Placental calcium provision in a lizard with prolonged oviductal egg retention

A prominent scenario for the evolution of viviparity and placentation in reptiles predicts a step-wise pattern with an initial phase of prolonged oviductal egg retention accompanied by progressive reduction in eggshell thickness culminating in viviparity; calcium placentotrophy evolves secondarily to viviparity. Saiphos equalis is an Australian scincid lizard with a reproductive mode that is uncommon for squamates because eggs are retained in the oviduct until late developmental stages, and the embryonic stage at oviposition varies geographically. We studied calcium mobilization by embryos in two populations with different oviductal egg retention patterns to test the hypothesis that the pattern of nutritional provision of calcium is independent of the embryonic stage at oviposition. Females from one population are viviparous and oviposit eggs containing fully formed embryos, whereas embryos in oviposited eggs of the second population are morphologically less mature, and these eggs hatch several days later. The reproductive mode of this population is denoted as prolonged oviductal egg retention. Yolk provided the highest proportion of calcium to hatchlings in both populations. Eggs of both populations were enclosed in calcified eggshells, but shells of the population with prolonged egg retention had twice the calcium content of the viviparous population and embryos recovered calcium from these eggshells. Placental transfer accounted for a substantial amount of calcium in hatchlings in both populations. Hatchling calcium concentration was higher in the population with prolonged egg retention because these embryos mobilized calcium from yolk, the eggshell and the placenta. This pattern of embryonic calcium provision in which both a calcified eggshell and placentotrophy contribute to embryonic nutrition is novel. The reproductive pattern of S. equalis illustrates that calcified eggshells are compatible with prolonged oviductal egg retention and that viviparity is not requisite to calcium placentotrophy.     

Influence of the evolution of viviparity on eggshell morphology in the lizard Lerista bougainvillii

In reptiles, the evolutionary transition from egg-laying to live-bearing is thought to involve a gradual increase in the duration of egg retention, with progressively more development occurring prior to oviposition, and culminating in the birth of fully developed offspring. However, prolonging the retention of fully-shelled eggs within the oviducts may pose serious gas-exchange problems for the embryos. Thus, evolutionary increases in the period of intrauterine retention may require correlated decreases in the thickness of eggshells and/or their degree of calcification to allow for adequate embryonic gas exchange. To test this evolutionary model, eggs of three distinct reproductive forms of the scincid lizard Lerista bougainvillii were examined to determine the evolutionary relationships between the thickness of the shell membrane, degree of eggshell calcification, and the duration of uterine egg retention. These comparisons revealed the predicted pattern of correlated shifts in eggshell morphology and embryonic stage at oviposition. Evolutionary increases in the duration of egg retention were accompanied by decreases in the thickness of the eggshell membrane and degree of eggshell calcification. This evolutionary model suggests that there may be a tradeoff between the advantages of extended egg retention and the disadvantages of a thinner eggshell. On the basis of this tradeoff, I propose that oviparous taxa with relatively thin eggshells may be preadapted to evolve viviparity. Comparative examination of the limited data available on eggshell thickness in lizards supports this possibility. © 1996 Wiley-Liss, Inc.     

Variation in eggshell characteristics and in intrauterine egg retention between two oviparous clades of the lizard Lacerta vivipara: insight into the oviparity-viviparity continuum in squamates

