Yolkless Eggs Research Articles

Long-term monitoring of dwarf eggs in clutches of Yellow-legged Gulls (Larus michahellis) breeding in a western Mediterranean colony

The present study provides data on clutches with dwarf eggs from a large sampling in a colony of Yellow-legged Gulls (Larus michahellis) over 31 years. Their occurrence was very low, with a global percentage of 0.26%. Significant variations were not detected among periods of 10 or 11 years. In all the cases, only one dwarf egg was found per clutch. Mean volume of dwarf eggs was 34% of that of non-dwarf eggs. Their content was mostly albumen and a very reduced quantity of yolk, and they were infertile. Several results of the study (the laying order of the dwarf eggs, their mean clutch size and the mean size of the non-dwarf eggs from clutches with dwarf eggs) support the hypotheses that runt eggs occur from a temporary disturbance to the reproductive tract.

Inferred Impacts of Extreme Environments on Hawksbill Turtle (Eretmochelys imbricata) Body Size and Reproductive Output

This study presents the first published data on the morphometrics of nesting hawksbill turtles (Eretmochelys imbricata) and their eggs and counts of yolked and yolkless eggs per clutch from Iranian Islands in the northern Persian Gulf. We found significant variation in some variables among 4 main nesting islands (e.g., weight of yolked eggs, p = 0.000; number of yolkless eggs per clutch, p = 0.017), but effect size was moderate or less (r < 0.5 or d < 0.8). The diameter (p = 0.039), weight (p = 0.028), and number of yolked eggs (p = 0.000) per clutch increased significantly with curved carapace length (CCL), but the effect size was only large for the number of yolked eggs (f2 = 0.152). The number of yolkless eggs did not vary with CCL (p = 0.453) or with the number of yolked eggs (p = 0.523). A meta-analysis of global hawksbill turtle morphometrics and reproductive output revealed significant variation in CCL (p = 0.000) and number of yolked eggs (p < 0.001), with nesting region having a very large effect size on both variables (g2 = 0.880 and 0.616, respectively). Hawksbill turtles from the Gulf were smaller than populations from the Gulf of Oman (p < 0.001), Arabian Sea (p = 0.000), Caribbean (p = 0.000), West Atlantic (p = 0.000), and Southwest Pacific (p = 0.000) but not the Red Sea (p = 0.104), and laid fewer yolked eggs than populations in the Caribbean (p < 0.001) and West Atlantic (p = 0.001) but not the Red Sea (p = 0.636). This may be due to hawksbill turtles nesting in the Gulf remaining within its waters postnesting so adult body size is restricted by the relatively poor foraging habitat and/or success and/or the extreme environments, subsequently limiting clutch size. More information on home range and foraging habitat is required to draw similar conclusions about hawksbill turtles nesting in the Red Sea. Hawksbill turtles nesting in the Gulf, Red Sea, and Arabian Sea also appear to lay larger number of yolkless eggs per clutch than other populations worldwide (mean = 17.6 ± 10.8 SD [range = 0–59]). The functional role of yolkless eggs, potentially in the maintenance of thermal and hydric conditions within tolerable conditions in shallow nests laid in extreme environments, requires further investigation. Similarly, the potential for yolkless eggs to be an adaptation to extreme nest environments in other sea turtle species also nesting in the northern Indian Ocean also warrants examination.

Cryptic massive nest colonisation by ants and termites in the world's largest leatherback turtle rookery

