Changes in egg colour, egg weight and oviposition rate with the number of eggs laid by wild females of the small heath butterfly, Coenonympha pamphilus

ABSTRACT. 1. The colour of eggs laid by individual Coenonympha pamphilus (L.) (Lep., Satyridae) females changed over their lifespan. The first laid eggs were green, but after having laid about 100 eggs, females laid only yellow eggs.
2. By following females in the field, or by capturing wild females, and noting the colour of their eggs, it was established that younger females showed higher oviposition rates and laid heavier eggs than older females.
3. Hence, wild C.pamphilus females are unable to sustain a constant egg production by extracting amino acids or any other nutrients from nectar. We hypothesize that this is a general phenomenon in nectar feeding butterflies.
4. The egg colour did not seem to match the colour of the substrate on which the female chose to deposit the egg.     

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.     

Lifetime egg production and egg mortality in the damselflyPyrrhosoma nymphula (Sulzer) (Zygoptera: Coenagrionidae)

Artificial oviposition sites were used to estimate egg deposition rates in the field. Females laid an average of 10.76 eggs/minute with a mean duration of 22.81 minutes, giving an average clutch size of 245 eggs. Since one mating corresponded to one clutch of eggs, lifetime mating success was used as a measure of the number of clutches produced. Mean lifetime clutch production was 5.91 clutches per female, equating to 1447 eggs per female per lifetime. Eggs were hatched in the laboratory at temperatures comparable with those in the field. Hatching was highly synchronised and the overall hatching success was 75.1%. Causes of egg mortality in the laboratory were limited to infertility and unhatchability. Since no other sources of egg mortality could be found at the study site, this value was a good reflection of hatching success in the field. Lifetime egg production and hatching success were used to estimate the number of viable offspring produced per female, giving a higher order estimate of reproductive success than has previously been published for a zygopteran.     

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 reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

In vitro storage of unfertilized eggs of the Eurasian perch and its effect on egg viability rates and the occurrence of larval malformations

Ova ageing is the most important factor affecting fish egg quality after ovulation. Long-term storage of fish ova, using cryopreservation and vitrification techniques, has been unsuccessful to date. Instead, short-term in vitro ova storage has been used successfully and optimized in some cultured fish species. In vitro ova storage can drastically improve mass production of larvae and juveniles in the hatcheries by providing the possibility of the synchronous artificial fertilization for different females. To study how long unfertilized eggs of Eurasian perch (Perca fluviatilis L.) can retain their fertilizing ability after stripping, eggs were stored at temperatures of 4°C, 8°C and 12°C for 72 h post-stripping (HPS). The stored eggs of four female perch were separately fertilized at 0 h (i.e. control eggs fertilized before storage) and at 6-hour intervals during the experimental period of 72 h. The embryos reaching the eyed-egg and hatched-larvae stages, eyed-egg mortality and larval malformation rates were recorded as indices of egg quality. The results indicated that the maximum eyed eggs and hatched larvae (86% and 63%, respectively) were observed for eggs fertilized immediately after stripping, whereas the storage of the eggs at 4°C for 48 HPS decreased the eyed-egg and hatched-larvae rates to 46% and 17%, respectively. The use of a higher storage temperature resulted in a more rapid decrease in egg viability: eyed-egg and hatched-larvae rates of 23% and 9%, respectively, were obtained after 48 HPS storage at 8°C and 2% and 1% for eggs stored at 12°C. Eyed-egg mortality and larval malformation rates were not significantly affected by post-stripping ova ageing for at least up to 36 h. Thereafter, both values increased significantly and were measured to be the highest in the most aged ova. The present study demonstrated that stripped Eurasian perch eggs can be stored for at least 12 h at 4°C to 12°C without a significant reduction in their quality.     