The concept of the oviparity-viviparity continuum refers to the wide range in the length of intrauterine egg retention and, hence, in the stage of embryonic development at oviposition existing in squamates. The evolutionary process underlying this continuum may involve not only a lengthening of egg retention in utero, but also a marked reduction in the thickness of the eggshell. The idea that there may exist a negative correlation between the developmental stage reached by the embryo at oviposition and the eggshell thickness within squamates, although supported by the comparison of oviparous vs. viviparous species, has seldom been evaluated by comparing eggshell thickness of oviparous forms with different lengths of intrauterine egg retention. Eggs of two distinct oviparous clades of the lizard Lacerta vivipara were compared. The eggs laid by females from Slovenian and Italian populations have thicker eggshells, contain embryos on average less developed at the time of oviposition, and require a longer incubation period before hatching than the eggs laid by females from French oviparous populations. Our data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates. The current hypotheses that may account for this correlation are presented and a few restrictions and refinements to those hypotheses are discussed. In particular, other changes, such as increased vascularization of the oviduct and of the extraembryonic membranes, may play the same role as the decrease of eggshell thickness in facilitating prolonged intrauterine egg retention in squamates. Future studies should also consider the hypothesis that the length of intrauterine retention might directly depend on the extent of maternal-fetal chemical communication through the eggshell barrier.     

THE PHYSIOLOGICAL ECOLOGY OF REPTILIAN EGGS AND EMBRYOS. AND THE EVOLUTION OF VIVIPARITY WITHIN THE CLASS REPTILIA

1. Eggs of Crocodilia and Chelonia, like those of birds, have a pair of egg membranes separating a thick layer of albumen from the calcareous shell. In contrast, eggs of oviparous Lepidosauria have only a single shell membrane, upon which relatively small amounts of calcium carbonate are deposited; and the volume of albumen in eggs is extraordinarily small at the time of oviposition. 2. With the possible exception of certain geckos and some chelonians, eggs of oviparous reptiles seem always to absorb water from the substrate during the course of normal incubation. In so far as the rate of water absorption exceeds the rate of water loss by transpiration from exposed surfaces, the eggs swell during incubation. The term ‘cleidoic’ cannot be used to describe eggs of this type. 3. Embryos of lizards and snakes influence the water potential of extra-embryonic fluids contained within their eggs, thereby maintaining or increasing the gradient in water potential that drives water absorption. 4. Embryos of Crocodilia and Chelonia obtain a substantial portion of the calcium used in ossification of skeletal elements from the inner surfaces of the eggshell. In contrast, embryonic lizards and snakes draw upon extensive reserves of calcium present in the yolk, and obtain little (if any) calcium from the eggshell. 5. All reptilian embryos seem to produce substantial quantities of urea as a detoxification product of protein catabolism. Contrary to expectation, uricotelism may not be common among reptilian embryos, even in those few instances where development takes place within a hard, calcareous egg. 6. In eggs of Crocodilia and Chelonia, respiratory gases seem to pass by diffusion through pores in the calcareous eggshell and through spaces between the fibres of the pair of egg membranes. No pores have been observed in the shell of lepidosaurian eggs, and so gases presumably diffuse between the fibres of the single (multilayered) shell membrane. 7. Metabolism of reptilian embryos is temperature-dependent, as is true for most ectothermic organisms. For each species, there appears to be a particular temperature at which embryonic development proceeds optimally, and departures from this optimum elicit increases in developmental anomalies and/or embryonic mortality. 8. Viviparity has evolved on numerous occasions among species of the Squamata, but seemingly never among Crocodilia or Chelonia. Since the evolution of viviparity entails a progressive reduction in the eggshell, only those organisms whose embryos do not depend upon the eggshell as a source of calcium may have the evolutionary potential to become viviparous. 9. Evolutionary transitions from oviparity to viviparity could have been driven by selection related to (i) thermal benefits to embryos consequent upon retention of eggs within the body of a parent capable of behavioural thermoregulation; (ii) protection of the eggs from nest predators and/or soil microbes; and (iii) more effective exploitation of a seasonal food resource by early emerging young.     

Biochemical Composition of the Eggs of the Freshwater Snail Lymnaea stagnalis and Oviposition-induced Restoration of Albumen Gland Secretion

Summary

Galactogen and protein form the main constituents of the eggs of Lymnaea stagnalis. The amount of galactogen per egg is fairly constant, irrespective of the size of the egg mass or the age of the snail.