Egg mortality is one of the main factors affecting life history and conservation of oviparous species. A massive and cryptic colonisation of many leatherback turtle (Dermochelys coriacea) eggs is presented in the most important rookery for the species in Gabon. A total of 163 nests were exhumed at Kingere beach, revealing that only 16.7% of eggs produced hatchlings. In the 59% of the nests, more than half of the eggs were dead and attacked by invertebrates and 94% had at least one egg affected by invertebrates. The rate of eggs and SAGs (yolkless eggs) affected by invertebrates within a clutch ranged from 0% to 100%, with an average proportion of 39% and 52%, respectively. The most common invertebrates interacting with the eggs were ghost crabs and insects that affected 51% and 82% of the nests, respectively. Crab and insect co-occurred in 33% of the affected nests. Ants, identified as Dorylus spininodis (Emery 1901) were found in 56% of the excavated nests. However, it was not possible to determine if the ants predated alive eggs or scavenged dead eggs. Very often, hundreds of ants were found dead within dead eggs. Termites and other invertebrates were associated with the clutch environment and identified as opportunistic feeders. An unusual ecological interaction within the leatherback clutches between termites and ants was found in 11% of the nests. The abrupt transition between the soil forest and the beach might be favouring a thriving microbial and invertebrate activity in the sand profile that colonises the nests.

Placenta-Like Structure of the Aphid Endoparasitic Wasp Aphidius ervi: A Strategy of Optimal Resources Acquisition

Aphidius ervi (Hymenoptera: Braconidae) is an entomophagous parasitoid known to be an effective parasitoid of several aphid species of economic importance. A reduction of its production cost during mass rearing for inundative release is needed to improve its use in biological control of pests. In these contexts, a careful analysis of its entire development phases within its host is needed. This paper shows that this parasitoid has some characteristics in its embryological development rather complex and different from most other reported insects, which can be phylogenetically very close. First, its yolkless egg allows a high fecundity of the female but force them to hatch from the egg shell rapidly to the host hemocoel. An early cellularisation allowing a rapid differentiation of a serosa membrane seems to confirm this hypothesis. The serosa wraps the developing embryo until the first instar larva stage and invades the host tissues by microvilli projections and form a placenta like structure able to divert host resources and allowing nutrition and respiration of embryo. Such interspecific invasion, at the cellular level, recalls mammal's trophoblasts that anchors maternal uterine wall and underlines the high adaptation of A. ervi to develop in the host body.

Impact of egg harvesting on breeding success of black-headed gulls, Larus ridibundus

Gull colonies world-wide have been harvested for their eggs for centuries with minimal knowledge of the impacts on breeding. Although most Laridae can replace lost eggs, they have comparatively high energetic demands for egg production. In this paper we assess the impacts of a licensed egg harvest on the breeding success of black-headed gulls Larus ridibundus, which nest colonially in an EU Special Protection Area in Hampshire, southern England. We compared egg volume, hatching and chick survival from harvested and un-harvested nests in central and fringe positions within colonies of various sizes, including colonies with no harvesting activity. Eggs from various laying stages were collected from harvested and un-harvested colonies of similar pre-harvest intrinsic quality, for comparison of their volumes, yolk-to-albumen ratios and eggshell thickness. Egg volume and the yolk-to-albumen ratio depended on laying time and location, with the largest eggs laid during the peak period by birds breeding in central positions on large colonies. Eggs produced by these peak layers also had the largest yolk-to-albumen ratios. Harvested sites were characterised by reductions in egg volume, yolk-to-albumen ratio and eggshell thickness, which translated to poorer hatching success and chick survival. Harvested sites also had a higher proportion of abnormal eggs, particularly taking the forms of small yolkless eggs and unpigmented eggs. The reduced breeding success on harvested colonies is likely to be linked to depletion of the female's endogenous reserves which can also reduce future survival and breeding propensity.

Puzzles of mammalian fertilization and beyond

A complexity imposed on the events of conception during the evolution of eutherian mammals is reflected not only in the placenta but also in a series of gamete-related novelties that involve the design of sperm and eggs, their interactions leading to fertilization, epididymal function, and even the scrotal state. While their functional significance has been difficult to determine, I suggest on the basis of present evidence that the genesis of these novel features relates ultimately to changes in the egg associated with nidation, that they imply a new fertilization strategy, and that most are causally linked--a major first 'domino' being the formidable zona pellucida. The eutherian zona pellucida stands out by virtue of an elastic resilience and thickness which allow it to stretch around the expanding blastocyst. However, this quality of the zona together with its relative protease-insensitivity creates a physical challenge which appears to have determined the design of the sperm head, its behaviour at fertilization, and indirectly even the pattern of sperm maturation in the epididymis. In turn, that pattern appears to have evoked the development of the sperm storage function of the cauda region, with both sperm capacitation and the scrotal state as ultimate legacies of this. Coincidentally, the vulnerability of the small yolkless egg to polyspermy appears to have selected for a unique parsimonious pattern of sperm transport in the Fallopian tube, and possibly for the role of the cumulus oophorus as a sperm sequestering device. These ideas are supported generally by evidence from marsupials, as well as by the deviant patterns seen in some insectivorous mammals.

