Low Hatchability Research Articles

Egg Storage and the Embryo

In domestic avian species, eggs are stored at cool temperatures until they can be placed into an incubator. The low temperature-induced diapause enables the embryo to survive until optimal temperature and humidity incubation conditions can be provided to support embryonic growth. Egg storage is a logistical necessity for the hatching egg industry both at the breeder farm and at the hatchery. However, it is well known that egg storage longer than 7 d negatively influences hatchability. At the cellular level, long-term egg storage induces cell death. This appears to be occurring both via necrosis and apoptosis. The result is higher embryonic mortality and, consequently, lower hatchability. In addition, long-term egg storage influences embryonic development and metabolism. Embryos of eggs stored long-term can be affected such that they do not initiate growth after proper incubation temperatures are provided; they initiate growth, but grow at a slower rate than eggs stored short term; and they are affected in both of the previously mentioned ways. Development of equipment to measure the embryonic metabolism of individually incubating eggs over the entire 21 d of incubation has provided further evidence that embryo metabolism has changed due to storage. One of the methods to reduce the negative effects of long-term storage has been to incubate eggs for short periods before storage. In both turkey and chicken eggs, this technique has been successful in improving the hatchability of long-term stored eggs. It is hypothesized that particular embryonic developmental stages are better able to survive long-term storage. Future research should focus on the mechanisms behind this improved ability to survive storage.

The Effect of Low-Density Diets on Broiler Breeder Performance During the Laying Period and on Embryonic Development of their Offspring

The effect of low-density diets on bird performance, egg composition, and embryonic development was studied with 2,100 female and 210 male Cobb broiler breeders from 25 to 60 wk of age. The experiment included 5 treatments. These included a control group with a normal density diet (ND, 2,800 kcal of AME/kg). Treatments 2 (LD11) and 3 (LD21) had a 11 and 21% lower nutrient density. Treatment 4 (LD11OP) had a 11% less dense diet, which was obtained by inclusion of other feed ingredients. In these 4 treatments similar diets were given during the rearing and the laying period. Treatment 5 combined LD12 in the rearing period and ND diets during the laying period (LD12-ND). Egg composition and embryonic development were measured in eggs of ND and LD21 birds at 29 and 41 wk of age. During the laying period from wk 25 to 60, live weights did not differ among treatments, except that birds fed LD11OP had lower live weights. A significantly higher rate of lay was provided by LD11 compared with ND. Egg weights were significantly higher when low-density diets were fed, particularly in LD11OP. Percentage of fertile eggs did not differ among treatments. Compared with the other treatments, LD11OP provided a significantly lower hatchability. We found that LD21 resulted in a better development of the area vitellina externa and heart and embryo weight at 29 wk of age. It was concluded that this was related to a higher egg weight and egg white proportion. This suggests that the amount of egg white in eggs of hens fed ND was limiting for embryonic development, particularly in eggs of young broiler breeders.

To hatch and hatch not: similar selective trade-offs but different responses to egg predators in two closely related, syntopic treefrogs

Risk-sensitive hatching is adaptive for species facing a trade-off between egg-stage and post-hatching risks, and environmental variation in one or both stages. Such plasticity has been found in amphibians, fishes, reptiles and spiders, with red-eyed treefrogs (Agalychnis callidryas) being the best-studied case. We assessed hatching plasticity and egg- and larval-stage risks in a closely related, syntopic species, the gliding leaf-frog (Agalychnis spurrelli). We found a lower hatching response to egg-eating snakes in A. spurrelli (9-28% of embryos escaped) than in A. callidryas (59-80% escaped). Levels of snake predation were similarly high for clutches of both species monitored at a pond in Costa Rica, and in fish predation experiments early-hatched A. spurrelli tadpoles were more vulnerable than later hatchlings, as has been shown for A. callidryas. A. spurrelli thus face a risk trade-off similar to A. callidryas, and likely would benefit from predator-induced hatching; their lower responsiveness to snakes appears nonadaptive. A. spurrelli embryos showed a stronger hatching response (57% hatched in 1 h) to submergence underwater than to snake attacks even though submergence is a less frequent risk. This suggests they have a greater capacity for early hatching than is expressed in the context of snake attacks, but have much lower sensitivity to snake cues than to flooding cues. Development in A. spurrelli is accelerated compared to syntopic A. callidryas, and spontaneous hatching is earlier and more synchronous. This is congruent with predictions based on selection by egg predators in the absence of a strong escape hatching response.

