Early Egg Research Articles

The evolution of virulence of West Nile virus in a mosquito vector: implications for arbovirus adaptation and evolution

BackgroundVirulence is often coupled with replicative fitness of viruses in vertebrate systems, yet the relationship between virulence and fitness of arthropod-borne viruses (arboviruses) in invertebrates has not been evaluated. Although the interactions between vector-borne pathogens and their invertebrate hosts have been characterized as being largely benign, some costs of arbovirus exposure have been identified for mosquitoes. The extent to which these costs may be strain-specific and the subsequent consequences of these interactions on vector and virus evolution has not been adequately explored.ResultsUsing West Nile virus (WNV) and Culex pipiens mosquitoes, we tested the hypothesis that intrahost fitness is correlated with virulence in mosquitoes by evaluating life history traits following exposure to either non-infectious bloodmeals or bloodmeals containing wildtype (WNV WT) or the high fitness, mosquito-adapted strain, WNV MP20 derived from WNV WT. Our results demonstrate strain-specific effects on mosquito survival, fecundity, and blood feeding behavior. Specifically, both resistance to and infection with WNV MP20, but not WNV WT, decreased survival of Cx. pipiens and altered fecundity and bloodfeeding such that early egg output was enhanced at a later cost.ConclusionsAs predicted by the trade-off hypothesis of virulence, costs of infection with WNV MP20 in terms of survival were directly correlated to viral load, yet resistance to infection with this virulent strain was equally costly. Taken together, these results demonstrate that WNV MP20 infection decreases the transmission potential of Cx. pipiens populations despite the increased intrahost fitness of this strain, indicating that a virulence-transmission trade-off in invertebrates could contribute significantly to the adaptive and evolutionary constraint of arboviruses.

Increase of clutch size triggers clutch destruction behaviour in common moorhens (Gallinula chloropus) during the incubation period

Conspecific brood parasitism (CBP) is common in a variety of animal taxa, including birds. In coots (Fulica spp.), and the closely related moorhens (Gallinula spp.), such parasitism is especially common, and hosts experience considerable costs through increased chick competition soon after hatching. Hence, these birds have evolved egg recognition and rejection abilities, e.g., egg counting, burying the foreign eggs, assigning them suboptimal positions within the mixed clutch, or deserting parasitized clutches. For common moorhens (Gallinula chloropus) it has been shown that desertion of parasitized nests pays most at the early egg laying stage. Later on, the costs of desertion exceed the costs of brood parasitism and acceptance is favoured. Here we tested moorhen egg discrimination behaviour during the incubation stage when acceptance of foreign eggs is expected. Four treatments were applied: (1) single added non-mimetic pale blue egg, (2) single added non-mimetic white chicken egg, (3) four foreign conspecific eggs added to the clutch and (4) four foreign conspecific eggs exchanged for four host eggs. Moorhens responded by egg destruction (47%) only to the increased clutch size but not to foreign egg colour and size match. In three nests where egg destruction occurred, all the eggs in the mixed clutch were destroyed by pecking, in two other nests one of the foreign eggs were pecked, while two other nests were deserted. These results are puzzling since moorhens have been shown to possess refined egg recognition abilities. To our knowledge, such destruction of parasitized clutches by moorhens during incubation has not previously been reported. We suggest that after clutch completion, moorhens use increase in clutch size as a cue to determine if they have been parasitized, and some individuals choose to reject parasitic eggs by deserting or destroying the whole clutch.

Effects of Nest Reuse and Onset of Incubation on Microbial Growth and Viability of Wood Duck Eggs

Abstract. In many birds, egg viability declines the longer that eggs remain unincubated (i.e., incubation delay), possibly because of increased levels of microbial infection. Reuse of nests is common in cavity-nesting species and may also increase exposure of eggs to microbes. Starting incubation before the clutch is complete may help protect early-laid eggs from microbial infection. In this study, we tested the effects of nest cleaning, length of incubation delay, and onset of night incubation on growth of microbes on Wood Duck (Aix sponsa) eggshells and examined the effect of microbial infection on hatching success. We used nest boxes that had been cleaned or not cleaned of previous nesting materials and sampled microbes on eggshells during early and mid egg laying and after the start of night incubation. We detected levels of eggshell microbes (101 colony forming units [CFU] egg-1) lower than at more tropical locations (103–4 CFU egg-1). Levels of heterotrophic bacteria were 2.2 times greater in unclea...