Intraspecific variability in egg maturation patterns and associated life‐history trade‐offs in a polyembryonic parasitoid wasp

1. Life‐history theory predicts a trade‐off between the resources allocated to reproduction and those allocated to survival. Early maturation of eggs (pro‐ovigeny) is correlated with small body size and low adult longevity in interspecific comparisons among parasitoids, demonstrating this trade‐off. The handful of studies that have tested for similar correlations within species produced conflicting results. 2. Egg maturation patterns and related life‐history traits were studied in the polyembryonic parasitoid wasp, Copidosoma koehleri (Hymenoptera: Encyrtidae). Although the genus Copidosoma was previously reported to be fully pro‐ovigenic, mean egg loads of host‐deprived females almost doubled within their first 6 days of adulthood. 3. The initial egg‐loads of newly emerged females were determined and age‐specific realised fecundity curves were constructed for their clone‐mate twins. The females' initial egg loads increased with body size, but neither body size nor initial egg load was correlated with longevity and fecundity. 4. The variation in initial egg loads was lowest among clone‐mates, intermediate among non‐clone sisters and highest among non‐sister females. The within‐clone variability indicates environmental influences on egg maturation, while the between‐clone variation may be genetically based. 5. Ovaries of host‐deprived females contained fewer eggs at death (at ～29 days) than on day 6. Their egg loads at death were negatively correlated with life span, consistent with reduced egg production and/or egg resorption. Host deprivation prolonged the wasps' life span, suggesting a survival cost to egg maturation and oviposition. 6. It is concluded that adult fecundity and longevity were not traded off with pre‐adult egg maturation.     

Evidence for the signaling function of egg color in the pied flycatcher Ficedula hypoleuca

A recent hypothesis proposes that the bright colors, especiallyblue and green, of many avian eggs may function as signals offemale or offspring phenotypic quality or condition to malesin species with biparental care, inducing them to allocate moreeffort to their offspring. The pigment determining blue andgreen egg colors is an antioxidant whose availability for eggshellcoloring may be limited. To test the signaling function on aspecies with blue eggs, the pied flycatcher Ficedula hypoleuca,we measured egg color with a spectrophotometer on the day oflaying and obtained two principal components from their reflectancespectra that together explained 99% of variation and representedshell lightness, and hue and saturation, respectively. We alsomeasured female immunocompetence during the nestling periodthrough the response to phytohemagglutinin as a measure of cell-mediatedimmunity and the response to a tetanus vaccination as a measureof humoral immunity. The total amount of immunoglobulins inblood of females and of nestlings before fledging was also estimated.Mean within-clutch egg darkness was positively associated withboth measures of female immunocompetence, while better femalecondition was associated with colors tending away from intermediateand toward short wavelengths. Ageing female laid lighter eggs.The mean within-brood level of nestling IgY was also associatedwith mean within-clutch egg colors tending away from intermediateand toward short wavelengths. Mean egg darkness decreased linearlyduring the laying sequence, suggesting pigment limitation. Maleswere observed frequently visiting nests during the laying period,allowing them to observe eggs before the start of incubation.These results support the signaling hypothesis for explainingbright colors of avian eggs.     

Seasonal variation in egg production and batch fecundity of European hake Merluccius merluccius (L.) in the Bay of Biscay

Sexually mature female hake Merluccius merluccius with hydrated ovaries were sampled on a monthly basis in the Bay of Biscay, from May 1996 to October 1997 and from March to April 1998. The batch fecundity was positively related to total length. The relative batch fecundity ( F _Brel) varied significantly among months and years, but not between areas, i.e. International Council for the Exploration of the Sea Divisions VIIIa and VIIIb within the Bay of Biscay. Two levels of F _Brel were found in 1997: the highest between January and April (mean ± s . e . 167 ± 5 eggs g⁻¹) and the lowest from May to October (112 ± 3 eggs g⁻¹). Population condition factor and gonado-somatic indices ( I _G) followed the expected trend in relation to the monthly changes in F _Brel during 1997. The F _Brel variation between years was 9% for 1996–1997 and 28% for 1997–1998, and the difference of the I _G was c. 14 and 36%, respectively. Population relative egg production varied from a high value in January to March (985 eggs g⁻¹) to a low egg production between April and October 1997 (445 eggs g⁻¹).     