SEMEN COLLECTION AND CHARACTERIZATION IN ROCKHOPPER PENGUINS (EUDYPTES CHRYSOCOME CHRYSOCOME)

Low egg fertility and hatchability is a common problem in captive populations of rockhopper penguins (Eudyptes chrysocome chrysocome). These conditions make sustaining a captive population challenging. A method for collecting and evaluating semen from rockhopper penguins was developed to assist in the evaluation of low egg fertility found in one captive population. Six adult male rockhopper penguins were conditioned to allow semen collection once a week from the start of breeding season until ejaculates no longer contained sperm. A total of 59 ejaculates was collected between 17 September and 31 December 2004. Forty-five of these samples were evaluated for volume, pH, sperm concentration, and sperm quality (motility, viability, and morphology). There was a large variation between individuals and between collections for each individual. The mean motility was 34.5% (+/- 22%). Mean volume of ejaculate was 0.23 ml (+/- .31 ml). Mean concentration was 16.9 x 10(6) sperm/ml (+/- 48.7 x 10(6) sperm/ml). Mean number of sperm per collection was 1.7 x 10(6) (+/- 4.2 x 10(6)). Mean percentage of living sperm was 82.9% (+/- 18.1%). Mean percentage of sperm with normal morphology was 82.1% (+/- 18.8%). Mean pH was 6.47 (+/- 0.49). During this season, only one of these males paired with a female. The pair produced one fertile egg, but the embryo died early in incubation. Male rockhopper penguins had low sperm concentration and low motility indicating that low male fertility may be contributing to the poor egg fertility rate. This work represents the first step in an ongoing study to improve captive breeding of rockhopper penguins.

Hypoxic adaptations of hemoglobin in Tibetan chick embryo: High oxygen-affinity mutation and selective expression

Tibetan chicks ( Gallus gallus) survived with high hatchability (35.0%) and Recessive White Feather broilers (RWF) from low elevations survived rarely and with a low hatchability (3.0%) after simulated incubation under hypoxia of 13% O 2. The functional mutation of Met-32D(B13)-Leu of α D globin chain was related with hypoxia based on allele distribution, homology model building and oxygen affinity assay. Whole embryos on days 3–8 and whole blood on days 9–18 were collected to investigate the stage expression profiles of all seven globins and HIF-1α by real-time PCR. Under hypoxia (12.0% O 2) on days 3–8, HbE was overexpressed, HbA was expressed earlier and HbP expression was restricted, which completely overturned the expression profile under normoxia. The amount of hemoglobin expression in Tibetan chicks was remarkablely higher than that of RWF. HIF-1α expression peaked early in both breeds, with. In conclusion, the special hypoxic expression profile on days 3–8 certainly is a common molecular mechanism of hypoxia tolerance in surviving Tibetan chick and RWF embryos; the mutation Met-32D(B13)-Leu and increasing hemoglobins are important mechanisms of hypoxia adaptation in Tibetan chick embryos, and we suggest that HIF-1α could be responsible for the hypoxic expression profile.

