The production of cloned fish in the medaka (Oryzias latipes)

The measurement of cellular DNA content by DNA microfluorometry revealed that medaka embryos that were fertilized with normal sperm and exposed to heat shock (41 degrees C for 3 min) or hydrostatic pressure (700 kg/cm2 for 10 min) at 85-95 min after insemination were tetraploid. Embryos fertilized with normal sperm and exposed to heat shock (41 degrees C for 2 min at 2-3 min after insemination) were triploid. These results suggest that heat shock or hydrostatic pressure at 85-95 min after insemination arrests the first cleavage, while heat shock at 2-3 min after insemination arrests the second meiotic division. Medaka clones have been produced by the following method: Eggs from orange-red or variegated variety were activated by UV-irradiated, genetically impotent sperm of wild-type fish (UV sperm). The haploid eggs obtained were diploidized by preventing the first cleavage with heat shock or hydrostatic pressure to produce homozygous females. Each of the two homozygous females was mated with vasectomized male in isotonic balanced salt solution to collect unfertilized eggs. The collected eggs were activated with UV sperm and converted from haploid to diploid by arrest of the second meiotic division with heat shock. Hatched fry of each homozygous diploid (all females) were fed with a methyltestosterone-containing diet (40 micrograms/gm diet) to produce sex-reversed males, which were mated with brood females, and thus two cloned lines were obtained.     

EGG ACTIVATION AND PARTHENOGENETIC REPRODUCTION IN INSECTS

1. Many insects reproduce by parthenogenesis. In one of the largest orders of the animal kingdom, the Hymenoptera, most of its members reproduce by arrhenotokous parthenogenesis. Egg activation in parthenogenetic animals obviously cannot be caused by fertilization of the egg. The question of what initiates egg development in parthenogenetically reproducing animals has been studied for a few insect species and is discussed in this article. 2. The grasshopper Melanoplus differentialis is one of several Orthoptera displaying accidental parthenogenesis. In this species, egg laying provides the stimulus to the completion of meiosis and start of embryonic development in unfertilized and probably also in fertilized eggs. The same holds true for the dipteran insect Drosophila melanogaster which exhibits rudimentary parthenogenesis, and for D. mercatorum showing accidental parthenogenesis. The precise way in which oviposition affects the egg is unknown. 3. The stick insect Carausius morosus reproduces by obligatory thelytoky. The triggering factor for removal of the meiotic block and initiation of embryonic development is oxygen from the air which penetrates to the egg through the micropyle immediately after oviposition. The oviposition act itself is not necessary for activation of the egg. 4. Comparative studies of the different types of oogenesis in the dipteran insect Heteropeza pygmaea show that in paedogenetically developing follicles meiotic arrest in prophase is of very short duration and a meiotic block at the end of oogenesis is absent. It is suggested that in this case triggering events for egg development are dispensable. On the other hand, under certain experimental conditions a meiotic block can be established in some of these follicles. 5. Investigations on the Ichneumonid wasp Pimpla turionellae have shown that unfertilized, male-determined eggs - and most likely also fertilized, femaledetermined eggs - are activated by mechanical stress exerted on the eggs during natural or imitated oviposition. This mechanical stress, in addition, activates a streaming system which is independent of meiotic completion and nuclear multiplication. Egg activation by egg distortion is also found in the Pteromalid species Nasonia vitripennis and occurs presumably in many other Hymenoptera. 6. Carausius morosus, Pimpla turionellae and Nasonia vitripennis are species with parthenogenetic reproduction for which the natural factors responsible for the initiation of egg development have been identified. The cases of Pimpla turionellae and Nasonia vitripennis are of particular interest because of the feasibility of artificially imitating the natural activating mechanism. 7. It is concluded that apart from fertilization various events at oviposition may trigger egg development. In addition, the occurrence of rudimentary parthenogenesis in many sexually reproducing animal species suggests that sperm entry and fertilization may frequently be necessary for the continuation of egg development rather than for its initiation.     

Delayed sperm injection and fertilization in parthenogenetically activated insect egg (Athalia rosae,Hymenoptera)

Summary Mature eggs dissected from the ovary of unmated females of Athalia rosae ruficornis Jakovlev (Hymenoptera, Tenthredinidae) can be activated to develop (into haploid parthenogenetic males) simply by exposing them to distilled water. These eggs, which are primary oocytes arrested at the first meiotic metaphase, resume meiosis upon activation and reach the first meiotic telophase in 20 min. Mature eggs immediately upon dissection have previously been shown to complete karyogamy and develop as fertilized diploid females if injected with sperm. We show here that the eggs activated in water for 20 min have a much higher rate of successful fertilization if injected with sperm, and that the eggs activated for 40 min, upon sperm injection, though at a reduced frequency still develop as diploid fertilized females. Eggs left in water for 60 min, however, are no longer fertilized upon sperm injection and develop as haploid males.     

