Influence of temperature on hatching of eggs of Lepidurus couesii (Crustacea,Notostraca)

Tadpole shrimps (Notostraca) occur sporadically in temporary ponds and their survival there depends largely upon the drought-resistant eggs they produce. Environmental conditions conducive to hatching of eggs of Lepidurus couesii were investigated in the laboratory. Almost all eggs hatched best at 20 °C, whether desiccated for a short or long period, with a prior freezing shock or without such a shock, with intact shells. Eggs that endured a longer period of desiccation and eggs with abraded shells displayed a more equivocal response to different temperatures for hatching. Long-term hatchability of eggs was demonstrated. Time required for successful hatching was shortest at 20 °C, with no discernible difference between 17 °C and 25 °C. Both short- and long-term survival of populations of the species appears to be fostered by the adaptive response to temperature shown by the eggs.     

Laboratory studies of factors affecting egg hatch of triops longicaudatus (LeConte) (Notostraca : Triopsidae)

Egg hatch was greatest (78.33%) for eggs not previously desiccated. A reduction in numbers hatched occurred as the relative humidity at which they were dried decreased. Some eggs hatched (0.67–79.33%) at pH levels of 3.10–10.01 with the highest hatch at pH 5.60. Water temperature greatly affected egg hatch. No hatch occurred until temperatures were above 14°C. A constant 29°C significantly inhibited hatching. Egg hatch increased 13.00 to 43.42% as salinity decreased from 2200 to 9.24 micromhos/cm. As little as 13 mm of flooded soil covering the eggs prevented them from hatching for 14 days. Eighteen percent hatch resulted when soil and eggs were redistributed to a 1 mm soil layer. Egg samples from the same parent, even though treated similarly, often hatched at greatly varying rates and only rarely was hatching 100% within a replication.     

Effects of ambient Lake Mohave temperatures on development,oxygen consumption,and hatching success of the razorback sucker

Synopsis Spawning of razorback suckers,Xyrauchen texanus, in Lake Mohave occurred from 10–22°C and larvae were collected at water temperatures from 10–15°C in 1982 and 1983. In the laboratory, hatching success was similar from 12–20°C, but reduced hatching success was found at 10°C while none hatched a 8°C. Development rate and oxygen consumption were positively related to incubation temperature. Direct effects of ambient Lake Mohave water temperatures on hatching success of razorback sucker embryos are considered minimal. Historical spawning temperatures for the species are hypothesized based upon successful incubation temperatures and comparison to the white sucker,Catostomus commersoni.     

Interspecific and intraspecific variations in egg hatching for British populations of the stoneflies Siphonoperla torrentium and Chloroperia tripunctata (Plecoptera: Chloroperiidae)

SUMMARY 1. The objective was to compare variations in egg hatching between the two species (interspecific variations) and between populations of the same species (intraspecific variations). There were significant interspecific, but not intraspecific, differences in female size, adult life-span, egg production, hatching success, incubation periods and hatching periods.
2. The optimum temperature for hatching success within the range 3.8–22.1°C in the laboratory and the range over which at least 50% of the eggs hatched were lower for Chloroperia tripunctata (Scopoli) (8.5°C, 4.2–17.3°C) than for Siphonoperla torrentium (Pictet) (12.8°C, 6.1–19.4°C). Few eggs hatched at 22.r°C.
3. The relationship between incubation period (d days) and water temperature (T°C) was given by: d=1219/T^1.368 for S. torrentium , d=253/T^0.459 for C. tripunctata . Both equations successfully predicted incubation periods for eggs placed in a stream. The period over which eggs hatched was much longer for C. tripunctata than for S. torrentium at all temperatures.
4. The shorter incubation period (at r>5.6°C) and shorter hatching period for S. torrentium ensure that larvae of this species are already growing when eggs of C. tripunctata start to hatch, but the prolonged hatching period of the latter species ensures a long period of larval recruitment to the population. These differences in egg hatching may reduce competition between the two closely-related species.     

