Temperature-controlled under-water egg dormancy and postflood hatching in Isotoma viridis (Collembola) as forms of adaptation to annual long-term flooding

Summary Incubation experiments with eggs of a population of Isotoma viridis, which is exposed to annual long-term flooding from about April to July, as well as field observations show that temperature controls both, underwater egg dormancy and immediate postflood hatching. The population is located at the Eder Freshwater Reservoir in Germany.If constant experimental temperatures are above 14°C, almost all eggs are nondormant. Dormancy is established at temperatures below 15°C, but embryonic development is completed. Experiments indicate that of the environmental factors that change drastically at the end of submergence (light, turgor pressure, oxygen, a.o.), only temperature acts as a hatching trigger. Hatching of the previously dormant eggs occurs at a constant threshold temperature of 16°C, mainly within 2 to 20 days after temperature elevation, but most of these eggs need even higher temperatures to hatch. Remaining eggs were partly stimulated to hatch by recooling them at 7°C for some days and then rewarming them again.The threshold temperatures observed are unusually high for Collembola and seem to be the result of selection by the special floodplain conditions. During normal years, the surface temperatures of submerged soil usually do not exceed threshold limits before summer drainage. This allows both, protection from under-water hatching and an optimal timing of hatching at the very beginning of the main terrestrial period. The experiments show that above the threshold temperature (in warm summers), individuals can hatch under water and survive submerged for 10–15 days. They can survive even longer in the water habitat, if emergent structures enable them to climb onto the water surface. Furthermore, a considerable polymorphism observed in some hatching properties improves the chance to survive under the unpredictable floodplain conditions.     

Environmental factors associated with the distribution of floodwater mosquito eggs in irrigated fields in Wrocław,Poland

A survey of distribution patterns of floodwater mosquito eggs related to environmental conditions such as moisture and plant associations was conducted by using soil samples from irrigated fields in Wroc?aw, Poland. Mosquito egg distribution was determined by repeatedly flooding the soil samples with aerated water at a temperature of 25° C. Under laboratory conditions, hatching in installments of Aedes caspius (Pallas) and Aedes vexans (Meigen) were commonly observed. The results show that ～75% of the larvae of Ae. caspius and Ae. vexans hatched after the first flooding under summer‐like conditions, whereas, following the second and third flooding, the numbers of hatched larvae were significantly lower. In our study, within one intermediate flooded field, a total of 66 plant species was identified and classified into six communities. All vegetation types were associated by varied egg densities and showed differences both in richness and Shannon‐Wiener diversity index as well as in ecological indices for moisture, soil reaction, and nutrient level. Small changes in elevation along the slope within the study area showed a large difference in the distribution of mosquito eggs. The highest average egg density was observed in zones with high occurrence of Phalaris arundinacea, usually prevalent in intermediate flooded and fertile areas. Knowledge of the indicators for the distribution of floodwater mosquito eggs in temporary breeding sites may be essential for organizing a successful, integrated mosquito control program with special regard to microbial control agents.     

Long-term storage and viability of Ochlerotatus albifasciatus (Diptera: Culicidae)

The viability of Ochlerotatus albifasciatus (Macquart) eggs stored at room temperature and at 5 degrees C was studied over 31 months. After 12, 18 and 31 months of storage, eggs were acclimatized at 22 degrees C for ten days, and then inundated twice every seven days. The effect of the storage period on the percentage of hatching was analyzed by one way ANOVA. Differences on the hatching response between the first and second flooding were analyzed by paired t-test. Differences on the hatching response between the two storage conditions were analyzed by Mann-Whitney rank test. Results showed that (1) Oc. albifasciatus eggs were able to survive and hatch over 31 months; (2) the percent hatching of eggs stored at 5 degrees C was higher than that of eggs stored at room temperature; and (3) low temperatures and long periods without water favor installment hatching.     

