A precise water displacement method for estimating egg volume

ABSTRACT.   Relationships between egg volume and an array of life-history traits have been identified for many bird species. Despite the importance of egg volume and the need for precise and accurate measurements, egg volume is usually estimated using a mathematical model that incorporates length and width measurements along with a shape variable. We developed an instrument that provides precise estimates of egg volume and can be easily used in the field. Using Clapper Rail ( Rallus longirostris ) eggs, we compared egg volumes measured using our instrument with estimates based on linear measurements. We found our instrument to be both precise and accurate. Compared with a method based on linear measurements of eggs, use of our instrument reduced variation in egg volume estimates by 1.6 cm³, approximately 8% of the volume of a Clapper Rail's egg. Further advantages of our technique include ease of use, increased accuracy of field-based volume estimates, and increased resolution of variation in egg volume estimates. In addition, our technique does not require postdata collection processing time and did not influence hatching success. Also, for Clapper Rails and similar species, our technique can be combined with other techniques (e.g., egg flotation) so that both egg volume and embryonic stage can be estimated at the same time.     

Affordable Egg Mortality: Constraining Copepod Egg Mortality with Life History Traits

The maximum egg mortality that a population can afford if itis not to wane, here labelled the affordable egg mortality,can be estimated from knowledge of life history traits, i.e.fecundity, development time, egg hatching time and post-eggmortality. Examination of changes in the affordable egg mort-alitywith variations in the life history traits yields two main conclusions:when development time is short, the affordable egg mortalityis maximized by reducing the egg hatching time, instead of bymaximizing fecundity. In contrast, when development time islong, or when post-egg mortality is high, the affordable eggmortality is maximized by a combination of low egg hatchingtime and very high fecundity, or by increasing the egg hatchingtime. For a growing population, the realized egg mortality shouldalways be less than the affordable mortality. This conditioncan be exploited to check the validity of measured mortalitycoefficients, and is illustrated with two examples from publishedfield studies on marine copepods. These examples reveal thatfor populations in temperate environments that typically displaygrowth in the winter and spring months, high egg losses (>>1 day^–1) cannot be sustained unless recruits are suppliedfrom outside the population.     

Calculating egg volume when shape differs: when are equations appropriate?

ABSTRACT Egg volume is often calculated from length and breadth, assuming little variation in egg shape within species. However, egg shape may vary among females, over time, or within clutches. If this variation is not predictable, volume should be estimated using another method. For example, in some species, egg shape changes consistently with laying order and volume can be estimated using laying‐order specific equations. We measured the length, breadth, volume, and mass of 249 Magellanic Penguin (Spheniscus magellanicus) eggs and regressed volume on length and breadth for first and second eggs separately. Differences between measured and calculated volume averaged <1% for both eggs. Using linear measurements, we calculated egg volume for 7085 clutches from 1983 to 2006. First and second eggs had similar calculated volumes (P > 0.05) in 19 of 24 yr; when they differed, the second egg was larger. In contrast, using single equations typically employed to compute egg volume, we erroneously concluded that first eggs were usually (20 of 24 yr) significantly larger than second eggs. Our regression equations should be applicable to other Spheniscus penguins because ratios of elongation coefficients (length divided by breadth) of first and second eggs are similar among these species. In other species of birds where egg shape changes with laying order, the volume of a sample of eggs should be measured to develop regression equations specific to the species and laying order. Slight variation in egg volume can have important evolutionary and ecological implications that would be erroneously interpreted without field tests to measure volume.     

The influence of molecular variation on protein interactions

We investigated the influence of solvation forces on protein-protein interactions for two forms of lysozyme: hen egg white (HEWL) and turkey egg white (TEWL). Turkey egg white has more surface exposed hydrophobic residues than HEWL and the protein-protein interactions of TEWL are shown to be more attractive than those of HEWL, for the conditions studied. The importance of including a solvation term in the potential of mean force model, to account for molecular variation in protein surface characteristics, is highlighted. We also show that the magnitude of this solvation term can be estimated using readily available data.     