Interspecific and intraspecific variations in egg hatching for British populations of Taeniopteryx nebulosa and Brachyptera risi (Plecoptera: Taeniopterygidae)

Adults were obtained from three populations of Taeniopteryx nebulosa and four populations of Brachyptera risi ; their eggs were incubated at seven constant temperatures (range 3.8–22.1°C). There were interspecific, but not intraspecific, differences in adult life-span, mean number of eggs laid per female, hatching success and egg incubation periods. The optimum temperature for hatching success and the range over which at least 50% of the eggs hatched were lower for T. nebulosa (6.5°C, 2.7–15.0°C) than for B. risi (9.0°C, 5.1–15.8°C). No eggs hatched at 22.1°C. The relationship between incubation period (d days) and water temperature (T°C) was given by; d = 326.4 T^−1.015 for T. nebulosa , d = 824.0 T^−0.739 for B. risi . Both equations successfully predicted incubation periods for eggs placed in a stream.
Hatching success and incubation periods were similar to those already published for a Norwegian population of T. nebulosa . The lack of significant intraspecific variation suggests that the genotypes associated with the variables examined in this study have remained remarkably stable in these two species in spite of the geographical isolation of their different populations.     

Effect of incubation and preservation on resting egg hatching and mixis in the derived clones of the rotifer Brachionus plicatilis

The marine rotifer Brachionus plicatilis typicus (Clone 8105A, Univ. of Tokyo) was cultured in 500 ml beakers to form resting eggs. Tetraselmis tetrathele was used as a culture food. Just after formation, resting eggs were exposed to various temperature (5–25 °C) and light regimes (24L: OD and OL : 24D). When eggs were exposed to light just after formation, the eggs hatched sporadically over a month. No hatching was observed for six months when eggs were preserved under dark conditions regardless of the temperature. These eggs hatched simultaneously after being exposed to light and eggs preserved at 5 °C showed twice as high hatching rate (40%) as that of eggs preserved at 15–25 °C (24%). Clones from resting eggs that were kept under different temperature and light regimes were reared individually to the third generation. Incubation at 25 °C with lighting produced the highest (5.4% and 5.2 %) rate of mictic females during their 2nd and 3rd generations, respectively. The lowest rates (0 and 1.5%) were found when the eggs were kept at 5 °C in total darkness for six months. A lower rate of amictic female production was found in clones with higher rates of mixis.     

Effect of fluctuating temperature on the duration of embryonic development in two Ecdyonurus spp. and Rhithrogena cf. hybrida (Ephemeroptera) from Austrian streams

Summary Eggs of Ecdyonurus picteti from the Herrnalmbach and Seebach, and E. venosus and Rhithrogena cf. hybrida from the Seebach were fertilized artificially and kept at fluctuating temperatures (range 2.8°–18.1° C) in the laboratory. The percentage of eggs that hatched at each sinusoidal temperature cycle ranged from 0 to 49% and values were similar to those obtained for eggs reared under constant temperature conditions. The hatching time (days after fertilization for 10, 50% and 90% of the eggs to hatch) decreased with increasing temperature and the relationship between the two variables was well described by a powerlaw within the range 2.8°–18.1° C for E. venosus. A similar relationship has been found for the effect of constant temperature on the hatching time of eggs of E. venosus. It appears that the effect of temperature on the rate of change in the hatching time and the rate of development is approximately similar for both constant and fluctuating temperatures.     