Costs of large communal clutches for male and female Greater RheasRhea americana

The breeding system of the Greater RheaRhea americanais almost unique among birds as it combines harem polygyny and sequential polyandry, with communal egg‐laying and uniparental male care. In this species, large communal clutches (more than 30 eggs) are rare and have a lower hatching success than smaller clutches. Here we analyse the proximate causes of hatching failures and the costs of large communal clutches (and therefore the costs of extensive polygyny) for males and females. We evaluated if length of the nesting period, egg viability, egg losses during incubation and male parental activity at the nest were affected by clutch size. We also evaluated if chicks hatched from large clutches have a lower survival during the first 2 months after hatching. Large clutches had longer nesting period and lower hatching success, mainly as a result of bacterial contamination of the eggs and increased hatching asynchrony. In addition, large clutches tended to lose more eggs as a result of accidental breakage or predation. Male activity at the nest and chick survival were not related to clutch size. Low hatching success, nest predation risk and energetic costs associated with large clutches penalize females that join large harems and males that accept additional eggs into the nest.

Seasonal dynamics and mortality rates of Calanus helgolandicus over two years at a station in the English Channel

The stage-specific abundance and egg production rates of Calanus helgolandicus were determined on a near-weekly basis over 2 yr at a 50 m deep station in the SW English Channel (Stn L4). Mortality rates were derived using a vertical life-table approach across eggs, nauplii and also the CV-adult stage pair. The results demonstrate strong seasonal patterns in the mortality rates of egg and nauplii and the CV-adult stage pair, but with different relative rates and somewhat dif- ferent seasonalities. Mortality was highest in the egg and egg-NI stages, averaging 6.1 and ~1.5 d -1 , respectively, with the percentage surviving through the egg-NI stage pair often <<10%. Although the instantaneous removal rate of eggs was significantly related to adult abundance (p < 0.001, r 2 = 0.221), densities of adult C. helgolandicus seemed too low to account for these rates. Examination of the relationship between CV-adult female mortality and the abundance of the dominant invertebrate predators revealed statistically significant relationships (p < 0.001 r 2 = 0.276 for chaetognaths; p < 0.001 r 2 = 0.125 for siphonophores); however, the variability explained by temperature was much higher (p < 0.001 r 2 = 0.652). The egg-NI and NI-NII stage pairs also showed a highly statistically significant positive relationship between mortality and temperature. For the first time we compared mortality rates for egg-NI using 2 vertical methods — one using measurements of egg and NI abun- dance (Method A) the other using egg production rates and NI abundance (Method B) — and found the two to be similar, although Method B gave higher values. Finally, as many mortality equations do not consider the bias resulting from the presence of eggs incapable of hatching in the field, we derived and applied new equations for mortality of eggs and egg-NI (Method A) that incorporated egg hatching success. At low hatching success or low mortality rates, this correction can alter esti- mates of mortality rates significantly.

Worker policing in the common wasp Vespula vulgaris is not aimed at improving colony hygiene

In insect societies, eggs laid by workers are frequently killed by other workers – a behaviour known as “worker policing”. The traditional explanation of worker policing is that it is a mechanism to resolve intracolony conflict, and maintain the reproductive monopoly of the queen. Recently, Pirk et al. (2004) proposed that worker policing instead is aimed at removing unviable worker-laid eggs and is ultimately just another example of hygienic behaviour. Here we test this hypothesis for the common wasp Vespula vulgaris, a species with highly effective worker policing. We show that worker-laid eggs from queenless colonies have a lower hatch rate (68%) than queen-laid eggs (82%). Analysis of egg laying rates of queens and workers, however, shows that the difference is not big enough to explain the apparent absence of adult worker-derived males in this species.

Feather mite abundance increases with uropygial gland size and plumage yellowness in Great Tits Parus major

Plumicolous feather mites are ectosymbiotic organisms that live on bird feathers. Despite their abundance and prevalence among birds, the ecology of the interaction between these organisms and their hosts is poorly known. As feather mites feed on oil that birds spread from their uropygial gland, it has been hypothesized, but never tested, that the number of feather mites increases with the size of the uropygial gland of their hosts. In this study the number of feather mites is considered with respect to uropygial gland size in a breeding population of Great Tits Parus major in order to test this hypothesis. As predicted, the number of feather mites correlated positively with the uropygial gland size of their hosts, showing for the first time that uropygial gland size can explain the variance in feather mite load among conspecifics. Previous studies relating feather mite load to plumage colour have suggested that feather mites may be parasitic or neutral. To confirm this, the yellowness of breast feathers was also assessed. However, the results ran in the opposite direction to that expected, showing a positive correlation between mite load and plumage yellowness, which suggests that further work is needed to give clear evidence for a specific nature of feather mites. However, Great Tits with higher mite loads had lower hatching and breeding success, which may support the idea that feather mites are parasites, although this effect must be taken with caution because it was only found in males. Age or sex effects were not found on the number of feather mites, and it is proposed that hormonal levels may not be sufficient to explain the variation in feather mite loads. Interestingly, a positive correlation was detected between uropygial gland size and plumage brightness, which could be a novel factor to take into account in studies of plumage colour.

