Do human eggs attract spermatozoa?

A key process in human fertilization is bringing the two gametes together, so that the complex molecular events involved in sperm and egg interaction can begin. Does nature allow fertilization to occur only as a consequence of a chance collision, or is there a precontact sperm-egg communication? This review summarizes the bioassays used in testing human spermatozoa for chemotaxis, emphasizing the necessity to distinguish between chemotaxis and other accumulation-causing processes, and the results obtained. It demonstrates that human sperm chemotaxis to a follicular factor(s) does occur, at least in vitro, and that only capacitated spermatozoa are chemotactically responsive. Substances that have been proposed as attractants for human spermatozoa are reassessed. The potential role of sperm chemotaxis in vivo is discussed. Faulty precontact sperm-egg communication may be one of the causes of male infertility, female infertility, or both. On the other hand, interfering with human sperm chemotaxis may represent an exciting new approach to contraception. BioEssays 21:203–210, 1999. © 1999 John Wiley & Sons, Inc.     

Why don't birds lay more eggs?

Fifty years ago David Lack put forward a key hypothesis in life-history theory: that avian clutch is ultimately determined by the number of young that parents can provide with food. Since then, a plethora of brood manipulations has shown that birds can rear more young than the number of eggs they lay, and prompted a search for negative effects of increased effort on future reproduction. However, recent studies have shown that the demands of laying and incubating eggs generally omitted from experiments, could affect parental fitness. Lack's hypothesis, and the tests of its validity, need to be extended to encompass the full demands of producing and rearing the brood.     

Why are birds’ eggs speckled?

Birds are unique in laying eggs with pigmented shells, but for most species (e.g. most passerines, which lay white eggs speckled with reddish spots of protoporphyrin) the pigments’ function is unknown. We studied a bird population at a geologically variable site, and considered a hitherto untested hypothesis: that protoporphyrin pigments might compensate for reduced eggshell‐thickness (caused partly by calcium deficiency), which is known to reduce eggshell‐strength and increase eggshell‐permeability. We found that pigment spots specifically demarcated thinner areas of shell, with darker spots marking yet thinner shell than paler spots. Variation in pigmentation was thus associated with variation in shell thickness both within and between clutches, so accounting for the eggshell's characteristic spot patterns. Geological variability at this site has resulted in a great range of calcium availability and, as predicted by the hypothesis, variation in calcium availability was found to affect between‐clutch variation in both eggshell‐mass (+) and pigmentation characteristics (?). We suggest a physiological mechanism and some important implications of these findings.     

Can birds count eggs in their nests?

Sensory mechanisms controlling avian clutch size have diversified into distinct types, according to the nature of the input that is used to disrupt the growth of ovarian follicles and hence halt egg‐laying. In an article on brood parasitism, Lyon (2003) claimed that female American Coots Fulica americana can reduce their clutch size on the basis of visual cues in response to eggs laid in their nests by other females; in this species, therefore, egg counting would be used to control clutch size. After a close examination of the physiological determination of clutch size in American Coots, I show that seven of 17 parasitized clutches were smaller than the range controlled through the mechanism using an input to disrupt follicular growth (7–10 eggs per clutch). My reanalysis suggests that American Coots are incapable of adjusting clutch size via counting and re‐asserts that a species that can count eggs has yet to be found among birds that rely upon their own body heat for incubation.     

How do hatcheries influence embryonic development of sea turtle eggs? Experimental analysis and isolation of microorganisms in leatherback turtle eggs

Many conservation programs consider translocation of turtle nests to hatcheries as a useful technique. The repeated use of the same incubation substrate over several seasons in these hatcheries could, however, be harmful to embryos if pathogens were able to accumulate or if the physical and chemical characteristics of the incubation environment were altered. However, this hypothesis has yet to be tested. We conducted two field experiments to evaluate the effects of hatchery sand and eggshell decay on the embryonic development of leatherback sea turtle eggs in Colombia. We identified the presence of both fungi and bacteria species on leatherback turtle eggs. Sea turtle eggs exposed to previously used hatchery substrates or to decaying eggshells during the first and middle third of the embryonic development produced hatchlings that were smaller and/or weighed less than control eggs. However, this did not negatively influence hatching success. The final third of embryonic development seems to be less susceptible to infection by microorganisms associated with decaying shells. We discuss the mechanisms that could be affecting sea turtle egg development when in contact with fungi. Further studies should seek to understand the infection process and the stages of development in which the fungi are more virulent to the eggs of this critically endangered species.     

Why do Luehdorfia butterflies lay eggs in clusters?