Thelytokous parthenogenesis in unmated queen honeybees (Apis mellifera capensis): central fusion and high recombination rates

The subspecies of honeybee indigenous to the Cape region of South Africa, Apis mellifera capensis, is unique because a high proportion of unmated workers can lay eggs that develop into females via thelytokous parthenogenesis involving central fusion of meiotic products. This ability allows pseudoclonal lineages of workers to establish, which are presently widespread as reproductive parasites within the honeybee populations of South Africa. Successful long-term propagation of a parthenogen requires the maintenance of heterozygosity at the sex locus, which in honeybees must be heterozygous for the expression of female traits. Thus, in successful lineages of parasitic workers, recombination events are reduced by an order of magnitude relative to meiosis in queens of other honeybee subspecies. Here we show that in unmated A. m. capensis queens treated to induce oviposition, no such reduction in recombination occurs, indicating that thelytoky and reduced recombination are not controlled by the same gene. Our virgin queens were able to lay both arrhenotokous male-producing haploid eggs and thelytokous female-producing diploid eggs at the same time, with evidence that they have some voluntary control over which kind of egg was laid. If so, they are able to influence the kind of second-division meiosis that occurs in their eggs post partum.     

Suitability of non-fertilized eggs of Homalodisca vitripennis for the egg parasitoid Gonatocerus morrilli

Gonatocerus morrilli (Howard) (Hymenoptera: Mymaridae) is an egg parasitoid used in California, USA to control glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae). Virgin GWSS females deposit non-fertilized eggs and mated females can exhaust sperm reserves for egg fertilization. However, nothing is known about Gonatocerus spp. performance when using non-fertilized GWSS eggs as hosts. Host age preference for oviposition and suitability of non-fertilized GWSS eggs as hosts for G. morrilli reproduction were investigated to determine whether non-fertilized eggs on sentinel plants could be used to monitor egg parasitoid populations. Gonatocerus morrilli parasitized all ages of GWSS eggs (1–8 days old) regardless if the host egg was fertilized or not. In choice tests (fertilized versus non-fertilized eggs), parasitoids failed to emerge as adults from non-fertilized eggs more often than from fertilized eggs. The results indicate that non-fertilized eggs were accepted by G. morrilli as suitable hosts for oviposition, but were less suitable for immature development compared to fertilized eggs.     

A comparative cytological investigation of the reproductive cycle of an amphimictic diploid and a parthenogenetic triploid form of Lumbricillus lineatus (O.F.M.) (Oligochaeta,Enchytraeidae)

Summary The cytology of a diploid amphimictic (2x=26) and a triploid parthenogenetic (3x=39) cytotype of Lumbricillus lineatus has been described. The triploid type never produces mature sperm, but it must be fertilized by sperm from the diploid cytotype in order to produce viable eggs. However, the sperm does not enter the egg, but eggs which have not been activated by sperm die at an early stage. Oogenesis in the triploid cytotype, which results ultimately in the restoration of the somatic chromosome number, follows a pattern which has not been described in other parthenogenetic organisms. The first meiotic division is asynaptic and no typical metaphase plate is formed; the univalents are distributed to opposite poles without undergoing an equational division. The first division is therefore numerically approximately reductional. The nuclei are at anaphase when the eggs leave the animal, whereas the nuclei of the diploid amphimictic cytotype are in MI when the eggs are laid. Following activation by spermatozoa, the first anaphase spindle is much elongated, and becomes V-shaped. The first anaphase spindle persists and no second anaphase spindle is formed. At the second division the chromosomes divide mitotically. The resulting four chromosome groups fuse two by two in such a way that two nuclei are formed each with the full somatic (triploid) chromosome set (cf. Figs. 14–16).The different steps involved in the evolution of this mechanism are discussed in relation to the evolution of the triploid cytotype.     

