Production Of Diapausing Eggs Research Articles

Viability of subitaneous copepod eggs following fish predation on egg-carrying calanoids

The viability of subitaneous eggs of the eggcarrying calanoid copepod Euryternora herdmani was examined following fish ingestion and evacuation. More than 90% of the copepod embryos recovered intact in the fecal material of Atlantic silversides Menidia rnenjdja hatched within 3 d of incubation at 12 C in both light/dark and completely dark regimes. Percentage hatch was comparable to that for uningested embryos removed from eggsacs and for uningested embryos within eggsacs both attached to, and excised from, maternal copepods. For E. herdmani, selective silvers~de predation on ovigerous females is countered by the capacity of their subitaneous eggs to resist digestion. Zooplankton features that influence prey selection by planktivorous fish include prey size (Ivlev 1961, Brooks 1968, Werner & Hall 1974, O'Bnen et al. 1976), pigmentation (Zaret & Kerfoot 1975, Hairston 1979a, b) and, in some egg-carrying copepods and cladocerans, the presence of highly visible eggs (Mellors 1975, Hairston et al. 1983). Prior to periods of intense fish predation, many crustaceans produce diapause eggs that are thick-walled, highly pigmented and digestion resistant (Proctor et al. 1967, Mellors 1975). It has been suggested that the production of diapause eggs acts as a survival strategy to offset the costs of selective feeding on egg-bearing females (Hairston & Munns 1984) and ultimately aids in the perpetuation of endemic populations (Uye 1985). There has been only one account of digestion resistance in nondiapause copepod eggs. Marcus (1984) showed that both subitaneous ('quick-hatch') and diapause eggs released by the marine copepod Labidocera aestiva are capable of surviving passage through the gut tracts of 2 benthic polychaete species. Egg mortality during gut transport however, was higher for ingested subitaneous embryos. Many other copepod Present address: Ocean Sciences Centre. Memorial University of Newfoundland, St. John's, Newfoundland, Canada

Distribution of overwintering calanoid copepod eggs in sea-bed sediments around southern Britain

Eggs of the calanoid copepodsLabidocera wollastoni (Lubbock) andCentropages hamatus (Lilljeborg) and others, which could not be reliably assigned to species, were identified from sediment samples taken during three cruises in December 1984, January 1986, and February 1987 in the southern North Sea, the English Channel, the Irish Sea and the Celtic Sea. Eggs were most abundant in sediment samples taken between 20 and 80 m depth, with bottom stress less than 10 dyn cm−2, and near to the positions of tidal fronts. It is suggested that sedimentation, resuspension and sediment transport contribute to the causes of these distributions, which have been found to be consistent with the distributions of species which are known to produce diapause eggs as an overwintering strategy. Nauplii ofL. wollastoni, C. hamatus, C. typicus (Kroyer)Temora longicornis (Muller) andAcartia sp. hatched from incubated sediment samples. The last noted hatchings ofL. wollastoni, Centropages spp. andT. longicornis all occurred more than 1 yr after the start of the incubation experiments.

A method for distinguishing subitaneous and diapausing eggs in preserved samples of the Calanoid copepod genus Diaptomus

The current method to distinguish freshwater diaptomid copepod subitaneous eggs from diapausing eggs involves hatching live eggs and cannot be used on preserved eggs. Comparisons of preserved Diaptomus minutus, Diaptomus sanguineus, and Diaptomus spatulocrenatus egg types revealed a space between the chorion and the vitelline membrane in subitaneous eggs that is absent in diapausing eggs. Ratios of subitaneous to diapausing eggs in preserved samples calculated with the presence or absence of the space were regressed on ratios obtained from hatching of live samples (r = 0.97, P < 0.001). With this method, determination of D. minutus egg types in preserved samples from a lake supported the trend in diapausing egg production indicated by cohort data.

