy developmental pathway is critical for the evolution of insect seasonality

Evolutionary change in the timing of dormancy enables animals and plants to adapt to changing seasonal environments and can result in ecological speciation. Despite its clear biological importance, the mechanisms underlying the evolution of dormancy timing in animals remain poorly understood because of a lack of anatomical landmarks to discern which phase of dormancy an individual is experiencing. Taking advantage of the nearly universal characteristic of metabolic suppression during insect dormancy (diapause), we use patterns of respiratory metabolism to document physiological landmarks of dormancy and test which of the distinct phases of the dormancy developmental pathway contribute to a month-long shift in diapause timing between a pair of incipient moth species. Here, we show that divergence in life cycle between the earlier-emerging E-strain and the later-emerging Z-strain of European corn borer (ECB) is clearly explained by a delay in the timing of the developmental transition from the diapause maintenance phase to the termination phase. Along with recent findings indicating that life-cycle differences between ECB strains stem from allelic variation at a single sex-linked locus, our results demonstrate how dramatic shifts in animal seasonality can result from simple developmental and genetic changes. Although characterizing the multiple phases of the diapause developmental programme in other locally adapted populations and species will undoubtedly yield surprises about the nature of animal dormancy, results in the ECB moth suggest that focusing on genetic variation in the timing of the dormancy termination phase may help explain how (or whether) organisms rapidly respond to global climate change, expand their ranges after accidental or managed introductions, undergo seasonal adaptation, or evolve into distinct species through allochronic isolation.

Differential regulation of heat shock protein genes by temperature in relation to initial diapause in the egg of the katydid Paratlanticus ussuriensis

AbstractThe lifecycle of Paratlanticus ussuriensis Uvarov can extend for longer than 1 year (plurennial) as a result of prolonged diapause. Eggs can overwinter by entering a facultative initial diapause in the early embryonic stage within the egg, followed by further overwintering by entering an obligatory final diapause at the fully developed embryonic stage. The initial diapause is temperature‐dependent and initiated by continuous incubation at 20 °C but not at 30 °C. To understand the mechanism of initial diapause at the molecular level, cDNAs of small heat shock protein genes (shsp), hsp90, as well as three hsp70 genes (hsp70a, hsp70b and hsp70c), are determined and the transcript levels of the five hsp genes are compared in eggs incubated at 20 or 30 °C for 60 days after oviposition using real‐time reverse transcriptase‐polymerase chain reaction analysis. At 30 °C, transcript levels of shsp, hsp70a, hsp70b and hsp90 increase in eggs with age. However, hsp70c levels uniquely peak only in 25‐day‐old eggs, corresponding to the time of initial diapause. At 20 °C, distinct levels of shsp, hsp70a and hsp90 appear in some stages and fluctuate throughout the 60‐day observation period, although both hsp70b and hsp70c are undetectable. These results suggest that each hsp may play a specific role in relation to initial diapause. In addition, up‐regulation of hsp70c may be associated with the mechanism of embryonic activation for averting initial diapause in warmer conditions.

Northern Drosophila montana flies show variation both within and between cline populations in the critical day length evoking reproductive diapause

Reproductive diapause, and its correct timing, plays an important role in the life cycle of many insect species living in a seasonally varying environment at high latitudes. In the present paper we have documented variation in the critical day length (CDL) for adult reproductive diapause and the steepness of photoperiodic response curves (PPRCs) in seven clinal populations of Drosophila montana in Finland between the latitudes 61 and 67°N, paying special attention to variation in these traits within and between cline populations. The isofemale lines representing these populations showed a sharp transition from 0% to 100% in females’ diapause incidence in the shortening day lengths, indicated by steep PPRCs. The mean CDL showed a clear latitudinal cline decreasing by 1.6h from North to South regardless of the age of the lines, variation within the populations (i.e. among lines) in this trait being up to 3h. The steepness of the PPRCs correlated with the age of the line and this trait showed no clear latitudinal cline. Further studies on a large number of lines from one D. montana population confirmed that while maintaining the flies in diapause preventing conditions in the laboratory has no effect on CDL, older lines had steeper PPRCs. High variation in CDL within and between D. montana cline populations is likely to be heritable and provide a good potential for the evolution of photoperiodic responses. Information on genetic variation in life-history traits, such as diapause, is of utmost importance for predicting the ability of insects to survive in seasonally changing environmental conditions and to respond to long term changes in the length of the growing period e.g. by postponing the timing of diapause towards shorter day length and later calendar date.