Egg hatching of mosquitoes Aedes caspius and Ae. vittatus stimulated by water vibrations

Simple laboratory experiments with eggs of wild-caught Aedes caspius (Pallas) and Aedes vittatus (Bigot) mosquitoes (Diptera: Culicidae) demonstrated that egg hatch rates (i.e. percentage hatching daily) increased significantly in response to water vibrations caused by finger-tip drumming on containers of submerged eggs. When disturbed by daily vibrations for only 30 s, eggs hatched sooner than when they remained flooded or were periodically drained and reflooded without agitation. For autogenous Ae. caspius from saltmarsh, egg hatch rates were three- to four-fold greater for groups of 50 eggs than for solitary eggs, possibly due to chemicals (functional kairomones) emanating from other eggs or larvae. For anautogenous Ae. vittatus from freshwater rock-pools, tapping the container daily (for 30 s each 2 h in 8 h) hatched 93% of eggs, compared with only 42% hatch of eggs agitated only when first flooded or 55% hatch of eggs dried and reflooded three times during 17 days without other disturbance. It is concluded that, apart from flooding and other factors, vibrations - simulating the patter of rainfall provide a very significant hatching stimulus for Aedes eggs.     

Developmental arrest during embryonic development of the common chameleon (Chamaeleo chamaeleon) in Spain

Embryonic development of the common chameleon, Chamaeleo chamaeleon, was monitored from oviposition to hatching at a field site in southwestern Spain and in the laboratory under five experimental temperature regimes. Embryos were diapausing gastrulae at the time of oviposition; developmental arrest in the field continued as cold torpor during winter. Postarrest development in the field commenced in April, and hatching occurred in August, for a total incubation period of 10.5 mo. In the laboratory, one group of eggs was incubated at a constant warm (26 degrees C) temperature. The remaining treatments simulated field conditions and consisted of initial periods of warm temperature of 0, 27, 46, and 71 d, a subsequent 4-mo period of cold winter (16 degrees C) temperature, and a final period of warm (26 degrees C) temperature. Embryos in the constant warm temperature treatment were in diapause an average of 3 mo, with clutch means ranging from 2 to 4 mo. Hatching among clutches occurred over 2 mo. In contrast, for field and experimental eggs that experienced cold winter conditions, hatching within treatments occurred over 2-14 d; "winter" conditions synchronized development. The length of time between the end of cold conditions and hatching did not differ among treatments; development thus resumed as soon as temperature was suitable regardless of the initial period of warm temperature. Diapause in nature thus insures that embryos remain gastrulae after oviposition despite nest temperatures that may be warm enough to support development.     

The hatching time of Locusta migratoria under outdoor conditions: role of temperature and adaptive significance

The present study investigates the time of hatching of the migratory locust Locusta migratoria using egg pods that are artificially buried in the soil under outdoor conditions. Most eggs hatch in the mid‐morning, with a peak between 11.00 and 12.00 h, and none hatch before 09.00 or after 16.00 h. Furthermore, most egg pods complete hatching within a day, although some take 2 or 3 days, and egg hatching is interrupted by rain. There are no large differences in hatching time from May to September. Laboratory experiments in which the eggs are exposed to temperatures simulating outdoor conditions show that soil temperature is the main factor controlling hatching activity. The increase in temperature in the morning appears to trigger egg hatching, as confirmed by laboratory experiments, which may explain the similar hatching times between seasons. The seasonal patterns of temperature variation and hatching time suggest that the hatching time of L. migratoria eggs may be adjusted to allow the hatchlings to be exposed to high temperatures in the afternoon so that they can harden their bodies quickly.     

Effects of temperature during chilling and pre-chilling periods on diapause and post-diapause development in a katydid, Eobiana engelhardti subtropica

In Eobiana engelhardti subtropica, early laid eggs reach the diapause stage in early autumn. For long periods before winter, the eggs are exposed to temperatures higher than their theoretical lower threshold for development. In contrast, late-laid eggs cannot reach their diapause stage before winter. Our study showed that E. e. subtropica copes with these difficulties via the thermal response involving embryonic diapause. In this katydid, the almost fully developed embryo undergoes an obligatory diapause. When diapause eggs were maintained at a temperature of 20 degrees C or higher, diapause persisted for a long time. Diapause was effectively terminated by temperatures ranging from 1 to 11 degrees C, and hatching occurred successfully at temperatures from 11 to 15 degrees C. In addition to the chilling temperature, pre-chilling temperature modified diapause intensity and hatching time. Diapause eggs hatched earlier after chilling when the pre-chilling temperature was lower, within a range of 14.5-25 degrees C. Thus, the low-temperature requirement for diapause termination prevents early laid eggs from untimely hatching in autumn, and low temperatures before and during winter decrease diapause intensity and shorten the hatching time in the following spring. When eggs were chilled before diapause, they tolerated chilling and averted diapause. Thus, even if eggs encounter low temperatures before diapause, they can hatch in the following spring.     