The Seed Bank of a Freshwater Crustacean: Copepodology for the Plant Ecologist

The spatial and temporal aspects of dormancy in a freshwater copepod, Diaptomus sanguineus, were investigated during three consecutive years in Bullhead Pond, Rhode Island. Patterns of diapausing egg production and deposition were monitored with plankton sampling and settling traps. Vertical and horizontal distributions of diapausing eggs in sediments were investigated by taking core samples. Diapausing eggs removed from sediments were tested in the laboratory for hatching ability. The long—term spatial and temporal patterns of emergence from the diapausing egg stage were documented in the field using inverted plastic funnel traps sampled weekly. The field data along with an estimated annual budget for diapausing eggs in the pond suggest that D. sanguineus has an egg bank, analogous to the seed banks of plants, that allows it to survive through harsh environmental periods.

Factors controlling the summer development of copepod populations in the southern bight of the North Sea

In two consecutive years an intensive sampling programmed was implemented at a fixed station in Dutch coastal waters to obtain a detailed record of the summer development of copepod populations in relation to phytoplankton and macroplankton abundance. The central question was whether densities of copepods are controlled by predation, in particular by invertebrate pelagic carnivores, or by food limitation. Methods applied to estimate daily predation by observed stocks of carnivores included analysis of gut contents and digestion rate, extrapolation of experimental feeding rates and of literature data on daily rations and maintenance needs. Chlorophyll- a and cell concentrations served as a rough measure for algal food supply. Since a decline in copepod densities manifested itself most clearly in decreasing naupliar numbers in both years, populations were assumed to be regulated mainly by recruitment or survival of these early life stages. Naupliar declines coincided with maximum densities of the hydromedusa Phialidium hemisphaericum, which dominated the macroplankton both in abundance and in biomass and reached a maximum density of 467 specimens·m −3 or 7 mg C·m −3. Copepod eggs appeared by far the most frequent prey item in their guts. However, these eggs are digested very slowly, if at all, and may often be ejected without any visible damage. The effect of egg predation on naupliar recruitment seems therefore relatively unimportant. Predation on swimming copepod stages was generally low. There was no evidence of selective feeding on nauplii. The maximum values of calculated predation pressure exerted by Phialidium populations matched daily copepod production only by way of exception. Impact of other invertebrate carnivores was negligible. As predation did not play a significant role, food availability seems the key factor underlying copepod population dynamics. The consequences of food limitation (reduced egg production, production of diapause eggs and enhanced cannibalism) are discussed. The observed coincidence of maximum predator abundance and minimum chlorophyll- a and diatom concentrations does not support the hypothesis that carnivores are able to indirectly benefit phytoplankton growth by reducing grazing pressure of herbivores.

In vivo and in vitro photoperiodic induction of diapause using isolated brain-suboesophageal ganglion complexes of the silkworm, Bombyx mori

By use of a bivoltine silkworm race which shows a long-day photoperiodic response after induction during the last (5th) instar, we tried to programme photoperiodic induction in the isolated brain-suboesophageal ganglion complex in vivo and in vitro. A pair of the complexes from a newly ecdysed 5th-instar female was transplanted into the abdomen of a late 5th-instar larva and exposed to long-day (20 h light: 4 h dark) or short-day (8 h light: 16 h dark) conditions for 3 cycles. The short-day-exposed complexes elicited the production of diapause eggs in the recipient silkworms destined to become non-diapause egg producers, whereas the long-day-exposed brain complexes produced non-diapause eggs. Transplant experiments of the brain-suboesophageal ganglion complex using isolated abdomens showed a similar result. The brain complexes from newly ecdysed females of the 5th-instar were cultured in Grace's insect medium under 20 h light: 4 h dark or 8 h light: 16 h dark for 4 cycles, respectively. After in vitro culture, a pair of complexes was implanted into the abdomen of a late 5th-instar larva destined to become a non-diapause egg producer, and the diapause incidence in the resultant moths was examined. The brain complexes which received the short-day cycles induced a large portion of diapause eggs, whereas those which received the long-day conditions induced non-diapause eggs. The connection of corpora cardiaca and corpora allata with the brain complex had no influence on the result. Suboesophageal ganglia which had been cultured in vitro and implanted elicited a remarkable production of diapause eggs, but cultured brains were ineffective in producing diapause eggs, regardless of the photoperiod experienced. These results demonstrate that photoperiodic induction of the silkworm can be programmed in in vivo and in vitro culture systems, and that components of the photoperiodic clock (photoreceptor, clock, and counter system) are located in the brain-suboesophageal ganglion complex, possibly in the brain itself.