Influence of nest location and yolkless eggs on the hatching success of leatherback turtle clutches in French Guiana

The hatching success of leatherback turtles, Dermochelys coriacea (Vandelli, 1761), is influenced by heterogeneously distributed ecological factors. However, the hatching success according to nest-site selection has rarely been studied and little is known about the role of nest-site selection and infertile (yolkless) egg production on the predation rate and development of fertile eggs in leatherback turtle nests laid in French Guiana. A field study of 99 leatherback turtle nests was conducted to quantify the relationships between hatching success and (i) the nest-site selection (i.e., vegetation line, sea tide line) and (ii) the infertile eggs, especially their state after incubation (i.e., hydrated or dehydrated) and their effects on predation rate. We found that hatching success on this beach was very low (38.2%). This study illustrates that nest-site selection influences the predation rate and the dehydration of yolkless eggs, while the production of yolkless eggs by leatherback turtles has consequences on nest success. The proportion of yolkless eggs in the clutch, as well as their status at the end of incubation (hydrated or not, preyed upon), correlates with predation rate, development of yolked eggs, and hatching success. There was a significant relationship between nest location (relative to high tide line and vegetation line) and both the predation rates of eggs and the percentage of dehydrated yolkless eggs within a clutch. The production of yolkless eggs was related to hatching success and supports the hypothesis that yolkless eggs have a positive effect on the future of the clutch.

Multihormonal Control of Vitellogenesis in Lower Vertebrates

The comparative approach on how and when vitellogenesis occurs in the diverse reproductive strategies displayed by aquatic and terrestrial lower vertebrates is presented in this chapter; moreover, attention has been paid to the multihormonal control of hepatic vitellogenin synthesis as it is related to seasonal changes and to vitellogenin use by growing oocytes. The hormonal mechanisms regulating vitellogenin synthesis are also considered, and the effects of environmental estrogens on the feminization process in wildlife and humans have been reported. It is then considered how fundamental nonmammalian models appear to be, for vitellogenesis research, addressed to clarifying the yolkless egg and the evolution of eutherian viviparity.

The yolkless egg and the evolution of eutherian viviparity.

All vertebrate follicles have the same basic structure. Viviparity also occurs in all vertebrates except birds, but it is the only form of reproduction in eutherians ("placental mammals"). Their mature follicles are vesicular, and their oocytes are yolkless. Clues to the origin of these unique characteristics are in the incidence of atresia and the role of yolk in reproduction. In broadcast spawning, atresia is as rare as it is common among eutherians and other nonspawning vertebrates. In all but the eutherians, at least the initial-and in most cases all-stages of embryogenesis depend crucially on the zygote's yolk. Eutherian reproduction, therefore, must have evolved in connection with genetic changes that caused fragility of the oocyte, instability of the follicle, and loss of the ability to produce vitellogenin (VTG), the main lipoprotein of yolk. Mutations can result in adaptations by uncovering hidden properties in a trait and/or its environment. Useful mutations in recessive alleles can spread through a population as heterozygotes, invisible until the number of homozygotes for the mutation is large enough for them to suddenly appear and form the nucleus of a new breeding population. Such a mutation probably truncated a long, oviductal-based, aplacental gestation of a small, lightly yolked zygote in an endothermic, mammal-like reptile and converted it into an early monotreme or marsupial-like mammal (pantothere). Against tremendous odds, another mutation later caused loss of the genes for VTG. The resultant yolkless zygote survived because 1). the mutation also affected a network of homeiotic genes controlling the ontogeny of the entire reproductive system and 2). the system contained enough hidden properties for the mutation to change the character of the oocyte, its granulosa cells and corpus luteum, the zygote, and the uterus in a way that virtually assured the new zygote's survival. Eutherian reproduction, however, is neither better nor worse than other forms; it is only different.