Luehdorfia butterflies lay eggs in clusters. Clones of their host plants (Asiasarum and Heterotropa) are distributed pacthily among the understory of deciduous forests. Groups of Luehdorfia larvae often exhaust the clones and may wander over the forest floor seeking new clones. The highest mortality observed is during this wandering period. To elucidate why Luehdorfia butterflies lay eggs in clusters, a simulation experiment was made for hypothetical populations which lay eggs in clusters or singly. Field data on larval mortality, consumption, density of host clones and leaf weight for Luehdorfia japonica were incorporated into the model. The predictions of the simulation were: (1) When the egg density is low, the single egg type could leave many more pupae than the egg clustering type, but when the egg density is high, the former might leave smaller number of pupae than the latter; and (2) There are optimal sizes of egg clusters for different egg densities and the optimal size becomes larger as the egg density increased.     

Why is mimicry in cuckoo eggs sometimes so poor?

I propose that the existence of imperfect adaptations (e.g. egg mimicry) in brood parasites and their hosts (e.g. discrimination abilities) could reflect age-dependent territory and nest-site selection patterns of the host. Studies of various passerines indicate that (1) older breeders tend to occupy nest sites of higher quality than do young birds (ideal despotic distribution resulting from interference competition), (2) nest-site selection affects the risk of parasitism in various habitats, (3) egg recognition in passerines has a strong learning component (therefore naive breeders tend to accept whereas older birds tend to reject parasitic eggs). Because young naive birds, who tend to accept parasitic eggs, usually breed in low-quality areas where they are frequently parasitised, while old experienced birds, who tend to reject parasitic eggs, breed in high-quality areas where they are rarely parasitised, the distribution of acceptors and rejecters with respect to the risk of parasitism is non-random, i.e. populations of some host species may consist of heavily parasitised acceptors and weakly parasitised rejecters. Therefore, the selection pressure exerted by the host on the parasite should be weaker than if brood parasitism was randomly distributed among naive and experienced breeders and affect adaptations such as egg mimicry. This could explain the existence of imperfect adaptations in some brood parasite-host systems.     

Why do Red-winged Blackbrids accept eggs of Brown-headed Cowbirds?

Summary Avian brood parasites usually severely depress the reproductive success of their hosts, yet many host species, including those presumably capable of ejecting parasitic eggs, accept them. Female, brood-parasitic, Brown-headed Cowbirds typically remove a host egg when they lay their own and damage some host eggs in the process of ejecting a host egg. Data from a field study of Red-winged Blackbirds show that these costs, which cannot be avoided by ejecting the parasitic egg, account for some of the reproductive losses attributable to parasitism, but part is due to the presence of the cowbird egg in the nest. To assess whether ejection would be favoured under current circumstances, the probable damage a female Redwing could cause to her own eggs by attempting to eject a cowbird egg needs to be determined.     

Can rats prey on gull eggs? An experimental approach

Black rat Rattus rattus populations can reach high densities on the Mediterranean islands, as has been the case on the Chafarinas Islands (Western Mediterranean coast) in the last decade. This archipelago holds the second largest breeding population of Audouin's gull Larus audouinii and an important population of yellow-legged gull Larus cachinnans. Circumstantial evidences of rat predation upon Audouin's gull eggs led to conservation concerns about the impact of rat predation on gull productivity. We studied the impact of rats on gull nests experimentally by building artificial nests into the breeding area of yellow-legged gulls. Two kinds of eggs were placed in the artificial nests: manipulated eggs, in which the shell had been previously opened, and intact (unmanipulated) eggs. Rats preyed extensively on opened eggs but only once on intact eggs, apparently due to lack of skills to prey on intact eggs, suggesting that rats do not normally have access to fresh gull eggs. Rats inhabiting breeding areas of gulls can scavenge on broken eggs rolled out of the nest or on eggs with softened shells after nest desertion, but it is unlikely that they prey on natural gull nests guarded by parents. We suggest that introduced black rats on Mediterranean islands can only marginally affect the productivity of gulls owing to egg predation.     

The problem with zeroes: why don't drosophilids lay eggs?

Summary We present some data on drosophilid oviposition and analyse the distribution of egg numbers over patches using an iterated negative binomial. This suggests that there are three different reasons for empty patches; patches are not found, patches are not suitable, or females are not able to lay eggs. This leads to five categories of site which can be disentangled using the iterated negative binomial. Since empty patches have important consequences for population dynamics and coexistence, this analysis will highlight how microscopic processes influence macroscopic behaviour in population biology.     

Incubation of rigid-shelled turtle eggs: do hydric conditions matter?