CLUTCH-SIZE, INCUBATION AND HATCHING SUCCESS IN THE HOUSE SPARROW AND TREE SPARROW PASSER SPP. AT OXFORD

Clutch-size, incubation and hatching success were studied in P. domesticus and P. montanus in 1961 and 1963–64 at Oxford. The most frequent clutch-size was four eggs in P. domesticus and five eggs in P. montanus . With one exception, colonies of P. domesticus showed no significant annual or local variations in its mean clutch-size; in P. montanus , however, there were significant annual variations in the mean clutch-size. Both species showed a seasonal increase followed by a decrease in their mean clutch-sizes.
Partial incubation occurred during the laying period of the clutch; sufficient incubation for continuous development of the embryo was apparently achieved when the last egg had been laid in clutches of two and three eggs in P. domesticus and in clutches of four eggs in P. montanus , but when the penultimate egg had been laid in larger clutches of both species. On average, hatching in P. domesticus occurred more or less synchronously in all eggs in clutches of two and three eggs, and in all eggs except the last one laid in larger clutches; the last egg in the larger clutches hatched up to a day after the others. It is suggested that this pattern of hatching was brought about by the pattern of incubation during the laying period.
P. domesticus had a lower hatching success than P. montanus , probably because fewer of its eggs were fertile.     

Relatively low upper threshold temperature in lizards from cool habitats

We used the slender forest skink (Scincella modesta) as a model animal to test for the hypothesis that the upper threshold of incubation temperature is relatively low in lizards using shaded (and thus, cool) habitats. Eight gravid females were collected in early May 2005 from a population in Hangzhou, Zhejiang (eastern China). All females laid a single clutch of 7–13 eggs between mid-May and early June. Eggs were incubated at 24, 28 and 30 (±0.2) °C. None of eggs incubated at 30 °C hatched. Eggs incubated at 24 and 28 °C differed in incubation length but not in hatching success. The incubation length at 24 and 28 °C averaged 22.3 and 20.3 days, respectively. Hatchlings from eggs incubated at 24 and 28 °C did not differ in all examined morphological traits, but hatchlings from eggs incubated at 28 °C performed apparently worse in the racetrack than did their counterparts from eggs incubated at 24 °C. The temperature of 28 °C is close to the upper thermal threshold for successful embryonic development in S. modesta. Compared to other oviparous lizards using open (and thus, warm) habitats, the upper thermal threshold and the range of optimal temperatures for embryonic development are both lower in S. modesta. Our study supports the previous conclusion that species living in thermally different habitats may differ in the upper thermal threshold and the range of optimal temperatures for embryonic development.     

Reproductive bionomics of the soft tick, Ornithodoros turicata (Acari: Argasidae)

The effects of different temperatures and relative humidities (RHs) were tested on various reproductive parameters of Ornithodoros turicata, an argasid tick that inhabits gopher tortoise burrows in Florida, USA. The pre-oviposition, oviposition and incubation periods of the ticks decreased as temperature increased. These periods were also affected by the RH. The number of eggs oviposited was affected significantly by the combined effect of temperature and RH. Fewer eggs were laid by ticks in the 24°C regimes and the 27°C/95%RH regime compared to those in the other temperature/RH groups. There was an inverse relationship between the number of eggs oviposited and the percentage of hatched larvae that was correlated with the temperature and RH. Ticks reared at 27°C/90%RH and 30°C/90%RH laid more eggs than those reared in the other combinations of temperature and humidity but fewer larvae hatched from these eggs. The reproductive fitness index (RFI) values were highest in females held in the 24°C groups and the 30°C/95%RH group, although significantly more larvae hatched at the lower temperatures. The optimum reproductive conditions for O. turicata under laboratory conditions appear to be 24°C and 90–95%RH. While mating occurred at all temperatures, none of the females laid eggs at 22°C. The ticks may move preferentially to low temperatures when not feeding to remain above the critical equilibrium humidity and/or below the critical metabolic level necessary for prolonged survival. However, most female ticks oviposited after 45 days when moved to 27°C/95%RH. Ornithodoros turicata females may have a limited capability to delay oviposition until an optimal microenvironment for egg deposition can be located in the burrow.     