Synchrony in the hatching of eggs in the desert locust <Emphasis Type="Italic">Schistocerca gregaria</Emphasis> (Orthoptera: Acrididae): egg condition influences hatching time in the laboratory and under simulated field temperatures

This study examined the time of hatching of the desert locust Schistocerca gregaria Forskål (Orthoptera: Acrididae) in the laboratory to test the effect of eggs within a pod versus individualized eggs. The pod organization of eggs is thought to play a role in controlling hatching time and to facilitate synchronous hatching at constant temperatures. In the present study, we examined the hatching times of eggs in a pod and individualized eggs under 24-h thermocycles and simulated field temperatures. We tested two patterns of thermocycles consisting of a 12-h thermoperiod (35 or 30 °C) and 12-h cryoperiod (low temperature period; 30 or 25 °C), and two patterns of field temperatures observed in a natural habitat, Mauritania, in May and September. The majority of eggs hatched during low temperature periods in all patterns tested. In addition, the variances of hatching times for individualized eggs were significantly greater than for egg pods in which a clear peak of time of hatching was observed. We show that egg condition influences hatching time under thermocycles of constant and fluctuating temperatures in the laboratory, and may play a role in the adaptive time of hatching.     

Resistance to freezing temperatures in Aedes (Ochlerotatus) albifasciatus (Macquart) eggs (Diptera: Culicidae) from two different climatic regions of Argentina

Aedes (Ochlerotatus) albifasciatus (Macquart) has the capacity to proliferate in different kinds of climates within its distribution range in South America. With the aim of studying local thermal adaptations of eggs, we exposed egg stocks from two climatically different localities: temperate humid pampa (Buenos Aires) and cold arid Patagonian (Sarmiento), to freezing conditions and then evaluated the effect on some features at this level. First, we thermally described the substrate where this species lays its eggs in the arid region. A typical thermal condition during winter was 10 h at ?12° C. Second, we evaluated the effect of freezing on primary hatching (vs total hatching) and embryo survival. We also compared the proportion of embryonated eggs from both populations. The proportions of embryonated eggs were not different between localities, with averages of 78% and 83% in Sarmiento and Buenos Aires, respectively. Survival was equally successful after freezing in the two localities with an average range between 94–99%. Whether or not the eggs from Buenos Aires and Sarmiento were under freezing conditions, hatching was more than 98% after the first flooding. The results suggest that eggs of Ae. albifasciatus from Sarmiento and Buenos Aires have the same ability to survive at extreme temperatures (<0° C), showing a regional thermal adaptation rather than a local one.     

The effects of exposure and microbes on hatchability of eggs in open-cup and cavity nests

Many avian species initiate incubation before clutch completion, resulting in an asynchronous hatch of their eggs. Several studies suggest that early laid eggs in birds that exhibit synchronous hatching may be more vulnerable to the negative impacts of ambient temperatures and/or trans-shell infection by microbes. However, nearly all of these studies have exposed fertile eggs to environmental conditions in artificial cavity nests, and thus, the effects of exposure of eggs to environmental conditions in open-cup nests remains largely unknown. Therefore, we directly compared hatchability and rates of trans-shell infection in fertile domestic chicken eggs that were exposed for 1–5 days in either open-cup or cavity nests. Eggs in open-cup nests had significantly higher rates of trans-shell infection and lower hatchability than those in cavity nests. These differences may result from different environmental conditions in open-cup nests, as well as in rates of microbial colonization of eggs. Cavity nests maintained slightly higher temperatures than did open-cup nests in the same location; thus, eggs in cavity nests were exposed for a longer period of time to temperatures ≥27°C, the temperature at which antibacterial enzymatic activity is initiated in the albumen. Moreover, microbial growth on eggs was much higher in open-cup nests even when eggs in these nests were cleaned daily with alcohol. It may be that the increased exposure to rain events in open-cup nests may facilitate microbial growth and egg infection. Thus, our data suggest that open-cup nesters may face constraints on reproduction different from those that cavity nesters face, and therefore may make choices regarding incubation that reflect these challenges.     