Effect of curcumin on in vitro early post-implantation stages of mouse embryo development

This study was designed to examine the embryotoxic potential of the curcumin at the blastocyst stage and during early post-implantation development of mouse embryos in vitro. Curcumin was administered to ICR mice embryos at a dose of 0, 6, 12, 24 μM throughout in vitro culture. A total of 1015 embryos were randomly assigned to the different dosage groups. The embryotoxic effects were studied by the exposure of curcumin at the blastocyst, implanted blastocyst and early egg cylinder stages, respectively. For assessment of implantation in vitro and further embryonic differentiation, blastocysts were cultured for 8 days. The cell proliferation of outgrowth blastocysts was analysed by Giemsa staining. Exposure to 24 μM of curcumin at the implanted blastocyst stage or early egg stage cause adverse effects on development. The percentage of embryos in the later stages of development was changed depending upon the dose of curcumin used. Furthermore, exposure to 24 μM of curcumin at the blastocyst stage was lethal to all embryos. The number of nuclei per outgrowth of the blastocyst decreased significantly after curcumin pre-treatment. The percentage of trophoblastic giant cells per outgrowth increased significantly after curcumin pre-treatment. These findings demonstrate that curcumin exerts an adverse effect on mouse embryos during the early post-implantation stages of development, equivalent to day 3-day 8 of gestation in vivo. Curcumin treatment or administration should be used carefully at the early post-implantation stage of gestation.

Variation in the ovocalyxin‐32 gene in commercial egg‐laying chickens and its relationship with egg production and egg quality traits

Avian eggshell quality is an important trait for commercial egg production, as the eggshell is the primary packaging material and antimicrobial barrier for the internal food resource. Strong eggshells are essential to ensure that eggs can reach their final destination without damage. Ovocalyxin-32 (OCX32) is a matrix protein found within the outer layers of the eggshell and in the cuticle. Numerous reports in the literature have identified association between variants in the gene encoding this protein, OCX32, and various eggshell quality traits. Thus, OCX32 is a candidate gene for selection for eggshell traits in commercial poultry populations. Sequencing of exons 2-6 of the OCX32 gene in eight elite brown and white eggshell commercial egg-laying lines revealed 28 SNPs and one SNP/indel. Eighteen of these SNPs were predicted to alter the amino acid sequence of the protein. Clusters of SNPs in complete linkage disequilibrium were found in both exons 2 and 6. A total of 19 different versions or protein-sequence haplotypes of the OCX32 protein were inferred, revealing considerable variation within commercial lines. Genotypes for 13 of the SNPs were determined for 330-1819 individuals per line. Trait association studies revealed a significant effect of OCX32 on shell color in white egg lines and line-specific significant effects on albumen height, early egg weight, puncture score, and yolk weight. Three of the lines showed a significant change in OCX32 frequency over time, indicating selection pressure for certain variants of this gene during the breeding program.

Acoustic markers of Atlantic cod (Gadus morhua) spawning in coastal Newfoundland

Knowledge of spawning location and timing is an essential component of ecosystem-based fisheries management. For Atlantic cod (Gadus morhua) in the northwest Atlantic, such knowledge is at best sparse. Acoustic and ichthyoplankton surveys of Smith Sound, coastal Newfoundland, from January to August in 2006 and 2007, indicated that the presence of vertically oriented pelagic behavior, or ‘spawning columns’, coincided with spawning times back-calculated from following early stage egg abundance peaks. Column numbers peaked in early April in both years and in mid-July in 2007 followed by peaks in egg densities. Maturity data from sampled fish confirmed that cod were not spawning in January, but between April and June between 5 and 40% of mature females were spawning at any one time. Column heights reached 30m at depths from 60 to 250m in the middle of the Sound in spring, moving to the outer part of the Sound as the spawning season progressed. Our results indicate that pelagic ‘column’ behavior, as observed on echosounders in this and other regions, comprises a simple, unobtrusive and non-lethal marker of the location and timing of cod spawning in coastal Newfoundland waters.