The restoration of the albumen gland, which produces the perivitelline fluid for the eggs, was studied in long-day (16 hr light-8 hr dark) snails after spontaneous oviposition. The wet wt of the gland and its galactogen and protein contents are markedly increased within 8 hr and reach a maximum at 32 hr after oviposition. These maxima correspond to the levels determined in snails that did not lay eggs for at least 1 to 2 days. The amounts of galactogen and of protein in the albumen gland are linearly related to the wet wt of this gland.

The restoration period of the albumen gland almost covers the mean egglaying interval. This implies synchronized cycles of albumen storage and egg formation.

The estimated amount of galactogen, released by the albumen gland during egg mass formation, is in accordance with that deposited in the eggs. In contrast, the wet wt of the eggs is 4.6 times higher than that of the released secretory material. Since after oviposition water uptake by the eggs in the egg mass is negligible, the perivitelline fluid, which is released by the albumen gland and surrounds the egg cell, must be diluted in the reproductive tract of the snail prior to oviposition.     

Oviposition Deterrence Is Likely an Effect,Not a Mechanism,in the Leaf Beetle <Emphasis Type="Italic">Chrysophtharta bimaculata</Emphasis> (Olivier) (Coleoptera: Chrysomelidae)

Oviposition deterrence is common in many insects as an evolutionary mechanism to reduce subsequent larval competition. We investigated a suspected case of oviposition deterrence by the paropsine chrysomelid, Chrysophtharta bimaculata. In paired choice tests, gravid females were found to prefer ovipositing on host leaves without conspecific eggs, confirming the presence of an apparent oviposition deterrence mechanism. Washing egg batches in water, hexane, or ethanol did not change this preference, suggesting that a soluble marking pheromone was not involved. Furthermore, it is unlikely that a plant-derived oviposition deterring substance is produced as beetles showed no significant oviposition preference between leaves which had been oviposited upon, but then had the eggs removed, and those that had never been oviposited upon. In trials using artificial leaves and mimic egg batches, “leaves” with “egg batches” placed near the tip of the leaf (the preferred site of oviposition in this species) were significantly less likely to be laid upon than artificial leaves where mimic eggs were placed away from the tip. In combination, the results strongly infer that oviposition deterrence in C. bimaculata is due to the mechanical blocking of the oviposition site by the first laid egg-batch, rather than a specific oviposition deterring cue. The apparent oviposition deterrence in this insect may well be an outcome or evolutionary effect of oviposition-site selection, rather than a clear adaptive mechanism to decrease larval competition.     

Determinants of embryonic stage at oviposition in the lizard Urosaurus ornatus

Relatively few squamate reptiles oviposit eggs with embryos at developmental stages greater than stage 30. To investigate potential proximate and ultimate bases of this phenomenon, we experimentally induced females of the lizard Urosaurus ornatus to retain their eggs past the normal time of oviposition (NTO). This procedure allowed us to determine whether the length of egg retention is fixed or facultative and to evaluate the effects of retention on embryos, hatchlings, and females. Females were able to retain eggs facultatively for at least 29 d past the NTO. However, retention resulted in arrested development of embryos; arrest occurred at stages 30-30.5, which is only slightly more advanced than that at the NTO (stage 29.5). Embryogenesis was reinitiated when eggs were removed from females and placed in incubation media. Hatching success of these eggs was high (87%), and incubation time was not affected by the number of days that development had been arrested. However, the snout-vent length and water content of hatchlings were negatively related to the length of retention, and they ran slower than hatchlings from control eggs obtained at the NTO. Retention of eggs past the NTO had no detectable effect on the body condition or running speeds of females. Developmental arrest and the adverse effects of retention on hatchling phenotype, if widespread among squamates, would account for the limited range of embryo stages at oviposition and act as major constraints on the evolution of viviparity.     