Factors regulating the reproductive phenology of Onychodiaptomus birgei (Copepoda: Calanoida)1

Reproduction in a population of Onychodiaptomus birgei inhabiting a shallow montane pond consisted of alternating pulses of subitaneous and diapausing eggs. Unlike the single seasonal transition from subitaneous to diapausing eggs typical of many populations of diaptomids, female O. birgei tend to switch from the production of subitaneous eggs as they age regardless of time of year. The reproductive phenology of individual females was investigated in the laboratory to determine the proximate factors inducing diapausing egg production. Dissolved oxygen concentrations below the minimum observed in the field (<3 mg liter−1) had no effect on diapause induction. Photoperiod (L:D 8:16, 12:12, 16:8 h) had a detectable effect only at very high copepod densities (>1,000 individuals liter−1). High copepod densities increased and low food levels decreased the incidence of diapausing egg production. Increases in the proportion of subitaneous clutches in the field were preceded by peaks in fifth copepodid abundance. Field studies with in situ enclosures corroborated the finding that young females initially produce subitaneous eggs and then switch to diapausing egg production.

Genetic differentiation of populations of the planktonic copepod Labidocera aestiva

Planktonic populations of the calanoid copepod Labidocera aestiva show significant biochemical genetic heterogeneity along the Atlantic coast of the USA. In summer, 1981, copepods were collected by surface tows at Beaufort Inlet, North Carolina; Fort Pierce Inlet, Florida; and Vineyard Sound, Massachusetts. Genetic variation within each population and genetic differentiation among the three populations were studied by micro-acrylamide gel electrophoresis of six loci encoding four enzymes. All six enzyme loci were polymorphic when all populations were considered together, but the North Carolina population was monomorphic at two loci. High genetic variability was indicated by the following: (1) the number of alleles per locus averaged over all loci was 2.57±0.26 SD; (2) the average proportion of loci for which the frequency of the most common allele was not greater than 0.95 was 0.78±0.10; (3) the frequency of heterozygous individuals was 0.25±0.07. Genetic differentiation among population samples in the three regions was demonstrated in several ways: allele frequencies at one aminopeptidase-I locus, Lap-1, differed significantly among samples of the three populations, and there were unique alleles of high frequency at this locus in two population samples. Values of the statistic of genetic distance (D) averaged 0.20±0.08 for pairwise comparisons between all samples. Compared to expected heterozygosity if individuals across the entire range sampled mated at random, there were highly significant heterozygote deficiencies at five of the six loci. Genetic differentiation of populations of L. aestiva may result from (1) differential selection on populations in the three regions, or (2) restricted gene flow between the populations. Gene flow may be limited by geographic separation or differences in life history, such as seasonal presence in the plankton and diapause egg production.

VARIATION IN THE DIAPAUSE RESPONSE OFLABIDOCERA AESTIVA(COPEPODA: CALANOIDA) FROM DIFFERENT LATITUDES AND ITS IMPORTANCE IN THE EVOLUTIONARY PROCESS

Labidocera aestiva were collected from three distantly separated sites along the Atlantic coast of the United States. Their offspring were reared in the laboratory under several combinations of photoperiod and temperature to assess the diapause response and genetic similarity of the populations. The results indicate that L. aestiva is not genetically homogeneous throughout its range. Differences in the percentage of subitaneous and diapause eggs produced by laboratory-reared and field-collected populations reflected the unique combination of environmental conditions occurring in the geographic regions from which the animals originated. In the Virginian province where planktonic stages of the species are seasonally present, diapause egg production is triggered by short day length photoperiods and cool temperatures. On the other hand in the Carolinian province where the planktonic stages tend to occur year-round diapause eggs are rarely produced by either field-collected females or their laboratory reared o...

