Individual Variation in Trophic Egg Production: Evidence for Maternal Manipulation in Response to Resource and Competition Levels

Females of the subsocial shield bug Parastrachia japonensis (Heteroptera: Parastrachiidae) incorporate trophic eggs (nutritive eggs) into their egg mass. Considerable variation occurs among females in trophic egg number and the proportion of an egg mass that is composed of trophic eggs. Because trophic eggs are essential to the development and survival of young, this variation could significantly impact female fitness. We tested the hypothesis that trophic egg abundance is induced by maternal phenotype (weight, body size) and resource exposure. We predicted that resource limitations would cause females to produce fewer fertile eggs and more trophic eggs and that larger and heavier females would produce more of each egg type. Females ovipositing early in the season are exposed to different resource conditions than those that oviposit late. Thus, we compared egg production patterns between these two groups and several other factors related to nesting. No correlation was seen between body size and trophic egg abundance, or, indeed, egg production, overall; however, heavier females produced heavier egg masses. Counter to our prediction, late females, which had greater access to food, produced significantly more total eggs, fewer fertile eggs, and more trophic eggs than early females. A binomial generalized linear model analysis indicated that the factors most correlated with the percentage of an egg mass destined to become trophic eggs were resource abundance, resulting from early or late oviposition, and distance of the nest from the host tree, with closer females producing more trophic eggs. The findings support our hypothesis that resource availability and, to a lesser extent, maternal phenotype affect trophic egg abundance.     

Effects of Ca2+ ions on the formation of metaphase chromosomes and sperm pronuclei in cell-free preparations from unactivated Rana pipiens eggs

Nuclei transplanted into unactivated amphibian eggs are known to condense into metaphase chromosomes whereas those transplanted into activated eggs decondense and enlarge. We have made cell-free cytoplasmic preparations from Rana pipiens eggs which can induce demembranated Xenopus laevis sperm to undergo changes similar to those seen in intact eggs. Sperm chromatin which is incubated for 3 hr in unactivated egg preparations made using a buffer containing 3 mM EGTA is induced to form metaphase chromosomes. However, decondensed interphase nuclei are formed when chromatin is incubated in unactivated egg preparations made without EGTA as well as in activated egg preparations. When Ca2+ ions are added to unactivated egg preparations made with EGTA, the preparations lose the ability to induce metaphase chromosome formation and become capable of decondensing sperm chromatin. Once the ability to decondense chromatin has developed, either in unactivated or activated egg preparations, it cannot be suppressed by the addition of EGTA. However, decondensation of sperm chromatin in activated egg preparations can be suppressed by the addition of unactivated egg preparations made with EGTA. In this case, the incubated sperm chromatin is induced to form metaphase chromosomes. These results may indicate that the chromosome condensation activity of unactivated egg cytoplasm can be sustained in cell-free preparations when Ca2+ ion levels are kept low, but when Ca2+ ion levels increase this activity is lost and replaced by a new activity which can decondense chromatin. Since this change in cytoplasmic activities is comparable to that occurring in the intact egg following fertilization, these results suggest that Ca2+ ions play a crucial role during activation in altering the cytoplasmic activities which control nuclear behavior.     

Determination of the dorsal-ventral axis in eggs of Xenopus laevis: Complete rescue of uv-impaired eggs by oblique orientation before first cleavage

Eggs of Xenopus laevis were exposed to ultraviolet (uv) radiation (2537 Å) on the vegetal hemisphere soon after fertilization at doses sufficient to impair greatly the subsequent development of dorsal structures. It was found that temporary orientation of irradiated eggs 90° off the natural vertical axis rescues these eggs, allowing them to develop into normal embryos. Complete rescue results when oblique orientation is initiated well before first cleavage, and eggs remain in this position until the 16-cell stage. Significant rescue is seen, however, in eggs which remain off axis for shorter periods of time or when eggs are obliquely oriented, even after first cleavage. Furthermore, a period of oblique orientation prior to uv irradiation results in insensitivity of eggs to irradiation. Ultraviolet irradiation is found to randomize the position of the dorsal side with respect to the sperm entrance point, whereas the position of the dorsal side of rescued embryos is strongly specified by the orientation of the egg during the rescue period, and not by the sperm entrance point. Other effects of uv irradiation on early development include decreased pigmentation differences among 4-cell stage blastomeres and delayed gastrulation. It is proposed (1) that oblique orientation promotes in irradiated eggs a set of internal rearrangements mimicking those normally accomplished by the unirradiated egg in a period prior to first cleavage and as part of an early dorsalization process, and (2) that the uv-sensitive targets are part of the morphogenic machinery used by the egg for internal rearrangements in this period and are not elements of a system of transmitted particulate dorsal determinants.     