Heritability, plasticity and canalization of Ural owl egg size in a cyclic environment

Avian egg size is highly variable on the population level, but is considered inflexible on the individual level. On the basis of 2969 measurements of individual eggs collected during 1981-2005, we analysed heritability, plasticity and selection on egg size in the Ural owl, a long-lived bird that preys on voles. Vole abundance varied in a 3-year cycle, creating varying food supply across the cycle's phases. Ural owl egg size is heritable (h(2) = 60%). Ural owls lay larger eggs in improved food conditions. On the basis of repeated breeding records of 59 females that bred in all vole cycle phases, we show that intra-individual adjustment (plasticity) explained 22.4% of the variation in egg size across phases. Egg size was under stabilizing selection. Extremely small and extremely large eggs had reduced hatchability, and individuals who laid either large or small eggs had lower lifetime fledgling production than the ones laying intermediately sized eggs. Our findings illustrate how maternal investment in egg size can both be heritable and highly responsive to variable environmental conditions, and suggest that variation in the investment in egg size across individuals is canalized.     

Effects of overripening on spawning behaviour and reproductive success of Atlantic salmon females spawning in a controlled flow channel

The influence of overripening on salmonid egg quality has often been described in artificial breeding. However, no information exists on the impact of this factor on fish reproducing naturally, although it is likely to be critical, especially in disturbed environments. Pairs of Atlantic salmon in which the size of the male and the female was evenly matched were released in a spawning channel from 1 to 12 days after ovulation. Handling did not affect egg quality. Overripening had a negative effect on egg viability. Egg mortality, infertility and malformations increased with the number of days after ovulation. In females which had just matured, 16·7% of their recovered eggs were dead, 3·1% were unfertilized and 1·7% were malformed, as compared to 25·4, 9·7 and 5·4%, respectively, in females that had been mature for at least a week. Overripening played a role in both female spawning behaviour and capacity to spawn, as females which had been mature for over a week released their eggs more quickly while they retained more ova in their abdominal cavity than early spawning females. Thus, in studies of reproductive behaviour and in particular of sexual selection, it is critical to take into account the maturation status of females since the duration of spawning activity is used by various authors to determine female sexual motivation. Alternatively, overripening may decrease the female selectivity for mates.     

Buoyancy variations in eggs of Atlantic cod (Gadus morhua L.) in relation to chorion thickness and egg size: theory and observations

Egg specific gravity is a function of egg volume, chorion volume, perivitelline space (PVS) and the specific gravity of chorion and ovoplasm. Experimental studies on cod ( Gadus morhua L.), a marine multiple batch spawner, showed that approx. forty per cent of the chorion volume is incorporated between batches and that the chorionic material has a mean specific gravity of 1·20 (range: 1·14–1·35). The chorion volume and specific gravity are low at the end of the spawning period in extremely fecund fish. Specific gravity of ovoplasm was observed to be 1·017 in marine eggs and calculated to be about 1·008 in brackish water eggs. Inherent variation in PVS is found to have little influence on egg specific gravity. With the other variables constant, egg specific gravity is inversely related to egg volume supported by studies on single batches of eggs. Measurements on every batch of eggs reveal that the production of large eggs (>1·3 mm) gives low density eggs initially and high density eggs towards the end of spawning, while the production of small eggs (<1·3mm) gives moderate specific gravity. These observations are discussed in relation to vertical distribution of the eggs and reproductive success of recruit and repeat spawners. There are indications that repeat spawners produce larger eggs.     