Manipulation of Life-History Decisions Using Leptin in a Wild Passerine

Seasonal timing of reproduction and the number of clutches produced per season are two key avian life-history traits with major fitness consequences. Female condition may play an important role in these decisions. In mammals, body condition and leptin levels are correlated. In birds, the role of leptin remains unclear. We did two experiments where we implanted female great tits with a pellet releasing leptin evenly for 14 days, to manipulate their perceived body condition, or a placebo pellet. In the first experiment where females were implanted when feeding their first brood offspring we found, surprisingly, that placebo treated females were more likely to initiate a second brood compared to leptin treated females. Only one second brood fledged two chicks while five were deserted late in the incubation stage or when the first egg hatched. No difference was found in female or male return rate or in recruitment rate of fledglings of the first brood, possibly due to the desertion of the second broods. In our study population, where there is selection for early egg laying, earlier timing of reproduction might be hampered by food availability and thus nutritional state of the female before egg laying. We therefore implanted similar leptin pellets three weeks before the expected start of egg laying in an attempt to manipulate the laying dates of first clutches. However, leptin treated females did not initiate egg laying earlier compared to placebo treated females, suggesting that other variables than the perceived body condition play a major role in the timing of reproduction. Also, leptin treatment did not affect body mass, basal metabolic rate or feeding rates in captive females. Manipulating life history decisions using experimental protocols which do not alter individuals' energy balance are crucial in understanding the trade-off between costs and benefits of life history decisions.

The effectiveness of the continuous underway fish egg sampler compared with standard vertical plankton hauls for sampling the eggs of demersal species in the southern North Sea

AbstractTo date, the continuous underway fish egg sampler (CUFES) has been used primarily to map the spawning areas of pelagic fish in upwelling regions. To assess its utility in mapping the spawning grounds of demersal species, species composition and densities of eggs collected by CUFES were compared with results obtained from ring‐net samples (VET: vertical egg trawl) from the southern North Sea over three annual cruises conducted in January/February. CUFES collected slightly fewer eggs per unit volume of water filtered when compared with vertically integrated samples but maps of egg distributions from both devices showed broadly similar patterns. Geostatistical analyses revealed that small‐scale variability was greater with CUFES than with VET. CUFES may thus be able to resolve finer spatial structuring of egg distributions. At the sampling station scale, species compositions (in terms of proportion and abundance) from both approaches were similar, with the notable exception of flounder, which was much more abundant in CUFES samples; these results were similar when considering early and older stage eggs. Results from regression modelling showed that it was difficult to estimate total egg abundance in the water column from CUFES data with linear regression techniques even when additional factors which affect the vertical distribution of the eggs, such as depth, bedstress and wind‐induced mixing, were included. CUFES therefore provides a suitable method for mapping egg distributions of the main fish species producing planktonic eggs during the winter and early spring season in the southern North Sea but may not be used easily when absolute measures of egg production are required. However, CUFES can be added to standard trawl surveys with little disruption to the baseline ground‐fish survey.

Relationships between yolk androgens and nest density, laying date, and laying order in Western Burrowing Owls (Athene cunicularia hypugaea)

Increases in yolk androgens within and among avian clutches have been correlated with decreased incubation time, increased aggression within a nest, increased begging behaviour, decreased immune response, and decreased life span. Although the mechanisms that lead to variability in yolk androgens within and between clutches are not completely known, yolk androgens can be a function of both social and environmental conditions. We were interested in if and how nesting density, laying date, and laying order influenced yolk androgens in Western Burrowing Owls ( Athene cunicularia hypugaea (Bonaparte, 1825)) in which nest density varies considerably. In 2006 and 2007, we used radioimmunoassay to quantify the concentrations of testosterone, 5α-dihydrotestosterone, and androstenedione in the egg yolks from one early and one late-laid egg in 47 nests of Burrowing Owls located in the Morley Nelson Snake River Birds of Prey National Conservation Area in southern Idaho. Nesting density had no detectable effect on yolk androgens. Yolk androgens varied temporally and peaked in the middle of the laying season while being low before and after this time period. Within nests, late-laid eggs had higher testosterone and dihydrotestosterone than early-laid eggs; adrostendione exhibited a similar pattern in one but not both years of our study. It is possible that the seasonal pattern in yolk androgens that we observed is related to aspects of mate quality for females or declining chances of fledging success for later nesting females, whereas rises in egg androgens between early and late eggs within clutches could reflect a mechanism to assist nestlings from late-laid eggs that hatch one to several days after their siblings to better compete for resources within the nest or promote survival in the presence of larger siblings.