Seasonal shifts in clutch size and egg size in the side-blotched lizard,Uta stansburiana Baird and Girard

Summary There is evidence that the side-blotched lizard, Uta stansburiana, and some other organisms of temperate latitudes produce fewer and larger eggs as the reproductive season progresses. There are at least two models that could explain this phenomenon.Proponents of the parental investment model claim that females are selected to increase egg size, at the cost of clutch size, late in the season in order to produce larger and competitively superior hatchlings at a time when food for hatchlings is in low supply and when juvenile density is high. In this model the selective agent is relative scarcity of food available to hatchlings late in the reproductive season, and the adaptive response is production of larger offspring.The alternative explanation (bet-hedging model) proposed in this paper is based on the view that the amount of food available to females for the production of late-season clutches is unpredictable, and that selection has favored conservatively small clutches in the late season to insure that each egg is at least minimally provisioned. Smaller clutches, which occur most frequently late in the season, are more likely to consist of larger eggs, compared to larger clutches, for two reasons. Firstly, unlike birds, oviparous lizards cannot alter parental investment after their eggs are deposited, and therefore, in cases of fractional optimal clutch size, the next lower integral clutch size is selected with the remaining reproductive energy allocated to increased egg size. With other factors constant, eggs of smaller clutches will increase more in size than eggs of larger clutches when excess energy is divided among the eggs of a clutch. Secondly, unanticipated energy that may become available for reproduction during energy-rich years will similarly increase egg size a greater amount if divided among fewer eggs.     

A comparative proteomic study of the undeveloped and developed Schistosoma mansoni egg and its contents: The miracidium, hatch fluid and secretions

The schistosome egg is the key agent responsible both for transmission of the parasite from human to molluscan host, and is the primary cause of pathogenesis in schistosomiasis. Characterisation of its proteome is a crucial step in understanding the egg’s interactions with the mammalian host. We devised a scheme to isolate undeveloped eggs from mature schistosome eggs by Percoll gradient and then fractionate the mature egg into miracidial, hatch fluid and secreted protein preparations. The soluble proteins contained within the five preparations were separated by two-dimensional electrophoresis and their spot patterns compared by image analysis. Large numbers of representative spots were then excised and subjected to tandem mass spectrometry to obtain identities. In this way, the principal components of each sub-proteome were established. Chaperones were the most abundant category, with heat shock protein 70 (HSP70) dominant in the undeveloped egg and Schistosoma mansoni protein 40 (Smp-40) in the miracidium. Cytoskeletal proteins were expressed at similar levels in the undeveloped egg and miracidium, with tubulins the most abundant. The proteins of energy metabolism reflected the change from anaerobic to aerobic metabolism as the miracidium developed. None of the above categories was abundant in the hatch fluid but this peri-miracidial compartment was highly enriched for defence proteins such as thioredoxin. Hatch fluid also contained several host proteins and schistosome proteins of unknown function, highlighting its distinct nature and potentially its role. The egg secretions could not be compared with the other preparations due to their unique composition featuring the previously characterised IL-4-inducing principal of S. mansoni eggs (IPSE), Omega-1, egg secreted protein 15 (ESP15), a micro-exon gene 2 (MEG-2) protein and two members of the recently described MEG-3 family. This last preparation contains the subset of egg proteins that probably enables eggs to escape from host tissues and may also initiate granuloma formation, emphasising the need to establish fully the roles of its components in schistosome biology.     