Determining Great Bittern Botaurus stellaris laying date from egg and chick biometrics

Capsule Great Bittern breeding phenology can be estimated from egg and chick biometrics.

Aims To estimate egg or chick ages in order to back-calculate egg-laying dates.

Methods Bittern nests were searched for in six French and three Belarussian sites between 1999 and 2004. Eggs and chicks were measured at each visit. By using a subsample of nests with known egg-laying (or hatching) dates, regression equations are determined using egg density and tarsus length in order to estimate, respectively, egg and chick ages. Additionally in Belarus, the ‘water test’ was used to estimate the incubation stage of the clutch.

Results A total of 141 Bittern nests were found. Egg density decreased linearly from 1.063 at laying to 0.915 the day before hatching. A regression equation therefore allows estimation of egg age from its density. A scale was also constructed to estimate egg age from its position in water, and the accuracy of the two methods is compared. Chick growth rates were similar between the two countries. Before the age of 25 days, chicks are best aged by tarsus length compared to other measurements (weight, bill length). No data were available after that age because chicks were no longer found on nests.

Conclusions Egg-laying date can be estimated to within ±3 days using egg density, and to within ±5 days, using the ‘water test’. Tarsus length can be used until the age of 25 days to age chicks to within ±2 days. These simple measurements provide efficient and accurate methods to record the breeding calendar of this endangered species.     

Life histories as sampling devices: optimum egg size in pelagic fishes*

In teleosts, egg size is an important determinant of larval size. The latter determines where larvae start feeding in the size spectrum of biomass particles. Egg and larval size also determine the size range of predators exploiting these early ontogenetic stages. Thus, egg size is important in determining the particle size range sampled during ontogeny. However, egg size also largely determines how many can be produced by a female. Optimum egg size for marine, pelagic fishes was estimated using a modification of a model developed by Ware. A numerical analysis using empirical information on size and temperature dependent mortality and growth in pelagic, marine systems suggests that allometry of size-dependent mortality and temperature are significant factors in determining optimum egg size. Allometry of mortality will depend on the frequency of encounters between particles of different sizes. Both empirical and modelling studies of such frequencies in pelagic and other environments are required.     

Estimation of genetic parameters for monthly egg production in laying hens based on random regression models

Heritability and genetic correlations of monthly egg production under random regression models were estimated. Three layer lines (A22, A88, K66) in six consecutive generations were analysed. A22 (13, 770 recorded hens) and A88 (13, 950 recorded hens) are maternal lines of Rhode Island White birds selected on egg production and shell colour; K66 (9, 351 recorded birds) is a paternal line of Rhode Island Red birds selected on egg weight. Eight models with different orders of Legendre polynomials were applied. Adequacy of the models was checked by the Akaike Information Criterion. According to the most adequate model including second order Legendre polynomials for fixed effects and third order for additive genetic and permanent environmental effects, relatively high heritabilities were estimated in the first (h²=0.3) and final (h² above 0.3) periods of production with a substantial decrease in heritability during the egg production peak. Methodology based on random regression animal models can be recommended for genetic evaluation of laying hens.     

The structure and dimensions of redds and egg pockets of the endangered salmonid, Sakhalin taimen

Each redd of the Sakhalin taimen Hucho perryi had a V–shaped pot that is specific to this species. The shape of each multiple–egg–pocket redd was a combination of one–egg–pocket redds, and the number of egg pockets in the redd could be estimated from the shape. False redds were small and did not have any V–shaped pots. The factors affecting redd size were examined numerically; consequently, numbers of egg pockets and eggs and female fork length were correlated significantly with tail length. Each egg pocket contained 11–920 eggs (mean: 546·7±95% CL 81·9) and the egg pocket depth was correlated significantly with female fork length. Mean number of redds per female was three, and the number of females could be estimated as one third of the redds.     