Plasticity and limitations of extended egg retention in oviparous Zootoca vivipara (Reptilia: Lacertidae)

The transition between oviparity and viviparity in reptiles is generally accepted to be a gradual process, the result of selection for increasingly prolonged egg retention within the oviduct. We examined egg retention plasticity in an oviparous strain of the lacertid lizard Zootoca vivipara, a species having both oviparous and viviparous populations. We forced a group of female Z. vivipara to retain their clutch in utero by keeping them in dry substrata, and assessed the effect on embryonic development and hatching success, along with offspring phenotype and locomotor performance. Forced egg retention for one additional week affected the developmental stage of embryos at oviposition, as well as hatchling robustness and locomotor performance. However, embryos from forced clutch retention treatment reached one stage unit more than control embryos at oviposition time. Embryos from control eggs were more developed than embryos from experimental eggs after approximately the same period of external incubation, showing that embryonic development is retarded during the period of extended egg retention, despite the high temperature inside the mother's body. Significant differences in external incubation time were only found in one of the two years of study. Hatching success was much lower in the experimental group with forced egg retention (21.1%) than in the control group (95.4%). Therefore, we conclude that there are limitations that hinder the advance of intrauterine embryonic development beyond the normal time of oviposition, and that extended egg retention does not represent clear advantages in this population of Z. vivipara. Nevertheless, the fact that some eggs are successful after forced egg retention could be advantageous for the females that are able to retain their clutch under unfavourable climatic conditions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 75–82.     

Influence of oviposition date and temperature upon embryonic development in Somatochlora alpestris and S. arctica (Odonata: Corduliidae)

In two bog-dwelling dragonflies, Somatochlora alpestris and S. arctica , the influence of oviposition date and temperature upon duration of embryonic development was studied. Egg diapause was facultative. With advancing season, the proportion of diapause eggs increases from 0 to 37% in S. alpestris and from 0 to 18% in S. arctica. Eggs needed at least 17 to 38 days for development. Hatching curves were temperature-independent in nearly all experiments but developmental rate increased at higher ambient temperature. In S. arctica , responses of developmental rate to temperature differed in eggs laid on different dates. In S. alpestris , duration of egg development decreased as season progressed. The duration of egg development of non-diapause eggs and proportion of diapause eggs in S. alpestris and possibly in S. arctica may also both be a function of female age at the time of oviposition. The ecological significance of the different development patterns is discussed.     

Effects of forced egg-retention in Aedes albopictus on adult survival and reproduction following application of DEET as an oviposition deterrent.

The insect repellent DEET (0.1% concentration), used as a mosquito oviposition deterrent in the laboratory, influenced the retention and maintenance of mature eggs by caged gravid female Aedes albopictus Skuse. This egg-retention mechanism could benefit survival because the gravid females were ultimately able to lay maintained eggs upon availability of water, but the length of forced egg-retention time reduced the number of eggs laid per female. Gravid females with retained eggs also laid a higher percentage of eggs that failed to tan, and this percentage increased with time duration of egg-retention. Percent egg hatch was not significantly affected by DEET when used as an oviposition deterrent; however, percent hatch was affected by time duration of egg-retention in both treated (exposed to DEET) and untreated (control) gravid females. The rate of egg hatch was considerably reduced after three weeks of retention; this reduction declined to zero for treated and control females at six and four weeks post-treatment, respectively. The fecundity and fertility of gravid female Ae. albopictus were affected by the time duration of forced egg-retention.     