Environmental Effects on Male Reproductive Success and Parental Care in the Florida Flagfish Jordanella floridae

Models of optimal parental care predict that parental investment should depend on offspring value or the effect parental care has on offspring benefits. Few studies have examined the effect of external factors that influence offspring survival and the cost of care. In this study on the Florida flagfish (Jordanella floridae), a species with male parental care, we examined whether environmentally induced changes in care result from changes in egg requirements or in parental costs. We manipulated salinity and temperature, as these factors are known to affect the metabolic rate in both eggs and parents. We predicted that if the change in care behavior is determined by costs to the male then it should be paralleled by changes in non‐egg‐directed behavior. Conversely, if egg‐directed behavior changes independently of other behavior it would suggest that behavior is determined primarily by egg requirements. In addition we examined patterns of mating success under the assumption that if male care is affected by environmental factors then female preferences may change accordingly. Males decreased egg‐directed behavior (fanning and cleaning of eggs) at high salinity. Non‐egg‐directed behavior was unaffected by salinity. Temperature had no effects on behavior. Thus, we conclude that changes in egg demands are primarily responsible for the observed results. Successful males were bigger and more aggressive. This suggests that male dominance was an important determinant of male mating success. Unsuccessful males showed significantly more variation in number of red stripes with respect to salinity than successful males. Unsuccessful males may be less able to regulate color expression under varying environmental conditions, in which case color may be an indicator of male quality. We replicated the experiment early and late in the season. Males did not change their effort in care over the season. However, care (fanning) in the absence of eggs increased towards the end of the season. Since pre‐mating fanning was positively correlated to a male’s eventual mating success we conclude that males increased their effort to attract mates late in the season.     

Parasitism and predation of stink bug (Heteroptera: Pentatomidae) eggs in Georgia corn fields

Nezara viridula L. and Euschistus servus (Say) are the predominant species of phytophagous stink bugs on corn, Zea mays L., in Georgia. Oebalus pugnax pugnax (F.) occurs in relatively low numbers, and the predatory stink bug Podisus maculiventris (Say) is commonly found. Limited information is available on natural biological control of these four stink bug species in Georgia corn fields; therefore, a 6-yr study of parasitism and predation of their eggs was initiated in 2003. Naturally occurring stink bug eggs were parasitized by six scelionid species, Trissolcus basalis (Wollaston), T. thyantae Ashmead, T. brochymenae (Ashmead), T. euschisti (Ashmead), Telenomus podisi Ashmead, Telenomus calvus Johnson, and one encyrtid species, Ooencyrtus sp. T. basalis was the most prevalent parasitoid of N. viridula, parasitizing E. servus and P. maculiventris eggs at low levels. T. podisi, the predominant parasitoid species emerging from eggs of E. servus and P. maculiventris, also parasitized O. p. pugnax eggs exclusively and parasitized N. viridula eggs at low levels. T. euschisti and T. thyantae parasitized E. servus egg masses. T. brochymenae parasitized eggs of both E. servus and P. maculiventris. T. calvus parasitized only P. maculiventris eggs. The same species of egg parasitoids that parasitized naturally occurring eggs of N. viridula and E. servus parasitized sentinel eggs of these bugs, except that no T. calvus and Ooencyrtus sp. were obtained from sentinel eggs, and T. thyantae and T. brochymenae emerged from sentinel eggs of N. viridula. Generally, parasitization of an egg mass was either greater than or equal to predation of sentinel eggs of N. viridula and E. servus. However, on some dates in late June and July, predation of sentinel egg masses was numerically approximately twice as high as parasitism. Results indicate stink bug egg parasitoids and predators are significant factors in the natural biological control of stink bugs in corn fields.     

非洲爪蟾胚胎细胞核移入花背蟾蜍成熟卵后的细胞学研究

This paper reports the development of the nuclear transplanted eggs obtained by transplanting Xenopus laevis blastomere nuclei to Bufo raddei. The formation of the donor nuclei is similar to that of the male pronuclei in the normal development egg in the early stage while shows degradation in the late stage after transplanting. The chromosome complement formes in some eggs 30 minutes after transplantation, which is assumed to contribute to the development of the transplanted eggs [Acta Zoologica Sinica 51 （5） ： 924 - 931, 2005].     

Xenopus laevis egg jelly contains small proteins that are essential to fertilization.