Nesting Ecology of the Leatherback Turtle, Dermochelys coriacea, at Parque Nacional Marino Las Baulas, Costa Rica: 1988–1989 to 1999–2000

Abstract We collected data on nesting ecology and identified individual turtles that nested at Parque Nacional Las Baulas, Costa Rica, one of the few remaining nesting sites for Pacific leatherbacks, from 1988–1989 to 1999–2000. We tagged individual female turtles with flipper tags and later with Passive Integrated Transponder (PIT) tags that permitted permanent identification. During the full calendars years of 1990 and 1995, over 93% of nests were laid between the beginning of October and the end of February. We found that 92.4 ± 1% of nesting attempts resulted in successful oviposition, with a mean clutch size of 64.7 ± 1.4 yolked and 38.5 ± 1.0 yolkless eggs (n = 1389). Mean standard curved carapace length and curved carapace width during the surveyed years ranged from 144.4 ± 0.6 cm to 147.6 ± 0.3 cm and from 103.9 ± 0.3 cm to 105.5 ± 0.6 cm, respectively. Reproductive output as determined by estimated clutch frequency (ECF) ranged from 4.3 ± 0.2 to 7.9 ± 0.3 clutches per female per nesting season. T...

Changes in Gonadal and Adrenal Steroid Levels in the Leatherback Sea Turtle (Dermochelys coriacea) during the Nesting Cycle

The reproductive endocrinology of nesting leatherback turtles (Dermochelys coriacea) was studied during the 1996–1997 and 1997–1998 nesting seasons at Los Baulas National Park, Playa Grande, Costa Rica. Blood samples were collected from nesting females throughout the season. Females were observed to nest up to 10 times during the nesting season. Plasma steroids were measured by radioimmunoassay and total plasma calcium was measured by flame atomic absorption spectrophotometry. Plasma testosterone and plasma estradiol levels declined throughout the nesting cycle of the female. Testosterone declined from a mean of 10.18 ± 0.77 ng/ml at the beginning of the nesting cycle to 1.73 ± 0.34 ng/ml at the end of the nesting cycle. Estradiol declined in a similar manner, ranging from a mean of 190.95 ± 16.80 pg/ml at the beginning of the nesting cycle to 76.52 ± 12.66 pg/ml at the end of the nesting cycle. Plasma progesterone and total calcium levels were relatively constant throughout the nesting cycle. Lack of fluctuation of total calcium levels, ranging from a mean high of 97.46 ± 11.37 μg/ml to a mean low of 64.85 ± 11.20 μg/ml, further suggests that vitellogenesis is complete prior to the arrival of the female at the nesting beach. Clutch size (both yolked and yolkless eggs) did not vary over the course of the nesting cycle.

Nesting Frequency and Clutch Size in Dermochelys coriacea in Malaysia

Analysis of 37,654 leatherback visit records shows that a mean of 81% (range 51-95%) of visits resulted in successful nests every year at Rantau Abang beach, peninsular Malaysia. The internesting interval within a season (intraseasonal interval) varied from 0-49 days, but the highest mode (polymodal histogram) was 9-10 days. The percentage of tagged turtles returning to breed in consecutive years and once in 2 years was 48.9 and 24.6, respectively. Few turtles returned after a long absence (e.g., 4 after 8 years). On average, each turtle returns to breed after an interval of 1.95 years (interseasonal interval). Most turtles (38% of the daily total) arrived at the beach at 0100-0300 hours, and laid at 0200-0400 hours. Mean clutch size for those turtles with only one clutch per season was 83 normal and 20 yolkless eggs. For those with more than one clutch, the mean total clutch of normal and yolkless eggs varied little (range 100-105) although yolkless eggs may be fewer in the later clutches (e.g., 11th and 12th). The major difference was in variation in the maximum and minimum number of normal and yolkless eggs in later clutches. For 3 clutches, the minimum-maximum normal and yolkless egg numbers were 84-85 and 18-22, respectively, while for 12 clutches the corresponding figures were 75-96 and 8-29. The number of yolkless eggs depended on the number of normal eggs laid (y = 47.13 - 0.34x (P < 0.001). Clutch size was also found to vary with the beach sector where the eggs were laid.