Feeding,egg production,and egg hatching success of the copepods Acartia tonsa and Temora longicornis on diets of the toxic diatom Pseudo-nitzschia multiseries and the non-toxic diatom Pseudo-nitzschia pungens

In 1987, there was an episode of shellfish poisoning in Canada with human fatalities caused by the diatom Pseudo-nitzschia multiseries, which produced the toxin domoic acid. In order to examine whether domoic acid in this diatom serves as a grazing deterrent for copepods, we compared feeding rates, egg production rates, egg hatching success and mortality of the calanoid copepods Acartia tonsa and Temora longicornis feeding on unialgal diets of the toxic diatom P. multiseries and the similarly-sized non-toxic diatom Pseudo-nitzschia pungens. Copepods were collected in summers of 1994, 1995 and 1996 from Shediac Bay, New Brunswick, Canada, near Prince Edward Island, the site of the 1987 episode of domoic acid shellfish poisoning. Rates of ingestion of the toxic versus the non-toxic diatom by A. tonsa and T. longicornis were similar, with only one significantly different pair of values obtained in 1994, for which A. tonsa had a higher mean rate of ingestion of the toxic than the non-toxic diatom. Thus, domoic acid did not appear to retard grazing. Analyses of copepods with high performance liquid chromatography (HPLC) revealed that copepods accumulated domoic acid when feeding on P. multiseries. Egg production rates of copepods when feeding on P. multiseries and P. pungens were very low, ranging from 0 to 2.79 eggs female^–1 d^–1. There did not appear to be differential egg production or egg hatching success on diets of the toxic and non-toxic diatoms. Mortality of females on the toxic diet was low, ranging from 0 to 20%, with a mean of 13%, and there was no apparent difference between mortality of copepods feeding on toxic versus non-toxic diatoms. Egg hatching success on both diets, although based on few eggs, ranged between 22% and 76%, with a mean percentage hatching of 45%. Diets of the non-toxic diatom plus natural seawater assemblages supplemented with dissolved domoic acid, revealed similar rates and percentages when compared to previous experiments. In summary, none of the variables measured indicated adverse effects on copepods feeding on the toxic compared to the non-toxic diatom.     

Life-history and ecological correlates of geographic variation in egg and clutch mass among passerine species

Broad geographic patterns in egg and clutch mass are poorly described, and potential causes of variation remain largely unexamined. We describe interspecific variation in avian egg and clutch mass within and among diverse geographic regions and explore hypotheses related to allometry, clutch size, nest predation, adult mortality, and parental care as correlates and possible explanations of variation. We studied 74 species of Passeriformes at four latitudes on three continents: the north temperate United States, tropical Venezuela, subtropical Argentina, and south temperate South Africa. Egg and clutch mass increased with adult body mass in all locations, but differed among locations for the same body mass, demonstrating that egg and clutch mass have evolved to some extent independent of body mass among regions. A major portion of egg mass variation was explained by an inverse relationship with clutch size within and among regions, as predicted by life-history theory. However, clutch size did not explain all geographic differences in egg mass; eggs were smallest in South Africa despite small clutch sizes. These small eggs might be explained by high nest predation rates in South Africa; life-history theory predicts reduced reproductive effort under high risk of offspring mortality. This prediction was supported for clutch mass, which was inversely related to nest predation but not for egg mass. Nevertheless, clutch mass variation was not fully explained by nest predation, possibly reflecting interacting effects of adult mortality. Tests of the possible effects of nest predation on egg mass were compromised by limited power and by counterposing direct and indirect effects. Finally, components of parental investment, defined as effort per offspring, might be expected to positively coevolve. Indeed, egg mass, but not clutch mass, was greater in species that shared incubation by males and females compared with species in which only females incubate eggs. However, egg and clutch mass were not related to effort of parental care as measured by incubation attentiveness. Ecological and life-history correlates of egg and clutch mass variation found here follow from theory, but possible evolutionary causes deserve further study.     