Developmental rates of heterozygous and homozygous rainbow trout reared at three temperatures

The hatching distributions of rainbow trout (Salmo gairdneri) with different genotypes at eight loci are compared in two experiments with the same strain. Embryos were incubated at temperatures colder (5 and 8°C) and warmer (12°C) than normally experienced by these fish (9.5°C). At hatching, embryos were separated into five hatching groups representing the chronological order of hatching. There is no significant correlation between multilocus heterozygosity and hatching time at any temperature in either experiment. Fish in the middle of the hatching distribution had the highest average heterozygosity. In both experiments, heterozygotes at the majority of loci examined tended to hatch relatively later within the hatching distribution at 12°C than at both 5 and 8°C. Fish with different genotypes atPgm2 andCk1 showed significant differences in hatching time that were consistent between experiments.Ck1 heterozygotes hatched sooner than homozygotes at 8°C but later at 12°C.Pgm2 heterozygotes hatched later than homozygotes at all temperatures and significantly later in four of five cases. At the other loci examined, however, the relative hatching distributions of fish with particular genotypes were not significantly different or repeatable between experiments.This research was supported by National Science Foundation Grant BSR-8300039 awarded to Dr. Fred W. Allendorf. Moira M. Ferguson was supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada.     

Observations on the effects of incubation at inhibitory temperature on subsequent hatching of anostracan cysts

Hatching progressively for cysts ofBranchinecta lindahli Packard when they were incubated for 6 and 12 hours at a temperature known to inhibit hatching (30 °C) prior to transfer to a favorable hatching temperature of 15 °C. Cyst ofThamnocephalus platyurus Packard, by contrast, hatched normally at 28 °C after transfer from 48, 72, and 96 hour incubation periods at the inhibitory low temperature of 10 °C.     

Induction of diapausing amictic eggs in Synchaeta pectinata

Amictic females of a clone of S. pectinata from Star Lake (Norwich, Vermont) may produce diapausing as well as non-diapausing (subitaneous) eggs. The proportion of diapausing eggs produced in cultures was unaffected by temperature (12 vs 19 °C) or rotifer population density (minima of 0.33 vs 3 ind. ml^–1) at 19 °C. However, at 19 °C this proportion was higher in cultures maintained at a low food level suppressing reproduction (5 × 10³ cells ml^–1 Cryptomonas erosa) than in those maintained at a high food level (2 × 10⁴ cells ml^–1); the treatment effect was marginally significant (p=0.067). Consistent with the effect of low food availability, a period of starvation was very effective in inducing the development of diapausing eggs. None of 19 females cultured individually from hatching at 19 °C on C. erosa (2 × 10⁴ cells ml^–1) in 1-ml volumes produced any diapausing eggs in 4 days (0 out of 349 eggs), while 13 out of 16 females subjected to a 15-hour starvation period 6 hours after birth produced one or more diapausing eggs during that time (34% of the 158 eggs produced by the 16 females were diapausing). Diapausing eggs produced and left at 19 °C hatched after 4 to 13 days. Those produced in cultures with a low food level took significantly longer to hatch (9.7 days) than those produced in cultures with a high food level (8.1 days) (p=0.022). In natural communities, S. pectinata should be able to respond directly and rapidly to poor food conditions by producing eggs that undergo an obligatory dormant period before resuming development.     

Phenotypic variation in hatchling Chinese ratsnakes (Zaocys dhumnades) from eggs incubated at constant temperatures

We incubated eggs of the Chinese ratsnake Zaocys dhumnades at four constant temperatures (24, 27, 30 and 30 °C) to examine the effects of incubation temperature on hatching success and hatchling phenotypes. Incubation length increased nonlinearly as temperature decreased, with the mean incubation length being 76.7 d at 24 °C, 57.4 d at 27 °C, 47.3 d at 30 °C, and 44.1 d at 33 °C. Hatching successes were lower at the two extreme temperatures (69% at 24 °C, and 44% at 33 °C) than at the other two moderate temperatures (96% at 27 °C, and 93% at 30 °C). Incubation temperature affected nearly all hatchling traits examined in this study. Incubation of Z. dhumnades eggs at 33 °C resulted in production of smaller hatchlings that characteristically had less-developed carcasses but contained more unutilized yolks. Hatchlings from eggs incubated at 27 and 30 °C did not differ in any examined traits. Taking the rate of embryonic development, hatching success and hatchling phenotypes into account, we conclude that the temperature range optimal for incubation of Z. dhumnades eggs is narrower than the range of 24−33 °C but should be wider than the range of 27−30 °C.     