Adaptive difference in daily timing of hatch in two locust species,Schistocerca gregaria and Locusta migratoria: The effects of thermocycles and phase polyphenism

This study examined the effects of temperature and phase polyphenism on egg hatching time in the desert locust, Schistocerca gregaria, and the migratory locust, Locusta migratoria. The two species exhibited differences and similarities in hatching behavior when exposed to different temperature conditions. In 12-h thermocycles of various temperatures, the S. gregaria eggs hatched during the cryoperiod (low temperature period), whereas L. migratoria eggs hatched during the thermoperiod (high temperature period). The eggs of both species hatched during the species-specific period of the thermoperiod in response to a temperature difference as small as 1 °C. Furthermore, the locusts adjusted hatching time to a new thermal environment that occurred shortly before the expected hatching time. In both species, the hatching of the eggs was synchronized to a specific time of the day, and two hatching peaks separated by approximately 1 day were observed at a constant temperature after the eggs were transferred from thermocycles 3 days before hatching. Eggs laid by gregarious females hatched earlier than those laid by solitarious females in S. gregaria but this difference was not observed in L. migratoria.     

Eggs in autumn: responses to declining incubation temperatures by the eggs of montane lizards

Facultative hatching in response to environmental cues may increase the viability of offspring, if the cue that stimulates hatching also predicts the negative consequences of delayed emergence. Declining incubation temperatures might provide such a cue for montane lizards, because eggs that fail to hatch before winter will perish in the nest. I tested this idea by incubating eggs of an alpine scincid lizard ( Bassiana duperreyi ) in the laboratory. For the first half of the incubation period the eggs were kept at nest temperatures typical of those experienced in summer in the field (daily cycle of 18 ± 7.5°C). I then transferred eggs at weekly intervals into cooler regimes (either 15 ± 7.5°C; or with daytime temperatures unchanged but dropping to 0°C overnight). Contrary to prediction, the eggs did not hatch early. However, transfer to lower temperatures caused only a relatively short delay in hatching, because of a virtual temperature-independence of developmental rates late (but not early) in incubation. Decreasing incubation temperatures also modified hatchling running speeds and post-hatching growth rates, even if the thermal decrease occurred only shortly before the usual time of hatching. These processes plausibly affect hatchling fitness in cold-climate reptiles, and might be adaptations to montane habitats. Alternatively, they may prove to be widespread in other (warmer-climate) reptile taxa, in which case no adaptive hypothesis need be proposed. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 71–77.     

Different thermal stimuli initiate hatching of <Emphasis Type="Italic">Daphnia</Emphasis> diapausing eggs originating from lakes and temporary waters

The simultaneous hatching of Daphnia resting eggs from a number of different lakes and ponds using one set of hatching cues can be difficult to achieve as environmental conditions differ considerably between water bodies. Therefore, optimal hatching conditions for ephippial eggs originating from shallow temporary waters may differ from those found in large lakes. The aim of our study was to compare the optimal thermal conditions for hatching ephippial eggs of Daphnia found in permanent lakes and those from shallow temporary ponds. We used ephippial eggs of Daphnia from the longispina species complex originating from two temporary city ponds and two deep lakes in Poland. The ephippia were protected against overheating at all stages of the field and laboratory work to prevent activation or killing of the eggs. After a refractory period (imposed storage in cool and dark conditions), ephippia were incubated at six different temperatures (6, 9, 12, 15, 18 and 21 °C) under a 16:8 L:D light regime. Our results indicate that hatching of resting eggs of Daphnia that inhabit lakes or ponds may require different thermal conditions. The hatching success of ephippial eggs originating from temporary waters was relatively high (30–56%) at all tested incubation temperatures, while for the ephippial eggs from the deep lakes it was lower (7–37%) and inversely related to water temperature. The divergent hatching responses of the ephippial eggs originating from temporary pools and lakes may reflect the typical thermal conditions during hatching in their native habitats. While in the deep lakes of the temperate zone Daphnia hatching typically occurs during the low water temperatures of early spring, in shallow ponds Daphnia hatching may occur throughout the year at varying water temperatures, from a few to over a dozen degrees Celsius.     