The status of marine turtles in the Egyptian Red Sea

Five species of marine turtle occur in the Egyptian Red Sea and three are recognised by local fishermen: Eretmochelys imbricata (L.), Chelonia mydas (L.), and Dermochelys coriacea (L.). The last named is rarely sighted, and although the other two nest, only Eretmochelys is common; possibly 500 nest yearly, mainly on offshore islands. Both nesting and feeding habitats appear to be extensive for this species, but clutches have an unusually high percentage of yolkless eggs. The significance of this is not understood, but it indicates that the animals are under pressures not experienced in other parts of their range. The small population of Chelonia is probably due to the scarcity of feeding habitat; marine pastures are generally small in area and standing crop. Dermochelys may be rarely sighted because local fishermen infrequently venture into epipelagic waters where this animal is most common, but the available data indicate that the species is a vagrant in Egypt. The enormous swarms of jellyfish that occur in the Egyptian Red Sea evidently do not attract these turtles, although seasonal concentrations of jellyfish are often accompanied by Dermochelys in other seas. Exploitation of turtles, mainly for meat and eggs, is slight, but habitat perturbations are intense from oil pollution and marine explosions. There is a great need for more basic information and rigorous management of the marine environment.

Some Aspects of the Nesting Behavior and Reproductive Biology of Sea Turtles

Synopsis. Basic reproductive data from 21 green turtle {Chelonia mydas), 8 leatherback (Dermochelys coriacea), 7 hawksbill (Eretmochelys imbricata), 7 olive ridley (Lepidochelys olivacea), 6 loggerhead (Caretta caretta), 1 Kemp's ridley (Lepidochelys kempi), and 1 flatback (Chelonia depressa) populations are provided. Some intraspecific and interspecific relation? ships between size of nester and clutch, egg size and hatchling size are analyzed. Mea? surements of reproductive rates (=numbers of hatchlings per female per year) in 11 populations varied from 35 to 200 in an olive ridley and loggerhead colony, respectively. Nesting behavior of each species is described in terms of type of nesting emergence and time spent on the nesting beach (=chelonery). The relatively large number of yolkless eggs laid by many leatherbacks and by some hawksbills invites further study. Some aspects of sea turtle nesting behavior and reproduction are compared to those of other chelonians.

Relationship between Production of Yolkless Dwarf Eggs and Ovulation

Twenty-eight hens which laid a yolkless dwarf egg are obtained from a flock of 17, 990 White Leghorn hens (1 1/2 years of age) throughout the experimental period of one month. Autopsy examinations on 20 hens revealed that the internal ovulation had taken place on the preceding day of the production of the dwarf egg. From the laying record on the remaining 8 hens following the production of the dwarf egg, it was found that the interval between the lay of dwarf egg and the succeeding normal egg was within a normal range.The insertion of artificial yolk (AY) into the oviduct near the time of natural or induced ovulation resulted in the production of well calcified dwarf eggs similar to those naturally produced. However, the calcified dwarf eggs were not produced when the AY was inserted soon after the lay of the terminal egg of a clutch.It is suggested that the production of yolkless dwarf eggs with shell seems to be associated with the incidence of ovulation.