The eggs of Xenopus laevis are surrounded by investment layers of egg jelly that interact with the sperm immediately prior to fertilization. Components of these egg jelly layers are necessary for the fertilization of the egg by incoming sperm. Eggs which are stripped of their jelly layers are refractile to fertilization by sperm, but the addition of solubilized jelly promotes fertilization. We have shown previously that the egg jelly layers are composed of a fibrous network of glycoconjugates which loosely hold smaller diffusible components. Extracts of these diffusible components were prepared by incubation of freshly ovulated eggs in high-salt buffers for 12 h at 4 degrees C. This diffusible component extract, when incubated with sperm, promoted the sperm's ability to fertilize dejellied eggs in a dose-dependent manner. In contrast, the high-molecular-weight "structural" glycoconjugates of jelly that remain after extraction of the diffusible components did not increase fertilization efficiency of dejellied eggs nor did nonspecific proteins, carbohydrate polymers, or organic polymers. The diffusible components, analyzed by SDS-PAGE, consisted of a mixture of proteins from 4 to 180 kDa. The protein responsible for fertilization rescue appeared to be <50 kDa and appeared to self-aggregate or to bind to larger proteins. This protein component was required during sperm binding to the egg, its action required an intact egg vitelline envelope, and its action was independent of large soluble polymers such as Ficoll.     

High-frequency twinning of Xenopus laevis embryos from eggs centrifuged before first cleavage

In embryos of the frog Xenopus laevis, the dorsal structures normally develop from regions of the egg opposite the side of sperm entry. Gravity and centrifugal force, applied at an angle of 90 degrees to the animal-vegetal axis of the egg, can override this topographic relationship and can cause the dorsal structures to be positioned according to the force vector (S. Black and J. Gerhart, 1985, Dev. Biol. 108, 310-324). We report here that at time 0.40 (40% of the first cleavage interval), an average of 60% of eggs centrifuged at 30g for 4 min in this orientation form conjoined twins with one body axis arising from the centripetal side of the egg and one arising from the centrifugal side of the egg. This positioning is observed regardless of the orientation of the side of sperm entry in the centrifugal field. If, after the 0.40 centrifugation, the eggs are inclined with the centripetal side up, they do not make twins; instead, they make only a single axis at the centripetal side. This indicates that the second axis in twins is caused to form by postcentrifugation gravity-driven internal rearrangements of materials that were displaced by the centrifugation. Twins also form at high frequency in eggs centrifuged twice, first at an inclination of 90 degrees, and then at an inclination of 0 degrees. The second centrifugation yields secondary axes even when it is begun midway in the second cell cycle, well after the time of grey crescent formation. Double centrifugation also causes twinning ("double rescue") of uv-irradiated eggs which otherwise would not develop axial structures. This suggests that the internal displacements caused by the centrifugations can substitute for a step in the normal axis specification process that is impaired in irradiated eggs.     

Cytological and biochemical analyses of the maternal-effect mutant embryos with abnormal cleavage furrow formation in Xenopus laevis

We describe an embryonic lethal mutation in Xenopus laevis that provokes regression of cleavage furrow formation. The mutant females (designated as af) were obtained by the back-cross of a female with one of her sons. All the fertilized eggs laid by the mutant females, regardless of the wild-type male used in the mating, failed to cleave although each furrow ran at a proper position superficially. Light and electron microscopic observations of the embryos revealed that the cleavage furrows stayed on the surface and cytoplasmic divisions did not take place at all, while nuclear divisions did. Two-dimensional gel-electrophoretic comparisons of af and wild-type embryos demonstrated that two proteins, having estimated molecular masses of about 38 kDa (pI 6.6) and 78 kDa (pI 7.6), were missing in af embryos. Microinjection of clear cytoplasm from a wild-type egg into fertilized af eggs provoked partial surface contraction and cleavage furrow formation in recipient af eggs. The results showed that the af females carry a lethal maternal-effect mutation which causes cleavage furrow regression by being deficient in a few proteins, and that cytoplasm of wild-type eggs can partially rescue the cleavage furrow formation of af eggs by furnishing the corrective material, presumably a product of the normal allele of af.     