Rigid-shelled eggs of the broad-shelled river turtle Chelodina expansa were incubated at 28 degrees C in wet (-100 kPa), intermediate (-350 kPa) and dry (-750 kPa) conditions. Incubation period was influenced by clutch of origin, but was independent of incubation water potential. Rates of water gained from the environment and pre-pipping egg mass were influenced by incubation water potential -- eggs incubating at higher (less negative) water potentials absorbing more water from their environment. Hatchlings from wet conditions had greater mass but a smaller amount of residual yolk than hatchlings from dry conditions and it is suggested that the amount of yolk converted to tissue is influenced by the amount of water absorbed by the egg during incubation. Water content of yolk-free hatchlings from the -100-kPa treatment was greater than those from the -350-kPa and -750-kPa treatments, but the water content of residual yolks was similar across all hydric conditions.     

Why do female lizards lay their eggs in communal nests?

1. In many reptile species, females oviposit communally (i.e. many clutches are laid within the same nest). This behaviour might result from constraint (scarcity of nest-sites offering suitable incubation conditions) or adaptation (direct fitness benefits accruing from the proximity of other eggs). 2. To test between these alternatives, we gathered field and laboratory data on montane scincid lizards Bassiana duperreyi from south-eastern Australia. Our data support the adaptationist hypothesis. 3. In the field, communal vs. solitary clutches were laid in similar sites, and the relative frequency of communal nesting was not predictable from nest-site availability. Thermal regimes for incubation did not differ between communal vs. solitary nests, nor between eggs at the core vs. periphery of a communal nest. In the laboratory, females selectively oviposited beside existing eggs rather than in otherwise identical potential nesting sites. 4. From cycling-temperature incubation in the laboratory, eggs incubated within a cluster of other eggs took up less water, but produced hatchlings that were larger and faster-running than were hatchlings from eggs incubated alone. 5. Hydric modifications of incubation conditions within a cluster of tightly packed eggs thus may provide a direct fitness benefit to communal oviposition.     

Effect of weight and storage time of broiler breeders’ eggs on morphology and biochemical features of eggs,embryogenesis, hatchability,and chick quality

The transfer of hatchability results obtained under experimental conditions to the commercial ground with a positive financial effect proves the value and usefulness of these data. On the other hand, finding results on commercial processes of broiler breeders’ egg incubation in the literature is challenging. The presented study aimed to determine the effects of egg weight and storage time on the physical, biochemical characteristics of hatching eggs, embryogenesis and hatchability in Ross 308 broiler breeders. On the laying day, the eggs were divided into four weight groups: S – small eggs (57–61 g), M – medium eggs (62–66 g), L – large eggs (67–71 g), and XL – extra-large eggs (72–76 g). The eggs were then stored for 3, 7, 14, and 21 days under controlled conditions. As the egg storage time increased, a decrease in the yolk quality (lower index) was observed. The highest Haugh units were found in eggs from the S and M groups. The cholesterol content of the M, L, and XL groups was lower on days 7, 14, and 21 as compared to that of eggs only stored for 3 days. Egg weight loss during incubation decreased with an increase in the egg weight. An extension of the egg storage time caused an increase in the loss of egg weight. On the 14th and 18th days of hatching, an increase in the eggshell temperature was noted with an increase in the weight of the egg. The eggs stored for 7 days were characterised by the highest shell temperature on each day. The highest hatchability percentage was recorded for the M group. The hatchability rate decreased with the prolongation of the storage time, while the number of crippled chicks after hatching increased. The results confirmed that the increased weight of the eggs and prolonged storage time (14 and 21 days) increased the weight and decreased the length of the newly hatched chicks, respectively. Chicks from the heaviest eggs and those stored for 14 and 21 days showed poor results on the Pasgar score® test. The observations indicate the need to adopt various (of those available) methods to assess the quality of newly hatched chicks in hatcheries in order to produce high-quality broiler chickens. The results also indicate that prolonged egg storing beyond 14 days may affect the thyroid hormone economy during the hatching of chicks, especially in the XL group.     

Analyzing the “Group effect”: Rheotropic responses of developingFucus eggs

Summary Zygotes of the brown alga speciesFucus furcatus were allowed to differentiate while being subjected to a steady laminar flow of sea water. The cell polarity was found, as a consequence, to be determined rheotropically. At pH 6.5, the cells tend to form their rhizoidal pole downstream, if the flow speeds range from 0.01 to 10 per second. The degree of this downstream orientation increases with flow speed in a way that indicates that it is brought about by convective redistribution of a macromolecular and locally effective growth stimulator with a diffusion constant of the order of 10^–8 cm²/second.Qualitatively, the downstream response concurs with thepositive group effect since both responses are due to a stimulator and are more or less restricted to pH<7.0. At two other pH values tested, 7.1 and 8.1, no relevant downstream orientation was detected. At flow speeds >1/second (pH 7.1 and 8.1) and 100/second (pH 6.5), a very strong upstream orientation of the rhizoid formation was found. This upstream response may be mediated by convective redistribution of a relatively mobile growth inhibitor.