Phase Contrast Synchrotron Microtomography: Improving Noninvasive Investigations of Fossil Embryos In Ovo

Fossil embryos are paramount for our understanding of the development of extinct species. However, although thousands of fossil amniote eggs are known, very few embryos in ovo have been described. First reports of fossil embryos were based on broken eggs, where the embryonic remains were already exposed, because destructive methods on complete eggs were avoided. Investigations of complete eggs therefore required nondestructive approaches, such as X-ray microtomography (μCT). However, due to the general low density contrast between fossilized bones and infilling matrix, only a few specimens have been reported using these techniques. Using propagation phase contrast X-ray synchrotron microtomography (PPC-SR-μCT), we report here the discovery of three well-preserved embryos in Early Cretaceous eggs from Thailand. By scanning these eggs using different imaging techniques, we show that vastly different interpretations can be made regarding the preservation state and/or the developmental stage of these embryos. PPC-SR-μCT also revealed differential contrast between bone categories, presumably reflecting the ossification pattern of these embryos. Applying such an approach to large-scale studies of fossil eggs could lead to more discoveries and detailed studies of fossil embryos, providing important developmental and phylogenetic information on extinct and extant amniotes.

Declining extra-pair paternity with laying order associated with initial incubation behavior, but independent of final clutch size in the blue tit

Although functional explanations for female engagement in extra-pair copulation have been studied extensively in birds, little is known about how extra-pair paternity is linked to other fundamental aspects of avian reproduction. However, recent studies indicate that the occurrence of extra-pair offspring may generally decline with laying order, possibly because stimulation by eggs induces incubation, which may suppress female motivation to acquire extra-pair paternity. Here we tested whether experimental inhibition of incubation during the laying phase, induced by the temporary removal of eggs, resulted in increased extra-pair paternity, in concert with a later cessation of laying, in blue tits (Cyanistes caeruleus). As expected, experimental females showed a more gradual increase in nocturnal incubation duration over the laying phase and produced larger clutches than controls. Moreover, incubation duration on the night after the first egg was laid predicted how extra-pair paternity declined with laying order, with less incubation being associated with more extra-pair offspring among the earliest eggs in the clutch. However, incubation duration on this first night was unrelated to our experimental treatment and independent of final clutch size. Consequently, the observed decline in extra-pair paternity with laying order was unaffected by our manipulation and larger clutches included proportionally fewer extra-pair offspring. We suggest that female physiological state prior to laying, associated with incubation at the onset of laying, determines motivation to acquire extra-pair paternity independent of final clutch size. This decline in proportion of extra-pair offspring with clutch size may be a general pattern within bird species.

Early Oral Ovalbumin Exposure during Maternal Milk Feeding Prevents Spontaneous Allergic Sensitization in Allergy-Prone Rat Pups

There are conflicting data to support the practice of delaying the introduction of allergenic foods into the infant diet to prevent allergy development. This study investigated immune response development after early oral egg antigen (Ovalbumin; OVA) exposure in a rat pup model. Brown Norway (BN) rat pups were randomly allocated into groups: dam reared (DR), DR pups challenged daily (days 4–13) with oral OVA (DR + OVAc), DR pups challenged intermittently (on day 4, 10, 12, and 13) with oral OVA (DR + OVAi), formula-fed pups (FF), and FF pups challenged daily with oral OVA (FF + OVA). Immune parameters assessed included OVA-specific serum IgE, IgG1, and IgA. Ileal and splenic messenger ribonucleic acid (mRNA) expression of transforming growth factor-beta (TGF-β1), mothers against decapentaplegic (Smad) 2/4/7, and forkhead box P3 (Foxp3) were determined. Ileum was stained for TGF-β1 and Smad4. Results. Feeding OVA daily to DR pups maintained systemic and local gut antibody and immunoregulatory marker mRNA responses. Systemic TGF-β1 was lower in DR + OVAi pups compared to DR and DR + OVAc pups. Feeding OVA to FF pups resulted in significantly greater OVA-specific IgE and IgG1, and lower IgA and TGF-β1 and Smad expression compared to DR pups. Conclusions. Early daily OVA exposure in the presence of maternal milk maintains immune markers associated with a regulated immune response, preventing early allergic sensitization.