Oviposition site choice under conflicting risks demonstrates that aquatic predators drive terrestrial egg-laying

Laying eggs out of water was crucial to the transition to land and has evolved repeatedly in multiple animal phyla. However, testing hypotheses about this transition has been difficult because extant species only breed in one environment. The pantless treefrog, Dendropsophus ebraccatus, makes such tests possible because they lay both aquatic and arboreal eggs. Here, we test the oviposition site choices of D. ebraccatus under conflicting risks of arboreal egg desiccation and aquatic egg predation, thereby estimating the relative importance of each selective agent on reproduction. We also measured discrimination between habitats with and without predators and development of naturally laid aquatic and arboreal eggs. Aquatic embryos in nature developed faster than arboreal embryos, implying no cost to aquatic egg laying. In choice tests, D. ebraccatus avoided habitats with fish, showing that they can detect aquatic egg predators. Most importantly, D. ebraccatus laid most eggs in the water when faced with only desiccation risk, but switched to laying eggs arboreally when desiccation risk and aquatic predators were both present. This provides the first experimental evidence to our knowledge that aquatic predation risk influences non-aquatic oviposition and strongly supports the hypothesis that it was a driver of the evolution of terrestrial reproduction.     

Egg activation and timing of sperm acceptance by an egg in honeybees (Apis mellifera L.)

Summary. Mechanical stresses by a narrow glass capillary were applied to unfertilized eggs of honeybees to determine whether the removal of meiotic blocks of the eggs could be caused by simple mechanical stimuli. The treated eggs developed into the anaphase of the first meiotic division at 15 min after treatment, whereas the untreated eggs remained arrested at the metaphase of the first meiotic division. The results of histological examination of the common oviduct showed that its inner widths were sufficiently narrow to cause the distortion of eggs passing through it. The distorted eggs could be fertilized and develop into diploid embryos if they were exposed to the semen immediately (within 30 sec) after egg distortion. However, this would not happen if the distorted eggs were exposed to semen later (30 min). The eggs exposed to the semen but not given mechanical stimuli could initiate the embryonic development with diploid chromosomes. The interval between mechanical distortion and sperm acceptance by eggs in vitro is compatible with that of natural oviposition of fertilized eggs by honeybee queens. These results suggest that egg activation by mechanical stresses in the common oviduct is valid for the natural oviposition in honeybees.     

Capsule walls as barriers to oxygen availability: Implications for the development of brooded embryos by the estuarine gastropod Crepipatella dilatata (Calyptraeidae)

Encapsulation of developing embryos imposes potential restrictions, because the capsule wall must allow for adequate inward diffusion of oxygen and for increased diffusion of oxygen as metabolic demand increases with continued development. Samples of egg capsules from the gastropod Crepipatella dilatata were used to document surface characteristics, composition of the different capsule wall layers, and alterations in wall thickness during development. The diffusion coefficient and capsule wall permeability were determined experimentally for capsules containing embryos at different developmental stages. We also determined oxygen consumption rates for various embryonic stages and for nurse eggs, which provide food for embryos during development. The capsule wall of C. dilatata possesses 2 differentiated layers: the external capsular wall (ECW) and the internal capsular wall (ICW). The ECW is compact and fibrous, features that remain invariable during development, and lacks surface features that might make some portions of the capsule wall more permeable to oxygen than others. On the other hand, the ICW is initially spongy and thick, but significantly decreases in thickness over time, particularly before the embryos begin feeding on nurse eggs. Although the capsule wall is a serious barrier to diffusion, permeability to oxygen increases over time by 112% due to the dramatic thinning of the inner capsule wall layer. Nurse eggs consume oxygen but at very low rates, supporting the idea that they correspond to living embryonic cells that have stopped their development. Respiration measurements indicated that embryos are initially supplied with enough oxygen within the egg capsules to carry out the activities characteristic of embryogenesis, even though the capsular walls show their maximum thickness and lowest permeability at this time. However, as the embryo develops its velum and becomes more active, capsule wall thickness decreases and capsule permeability to oxygen increases. Correspondingly, the oxygen demands of metamorphosed but still encapsulated specimens are approximately 135% higher than those of pre-metamorphosed sibling embryos.     