---

Zusammenfassung Fucus-Zygoten wurden in der Zeit zwischen 3 und 18 Stdn. nach ihrer Befruchtung konstant und laminar strömendem Seewasser ausgesetzt: Je nach pH-Wert und Strömungsgeschwindigkeit entwickelten daraufhin bis zu 60% einer Zellpopulation ihre Polaritätsachse parallel zur Strömungsrichtung.Bei pH 6,5 und Strömungsgeschwindigkeiten von 0,01 bis zu 10/sec bildeten die Zellen ihren Rhizoidpol stromabwärts. Die quantitative Analyse dieser rheotropischen Reaktion benutzte ein früher entwickeltes Modell, welches beschreibt, wie die Verteilung einer Substanz um ihre kugelförmige Quelle in Abhängigkeit von der Geschwindigkeit eines umgebenden strömenden Mediums zu Konzentrationsunterschieden zwischen Luv- und Leepol der Kugel führt. Nun wächst die gefundene rheotropische Reaktion in gleicher Weise mit der Strömungs-geschwindigkeit und strebt auch dem gleichen Maximalwerte um 25% zu, wie der Konzentrationsunterschied im Modell; vgl. die Spalten 2 und 3 in Tabelle 2. Diese übereinstimmung erlaubt den Schluß, daß die rheotropische Reaktion auf der Umverteilung eines von der Zelle emittierten Wuchsstoffes beruht, dessen Diffusionskonstante 10^–8 cm²/sec beträgt; der unbekannte Wuchsstoff muß daher hochmolekular sein (M>10⁷). Qualitativ entspricht diese rheotropische Reaktion bei pH 6,5 dempositiven Gruppeneffekt; beide Reaktionen sind nur bei pH-Werten <7,0 reproduzierbar. Andererseits spricht die sehr niedrige Diffusionskonstante des rheotropisch wirksamen Stoffes gegen dessen Rolle als Mittler despositiven Gruppeneffektes.Bei Strömungsgeschwindigkeiten > 1/sec (pH 7,1 und 8,1) sowie 100/sec (pH 6,5) treiben die Zellen das Rhizoid am stromaufwärtigen Pol aus. Dabei weicht das Ausmaß der Reaktion so stark vom theoretisch erwartbaren ab, daß der verantwortliche, hier wuchshemmende Stoff nicht näher charakterisiert werden kann; er ist wesentlich beweglicher, somit von viel geringerem Molekulargewicht als sein wuchsförderndes Gegenstück. Ein anderer Mechanismus als das Zusammenspiel von Konvektion und Diffusion kommt auch hier kaum in Frage, da eine Erhöhung der Viskosität des Seewassers (auf das Zwölffache) die rheotropische Reaktion nicht berührt.

---

---

This work was supported by National Science Foundation Grant GD-2446.     

Inhibitory effect of α-hydrazinoornithine on egg cleavage in sea urchin eggs

In fertilized sea urchin eggs which are kept in sea water containing α-hydrazinoornithine (αHO) at a concentration above 1 mM from the time of fertilization, cleavage is delayed markedly. The third cleavage is almost completely blocked by 3 mM αHO. Hydrazine, as well as ornithine, exerts no harmful effect on egg cleavage. αHO causes competitive inhibition of ornithine decarboxylase (ODC) in the egg homogenate. Polyamine levels decrease in fertilized eggs treated with αHO. The addition of ornithine (above 3 mM) to an egg culture containing αHO prevents the αHO-induced delay of cleavage. Putrescine (0.2–0.5 mM), which is the product of the reaction catalyzed by ODC, also relieves egg cleavage from the inhibited state. The same effect occurs in the presence of spermidine (0.2–0.5 mM) or spermine (0.1–0.8 mM). Especially, spermine (0.5 mM) completely cancels the inhibitory effect of αHO on egg cleavage. Egg cleavage is delayed only slightly in the presence of each polyamine (above 2 mM).     

Emi1 and Erp1: who can stop these eggs?

Vertebrate eggs prevent parthenogenetic development by producing cytostatic factor (CSF), which blocks exit from metaphase of meiosis II until fertilization. CSF was never purified but recently suspected to inhibit the anaphase-promoting complex (APC), an ubiquitin ligase required for entry into anaphase. In a recent paper in Genes & Development, Schmidt et al. describe the Xenopus APC inhibitor Erp1, which seems to be the best candidate yet for the downstream effector of CSF activity.