An egg‐laying device to estimate the induction of sterility in Ceratitis capitata (Diptera: Tephritidae) sterile insect technique programmes

Area‐wide environmentally friendly pest control methods such as the sterile insect technique (SIT) are being developed and improved to contribute in managing agricultural, environmental and public health problems. A key aspect to evaluate performance of sterile males is to directly measure sterility induction in the field. Sterility induction has been estimated for tephritid fruit flies by recovering egg from host fruit in the field, the method is, however, impractical, and past efforts to develop artificial egg‐laying devices have not prospered. Here, we evaluated response of wild gravid Ceratitis capitata (Medfly) females to long‐distance fruit‐based chemical attractants, visual and tactile stimuli to develop an artificial egg‐laying device. The device combining the most attractive features was further tested under two deployment schemes. Finally, devices and deployment tactics were used to compare fertility levels between feral Medfly females under conventional management and under SIT. Agar spheres wrapped in plastic film, baited with pressed peach juice and visually enhanced with yellow discs received more egg than other combinations of attractive features. Such devices also received more eggs when deployed on fruitless trees and when placed on the orchard perimeter. The egg hatch in an orchard under conventional management was estimated at 86%, whilst egg hatch in an area under SIT was reduced to 31%. The egg‐laying devices are therefore useful to measure sterility induction and can be further improved by refining long‐distance attraction and deployment schemes.     

Quantifying the costs and benefits of protective egg coating in a Chrysomelid beetle

Abstract.  1. The costs and benefits of behavioural care of offspring can often be easily quantified through observations and experiments. Other forms of parental investment, on the other hand, are usually less amenable to cost–benefit analysis.
2. Here, the costs and benefits are estimated for protective egg coating by a chrysomelid beetle, Cryptocephalus hypochaeridis , where the female spends a considerable amount of time adding extra structural components to each of the eggs after laying them.
3. Adding this protective coating was very costly, both in terms of material and energy used: the mass of the extrachorion is equivalent to half the mass of the egg, and water loss and energy expenditure while coating the egg is equivalent to half what would be lost while laying a further egg.
4. Choice tests with egg predators demonstrated that these high costs are offset by benefits in terms of protection against predation: whereas uncoated eggs are readily eaten by predators, coated eggs are always rejected.     

Sibling-size variation in brown trout Salmo trutta in relation to egg size and stream size

Sibling-size variation (SSV), estimated as the coefficient of variation of egg size, was investigated for 13 populations of brown trout Salmo trutta . SSV was negatively correlated with mean egg size both at the population and individual levels. After correction for the effect of mean egg size, SSV was also negatively correlated with stream size. These results provide new information about how salmonid SSV can vary at different ecological scales (individual, population and region). The results are discussed in light of competing theories for explaining SSV: (1) the passive effect hypothesis, stating that egg size variation follows passively from selection on egg size and (2) the bet-hedging hypothesis, stating that high SSV is adaptive in unpredictable environments.     

Using net sacks to examine the relationship between egg size and young size in Common Pochards

ABSTRACT.   Investigators studying the relationship between egg size and young size often face difficulties in assigning particular young to particular eggs. We present a new method based on the use of separate net sacks for each egg that allowed us to study this phenomenon in Common Pochards ( Aythya ferina ) without excessive disturbance of breeding birds. We found a positive isometric relationship between duckling body mass and estimated fresh egg mass ( P < 0.001). However, we found no relationship between estimated fresh egg mass and structural measurements of ducklings (tarsus and bill length, both P > 0.29). In addition, we found a weak positive relationship between estimated egg mass and the size of ducklings ( P = 0.049). Greater hatchling mass typically means a larger yolk supply, and more yolk may provide energy crucial for survival during the first few days after hatching. In addition, ducklings with longer tarsi may be better swimmers and better at finding food and escaping from predators. Although our method has certain limitations and investigators should consider risks when applying it in over-water nests or in nests with large clutches, we believe it is a reliable way to assign young to particular eggs in waterfowl and possibly other bird species.     

Comparative studies on immunochemical properties of female-specific serum protein and egg yolk proteins in rainbow trout (Salmo gairdneri).