Maternal antibodies in a wild altricial bird: effects on offspring immunity, growth and survival

1. In many animals immunity is not fully developed until adulthood but the young still need protection against various sets of pathogens. Thus, bird nestlings are highly dependent on antibodies received from their mother (in the eggs) during their rapid early growth period. The relationship between maternal immunity and the development of neonates' own immunity has been poorly studied. 2. It has been suggested that immune function plays an important part in mediating resource competition between different life-history traits, e.g. growth and reproduction. Maternal investment of antibodies has potentially permanent effects on offspring phenotype. Thus, the trade-offs between the immune function and other important life-history traits in the offspring will also affect the fitness of the mother. 3. Our supplemental feeding experiment in the magpie Pica pica indicates that the immunoglobulin levels of offspring at hatching are dependent on a mother's nutritional condition. In addition, the amount of maternal immunoglobulins transferred to offspring increases along the laying order within a nest. 4. We also found that at the age of 8-10 days the immunoglobulin production of the offspring has already begun. Furthermore, the maternal immunoglobulin levels of the offspring at hatching were positively related to their immunoglobulin levels on day 10. 5. Maternal immunoglobulins did not significantly affect offspring growth, but there was a negative relationship between self-produced immunoglobulins and growth over the first 10 days, indicating a trade-off between these traits. Nestlings' weight, however, had a positive relationship with immunoglobulin production suggesting that the observed trade-off between growth and immunoglobulin production is due to catch-up growth of nestlings with a low hatching weight. We found that within nests nestlings with higher maternal antibody levels had higher survival rate until day 20, but between nests there was an opposite relationship. 6. Evidently, there is a trade-off, in magpies, between maternal resources, immune function and growth, shaping the evolution of maternal investment in offspring immunity.

The effects of heat stress, predation risk and parental investment on Malaysian plover nest return times following a human disturbance

Waders leave nests and conduct distractive displays when approached by people. The time taken for waders to return to nests depends on numerous factors that affect the costs and benefits of incubation and anti-predator behavior. Understanding this trade-off may help assess the reproductive consequences of different nest return times and identify variables to consider in breeding disturbance studies. We subjected 73 Malaysian plover ( Charadrius peronii) nests to standardized human disturbances and an analysis of covariance was used to determine how weather, time of day, embryonic age, weeks into breeding season and nest attendance (proportion of time adults incubated nests) influence nest return times. Egg temperatures were estimated using a regression model that predicted the temperature inside unshaded eggs from air temperature, cloud cover and time of day ( r 2 = 0.88). We assessed the relationship between nest return times and hatch success. Plovers returned to nests faster at higher modeled egg temperature ( P = 0.010), in the morning ( P = 0.003), if they had younger clutches ( P = 0.038), and if they had high nest attendance prior to the disturbance ( P = 0.015). Pairs that returned to nests faster had lower hatch success ( P = 0.021). This may be because pairs that spend more time distracting humans may also do so for predators. These results suggest that short nest return times may not indicate low fitness costs of disturbance. The thermal and predation environment in addition to nest return times should be taken into account when assessing the deleterious effects of human disturbance.