Holding temperature during the breeding season influences final maturation and egg quality in common wolffish

Mature common wolffish, Anarhichas lupus L., previously held at 8°C for several months, were exposed to 4, 8 or 12°C throughout the breeding season (November-January). Regardless of temperature, some females ovulated in early-November, but thereafter ovulation was delayed in the 8 and 12°C groups compared with the 4°C group. Temperature experienced by the adult fish also affected egg development and survival even though eggs were incubated at a common temperature of 6°C. The percentages of normally cleaved eggs (at the 32-cell stage) and egg survival to the eyed stage were significantly lower in the 12°C group (8%) than in the 4°C (73%) and 8°C (48%) groups. The differences in egg survival were also significant between the 4 and 8°C groups. Egg survival was also influenced by the length of time the broodfish had been exposed to the different temperatures: at 4 and 12°C there were significant positive and negative relationships, respectively, between egg survival and the number of days for which the female had been exposed to the given temperature prior to ovulation. Temperature experienced by the female did not affect egg size, relative egg weight, fertilization rate, relative fecundity or the number of ovulating individuals. The results indicate that both the timing of ovulation and egg quality of common wolffish are affected by the temperature experienced during the breeding season.     

Distribution of second generation European corn borer,Ostrinia nubilalis, egg masses in field corn and relationship to subsequent tunneling damage

The relationship between second generation European corn borer (Ostrinia nubilalis Hübner) egg mass numbers and subsequent field corn damage, as measured by stalk cavity numbers, was studied in 79 fields in northeastern North Carolina over three years. A mean of 0.028 egg masses per plant (645 egg masses/23400 plants) was found over the course of the study. Significant differences in oviposition rate were detected between fields and years. Ca. 85% of egg masses were deposited in a five leaf zone surrounding the primary ear; of these, 89% were found on the lower four leaves in this zone. Egg masses appeared to be distributed randomly within fields but at low rates of incidence, and oviposition was relatively uniform between sampling areas within individual fields. Under moderate to high oviposition pressure (mean number of egg masses per plant over the duration of the oviposition period >ca. 0.02), eggs laid during the early phases of the oviposition period account for more subsequent stalk damage than eggs laid during the later phases of the oviposition period. Variations in second generation egg mass numbers accounted for ca. 70% of variation in stalk cavity numbers.     

The role of partial incubation and egg repositioning within the clutch in hatching asynchrony and subsequent effects on breeding success

The main mechanism to achieve hatching asynchrony (HA) for incubating birds is to start heating the eggs before clutch completion. This might be achieved through partial incubation and/or early incubation. Even in the absence of incubation behaviour during the laying phase, clutches still experience a certain degree of asynchrony. Recent studies have shown that eggs located in the centre of the nest receive more heat than peripheral ones during incubation. As eggs receiving more heat would develop faster, we hypothesized that HA should be shorter in nests where eggs were moved homogeneously along the centre–periphery space during incubation than in those nests where eggs repeatedly remained in the same locations, either centrally or peripherally. We explored the relative roles of egg repositioning and partial incubation in determining HA in wild birds by (1) removing eggs from 20 Great Tit Parus major nests on the day of laying and replacing them with fake eggs to avoid partial incubation, and returning them when full incubation began; (2) monitoring twice a day the position of each individually marked egg relative to the clutch centre during incubation, and estimating the coefficient of variation of the distances; and (3) determining HA in each nest. Preventing partial incubation reduced HA by 51% days in experimental nests. It also caused negative effects for the incubating females (lengthening the full incubation period) and positive effects for the brood (increasing fledging success). However, our hypothesis about the role of egg repositioning on HA was not supported: all the females moved the eggs with remarkable consistency, generally attaining a coefficient of variation of the distances around 33%, and it was not related to the HA experienced. We therefore conclude that partial incubation is an important factor regulating HA, and females compensate for the potential effects of differential heating by moving the eggs homogeneously within the clutch.     