Quantification of spermatozoa in the sperm-storage tubules of turkey hens and the relation to sperm numbers in the perivitelline layer of eggs

This study was conducted to determine the number of spermatozoa residing in the oviduct sperm-storage tubules (SST) and the relationship between these numbers and the number of spermatozoa embedded in the perivitelline layer of oviductal eggs after a single insemination of 200 x 10(6) spermatozoa. The SST of hens inseminated within one week before the expected onset of egg production were filled faster (4 h vs. 2 days) and possessed more spermatozoa (4.1 vs. 2.0 x 10(6)) than the SST of hens inseminated after the onset of egg production. Furthermore, for hens in egg production, significantly fewer spermatozoa were recovered from the SST if the hen was inseminated within 2 h before or after oviposition than if inseminated more than 2 h before or after the oviposition. There was a strong positive correlation between the number of spermatozoa in the SST and the number of spermatozoa embedded in the perivitelline layer of the oviductal eggs (r = 0.85, p less than 0.01). These data show that the population of spermatozoa actually accepted by the SST is quite small relative to the number of spermatozoa inseminated and that maximum sperm-storage is achieved when the hen is inseminated just prior to the onset of egg production. It is suggested that the sperm-storage capacity of the oviduct and the quality of the semen sample can be estimated on the basis of numbers of spermatozoa embedded in the egg perivitelline layer.     

Ovulation and fertilization of primary and secondary oocytes in LT/Sv strain mice

In this study, the chromosome constitution of both unfertilized oocytes and fertilized eggs isolated from the oviducts of LT/Sv strain mice were analyzed. Air-dried chromosome preparations from unfertilized oocytes revealed that about one-third of those examined were ovulated as primary oocytes. These were arrested at metaphase of the first meiotic division and exhibited the characteristic “tetrad” chromosome configuration. The remaining two-thirds of the unfertilized oocytes were ovulated at metaphase of the second meiotic division. The fertilized eggs were isolated from the oviducts of LT/Sv females previously mated to (C57BL × CBA) F1 hybrid males. Analysis of the fertilized eggs at metaphase of their first cleavage mitosis revealed that about one-third of the eggs examined were digynic triploids, whereas the remaining two-thirds had the normal diploid chromsome constitution. In the triploids, the 40 female chromosomes present (mouse, n = 20) were derived from a single diploid pronucleus formed after the extrusion of a first polar body, and following the monospermic fertilization of primary oocytes. The female pronuclear-derived chromosomes invariably exhibited “homologous pairing,” and these were associated at their centromeres. The ovulation, penetration, and subsequent fertilization of primary oocytes is an extremely unusual phenomenon in mammals and only appears to occur on a regular basis in LT/Sv mice. The premature “cytoplasmic maturation” of these oocytes is of interest, as they clearly have the same developmental capacity as secondary oocytes. The significance of these observations in relation to folliculogenesis and litter size in LT/Sv mice is discussed.     

中华蜜蜂卵表面微观结构及化学成分初步研究

为认识蜜蜂的工蜂监督机制,利用扫描电镜分别观察了中华蜜蜂Apis cerana cerana不同类型卵（蜂王产的受精卵、未受精卵以及工蜂产的未受精卵）的表面超微结构,同时用气 质联用技术测定了各类型卵新产卵（0 h）和5 h卵的表面化学信息素成分。结果表明：中华蜜蜂3种卵表面均覆有六边形的结构,结构内充满小突起,3种卵的大小及表面超微结构无显著差异。受精卵表面化学信息素种类比未受精卵更为丰富,C27∶2和C27∶1可能是卵带有的标记化学信息素。     

Egg Deposition Behavior in the Haplodiploid Sawfly Athalia rosae ruficornis Jakovlev (Hymenoptera: Symphyta: Tenthredinidae)

The egg deposition behavior of the turnip sawfly, Athalia rosae (Hymenoptera: Symphyta), is described. Both unmated and mated females lay eggs individually inside of fresh young leaves of cruciferous plants. During an oviposition event, females exhibit a distinct pause in abdominal contractions just before the actual egg deposition act. Unmated females show a longer pause (11.31 s on average) than mated females (4.38 s on overall average). By employing an eye color mutation, the sex of the eggs laid by females was ascertained. Females mated once lay mostly fertilized (diploid female) eggs initially but begin to lay a considerable number of unfertilized (haploid male) eggs later in life. The laying of an unfertilized egg is associated with a longer pause (6.98 s on average) than the laying of a fertilized egg (3.76 s on average). These results are in contrast to previous reports on apocritan Hymenoptera, where the presence of a pause or a longer pause during oviposition was associated with the deposition of fertilized eggs rather than unfertilized eggs. The possibility that mated Athalia rosae females control fertilization and its implications for sex allocation strategies are discussed.     