Geographic variation in diapause induction and mode of diapause inheritance in Tetranychus pueraricola

Abstract: Diapause induction and photoperiodic response curves were determined for 33 strains of Tetranychus pueraricola derived from kudzu vine at three constant temperatures (15, 18 and 20°C) under a short‐day condition (10 : 14 h; light : dark). Females of all but one of the strains entered diapause at all three temperatures with little variation in diapause percentages among the strains. The exception was the southernmost strain, which was found to be a non‐diapause (ND) strain. The critical photoperiod gradually decreased towards the south at a rate of about 1 h for each 5 degrees of latitude. The diapause strains (D1 and D2) exhibited 100% diapause, whereas the ND strain exhibited 0% diapause. By crossing these strains, we determined that ‘non‐diapause’ was a dominant character over ‘diapause’ and the character was controlled by simple Mendelian inheritance. To clarify why the female progeny from the crosses between the D1 and ND strains did not segregate into the diapause and non‐diapause phenotypes in a 1:1 ratio in the B1 generation, round‐robin crosses were carried out among the three strains. The results showed that the F1 generation was reproductively compatible and showed high egg hatchability with a female‐biased sex ratio. In the B1 generation, the crosses between the D1 and ND strains and between the D1 and D2 strains exhibited extremely low egg hatchability and produced mostly female progeny, whereas offspring from the crosses between the D2 and ND strains showed more than 50% hatchability for B1 eggs and a female‐biased sex ratio. Thus, the absence of segregation observed in the crosses between the D1 and ND strains appears to be due to the severe hybrid breakdown that occurred in the B1 generation.

Effect of irradiation on female painted apple moth Teia anartoides (Lep., Lymantriidae) sterility and attractiveness to males

Abstract: Live female painted apple moths are being used to monitor the distribution of this invasive species in Auckland as part of a major eradication effort, and the goal of this project was to develop a method to minimize the risk of unwanted live insect propagation from the trapping programme as a result of vandalism or ‘eco‐terrorism’. Female pupae were irradiated with a range of doses and their egg viability assessed, and also tested to determine the impact of irradiation on male moth catch in the field. Female painted apple moth pupae, irradiated at a range of doses from 100 to 500 Gy, were placed in cages in traps at 10 m spacings from non‐irradiated females, near a central release site of irradiated males. Untreated control females alternated along orthogonal transects with irradiated females. The results indicated no significant effect of female irradiation on catch of males. There was no correlation between dose and catch, within the range of exposures tested. There was a very low hatch rate of eggs from females irradiated at all doses tested (100–500 Gy). These results suggest that irradiated females could be used in traps to reduce potential risks of deliberate spread of the unwanted organism by activists, without affecting the effectiveness of monitoring males.

Habitat structure in Mediterranean deciduous oak forests in relation to reproductive success in the Blue Tit Parus caeruleus

Capsule Effects operate during laying and incubation and with less success in breeding territories characterized by a young and immature vegetation structure. Aims To explore relationships between habitat characteristics at the breeding territory level and reproductive timing and success of Blue Tits Parus caeruleus in Pyrenean Oak Quercus pyrenaica woods in central Spain. Methods Habitat structure of the breeding territories was measured in a sampling plot centred on a nestbox, with a radius of 25 m. A principal component analysis was performed to obtain a factor of ‘territory vegetation maturity’ summarizing the characteristics of the territory. Reproductive parameters were obtained by frequent visits to the nests during the breeding season. Adults were captured at the nest to obtain morphological measurements, and nestling tarsus length and body mass were measured on day 15 after hatching. Results Habitat effects on reproductive performance seem to operate at the beginning of reproduction in these montane oak woods and through female body condition during the first stages of breeding. Female Blue Tits in breeding territories with immature and degraded vegetation started reproduction later and had lower hatching and breeding success. Laying date was strongly related to female body condition. Total reproductive failure occurred mainly during the incubation period and was associated with immature breeding territories. However, nestlings raised in mature forest territories did not differ in size and mass from those in degraded, immature territories. Conclusions The effects of habitat structure on Blue Tit reproductive success operate during laying and incubation in this Mediterranean forest type. The results are discussed in terms of the implications of management of Mediterranean oak woods for the conservation of forest bird populations.