The microbial environment and intestinal nematode infections of Heligmosomoides polygyrus in laboratory mice

The difficulty of establishing primary infections of Heligmosomoides polygyrus (= Nematospiroides dubius) in ASH/CSI mice in the Laboratory Animal House at Royal Holloway and Bedford New College during a recent autumn and spring period was associated with a syndrome of worm distortion, together with zero or low worm establishment and reduced fecundity (eggs/female worm). The eggs produced were non-viable and the egg capsule comprised a rumpled lipid and ruptured chitin layer. The egg size and peaks of egg production were also reduced and the total egg output ceased entirely by day 28 post-infection in male mice. The syndrome was repeated when control LACA mice harbouring 'normal' infections of H. polygyrus were housed on the same source of peat bedding material as the ASH/CSI mice. An increase in H. polygyrus egg production in ASH/CSI mice, removed from the peat or treated with 0.04% oxytetracycline hydrochloride suggested that the cause of the syndrome was microbial in origin. A microbiological assay of the peat, which was the common denominator of all syndrome infections, revealed an abundance of chitinase secreting species of bacteria (Bacillaceae). Bacterial chitinase was therefore likely to rupture the chitin layer of the egg capsule producing nonviable eggs and either abnormal or no larvae. Preliminary in vitro studies using chitinase from Streptomyces griseus indicated that the hatching success of eggs of H. polygyrus was reduced as the concentration of chitinase increased.     

Artificial fertilization by intracytoplasmic sperm injection in a teleost fish, the medaka (Oryzias latipes)

Intracytoplasmic sperm injection (ICSI) is a technique that has been successfully used for assisting reproduction in mammals. However, this method is still not reliable in nonmammalian species, including teleosts. We succeeded in producing medaka individuals by ICSI with a rate of 13.4% (28 hatched embryos out of 209 eggs fertilized by ICSI), the best value reported so far in teleosts, including zebrafish and Nile tilapia. Although the technique was based on that developed for mammalian eggs, some critical modifications were made to adjust it to the medaka egg, which has a thick and hard envelope (the chorion) and a single sperm entry site (the micropyle). Medaka ICSI was performed by injecting a demembranated spermatozoon into an egg cytoplasm through the micropyle 10-15 sec after egg activation induced by a piezo-actuated vibration, the site and timing of sperm penetration being consistent with those in normal fertilization in medaka. To increase the efficiency of ICSI in medaka, we found that the fertilization by ICSI should precisely mimic the fertilization by insemination with intact sperm, both spatially and temporally. The success rate of ICSI was highly variable in batches of eggs (ranging from 0% to 56%), suggesting that the conditions of eggs are important factors in stabilizing the production of individuals by ICSI. The success in medaka ICSI provides a basis for future research to understand the basic mechanisms in gamete biology of teleosts as well as for development of new technology that can yield valuable applications in fisheries science.     

Relationships among salinity, egg size, embryonic development, and larval biomass in the estuarine crab Chasmagnathus granulata Dana, 1851

We studied interrelationships between initial egg size and biomass, duration of embryogenesis at different salinities, and initial larval biomass in an estuarine crab, Chasmagnathus granulata. Ovigerous females were maintained at three different salinities (15‰, 20‰ and 32‰); initial egg size (mean diameter), biomass (dry weight, carbon and nitrogen) as well as changes in egg size, embryonic development duration, and initial larval biomass were measured.

Initial egg size varied significantly among broods from different females maintained under identical environmental conditions. Eggs from females maintained at 15‰ had on average higher biomass and larger diameter. We hypothesise that this is a plastic response to salinity, which may have an adaptive value, i.e. it may increase the survivorship during postembryonic development. The degree of change in egg diameter during the embryonic development depended on salinity: eggs in a late developmental stage were at 15‰ significantly larger and had smaller increment than those incubated at higher salinities. Development duration was longer at 15‰, but this was significant only for the intermediate embryonic stages. Initial larval biomass depended on initial egg size and on biomass loss during embryogenesis. Larvae with high initial biomass originated either from those eggs that had, already from egg laying, a high initial biomass (reflecting individual variability under identical conditions), or from those developing at a high salinity (32‰), where embryonic biomass losses were generally minimum. Our results show that both individual variability in the provisioning of eggs with yolk and the salinity prevailing during the embryonic development are important factors causing variability in the initial larval biomass of C. granulata, and thus, in early larval survival and growth.     