Population dependent effects of photoperiod on diapause related physiological traits in an invasive beetle (Leptinotarsa decemlineata)

Organisms undergoing latitudinal range expansion face a change in the photoperiod which can lead to a mismatch between the timing of seasonal changes in physiological and life history traits with seasonal environmental changes. This mismatch can lead to lowered survival, for example, due to unsynchronized diapause timing. Successful range expansion even in recent introductions requires that organisms which use the photoperiod for seasonal predictions should show interpopulational differences in photoperiodic responses at different latitudes, as the photoperiod is a function of latitude. We investigated among population differences in photoperiodic responses of life history and physiological traits linked to diapause in the invasive beetle Leptinotarsa decemlineata. Beetles from a northern marginal and a southern European population were reared under short day (12:12L:D) and long day (18:6L:D) photoperiods. Both populations reacted similarly to the short day photoperiod. Their abdominal total lipid content increased and water content decreased which suggests that the beetles prepared for diapause. This was also indicated by low mortality during diapause. In the long day photoperiod large interpopulational differences were found, the southern population ceased lipid accumulation after 5days, while the northern population continued lipid accumulation as beetles in the short day photoperiod. This indicates that the northern population has a longer critical photoperiod than the southern one. Abdominal total lipid stores in 10day old beetles were shown to be predominantly composed of neutral lipids (85%), most likely representing storage triacylglycerols. Fatty acid profiles of both the neutral lipids and the phospholipids showed large shifts during the first 10day of adult life, predominantly in the fractions of 18:0, 18:1ω9, 18:2ω6 and 18:3ω3. Although the degree of unsaturation increased with age, it was not higher in diapausing than non-diapausing beetles. This indicates that this species does not increase diapause related cold tolerance via homeoviscous adaptation, and might have developed other means to cope with suboptimal temperatures, such as behavioral adaptations.

Diapause Induction inGratiana boliviana(Coleoptera: Chrysomelidae), a Biological Control Agent of Tropical Soda Apple in Florida

AbstractThe South American leaf-feeding beetle Gratiana boliviana Spaeth (Coleoptera: Chrysomelidae) has been released since 2003 in the southeastern United States to control the invasive weed tropical soda apple, Solanum viarum Dunal (Solanaceae). Successful establishment of a biological control agent in temperate and subtropical regions depends on several life-history adaptations, including winter diapause. The timing of diapause allows the syncronization of insect herbivores with the phenology of plants, and field observations in Florida suggested that G. boliviana overwinters as an adult in diapause. The objectives of this study were to describe the diapause of G. boliviana and determine the effect of temperature and photoperiod on diapause induction. Compared with nondiapause adults, diapausing adults were yellow rather than green, had hypertrophied fat bodies, contained little food in the digestive tract, showed negligible ovarian development, and minimal movement of the hind wings when the beetles were placed on their dorsal sides. Although all nondiapause females laid eggs during a 30-d period, only five of 76 diapausing females laid eggs and this occurred only during the first 15 d of the treatment period. Consistent with morphological indicators of diapause, the respiration rate was 2.3 times lower and fat content was 2–3 times greater in diapausing adults compared with nondiapause adults. In a laboratory study, the critical daylength for diapause induction was found to be 12 h:28 min.

Calanus finmarchicus diapause initiation: new view from traditional life history-based model

Organisms have evolved to optimally align the timing of diapause with the seasonal- ity of environmental conditions in order to maximize their fitness. Observations from the North- west Atlantic suggest that Calanus finmarchicus diapause initiation date varies significantly by geographic location, inconsistent with patterns of seasonal changes of any single environmental factor such as photoperiod, sea surface temperature, or food availability. In the present study, a life history-based model was used to reconcile the apparent inconsistency. The model results suggest that (1) the induction of diapause involves multiple environmental factors as a result of fitness maximization, and (2) in addition to temperature and food condition, predation pressure is another key factor that could affect diapause initiation process. It is further suggested that phenotypic plasticity is likely to be the major source of variation in the timing of diapause initiation for C. finmarchicus.