Plasticity of hatching in amphibians: evolution, trade-offs, cues and mechanisms

Many species of frogs and salamanders, in at least 12 families, alter their timing of hatching in response to conditions affecting mortality of eggs or larvae. Some terrestrially laid or stranded embryos wait to hatch until they are submerged in water. Some embryos laid above water accelerate hatching if the eggs are dehydrating; others hatch early if flooded. Embryos can hatch early in response to predators and pathogens of eggs or delay hatching in response to predators of larvae; some species do both. The phylogenetic pattern of environmentally cued hatching suggests that similar responses have evolved convergently in multiple amphibian lineages. The use of similar cues, including hypoxia and physical disturbance, in multiple contexts suggests potential shared mechanisms underlying the capacity of embryos to respond to environmental conditions. Shifts in the timing of hatching often have clear benefits, but we know less about the trade-offs that favor plasticity, the mechanisms that enable it, and its evolutionary history. Some potentially important types of cued hatching, such as those involving embryo-parent interactions, are relatively unexplored. I discuss promising directions for research and the opportunities that the hatching of amphibians offers for integrative studies of the mechanisms, ecology and evolution of a critical transition between life-history stages.     

Environmental effects on bet hedging in <Emphasis Type="Italic">Aedes</Emphasis> mosquito egg hatch

We used a path analysis procedure to examine the influence of environmental effects on the egg hatching response of the container breeding mosquito, Aedes triseriatus. A. triseriatus eggs were collected from 22 different sites across the eastern US, and exposed to repeated hatch stimuli in the laboratory. The resulting data were used to construct hatch indexes for each site. Structural equation modeling was used to discriminate among hypotheses relating to the functional relationships between population hatch trait and local climatic conditions. The results suggest that the delayed hatch pattern is an adaptive bet-hedging strategy that allows the species to manage desiccation risks. The selected model indicates that environmental variables differentially affect the immediate and the delayed, long term hatch patterns. High temperatures directly reduce the number of egg hatching on the first stimulus, but only indirectly affect the delayed hatch pattern. Low precipitation and high variability in precipitation directly increase the delaying pattern. The hatch trait appears to be a critical adaptation that allows the species to occupy a broad range in east North America.     

Partial flooding enhances aeration in adventitious roots of black willow (Salix nigra) cuttings

Black willow (Salix nigra) cuttings are used for streambank stabilization where they are subjected to a range of soil moisture conditions including flooding. Flooding has been shown to adversely impact cutting performance, and improved understanding of natural adaptations to flooding might suggest handling and planting techniques to enhance success. However, data assessing the root aeration in adventitious roots that are developed on cuttings of woody species are scant. In addition, it appears that no data are available regarding aeration of the root system under partially flooded conditions. This experiment was designed to examine the effects of continuous flooding (CF) and partial flooding (PF) on aerenchyma formation and radial oxygen loss (ROL) in black willow cuttings. Photosynthetic and growth responses to these conditions were also investigated. Under laboratory condition, replicated potted cuttings were subjected to three treatments: no flooding (control, C), CF, and PF. Water was maintained above the soil surface in CF and at 10 cm depth in PF. Results indicated that after the 28-d treatments, root porosity ranged between 28.6% and 33.0% for the CF and C plants but was greater for the PF plants (39.2% for the drained and 37.2% for the flooded portions). A similar response pattern was found for ROL. In addition, CF treatment led to decreases in final root biomass and root/shoot ratio. Neither CF nor PF had any detectable adverse effects on plant gas exchange or photosystem II functioning. Our results indicated that S. nigra cuttings exhibited avoidance mechanisms in response to flooding, especially the partially flooded condition which is the most common occurrence in riparian systems.     

Better eggs today than psocids tomorrow: Aedes aegypti (Diptera: Culicidae) eggs exposed to Liposcelis sp. (Psocodea: Liposcelididae) has reduced hatching rates

For different research purposes, there is a need to mass rear mosquitoes, such as Aedes aegypti, under laboratory conditions. The rearing process begins with egg production followed by egg storage in a dry environment, inside containers. Stored eggs are susceptible to environmental threats when storage conditions are suboptimal. Some terrestrial insects can invade this environment and attack stored eggs. In this brief report, we assessed whether Ae. aegypti eggs exposed to Liposcelis sp. individuals had reduced hatching and immature development rates. We exposed 100 eggs in different treatment conditions (fixed in porous paper and loosed) to 30 Liposcelis sp. individuals for ten days and then we induced hatching. We observed a hatching rate of 99% reduced for those eggs adhered to porous paper and loosed eggs showed a hatching rate of 45% decreased for those eggs exposed to Liposcelis sp. The remaining larvae took longer to develop into pupae as well, showing a four-day delay on average to the final metamorphosis of the aquatic stage. These results reinforce the need to frequently monitor egg storage conditions to maintain laboratory colonies stable and free from pests that can interfere with mosquito life-history traits.     