Western corn rootworm (Diabrotica virgifera virgifera LeConte) (Coleoptera: Chrysomelidae) oviposition can be released by decapitation

Nervous system control of western corn rootworm (Diabrotica virgifera virgifera LeConte, WCR) (Coleoptera: Chrysomelidae) oviposition was studied using decapitation. Gravid females (n = 364) were decapitated with scissors and floated in water-filled Petri dishes. Oviposition by individuals was observed at 30 min intervals for 4 hr after decapitation; cumulative oviposition was tallied at 48 hr post-treatment. Overall, 82.7% of females laid eggs within 48 hr. Oviposition commenced quickly; 78.4% of females laid eggs during the observation period, 81.8% of these began egg laying within 30 min of decapitation. Egg-laying females deposited a total of 66.8 ± 2.1 eggs (mean ± SEM); this was 85.1% of the total mature egg load. Dissection revealed that 31.9% of n = 301 laying females and 14.3% of 63 non-laying females had a rupture of the common oviduct, manifest as an egg-filled hernia containing a mean of 8.17 ± 1.3 eggs (range: 1–83). Among n = 237 females that laid eggs during observations, females with hernias laid significantly fewer eggs (35.8 ± 4.2) than intact females (48.0 ± 2.7) during the 4-hr interval. There was no difference in the mean proportion of hatch for eggs collected from the same n = 10 females before (0.88 ± 0.03) or after decapitation (0.84 ± 0.04). Rapid oviposition following decapitation suggests that WCR egg laying is under constant descending neural inhibition; the motor programme controlling egg laying must reside posterior to the head. Decapitation can be used to quickly collect mature, fertilized WCR eggs.     

High efficiency of meiotic gynogenesis in sea lamprey Petromyzon marinus

Induction of androgenesis and gynogenesis by applying a pressure (PS) or heat shock (HS) to double the haploid chromosomal set results in progenies possessing only chromosomes from a single parent. This has never been accomplished in representatives of Agnatha. The objective of this study was to induce gynogenesis and androgenesis in sea lamprey Petromyzon marinus. For gynogenesis experiments, ultraviolet (UV)-irradiated sperm was used to activate sea lamprey eggs and HS or PS were applied to inhibit the second meiotic division and consequently induce diploidy in the embryos. The UV irradiation of immobilized sperm was performed for 1 min at 1,719 J m(-2). HS of 35+/-1 degrees C for 2 min and PS of 9,000 psi for 4 min were applied at different times after egg activation (8, 12, 20, and 24 min or 8, 16, and 24 min for HS or PS, respectively). Regardless of the induction time of the HS, survivals at pre-hatching stage were similar. In contrast, PS applied 8 min after activation appears to increase survival rate of pre-hatched embryos in comparison to 16 and 24 min after activation. In control groups, without shock treatment (no diploidization), there were no survivors. All deformed, gynogenetic embryos were confirmed to be haploids and died prior to burying themselves in the sand. We confirmed by flow cytometry that progenies produced using both shock methods surviving to the next stage, burying in the substrate, were diploid gynogenetic. For the androgenesis experiments, UV-irradiated eggs (1,719 J m(-2) for 1 min) were fertilized with non-treated sperm and HS was applied to restore diploidy of the eggs. Several attempts have been made to optimize the parameters used. HS of 35+/-1 degrees C was applied 110, 140, 170, 200, and 230 min after activation for 2 min. Low yields of androgens were obtained and all animals died within a week after hatching. These techniques will allow to establish meiotic gynogenetic lines of sea lamprey for determining sex differentiation in this species and to analyze its hormonal and environmental regulation.     

Distribution ofChilo partellus (Lepidoptera: Pyralidae) egg batches on maize

Distribution ofChilo partellus egg masses was studied in field, greenhouse, and laboratory experiments. The eggs were laid in batches mainly on the lower side and the lower leaves of the plant. The egg batch size ranged from 1 to 169 eggs, with a median of 33.5 eggs per batch (average, 40.5). Oviposition ofC. partellus is described at two levels. The first level, choice of oviposition plants, followed a random distribution. The second level, number of egg batches per plant, followed an aggregated distribution in the field, where more than one egg batch was deposited on the same plant by the same female, which was found on 25% of the oviposition plants. A mechanism for egg-layingC. partellus females to perceive preceding oviposition or injured plants could not be detected. Oviposition site choice seemed to be mediated by tactile stimuli.     