Relationship between photoperiod and secretion of the diapause hormone during larval stages of the silkworm, Bombyx mori L., reared on an artificial diet

The suboesophageal ganglion of the silkworm, Bombyx mori synthesizes sufficient diapause hormone to produce diapause eggs, regardless of the photoperiodic conditions experienced during the larval stages. When larvae destined to produce non-diapause eggs are implanted with the brain-suboesophageal ganglion complex from larvae which have been reared under short-day conditions, the resulting adults lay diapause eggs. The larvae receiving the complex from larvae reared under long-day conditions gave rise to adults which did not produce any diapause eggs. The brains from pupae which have been reared under long-day conditions show an activity inhibiting the secretion of diapause hormone by the suboesophageal ganglion. The mechanism through which the brain controls the secretion of diapause hormone from the suboesophageal ganglion can be modified by photoperiodic conditions during the larval stages.

PHOTOPERIODIC AND TEMPERATURE REGULATION OF DIAPAUSE INLABIDOCERA AESTIVA(COPEPODA: CALANOIDA)

The calanoid copepod Labidocera aestiva was reared in the laboratory to ascertain the effects of photoperiod and temperature on subitaneous and diapause egg production. The results indicate that photoperiod is the primary stimulus regulating the type(s) of eggs produced by a female, but that the temperature regimen can modify this effect. Under short daylength photoperiods (e.g., 8L:l6D) subitaneous egg production is increased by increasing the temperature regimen from 15.0°C or 19.0°C to 25.0°C. However, under long daylength regimens (e.g., 18L:6D) females appear to be unresponsive to temperature changes within the range of 15.0°C to 25.0°C. It is suggested that this response to photoperiod and temperature more accurately couples the life cycle of L. aestiva with seasonal environmental fluctuations.

PRODUCTION OF DIAPAUSE EGGS BY THE AUSTRALIAN PLAGUE LOCUST AFTER MIGRATION

ABSTRACTPlague locusts, Chortoicetes terminifera (Walker), that emigrated from Longreach to Cunnamulla, Queensland, produced non‐diapause eggs. Those that emigrated further to Tottenham, N.S.W. produced diapause eggs within 7 days indicating that diapause induction is rapid and can occur in fully grown adults.

Induction of egg diapause in Bombyx mori by some cephalo-thoracic organs of the cockroach, Periplaneta americana

Induction of egg diapause in the silkworm, Bombyx mori by some cephalo-thoracic organs of the cockroach, Periplaneta americana was examined. All tissues tested such as brain, corpora cardiaca, corpora allata, suboesophageal and thoracic ganglia and nerve cords between thoracic ganglia were able to produce diapause eggs in non-diapause egg producers both by transplantation and injection of their crude homogenates. The homogenate of thoracic ganglia was effective even in pharate adults with the suboesophageal ganglion removed or in isolated abdomens of pharate adults. From these results, it was surmised that some endocrine organs, as well as the central nervous system in the cephalo-thorax of Periplaneta americana, contained the active principle responsible for egg diapause in Bombyx mori.

Stage Dependency of Diapause Egg Production by Corpora Cardiaca and Corpora Allata Complex of the Silkworm, Bombyx mori (Lepidoptera : Bombycidae)

Stage Dependency of Diapause Egg Production by Corpora Cardiaca and Corpora Allata Complex of the Silkworm, Bombyx mori (Lepidoptera : Bombycidae)

Induction of egg diapause by implantation of corpora cardiaca and corpora allata in Bombyx mori

Diapause egg production was examined in non-diapause egg producers by implantation of various cephalic organs into pharate adults 4 days after larval-pupal ecdysis. The implantation of five pairs of corpora cardiaca or corpora allata induced a great amount of egg diapause. Implantation of these organs was effective in inducing egg diapause even when the suboesophageal ganglion of the recipients had been removed, although the effect of the corpora allata decreased moderately. The injection of juvenile hormone into 4-day-old pharate adults did not greatly increase production of diapause eggs.

Effect of Different Wave-length of Light under Long Day Condition During Incubation Period of Egg on Diapause in Silkworm, Bombyx mori L.