Use of neural network models to estimate early egg production in broiler breeder hens through dietary nutrient intake

In this study, neural network (NN) models were constructed to predict early egg production in broiler breeder hens. By breaking down the early egg production data collected from 98 breeder houses into weekly intervals, 5 NN-based models were developed for 25 to 29 wk of age. Starting with 98 data lines for each week, the NN models were trained by 69 data lines and the remainder (n = 29) were considered as the testing set. The variables of interest for developing the models were ME (kcal/bird per day) and CP, TSAA, Lys, Ca, and available P (g/bird per day). The constructed models were subjected to an optimization algorithm. Therefore, the optimal values for the input variables to maximize early egg production in broiler breeder hens were obtained. Based on the considered criteria to evaluate the goodness of fit, the efficiency of NN-based models to estimate early egg production was confirmed. The optimization results revealed that the breeder hens consuming 407, 457, 470, 486, and 487 kcal of ME/bird per day showed the highest egg production during 25, 26, 27, 28, and 29 wk of age, respectively. Moreover, optimal performance of hens required the intake (g/bird per day) of the following during 25, 26, 27, 28, and 29 wk of age, respectively: CP: 20.3, 22.6, 25, 25.8, and 26; TSAA: 0.88, 1.02, 1.06, 1.07, and 1.07; Lys: 0.98, 1.0, 1.2, 1.3, and 1.32; Ca: 4.5, 4.6, 5.3, 5.0, and 5.4; and available P: 0.48, 0.55, 0.6, 0.61, and 0.62. Although the results showed that the energy and other nutrient requirements of broiler breeder hens during early egg production do not change in parallel with age, it seems that the company recommendations underestimated the nutrient requirements of hens during these weeks.

STR-33, a Novel G Protein-coupled Receptor That Regulates Locomotion and Egg Laying in Caenorhabditis elegans

Despite their predicted functional importance, most G protein-coupled receptors (GPCRs) in Caenorhabditis elegans have remained largely uncharacterized. Here, we focused on one GPCR, STR-33, encoded by the str-33 gene, which was discovered through a ligand-based screening procedure. To characterize STR-33 function, we performed UV-trimethylpsolaren mutagenesis and isolated an str-33-null mutant. The resulting mutant showed hypersinusoidal movement and a hyperactive egg-laying phenotype. Two types of egg laying-related mutations have been characterized: egg laying-deficient (Egl-d) and hyperactive egg laying (Egl-c). The defect responsible for the egg laying-deficient Egl-d phenotype is related to Gα(q) signaling, whereas that responsible for the opposite, hyperactive egg-laying Egl-c phenotype is related to Gα(o) signaling. We found that the hyperactive egg-laying defect of the str-33(ykp001) mutant is dependent on the G protein GOA-1/Gα(o). Endogenous acetylcholine suppressed egg laying in C. elegans via a Gα(o)-signaling pathway by inhibiting serotonin biosynthesis or release from the hermaphrodite-specific neuron. Consistent with this, in vivo expression of the serotonin biosynthetic enzyme, TPH-1, was up-regulated in the str-33(ykp001) mutant. Taken together, these results suggest that the GPCR, STR-33, may be one of the neurotransmitter receptors that regulates locomotion and egg laying in C. elegans.