Embryonic stage of obligatory diapause and effects of abiotic conditions on egg hatching in the balsam twig aphid,Mindarus abietinus

Diapause‐mediated dormancy in overwintering insect eggs has rarely been studied with regard to the ecological factors controlling postdiapause development. In insects of temperate latitudes, water availability at the end of winter, in interaction with temperature, could control the resumption of development for insect stages in postdiapause quiescence. The balsam twig aphid, Mindarus abietinus Koch (Hemiptera: Aphididae), overwinters as eggs in southern Québec, Canada, on balsam fir, Abies balsamea (L.) Miller (Pinaceae), in Christmas tree plantations, where it is known as a pest. Previous work has shown that eggs of this aphid maintain low water content during winter, presumably to survive sub‐zero temperatures. Conversely, in late winter and early spring, they passively or actively absorb surrounding moisture, which is accompanied by notable changes in size, shape, and fresh mass. The primary objective here was to determine the embryonic stage at which winter diapause starts and is maintained in M. abietinus, a relatively primitive aphid. Secondly, we tested the hypothesis that free water availability to postdiapause eggs, in combination with temperatures above developmental threshold, is essential for embryonic development and hatching, by experimentally soaking field‐collected eggs in water at controlled frequencies. We observed that embryogenesis starts at the time of egg laying and stops after a few days, before the anatrepsis stage of blastokinesis is complete, when the germ band has not yet entirely immersed itself into the yolk. We also found that water surrounding overwintered eggs on fir shoots, in interaction with temperature regime, significantly increases M. abietinus egg hatching rates. Potential impacts of environmental factors such as precipitation are discussed in relation to M. abietinus egg hatching rates and potential for population growth in spring.     

Sexual dimorphism, female reproduction and egg incubation in the oriental leaf-toed gecko (Hemidactylus bowringii) from southern China

We studied sexual dimorphism, female reproduction and egg incubation of the oriental leaf-toed gecko (Hemidactylus bowringii) from a population in southern China. The largest male and female in our sample were 60 and 57 mm snout-vent length (SVL), respectively. Males are the larger sex; sexual dimorphism in head size and tail length (TL) is evident in juveniles and adults, with males having larger heads as well as longer tails than females. Oviposition occurred between late May and late July. Females switched from laying two eggs early in the breeding season to 1-2 eggs later in the season. Clutch mass and egg mass were both independent of female SVL, whereas relative clutch mass was negatively correlated with female SVL. The previous conclusion that female H. bowringii lay a single clutch of eggs per breeding season is unlikely to be true. Thermal environments experienced by H. bowringii eggs affect incubation length as well as morphological and locomotor phenotypes of hatchlings. Hatchlings from eggs incubated at 30 degrees C were larger (SVL, tail length and body mass) and performed better in the racetrack than their counterparts from eggs incubated at 24 degrees C. Temperatures suitable for embryonic development are relatively high in H. bowringii, primarily as a consequence of the adaptive response to warm environments in southern China.     

Seasonal patterns of egg production in field colonies of the termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera: Rhinotermitidae)

This is the first report on the annual egg production patterns in mature termite colonies in the field. Data on the seasonal patterns of egg production in field colonies are very important for understanding the annual colony growth schedule, resource allocation, and population dynamics of the termites. However, collecting the eggs from a sufficient number of colonies is extremely difficult in Reticulitermes termites because their multiple-site nesting makes it difficult to find the reproductive center of the colonies. Here, we first show the seasonal pattern of egg production in the subterranean termite Reticulitermes speratus by collecting the reproductive center of ten colonies each month from April through October. We had to destructively examine dozens of nests to find eggs from enough field colonies each month. Mature field colonies began to produce eggs in late May, soon after the swarming season, and the egg production rate (EPR) reached its maximum in early July. The eggs hatched until late October. The EPR was significantly correlated with the average monthly temperature. Additional investigation of the egg distributions in the nests showed that most eggs were kept around the royal cell, which contained the reproductives. The largest colony had 109 supplemental queens and 94,023 eggs, suggesting that each queen produced an average of 24.7 eggs per day, based on the known mean hatching period of an inseminated egg of 34.95±0.12 (SE) days.     