THE EMERGENCE OF LARVAE FROM FREE EGGS OF THE POTATO-ROOT EELWORM HETERODERA ROSTOCHIENSIS (WOLL.)

A technique for conducting hatching experiments on eggs freed from cysts is described. The form of the hatching response was found to be similar to that of eggs contained within cysts, but the response of the free eggs to the hatching stimulus was slightly more rapid. Investigations into factors affecting free egg hatching showed that it was necessary to presoak cysts before extracting the eggs from them for hatching. Eggs taken from dry cysts or from cysts that had been opened or cracked before presoaking did not respond to diffusate. When free eggs and whole cysts were exposed to the same graded series of dilutions of diffusate, the L.A. values (i.e. log concentrations of hatching factor) derived from plotting the hatching curves were in very close agreement.     

Egg incubation temperature differently affects female and male hatching dynamics and larval fitness in a leafhopper

Temperature effects on ectotherms are widely studied particularly in insects. However, the life-history effects of temperature experienced during a window of embryonic development, that is egg stage, have rarely been considered. We simulated fluctuating temperatures and examined how this affects the operational sex ratio (OSR) of hatching as well as nymph and adult fitness in a leafhopper, Scaphoideus titanus. Specifically, after a warm or cold incubation we compared males and females hatching dynamics with their consequences on the sex ratio in the course of time, body size, weight, and developmental rate of the two populations, all reared on the same posthatching temperature. Males and females eggs respond differently, with females more sensitive to variation in incubation temperature. The different responses of both sexes have consequences on the sex ratio dynamic of hatchings with a weaker protandry after warm incubation. Temperatures experienced by eggs have more complex consequences on posthatching development. Later nymphal instars that hatched from eggs exposed to warm temperature were larger and bigger but developmental rate of the two populations was not affected. Our study demonstrates how incubation temperature could affect operational sex ratio and posthatching development in an insect and how this may be critical for population growth.     

Effect of soil flooding on photosynthesis,carbohydrate partitioning and nutrient uptake in the invasive exotic Lepidium latifolium

Lepidium latifolium L. is an invasive exotic crucifer that has spread explosively in wetlands and riparian areas of the western United States. To understand the ecophysiological characteristics of L. latifolium that affect its ability to invade riparian areas and wetlands, we examined photosynthesis, chlorophyll concentration, carbohydrate partitioning and nutrient uptake in L. latifolium in response to soil flooding. Photosynthesis of flooded plants was about 60–70% of the rate of unflooded controls. Chlorophyll concentrations of flooded plants were about 60–70% of the unflooded plants during 15–50 days of flooding. Flooding resulted in an increase in leaf starch concentration, but root starch concentration was not significantly affected. However, concentrations of soluble sugar were significantly higher in both leaves and roots of flooded plants than unflooded controls. On day 50 after initial flooding, the concentrations of N, P, K and Zn in leaves of flooded plants were lower than in control plants. The concentrations of Mn and Fe in leaves of flooded plants were eight and two times those of control plants, respectively. In contrast, N, P, K and Zn concentrations of roots of flooded plants were slightly higher than in unflooded plants. The concentrations of Fe and Mn in roots of flooded plants were 15 and 150 times those of the control plants, respectively. The transport of P, K, and Zn to shoots decreased and that of Mn increased under flooding. The accumulation of N, K and Zn in roots decreased and that of Mn increased in response to flooding. The results suggested that the maintenance of relatively high photosynthesis and the accumulation of soluble sugar in roots of flooded plants are important adaptations for this species in flooded environments. Despite a reduction in photosynthesis and disruption in nutrient and photosynthate allocation in response to flooding, L. latifolium was able to survive 50 days of flooding stress. Overall, L. latifolium performed like a facultative hydrophyte species under flooding.