Dwarf Eggs Laid by a Starling

Dwarf Eggs Laid by a Starling

Dwarf Eggs and the Timing of Ovulation in the Domestic Fowl

THE production of eggs considerably smaller than the normal has been reported in various birds1 and has been well documented for the domestic fowl2. Such eggs have been described as “witch eggs”, “cock eggs”, “dwarf eggs” and “wind eggs”—the latter term also being applied to infertile eggs3. It was known as early as the seventeenth century3 that the yolks of such eggs were frequently absent, but that there was a central nucleus around which albumin was secreted. In an investigation of 236 dwarf eggs, Pearl and Curtis2 reported that 35 per cent of all dwarf eggs were without a yolk, 55 per cent contained free yolk and 15 per cent had a complete yolk.

Effects of cortisone upon blood, adrenal cortex, gonads, and the development of osteoporosis in birds.

Domestic birds exhibited a high tolerance for massive doses of cortisone and developed osteoporosis that was very slight in the rooster, moderately severe in the capon, and severely destructive in the hen. After four weeks of treatment, the adrenals and gonads were atrophied, and there was hypercalcemia, associated with an elevation in the ultrafilterable fraction of the serum calcium. Egg production generally ceased within one week, but a few birds continued to lay irregularly, or briefly, and produced shell-less dwarf eggs with a membranous stalk. Bone was resorbed from the endosteal surface of the cortex of the skeleton by means of a local mechanism that did not require formation of osteoclasts. Estrogen injected into cortisone-treated birds produced the phosphoproteinemia, phospholipidemia, and lipema (associated with twenty-fold rise in the non-ultrafilterable fraction of the serum calcium), the same as in normal birds. Estrogen, without androgen, did not give the hen protection against osteoporosis....

Presence of iodinated amino acids in unhydrolyzed thyroid and plasma.

larger amount of albumen at the disposal of the embryo is of special value in giving it a better start in life outside the capsule. Three years of laboratory culture of Ancylus fluviati, lis Muller have shown that this species has a higher percentage of abnormalities (20%) in the than any other species examined. The frequency of the different kinds of abnormal and egg cells is shown in Table 1. Most common in all three years are dwarf eggs, smaller than ordinary size (1.42x1.20 mm). Dwarf may be a phenomenon definitely connected with the starting or stopping of oviposition. In both series of eggs, those throughout the egg-laying period and those in a single capsule, dwarf are found mainly at the end of each series, but partly at the beginning. The percentages in which they occur in different positions within the capsules are given in Table 2. The considerable number of dwarf and other irregularities given in Table 1 also make Ancylus fluviatilis Muller an interesting subject for studies of the earliest phases of embryonic development. Even when still in ovo the embryos may meet with various influences that interfere with their normal development-e.g., variations in the quantity of albumen, crowding because of abnormal development of a neighboring embryo or accidental formation of nurse eggs (competition), or abnormal development of the egg cell itself, determined by intrinsic factors (e.g., lack of fertilization) or extrinsic factors (e.g., crushing of the egg cell during the formation of the capsule). The advantages of the egg capsules of Ancylus fluviatilis Muller as experimental material can be summarized as follows. The limpet is a suitable animal for studying oviposition and embryogenesis under laboratory conditions. The apparatus described makes it possible to obtain living eggs, laid in transparent capsules, for microscopic investigation of living preparations. The capsule is easily turned, and the can be studied in series exactly in the order in which they were laid. The frequency of abnormalities of several sorts in the make the capsules particularly well suited for studies of cell physiology and other aspects of experimental biology.

Experiments on the Physiology of Egg White Secretion

INTRODUCTIONUPON resecting part of the chalaziferous region of the oviduct, Burmester and Card (1939) observed that a large proportion of the hens which laid after such an operation produced a high percentage of yolkless eggs. Since the majority of these eggs contained no yolk or other foreign material, a mechanical stimulus in the lumen of the magnum was not present to initiate white secretion. Asmundson (1931) suggested that white secretion for a dwarf egg may be initiated by a stimulus arising from the yolk partly entering the funnel and then escaping into the body cavity. However, Burmester and Card (1939) described a case in which yolkless eggs were laid by a hen whose funnel had been removed from the oviduct by transection, and the latter had grown closed.It is the purpose of this paper to report on further experiments on the alteration of the oviduct by operative procedure, .