Response of diapausing eggs hatching to changes in temperature and the presence of fish kairomones

It has been hypothesized that the production of diapausing eggs in Daphnia can be induced by fish kairomones. A population of Daphnia could survive severe predation using this predator avoidance strategy. However, in changing environments, diapausing eggs experience various temperature conditions, and hatchlings at emergence may be exposed to the same predation risks as their mothers. Therefore, staying in diapause or an immediate response upon hatching to available environmental information could be important for hatchling survival. For this study, we investigated the impact of water temperature (10, 15, 20, and 25°C) in the presence and absence of fish kairomones (Lepomis macrochirus) on the hatching success of resting eggs (D. galeata). Results show that no diapausing eggs hatched at the lowest temperature (10°C), and the highest hatch percentage occurred at 15°C. Although higher water temperatures reduced hatching success, diapausing eggs hatched more quickly. The number of hatchlings was significantly higher after exposure to fish kairomones, and this was more noticeable at higher temperatures (20 and 25°C). The present results suggest that the diapausing eggs were produced as a predator avoidance strategy in Daphnia; however, the presence of fish works as a positive signal to increase hatchlings when the diapausing stage is terminated.     

Artificial incubation of eggs of the green iguana (Iguana iguana)

Successful hatching of large numbers of artificially incubated eggs from the green iguana, Iguana iguana, are reported. Gravid females were captured at a nesting site in Summit Gardens, Soberania, Parque Nacional, Panama, and released into an enclosure with an artificial nesting area. Females dug their own tunnels and nest chambers or used artificial nest chambers for egg deposition. Eggs (n = 829) from 21 clutches were removed from the nests and artificially incubated. Average hatching success per clutch was 94.6% and the mean clutch incubation time was 92.1 days. A distinct odor was noticed in the incubation containers several days before the eggs began to hatch. At this time, the substrate layer was removed exposing the top surface of all eggs, and the eggs desiccated to some degree prior to hatching. High incubation temperature, hydric conditions, and egg arrangement are all implicated as contributing factors in low hatching success in previous studies using artificial incubation techniques.     

Male brooding behaviour of the giant water bugLethocerus deyrollei vuillefroy (Hemiptera: Belostomatidae)

The male brooding behaviour ofLethocerus deyrollei was investigated. Eggs were laid as masses on sticks above the water surface. Males did not leave the sticks until the eggs hatched. They mainly stayed at the bases of the sticks in water in the day, and frequently climbed up at night covering the egg-masses with their bodies. Eggs with male brooding had a 94.3% hatching rate. Eggs without male brooding failed to hatch and desiccated. Eggs with brooding considerably increased in wet weight in development; eggs without brooding decreased in wet weight. Eggs without male brooding and artificially supplied with water had a 93.2% hatching rate. Male brooding is considered to supply eggs with water.     

Effect of intermittent incubation and clutch covering on the probability of bacterial trans‐shell infection