Selection for reproductive traits in white egg stock using independent culling levels

The objective of this study was to report the response to selection for fertility and hatchability in white egg layers strains, based on sire and dam performance, and the effects of inbreeding on these traits. Two selected white egg strains (CC and DD) from Embrapa´s poultry program under multiple trait selection were compared to a control strain (CCc). The control strain was established by randomly mating one male from each sire family to a non-related female from each dam family and was used to monitor genetic change in the selected lines. CC and DD were selected using family and individual information on hen-day egg production up to 40 weeks of age, egg weight, sexual maturity and 16-week-old body weight over five generations. Independent culling levels (ICL) were also used during population expansion to eliminate sires and dams with low fertility (FERT) and hatchability (HATC). Initially, FERT and HATC were over 90.0% in both selected and control strains. FERT and HATC of the selected and the control strains were compared during the last generation. FERT averages were 93.8, 93.8 and 94.4%, and HATCH averages were 93.2, 91.6 and 93.1% for CC, DD and CCc respectively. FERT and HATCH means were not different among strains. Estimated inbreeding increased at a rate of 0.4% per generation in all strains. Selection using ICL was able to effectively maintain the high initial FERT and HATC levels, and provide potential for high selection intensity in other traits. Inbreeding depression was not observed for any trait, indicating that selection compensated for any negative effects of inbreeding.

Stressed mothers lay eggs with high corticosterone levels which produce low‐quality offspring

Organisms frequently encounter stressful ecological conditions. In vertebrates, a major mechanism of physiological response to stress is mediated by the hypothalamic-pituitary-adrenal axis and results in increased secretion of glucocorticosteroids, which can have adverse consequences on diverse phenotypic traits affecting fitness. Maternal stress may thus have carry-over effects on progeny if it influences pre-natal offspring environment in terms of glucocorticosteroid concentration, although this hypothesis has never been tested in any species under field conditions. We manipulated stress experienced by female barn swallows Hirundo rustica, by exposing them to a predator during laying and measured egg corticosterone concentration. Stressed females laid eggs with greater corticosterone concentration than controls exposed to a herbivore. In another experiment, we injected physiological doses of corticosterone in the egg albumen and compared the phenotype of offspring originating from these eggs with their control siblings originating from either sham-inoculated or unmanipulated eggs and reared in the same nest. Eggs injected with corticosterone had lower hatchability and produced fledglings with smaller body size and slower plumage development than did control eggs. Nestling body size in our study population predicts long-term survival. Thus, maternal stress impaired offspring phenotype and viability by increasing transmission of glucocorticosteroids to the eggs. This study identifies a novel mechanism mediating early maternal effects whereby maternal stress affects offspring quality. These results are relevant to biological conservation because they disclose a mechanism that can link environmental conditions to population productivity and viability.

Effects of fentin hydroxide on reproduction of the Japanese quail ( Coturnix coturnix japonica)

In a one-generation reproductive study, the fungicidal compound triphenyltin hydroxide (fentin) was administered to adult Japanese quail for 6 weeks at dietary levels of 3 and 30 ppm. Reproduction was significantly impaired in the high-dose group. The principal adverse finding was a marked increase in embryonic mortality, resulting in a lower hatch rate. Furthermore, a reduction in egg production was observed with ongoing duration of treatment. Most of the other reproduction-related parameters were not affected. The in ovo losses are assumed to result from a direct toxic effect of the test substance on chick embryos. At the low dietary level, reproduction was not altered. In contrast to the obvious reproductive toxicity, there was only limited evidence of adverse treatment-related findings in the adult birds. However, because such minor effects as an increase in mean liver weight, which was accompanied by macroscopic liver findings and a decrease in T4 serum concentration, were still seen at 3 ppm, a no-observed-effect level could not be established.