Estimates of genetic parameters, and cluster and principal components analyses of breeding values related to egg production traits in a White Leghorn population

The objectives of this paper were to identify the phenotypic egg-laying patterns in a White Leghorn line mainly selected for egg production, to estimate genetic parameters of traits related to egg production and to evaluate the genetic association between these by principal components analysis to identify trait(s) that could be used as selection criteria to improve egg production. Records of 54 wk of egg production from a White Leghorn population were used. The data set contained records of the length:width ratio of eggs at 32, 37, and 40 wk of age; egg weight at 32, 37, and 40 wk of age; BW at 54 and 62 wk of age; age at first egg; early partial egg production rate from 17 to 30 wk and from 17 to 40 wk of age; late partial egg production rate from 30 to 70 wk and from 40 to 70 wk of age; and total egg production rate (TEP). The estimates of genetic parameters between these traits were estimated by the restricted maximum likelihood method. Multivariate analyses were performed: a hierarchical cluster analysis, a nonhierarchical clustering analysis by the k-means method of weekly egg production rate to describe the egg-laying patterns of hens, and a principal components analysis using the breeding values of all traits. The highest heritability estimates were obtained for BW at 54 wk of age (0.68 ± 0.07) and age at first egg (0.53 ± 0.07). It is recommended that a preliminary clustering analysis be performed to obtain the population structure that takes into account the pattern of egg production, rather than the TEP, because hens may have the same final egg production with different patterns of egg laying. Early partial production periods were not good indicators for use in improving total egg production because these traits presented an overestimated genetic correlation with TEP because of the part-whole genetic correlation component. Egg production might be improved by selecting individuals based on TEP.

Strong maternal effects and extreme heterogeneity of progeny development in the caridean shrimp Sclerocrangon boreas (Crangonidae)

Sclerocrangon boreas is uncommon among marine coastal carideans in having a non-dispersing, abbreviated (2-stage) larval phase. We investigated the implications of this strategy in terms of fecundity, offspring provisioning and brood care in S. boreas from the St. Lawrence Gulf and Estuary in 2009–2010. Fecundity scaled positively to female body size but was low due to the production of large, lipid-rich eggs. Offspring size at all stages of development was positively related to female size. Larval traits and lipid dynamics indicate obligatory lecithotrophic development from hatching to juvenile. The larva becomes a juvenile on the mother and remains associated with her for sometime after. The co-occurrence of early egg stages among many juveniles in some clutches raises the possibility that maternal care of juveniles includes the provisioning of trophic eggs or eggs reclaimed from other females.

Innexin2 gap junctions in somatic support cells are required for cyst formation and for egg chamber formation in Drosophila

Germ cells require intimate associations with surrounding somatic cells during gametogenesis. During oogenesis, gap junctions mediate communication between germ cells and somatic support cells. However, the molecular mechanisms by which gap junctions regulate the developmental processes during oogenesis are poorly understood. We have identified a female sterile allele of innexin2 ( inx2), which encodes a gap junction protein in Drosophila. In females bearing this inx2 allele, cyst formation and egg chamber formation are impaired. In wild-type germaria, Inx2 is strongly expressed in escort cells and follicle cells, both of which make close contact with germline cells. We show that inx2 function in germarial somatic cells is required for the survival of early germ cells and promotes cyst formation, probably downstream of EGFR pathway, and that inx2 function in follicle cells promotes egg chamber formation through the regulation of DE-cadherin and Bazooka (Baz) at the boundary between germ cells and follicle cells. Furthermore, genetic experiments demonstrate that inx2 interacts with the zero population growth ( zpg) gene, which encodes a germline-specific gap junction protein. These results indicate a multifunctional role for Inx2 gap junctions in somatic support cells in the regulation of early germ cell survival, cyst formation and egg chamber formation. Inx2 gap junctions may mediate the transfer of nutrients and signal molecules between germ cells and somatic support cells, as well as play a role in the regulation of cell adhesion.