Microbial infection is considered a critical cause of hatching failure in birds. Although several behavioural mechanisms are believed to improve reproductive success in birds, their direct effect on the risk of bacterial trans‐shell infection (BTSI) remains to be tested. Here, we focus on the protective roles of intermittent incubation and covering of the clutch with nest lining during the laying period, when eggs are highly susceptible to BTSI. To our knowledge, this study is the first to use culture‐independent PCR‐based methods to measure quantitative and qualitative indices of BTSI. In our experiment, we exposed Mallard Anas platyrhynchos eggs that were either intermittently incubated (I‐INCUB) or un‐incubated (I‐UNINCUB), and covered (COV) or uncovered (UNCOV) with nest lining. Hatchability of I‐INCUB eggs was twice that for I‐UNINCUB eggs. The presence and degree of BTSI had no effect on hatching success of experimental eggs. The residual weights of ducklings hatched from infected and I‐INCUB eggs were lower than those from uninfected and I‐UNINCUB eggs. In addition, ducklings originating from COV eggs were heavier than those hatched from UNCOV eggs. Intermittent incubation and clutch covering had no effect on the probability or degree of BTSI. Although the effect of BTSI is considered less detrimental in temperate birds, we show that the presence of BTSI inside the egg may significantly affect hatchling phenotype. This represents a novel insight into the role of BTSI in the reproductive success of birds and implies that the use of molecular PCR‐based methods is required in future studies for a better understanding of such causality.     

The influence of processing and temperature conditions on hatching of resting eggs of Streptocephalus proboscideus (Crustacea: Branchiopoda: Anostraca)

In large freshwater branchiopods, erratic hatching success of resting eggs is a major obstacle to various applications. Lack of knowledge of the diapause-regulating processes makes control of hatching difficult. In the Sudanese fairy shrimp Streptocephalus proboscideus cysts are considered to include a diapausing and a quiescent fraction. To effect hatching, diapausing cysts have to be activated, while the quiescent portion has to be triggered by suitable environmental conditions. Of several attempts to control hatching with varying production, processing, and incubation conditions, only a few treatments proved consistently successful. Cysts were produced in an indoor culture system under controlled conditions and were harvested, washed, and dried according to defined procedures before processing (if any) and incubation. Hatchability (first-day and cumulative) was consistently higher in chemically decapsulated than in untreated (non-decapsulated) cysts at 25 °C. At a temperature of 28 °C, hatching was comparable in untreated and in decapsulated cysts and was significantly higher than at 25 °C. Pre-treatment with 7.5% NaOCl for 5–10 minutes, resulted in higher hatching than other decapsulation procedures and durations. It is believed that the decapsulation and temperature treatments were only effective in triggering quiescent cysts but did not activate the diapausing fraction.     

Differences in egg size, shell thickness, pore density, pore diameter and water vapour conductance between first and second eggs of Snares Penguins Eudyptes robustus and their influence on hatching asynchrony

Brood reduction in birds is frequently induced by hatching asynchrony. Crested penguins (genus Eudyptes) are obligate brood reducers, but in contrast to most other birds, first‐laid eggs are considerably smaller in size than second‐laid eggs; furthermore, first‐laid eggs hatch after their siblings. The mechanisms underlying this reversal in size and hatching order remain unclear. In this study, we tested whether the second‐laid eggs of Snares Penguins Eudyptes robustus have a higher eggshell porosity allowing them to maintain a higher metabolic rate throughout incubation and to hatch before their first‐laid siblings. We investigated differences in egg size, shell thickness, pore density, pore diameter and water vapour conductance between first and second eggs within clutches and examined the influence of these shell characteristics on hatching asynchrony. First‐laid eggs of Snares Penguins were approximately 78% of the size of the larger second eggs. Second‐laid eggs had considerably thicker shells and more pores per cm² than first eggs, whereas pore diameter did not differ between eggs. Water vapour conductance was greater in second‐ (16.8 mg/day/torr) than in first‐laid eggs (14.9 mg/day/torr). The difference in water vapour conductance between first‐ and second‐laid eggs within clutches was related to hatching patterns. In nests where second eggs hatched before first‐laid eggs, second eggs had a considerably greater water conductance than their sibling, whereas in nests where both eggs hatched on the same day, the difference in water conductance between eggs was very small, and in a few nests where small first eggs hatched before their larger sibling, they had a greater water conductance than their larger second‐laid nestmate. Surprisingly few studies have investigated differences in shell characteristics between eggs within clutches and associated effects on hatching asynchrony. This study has demonstrated that such differences exist between eggs within clutches and that they can influence hatching patterns.