Incubation media affect the survival,pathway and time of embryo development in Neotropical annual fish Austrolebias nigrofasciatus (Rivulidae)

To analyse the survival, pathway and time of embryo development in the annual fish Austrolebias nigrofasciatus eggs were monitored in four liquid media and two damp media under experimental conditions for 130 days until their development was complete. Eggs kept in the same breeding water from oviposition remained in diapause I (DI) during all experiments. In constrast, up to the stage prior to entering diapause II (DII), the other media had no influence on development. Embryos at this stage (DII), however, show longer development time when treated in medium with water and powdered coconut shell so that about 80% of embryos remained in DII at 100 days. In contrast, all other treatments had a significantly lower proportion of embryos remaining in DII. When treated with Yamamoto's solution in humid media, embryos showed the fastest development. The first fully developed embryos (DIII) were seen at 27 days after oviposition. It took an average of 46–58 days for 50% of eggs in each treatment to reach DIII. Compared with other studies, survival in all incubation media was high at between 70 and 98%. Taken together, it can be concluded that all incubation media were found to be viable for maintaining embryos. Altering developmental trajectories through the manipulation of diapauses in different media makes this species a potential model organism for laboratory studies.     

PROPERTIES OF AVIAN EGG SHELLS AND THEIR ADAPTIVE VALUE

I. An arbitrary classification of avian eggshells is proposed.
2. The role of the eggshell in conserving the water in eggs at oviposition is discussed. There is as yet no correlation between this property and the pore systems in avian eggshells.
3. The pore systems may act as diffusion pathways and the hypothesis has been advanced that in many eggs the shells are adapted so that restriction of gaseous diffusion by mud, preening oils and nest debris is prevented.
4. The mechanical properties of the shell are considered in the novel context of defence against (a) attrition that could lead to the pores being blocked with dust, and (b) cracking that would destroy the diffusion pathways noted in 3.
5. The overall objective of the review was to discuss the concept that avian eggshell are adapted to fit an egg to the nest environment.     

Oviposition cycle in the oviparous fish Xenopoecilus sarasinorum

To clarify the reproduction of the oviparous teleost Xenopoecilus sarasinorum, changes in oocyte composition and oviposition cycle were investigated. After release, a batch of spawned eggs hung from the urogenital pore by attaching filaments (36.3+/-0.8 in number, n=31; about 4.3-7.8 mm in length, 5-8 microm in diameter) on the chorion (egg envelope) in the vegetal pole region. Females accommodated a cluster of fertilized eggs in a belly concavity until the embryos hatched. Hatching of embryos took place from 18-19 days after oviposition (25 degrees C). Between 0-2 days following hatching, the attaching filaments disappeared from the urogenital pore. Between 3 and 4 days following hatching, most of the females spawned again. The growth of oocytes proceeded slowly throughout the period when the egg cluster was carried in the belly, and no ovulation occurred during this period. If the current brood was accidentally lost, the day of the next oviposition was sooner. This might imply that carrying embryos in the belly affects endocrine activity, as in viviparous reproduction.     

Trade-off in oviposition strategy: choosing poor quality host plants reduces mortality from natural enemies for a salt marsh planthopper

Abstract.  1. Both host plant nutrition and mortality from natural enemies have been predicted to significantly impact host plant selection and oviposition behaviour of phytophagous insects. It is unclear, however, if oviposition decisions maximise fitness.
2. This study examined whether the salt marsh planthopper Pissonotus quadripustulatus prefers higher quality host plants for oviposition, and if oviposition decisions are made so as to minimise mortality at the egg stage.
3. A controlled laboratory experiment and 4 years of field data were used to assess the rates of planthopper oviposition on higher quality 'green' and lower quality 'woody' stems of the host plant Borrichia frutescens . The numbers and percentages of healthy eggs and eggs that were killed by parasitoids or the host plant were recorded.
4. In all years, including the laboratory experiment, Pissonotus planthoppers laid more eggs on lower quality woody stems than on higher quality green stems. While host plant related egg mortality was higher in woody stems, the percentage of eggs parasitised was much greater in green stems. This resulted in a lower total mortality of eggs on woody stems.
5. The results of this study demonstrate that, although Pissonotus prefers lower quality host plants for oviposition, this actually increases fitness. These data seem to support the enemy free space hypothesis, and suggest that for phytophagous insects that experience the majority of mortality in the egg stage, oviposition choices may be made such that mortality is minimised.     