1. Female-specific serum protein (FS) and egg yolk proteins of mature female rainbow trout (Salmo gairdneri) were studied comparatively with reference to their immunological and some physicochemical properties. 2. FS was considered to be composed of two egg proteins, E1 and E2, which were isolated from the egg yolk by gel filtration. 3. The molecular weights of FS, E1 and E2 were estimated by gel filtration to be approx 600,000, 300,000 and 35,000, respectively. 4. The analysis with sodium dodecyl sulphate electrophoresis indicated that E1 consisted of two subunits with molecular weights of 90,000 and 15,000, and E2 was estimated to be a dimer of a molecule of 15,000. 5. Male and immature female trout were injected with estradiol-17 beta, and the production of proteins with the same antigenicity with FS was demonstrated.     

葛洲坝下游江段中华鲟产卵场食卵鱼类资源量估算

为定量评估食卵鱼类对中华鲟资源的危害,1997－2001年间,对中华鲟产卵场所在的葛洲坝水利枢纽坝址至下游庙嘴之间长约5km的江段,进行了渔业捕捞样本抽样和解剖检测,运用体长股分析方法并结合淦获物中不同种类的相对数量比例估算出食卵鱼类资源量,研究结果表明,吞食中华鲟卵的主要有圆口铜鱼,铜鱼,瓦氏黄颡鱼等11种鱼类,其年度资源量为197487－744487尾,多年平均444822尾。     

Estimation of genetic parameters for partial egg production periods by means of random regression models

We estimated genetic parameters for egg production in different periods by means of random regression models, aiming at selection based on partial egg production from a generation of layers. The production was evaluated for each individual by recording the number of eggs produced from 20 to 70 weeks of age, with partial records taken every three weeks for a total of 17 periods. The covariance functions were estimated with a random regression model by the restricted maximum likelihood method. A model composed of third-order polynomials for the additive effect, ninth-order polynomials for the permanent environment, and a residual variance structure with five distinct classes, was found to be most suitable for adjusting the egg production data for laying hens. The heritability estimates varied from 0.04 to 0.14. The genetic correlations were all positive, varying from 0.10 to 0.99. Selection applied in partial egg production periods will result in greater genetic profit for the adjacent periods. However, as the distance in time between periods increases, selection becomes less efficient. Selection based on the second period (23 to 25 weeks of age), where greater heritability was estimated, would note benefit the final egg-laying cycle periods.     

Cestode egg production dynamics and fertility in Diphyllobothrium dendriticum (Cestoda, Pseudophyllidea)

Dynamics of egg production of the tapeworm Diphyllobothrium dendriticum has been estimated experimentally in nestlings of the herring gull Larus argentatus per day and per reproductive period. The number of eggs in strobiles has been estimated for the maturation period. Mean egg production of the tapeworm per day (10.43 +/- 2.72 mln) is two orders of magnitude as high as the maximum number of eggs in a mature strobile (0.206 +/- 0.007). It is proposed to estimate coefficient of reproduction intensity as the ratio of egg output per unit of time and maximum egg number in a mature strobile.     

Partner fidelity and egg reciprocation in the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema

The mating system of the simultaneously hermaphroditic polychaeteworm Ophryotrocha diadema consists of a regular egg exchangebetween partners of a pair. Such reciprocal egg exchange hasbeen considered a form of cooperation, where one partner cooperatesby offering its eggs to be fertilized and expects to receivepartner's eggs to fertilize. Frequency of cases in which hermaphroditescheated (i.e., failed to give up eggs at their turn) and responsesto cheating were estimated by analyzing the behavior of 38 triplets of ovigerous hermaphrodites over a 2-week period. Thepartner did not reciprocate 8% of egg layings. The cheatedpartner did not detect most cases of cheating (16 out of 25).Such a low frequency of cheating can explain why no retaliationmechanism evolved in this species. Sixty-eight percent of the individuals from the original pairs deserted even if their partnersnever cheated them; therefore, cheating cannot be consideredthe cause of desertion. Rather, desertion appeared to be aconsequence of availability of a new partner whose oocyteswere riper than those of the old partner. It occurred becausethe opportunity arose for an immediate reward, indicating thatO. diadema egg exchange differs from that originally describedin some serranid fish as egg trading. The relationship betweencosts of desertion and population size is discussed.     