Xenopus laevis Egg Jelly Contains Small Proteins That Are Essential to Fertilization

The eggs of Xenopus laevis are surrounded by investment layers of egg jelly that interact with the sperm immediately prior to fertilization. Components of these egg jelly layers are necessary for the fertilization of the egg by incoming sperm. Eggs which are stripped of their jelly layers are refractile to fertilization by sperm, but the addition of solubilized jelly promotes fertilization. We have shown previously that the egg jelly layers are composed of a fibrous network of glycoconjugates which loosely hold smaller diffusible components. Extracts of these diffusible components were prepared by incubation of freshly ovulated eggs in high-salt buffers for 12 h at 4°C. This diffusible component extract, when incubated with sperm, promoted the sperm's ability to fertilize dejellied eggs in a dose-dependent manner. In contrast, the high-molecular-weight “structural” glycoconjugates of jelly that remain after extraction of the diffusible components did not increase fertilization efficiency of dejellied eggs nor did nonspecific proteins, carbohydrate polymers, or organic polymers. The diffusible components, analyzed by SDS–PAGE, consisted of a mixture of proteins from 4 to 180 kDa. The protein responsible for fertilization rescue appeared to be <50 kDa and appeared to self-aggregate or to bind to larger proteins. This protein component was required during sperm binding to the egg, its action required an intact egg vitelline envelope, and its action was independent of large soluble polymers such as Ficoll.     

The effect of climate change on the correlation between avian life-history traits

The ultimate reason why birds should advance their phenology in response to climate change is to match the shifting phenology of underlying levels of the food chain. In a seasonal environment, the timing of food abundance is one of the crucial factors to which birds should adapt their timing of reproduction. They can do this by shifting egg‐laying date (LD), and also by changing other life‐history characters that affect the period between laying of the eggs and hatching of the chicks. In a long‐term study of the migratory Pied Flycatcher, we show that the peak of abundance of nestling food (caterpillars) has advanced during the last two decades, and that the birds advanced their LD. LD strongly correlates with the timing of the caterpillar peak, but in years with an early food peak the birds laid their eggs late relative to this food peak. In such years, the birds advance their hatching date by incubating earlier in the clutch and reducing the interval between laying the last egg to hatching of the first egg, thereby partly compensating for their relative late LD. Paradoxically, they also laid larger clutches in the years with an early food peak, and thereby took more time to lay (i.e. one egg per day). Clutch size therefore declined more strongly with LD in years with an early food peak. This stronger response is adaptive because the fitness of an egg declined more strongly with date in early than in late years. Clearly, avian life‐history traits are correlated and Pied Flycatchers apparently optimize over the whole complex of the traits including LD, clutch size and the onset of incubation. Climate change will lead to changing selection pressures on this complex of traits and presumably the way they are correlated.     

Transplantation of Nuclei from Lymphocytes of Adult Frogs into Enucleated Eggs

The technique of transplantation of nuclei from adult lymphocytes into enucleated eggs from Xenopus laevis (South African clawed toad) is described. The splenic lymphocytes from the one nucleolus mutant were bound via their immunoglobulin receptors to nylon fibers, derivatized with the antigen used for immunization. A technique for coupling other cell types with Woodward reagent is also described. The cells were broken by aspiration into a micropipette and injected into enucleated eggs. The egg pronucleus was eliminated by UV treatment followed by surgical removal. The origin of the genome of developing embryos was determined on karyotype preparations by looking for the nucleolar organizer on the chromosome pair No. 12. Participation of egg pronucleus in development was frequent as judged by the incidence of gynogenetic diploid individuals and of tetraploid animals exhibiting characteristics of both recipient egg and somatic cell donor karyotypes. Apparently normal, lymphocyte-derived tadpoles were obtained, but they died at 12 days. This shows that differentiated cells from adults, such as lymphocytes, can re-express the genes necessary for ontogeny.