Evolution of viviparity in sceloporine lizards: in utero PO2 as a developmental constraint during egg retention

Reptilian viviparity evolves through selection for increasingly prolonged egg retention within the oviduct. In the majority of sceloporine lizard species, however, egg retention past the normal time of oviposition results in retarded or arrested embryonic development. In this study, we tested the hypothesis that the amount of embryonic development normally attained in utero is directly related to in utero oxygen partial pressure (PO(2)). The three species of sceloporine lizards we used are characterized by developmental arrest (Urosaurus ornatus), retarded development (Sceloporus virgatus), and normal development (Sceloporus scalaris) when eggs are retained. We incubated eggs of these species for 10 d under conditions that simulated retention in the oviduct at a range of experimental oxygen partial pressures (PO(2)). We estimated in utero PO(2) from a standard curve generated from the stage and dry mass of experimental embryos incubated for 10 d at known PO(2). The standard curve was then used to predict the PO(2) associated with the observed rate of development of embryos retained in utero. The results of this study showed that the degree of embryonic development attained in utero during egg retention was positively associated with in utero PO(2). The results indicate that oxygen availability in utero is associated with interspecific differences in the capacity to support intrauterine development in sceloporine lizards.     

A nondestructive method for obtaining maternal DNA from avian eggshells and its application to embryonic viability determination in herring gulls (Larus argentatus)

Many avian studies, aimed at collecting samples for genetic analysis, rely upon invasive procedures involving the capture and handling of parents and their offspring. Our goal was to develop a nondestructive method for sampling maternal DNA that would not require blood collection from the mother. Herein, we describe a method for isolating genomic DNA from eggshell powder, obtained by filing the outer shell of an avian egg. Comparison of microsatellite profiles, obtained from genomic DNA found within eggshell matrices and their corresponding parents, verified the presence of maternal DNA in the eggshell matrix in 100% of the herring gull nests assessed (n= 11). In addition, the microsatellite profiles of eggshell DNA were identical among eggs from the same clutch. The ability to rapidly obtain a DNA sample from an avian eggshell in a noninvasive manner could aid in a wide range of genetic sampling studies, and in this study, we provide one potential application of this finding: assessing the fertilization status of nonviable herring gull (Larus argentatus) eggs from the Laurentian Great Lakes. Detection of fertilization was successful as the microsatellite profiles of eggshell powder (maternal only) and the fertilized embryonic contents of those eggs did not match. Ideally, the application of such an approach will help to discriminate unfertilized eggs from embryos aborted early in development and provide insights into avian reproductive health.     

Regulation of ooplasmic sodium and potassium activities in developing locust eggs

Ooplasmic activities of potassium and sodium were measured with ion sensitive microelectrodes before and during the period of maximal water uptake which occurs 3–5 days after oviposition for eggs incubated at 37°C. Potassium activity increased from 84 mM in eggs before fertilization at 118 mM in eggs 1 day after fertilization (d1). Sodium activity increased from 8 mM to 29 mM over the same period. These changes exceeded those predicted from the decrease in water content (8%) during the first day after oviposition. Between d1 and d3, potassium and sodium activities decreased to values predicted on the basis of the 88% increase in egg water content. Although water content increased an additional 46% between d3 and d5, ooplasmic sodium activity remained constant at 11 mM and potassium activity increased from 64 mM to 74 mM during this time. Declines in concentrations of sodium and potassium measured in whole eggs by atomic absorption spectrometry mirrored the increase in egg water content. The results suggest that regulation of ooplasmic sodium and potassium activities is accomplished by release of these ions from internal stores, possibly the york spheres. © 1992 Wiley-Liss, Inc.