No Evidence for Bacteriophage WO orf7 Correlation with &lt;I&gt;Wolbachia&lt;/I&gt;-Induced Cytoplasmic Incompatibility in the &lt;I&gt;Culex pipiens&lt;/I&gt; Complex (Culicidae: Diptera)

Gene flow between populations of Culex pipiens L. is relevant to observed differences in disease transmission, insecticide resistance, behavior, and physiology. Intracellular Wolbachia bacteria have been hypothesized to affect gene flow in insects. Specifically, Wolbachia cause a form of embryonic mortality known as cytoplasmic incompatibility (CI) in crosses between individuals with different Wolbachia types. Incompatibility in Culex is exceptional in that it represents the most complex CI pattern known, and yet Culex populations are not infected with divergent Wolbachia strains. This has led to the hypothesis that extrachromosomal factors such as phages or mobile genetic elements may be involved in determining CI phenotype. Recent molecular characterization of Culex laboratory strains has identified variation in the orf7 locus of the Wolbachia-associated bacteriophage WO. Here, crosses between eight Culex strains differing in their orf7 type were conducted to examine for the hypothesized involvement of bacteriophage WO in determining CI in Culex. Although crossing results show examples of compatibility, partial compatibility, and incompatibility, the results fail to show a correlation between the CI phenotypes and orf7 type. Specific examples include high egg hatch resulting in crosses between Culex strains that differ significantly in their orf7 type and low egg hatch resulting in crosses between Culex strains with similar orf7 types. Thus, the phage orf7 locus alone cannot predict CI type in the Culex strains examined in this study. However, rejection of the hypothesized role of WO phage in Culex CI will require the characterization of additional phage loci.

No Evidence for Bacteriophage WO orf7 Correlation withWolbachia-Induced Cytoplasmic Incompatibility in theCulex pipiensComplex (Culicidae: Diptera)

Gene flow between populations of Culex pipiens L. is relevant to observed differences in disease transmission, insecticide resistance, behavior, and physiology. Intracellular Wolbachia bacteria have been hypothesized to affect gene flow in insects. Specifically, Wolbachia cause a form of embryonic mortality known as cytoplasmic incompatibility (CI) in crosses between individuals with different Wolbachia types. Incompatibility in Culex is exceptional in that it represents the most complex CI pattern known, and yet Culex populations are not infected with divergent Wolbachia strains. This has led to the hypothesis that extrachromosomal factors such as phages or mobile genetic elements may be involved in determining CI phenotype. Recent molecular characterization of Culex laboratory strains has identified variation in the orf7 locus of the Wolbachia-associated bacteriophage WO. Here, crosses between eight Culex strains differing in their orf7 type were conducted to examine for the hypothesized involvement of bacteriophage WO in determining CI in Culex. Although crossing results show examples of compatibility, partial compatibility, and incompatibility, the results fail to show a correlation between the CI phenotypes and orf7 type. Specific examples include high egg hatch resulting in crosses between Culex strains that differ significantly in their orf7 type and low egg hatch resulting in crosses between Culex strains with similar orf7 types. Thus, the phage orf7 locus alone cannot predict CI type in the Culex strains examined in this study. However, rejection of the hypothesized role of WO phage in Culex CI will require the characterization of additional phage loci.

Possible Effect of 30K Proteins in Embryonic Development of Silkworm &amp;lt;italic&amp;gt;Bombyx mori&amp;lt;/italic&amp;gt;

The silkworm Bombyx mori possesses a 30K protein family of 3x10(4) Da, the biological functions of which have not been fully identified. The relationship between the 30K protein family and the embryonic development of temperature sensitive sex-linked mutant strain of silkworm was investigated by two dimensional polyacrylamide gel electrophoresis (2D-PAGE) and Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The results show that protein spots 1-5 of the 30K protein family, mainly existing in normal strain, are possibly related to embryonic development. The early consumption of a 30K protein named 6G1-30K-1 and the accumulation of 30K proteins named 6G1-30K-3 and 6G1-30K-4 are likely caused by the destruction of physiological balance in normal embryonic development, which may lead to lower hatchability of the temperature sensitive strain. The results suggest that reasonable metabolism of 30K proteins is a prerequisite for the embryo's normal development.