Ability of ovipositing seed beetles to discriminate between seeds with differing egg loads

Abstract. 1. Previous work has shown that ovipositing females of Callosobruchus maculatus (F.) avoid seeds already bearing eggs, and thereby reduce competition among their larval progeny within seeds.
2. This study demonstrates that females also detect small differences in egg density, and prefer to oviposit on seeds with a lower-than-average number of eggs. A nearly uniform dispersion of eggs is thus maintained even after all seeds bear several eggs.
3. In addition, variation in egg load influences oviposition rate. Transfer of females from seeds with few eggs to seeds with many eggs inhibits oviposition; the reverse transfer stimulates it.
4. The upper surface of the egg chorion or egg 'cover' remains intact on the seed surface after the larva has entered the seed and continues to deter egg-laying for at least as long as the period required for larval development. 14-day-old egg covers provide as much deterrence as freshly laid eggs.     

The evolution of egg clustering in butterflies: A test of the egg desiccation hypothesis

Females of many insect species cluster their eggs. Egg clustering by lepidopteran species usually results in aggregation of larvae that are more often conspicuously coloured and apparently distasteful or unpalatable than larvae of solitary species. While the costs and benefits of aggregation in terms of larval survival and growth are well documented, the evolutionary ecology of egg clustering has been long debated and is still unresolved. We tested the egg desiccation hypothesis, first proposed by Stamp (1980), which to our knowledge has never been examined experimentally. The egg desiccation hypothesis proposes that egg clustering is adaptive per se (i.e. increases fitness of females) by reducing egg mortality via desiccation.We tested this hypothesis for the Nymphalid butterfly, Chlosyne lacinia, an egg-clustering species on its sunflower host plant, Helianthus annuus. We first documented natural variation in batch size for this butterfly. We then tested experimentally hatch success of varying batch sizes and egg-layering arrangements under controlled humidity levels. Hatch success was positively related to relative humidity. Eggs in larger groups with greater number of layers had greater hatch success than smaller, monolayered egg batches, especially when relative humidity was low. Our results indicate that, not only number of eggs, but also the arrangement (i.e. layering and density), increase batch survival by protecting eggs from desiccation. However, despite increased hatch success in dense, multilayered clusters, we found wide variation in layering and density in natural populations of C. lacinia. This variation is probably maintained by trade-offs in egg survival, such as increased cannibalism of eggs by siblings, in dense clusters. Nevertheless, protection from egg desiccation provides an alternative explanation for the origin and maintenance of egg clustering in lepidopterans and possibly other insects. The pattern of egg deposition in the Nymphalidae supports this hypothesis, since most North American species cluster their eggs tightly, whereas most species in tropical regions lay eggs singly or in loose monolayers.     

Effects of experimental calcium availability,egg parameters and laying order on Great Tit Parus major eggshell pigmentation patterns

Many bird species lay eggs speckled with protoporphyrin‐based spots, however, for most of them the function of eggshell spotting is unknown. A plausible hypothesis is that protoporphyrin might have a structural function in strengthening the eggshell and is therefore deposited when calcium is scarce. In this study, we experimentally provided Great Tit Parus major females with supplemental calcium to examine its effect on the protoporphyrin‐based maculation of their eggs. In addition, we studied variation in eggshell pigmentation patterns in relation to other egg parameters and laying order. Calcium‐supplemented females laid larger eggs but shell thickness was not significantly affected by the treatment. Calcium supplementation may reduce the time and energy females devote to searching for calcium‐rich material, so that they can collect more nutrients and so lay larger eggs. Furthermore, pigment darkness was associated with egg volume and shape, which suggests that female quality and environmental food availability may also influence the shell pigmentation pattern. Within clutches, later‐laid eggs had larger and darker spots that were distributed more unevenly on the shell surface. This within‐clutch pattern could be explained by the increase in egg volume and egg shape and a decline in shell thickness with egg‐laying order, which characteristics were all related to shell‐spotting pattern. Eggs with a coronal ring had thinner shells, but pigment intensity and spot size were not related to shell thickness. Thus, our results suggest that concentrated spotting distribution may have a mechanical function, supporting the structural‐function hypothesis.