To confirm a photorecepter in the embryo having a concern in embryonic diapause induction in next generation. First of all, effects of different wavelength on diapause formation in the silkworm, Bombyx mori, irradiated for 17 hr daily during incubation period of egg at 18-19°C, were examined with those races, J106 × Daizo and (w2 × Daizo) × W2.(1) It was found that lower light intensity limits for the production of moths laying diapause eggs were below 1.3 μW·cm-2 at the wave-length of both 483 nm and 503 nm, and between 0.0084 and 0.039 μW·cm-2 at 525 nm.(2) It was also found that higher limits for non-diapause eggs were beyond 13 μW·cm-2 at both 483 nm and 503 nm, and between 3.9 and 17.8 μW·cm-2 at 525 nm.(3) From the examination on the effects of light of wave-length from 356 nm to 687 nm at equal light intensities of 10 or 13 μW·cm-2, it became evident that longer wave-length than 640 nm had no effect upon the production of diapause eggs, likewise in darkness, while shorter wave-length than this showed a distinct effect upon it, as the white light did.

Diapause in the aestivating egg of Halotydeus destructor (Acari : Eupodidae)

The occurrence of an aestivating diapause in the eggs of the red-legged earth mite, H. destructor, is established. The production of diapause eggs in females is influenced by the increasing maturity of food plants in the spring. Morphogenesis is resumed following exposure to early summer conditions for 4-6 weeks in the field. In the laboratory, diapause development was achieved by exposing the eggs to various combinations of temperature and relative humidity. The most effective treatment was exposure for 32 days to 52DC and 50% R.H., although diapause development occurred within the temperature range 15-70DC and relative humidity range 10-100%, and even when the eggs were completely immersed in water. It was most successfully promoted in atmospheres having vapour pressures of about 40 mmHg, at all temperature and humidity combinations. At 20% R.H., diapause development was relatively slower than at humidities above and below this, whereas tolerance to high temperatures was greatest at this humidity. Diapause eggs were not harmed either by complete immersion in water or by periodical desiccation and re-moistening.

The ecology of Sminthurus viridis (Collembola) II. Diapause in the aestivating egg

The existence of an aestivating diapause in the egg batches of S. viridis is established. The production of diapause eggs is influenced in females by the increasing maturity of food plants in the spring. Morphogenesis is resumed in diapause eggs following physical removal of the soil covering in the laboratory or exposure to summer field conditions for a period of 2-3 months. The mechanisms of the egg diapause in S. viridis are studied experimentally, and their adaptive significance for the species is discussed.

The response of the pupal ovaries of the silkworm to the diapause hormone with special reference to their physiological age

Whether pupal ovaries of the silkworm produce diapause eggs or not is under the control of the diapause hormone secreted from the sub-oesophageal ganglion (SG). The response of pupal ovaries to this hormone has been studied by the extirpation of the SG at different pupal ages of ‘diapause’ silkworms. SG-removal at any pupal age caused blood trehalose to increase and ovary glycogen to decrease, the effect being proportional to age, i.e. the earlier the removal the greater the effect. Diapause eggs are not produced when SG-removal is performed up to the third day after pupation, but it is produced more or less according to pupal age thereafter. The production of diapause eggs is discussed from the standpoint of both the metabolic transition in the ovaries and the physiological age of the oöcytes.

Studies On the Mode of Action of the Diapause Hormone in the Silkworm, Bombyx Mori L

ABSTRACT The action of the diapause hormone has been studied by injecting extracts of the heads of male moths or of the brain-suboesophageal ganglion complexes of pupae into pupae expected to produce non-diapause eggs. The effect of the injection of hormone upon young oocytes is to make them develop into diapause eggs. Older oocytes, which have already acquired non-diapause characters, are not affected. The hormone is almost completely inactivated when injected on the day of pupation. The hormone is most effective when injected into pupae 2-3 days old, at which stage the ovarioles have started to grow vigorously. It is ineffective 1-2 days before adult emergence, by which time all the oocytes have acquired non-diapause characters. The hormone is inactivated in all pupae irrespective of whether they are destined to produce diapause eggs or non-diapause eggs. Inactivation of diapause hormone (in contrast to that of juvenile hormone) is partially relieved by exposure to low temperature or by simultaneous injection of indian ink. The extracts prepared as in (1) above do not serve as a stimulant for the brain causing the suboesophageal ganglion to produce diapause hormone. The action of the extract faithfully reflects the function of the diapause hormone which originates in the suboesophageal ganglion.