Measuring egg size using digital photography: testing Hoyt's method using Florida Scrub-Jay eggs

ABSTRACT.   Egg volumes are most often estimated using a mathematical model that incorporates length and width measurements and a species-specific shape variable. Although adequate in many respects, this technique does not account for intraspecific variation in egg shape. We developed a computer-automated technique that uses calibrated digital photographs to render precise measurements of several egg-size parameters including length, width, volume, and surface area. The system extracts egg outlines from photographs, and divides each egg into latitudinal slices that are subsequently regarded as simple geometric shapes (cylinders or cone frustra) with volumes and surface areas that can be summed to generate size parameters for the entire egg. We tested this technique using 491 eggs from Florida Scrub-Jay ( Aphelocoma coerulescens ) nests and compared the resulting egg volumes with volumes calculated using the preeminent method of estimating volume from linear measurements. Our method was highly accurate, and differences between the volumes from our method and the alternative method were strongly associated with variation in egg shape. Advantages of our technique include decreased handling of eggs and increased accuracy. Software resources and additional information regarding the technique are available at http://www.archbold-station.org/abs/data/birddata/Bridge-JFO-eggsize.htm .     

Schistosoma japonicum: day to day variation in excretion and hatchability of parasite eggs in the domestic pig, Suis suis

The aim of the present study was to describe the course of an Schistosoma japonicum infection in individual pigs over time, with special regards to fecal egg counts and egg hatchability, emphasizing the extent of variation during and between days. Five specific pathogen free Danish Landrace/Yorkshire/Duroc crossbred male pigs were each given 3500 cercariae intramuscularly. From day 36 to 62 post infection, fecal samples were collected from each pig, morning and evening. Pigs were perfused 62 days post infection. Actual fecal egg counts, miracidial counts, and worm burdens were determined. The trend of fecal egg excretion was adequately described with a third order polynomial and logarithmic link function. Miracidial counts were related directly to morning fecal egg counts through a simple linear function. The study revealed a fairly similar overall pattern of egg excretion for all pigs, showing an increase in egg excretion until week 8, followed by a marked reduction to almost zero. In general, large fluctuations around this trend were seen for all pigs, as revealed in variations in egg counts within the same day as well as between days. However, as revealed by the estimated model lines, these fluctuations are due to random variation in egg density in stools rather than being caused by biologically determined cycles. An exact time for both first occurrence of eggs in feces (days 35-38 post infection) and for peak egg counts (days 44-48 post infection) was predicted for each individual pig. Furthermore, the model revealed that miracidial counts can be related directly to the expected fecal egg counts of the same day through a parameter, which represents hatchability. This hatchability parameter was found to be independent of time post infection for each pig, but large individual differences were seen in hatchability between the pigs.     

Identifying reproductive events using archival tags: egg‐laying behaviour of the small spotted catshark Scyliorhinus canicula

The use of archival depth telemetry as a means of remotely assessing the reproductive rates of free‐ranging fishes is explored. This is achieved by electronically tracking the vertical movements of individual female small spotted catsharks Scyliorhinus canicula in the natural environment, whilst simultaneously evaluating the temporal and vertical distributions of egg‐laying in this species. Distinctive patterns of short‐term (0·3–3·7 h), shallow‐water activity are documented in the time–depth profiles of female S. canicula that occur at an appropriate depth (1·0–2·3 m) and periodicity (every 10–12 days) to represent egg‐laying behaviour. Putative egg‐laying behaviour was exhibited simultaneously by two individually tracked female S. canicula during late‐spring and early‐summer. The results highlight that, provided species behaviour is suitable and complementary methods such as previous data, laboratory experiments and field surveys can be used to validate the patterns observed, archival depth telemetry offers an unobtrusive means by which egg production and egg‐laying behaviour of free‐living fishes can be estimated. As precise information regarding life‐history parameters is difficult to obtain for free‐ranging fish species, this technique could be used to improve the parameterization of species demographic models that are relevant to the management of wild fish populations.