Light and electron microscopy observations of embryogenesis and egg development in the human liver fluke, Opisthorchis viverrini (Platyhelminthes, Digenea)

Eggs of most species digenean flukes hatch in the external environment to liberate larvae that seek and penetrate a snail intermediate host. Those of the human liver flukes, Opisthorchis viverrini, hatch within the gastrointestinal canal of their snail hosts. While adult parasites are primarily responsible for the pathology in cases of human opisthorchiasis, their eggs also contribute by inducing granulomata and in serving as nidi for gallstone formation. In view of the peculiar biology of O. viverrini eggs and their contribution to pathology, we investigated embryogenesis in this species by light and transmission electron microscopy. Egg development was traced from earliest stages of coalescence in the ootype until full embryonation in the distal region of the uterus. Fully mature eggs were generally impermeable to resin and could not be examined by conventional electron microscopy methods. However, the use of high-pressure freezing and freeze-substitution fixation of previously fixed eggs enabled the internal structure of mature eggs, particularly the subshell envelopes, to be elucidated. Fertilization occurs in the ootype, and the large zygote is seen therein with a single spermatozoon wrapped around its plasma membrane. As the zygote begins to divide, the spent vitellocytes are pushed to the periphery of the eggs, where they progressively degrade. The early eggshell is formed in the ootype by coalescing eggshell precursor material released by approximately six vitelline cells. The early eggs have a thinner eggshell and are larger than, but lack the characteristic shape of, mature eggs. Characteristic shell ornamentation, the "muskmelon" appearance of eggs, appears after eggshell polymerization in the ootype. Pores are not present in the shell of O. viverrini eggs. The inner and outer envelopes are poorly formed in this species, with the outer envelope evident beneath the eggshell at the opercular pole of the mature egg. The miracidium has a conical anterior end that lacks the distinctive lamellar appearance of the terebratorium of other digeneans, such as the schistosomes. The miracidium is richly glandular, containing an apical gland in the anterior end, large cephalic gland, and posterior secretory glands. Each gland contains a secretory product with different structure. The paucity of vitelline cells associating with eggs, the reduced size of eggs, and reduced complexity of the extraembryonic envelopes are interpreted as adaptations to the peculiar hatching biology of the miracidia.

Beach characteristics mitigate effects of onshore wind on horseshoe crab spawning: implications for matching with shorebird migration in Delaware Bay

Disruption of food availability by unfavorable physical processes at energetically demanding times can limit recruitment of migratory species as predicted by the match–mismatch hypothesis. Identification and protection of disruption-resistant habitat could contribute to system resilience. For example, horseshoe crab Limulus polyphemus spawning and shorebird stopover must match temporally in Delaware Bay for eggs to be available to shorebirds. Onshore winds that generate waves can create a mismatch by delaying horseshoe crab spawning. We examined effects of beach characteristics and onshore winds on spawning activity at five beaches when water temperatures were otherwise consistent with early spawning activity. Onshore winds resulted in reduced spawning activity during the shorebird stopover, when spawning typically peaks in late May. During the period with high onshore wind, egg density was highest on the foreshore exposed to the lowest wave heights. Onshore wind was low in early June, and spawning and egg densities were high at all sites, but shorebirds had departed. Beaches that can serve as a refuge from wind and waves can be identified by physical characteristics and orientation to prevailing winds and should receive special conservation status, especially in light of predicted increases in climate change-induced storm frequency. These results point to a potential conservation strategy that includes coastal management for adapting to climate change-induced mismatch of migrations.

Sensitivity analysis of an early egg production predictive model in broiler breeders based on dietary nutrient intake

SUMMARYNeural networks (NNs), especially the group method of data handling-type NN (GMDH-type NN), are new tools in modelling growth and production in poultry systems. In the present study, the GMDH-type NN was used to model early egg production (EEP, eggs/bird) in Ross 308 broiler breeders (BBs) from 24 to 29 weeks of age based on their dietary energy and nutrient intake. The selected input variables were intake levels of metabolizable energy (ME; MJ/bird/day), crude protein (CP; g/bird/day), methionine (Met; g/bird/day), and lysine (Lys; g/bird/day). A sensitivity analysis (SA) technique was utilized to evaluate the relative importance of input variables on model output. The GMDH-type NN revealed a high ability in the modelling of EEP based on the input variables investigated. The SA results indicated that the models developed showed most sensitivity to dietary intake of Met, followed by dietary intake of Lys, ME and CP, respectively. The maximum sensitivity of each input variable was considered as the optimum value for maximizing EEP in BB. The suggested optimum values for dietary nutrient intake were as follows: 1·9–2·1 MJ/bird/day for ME, 23 g/bird/day for CP, 0·65–0·8 g/bird/day for Met and 1·4–1·5 g/bird/day for Lys.