NUCLEAR-CYTOPLASMIC RELATIONS IN THE MITOSIS OF SEA URCHIN EGGS : III. γ-Ray-Induced Damage to Whole Eggs and Nucleate and Anucleate Half-Eggs

Sea urchin eggs were cut into halves. The nucleate and anucleate halves and whole eggs were irradiated with γ-rays and then fertilized with normal sperm. The first mitosis of the diploid half-egg was more delayed than the division of the whole egg. There was a small, but highly significant, delay of the mitosis of the haploid half-egg, thus demonstrating cytoplasmic sensitivity to ionizing radiation. Since the sensitivity of nucleate cells is influenced by cytoplasmic volume, the problem of the role of cytoplasm in repair is considered in relation to these data and other reports in the literature.     

Effect of the venom of the endoparasitoid,Apanteles kariyai Watanabe,on the cellular defence reaction of the host,Pseudaletia separata Walker

Although a venom apparatus is present in all female braconid wasps, the function of the venom injected into the host at the time of oviposition by the endophagous members of this group is unknown. Eggs laid by females of Apanteles kariyai, from which the venom apparatus had been removed, were encapsulated, which suggests that the fluid is necessary to enable the parasitoid eggs to escape the cellular defence reaction of the host. Studies with anti-venom serum demonstrated that the venom is attached to the surface of the egg. However, injection of DEAE-Sephadex A-50 particles (Sephadex particles) revealed that the venom alone is insufficient to inhibit the encapsulation reaction. Calyx and venom fluids together seem to be essential for evasion of the host defence reaction by the parasitoid eggs. Eighty-five % Sephadex particles, injected together with calyx and venom fluids, fail to become fully encapsulated, whereas 46% of particles injected with only the calyx fluid avoided encapsulation. Furthermore, when eggs from the lateral oviduct were injected into unparasitized larvae, together with the calyx and venom fluids, a few eggs developed successfully although they had undergone no mechanical distortion.     

Die Zytologie der bisexuellen und parthenogenetischen Fortpflanzung von Heteropeza pygmaea Winnertz,einer Gallmücke mit pädogenetischer Vermehrung

Heteropeza pygmaea (syn. Oligarces paradoxus) can reproduce as larvae by paedogenesis or as imagines (Fig. 1). The eggs of imagines may develop after fertilization or parthenogenetically. The fertilized eggs give rise to female larvae, which develop into mother-larvae with female offspring (Weibchenmütter). Only a few of the larvae which hatch from unfertilized eggs become motherlarvae with female offspring; the others die. Spermatogenesis is aberrant, as it is in all gall midges studied to date. The primary spermatocyte contains 53 or 63 chromosomes. The meiotic divisions give rise to two sperms each of which contains only 7 chromosomes (Figs. 5–11). The eggs of the imago are composed of the oocyte and the nurse-cell chamber. In addition to the oocyte nucleus and the nurse-cell nuclei there are three other nuclei in the eggs (Figs. 15–17). They are called small nuclei (kleine Kerne). In prometaphase stages of the first cleavage division it could be seen that these nuclei contain about 10 chromosomes. Therefore it is assumed that these nuclei originate from the soma of the mother-larva. The chromosome number of the primary oocyte is approximately 66. The oocyte completes two meiotic divisions. The reduced egg nucleus contains approximately 33 chromosomes. The polar body-nuclei degenerate during the first cleavage divisions. The fertilized egg contains 2–3 sperms. The primary cleavage nucleus is formed by the egg nucleus and usually all of the sperm nuclei and the small nuclei (Figs. 21–29). The most frequent chromosome numbers in the primary cleavage nuclei are about 77 and 67. The first and the second cleavage divisions are normal. A first elimination occurs in the 3rd, 4th, and 5th cleavage division (Fig. 30). All except 6 chromosomes are eliminated from the future somatic nuclei. Following a second elimination (Figs. 33, 34), the future somatic nuclei contain 5 chromosomes. No elimination occurs in the divisions of the germ line nucleus. In eggs which develop parthenogenetically the primary cleavage nucleus is formed by the egg nucleus and 2–3 small nuclei. It's chromosome number is therefore about 53 or 63. After two eliminations, which are similar to the ones which occur in fertilized eggs, the soma contains 5 chromosomes. The somatic nuclei of male larvae which arrise by paedogenesis contain 5 chromosomes; while the somatic nuclei of female larvae of paedogenetic origin contain 10 chromosomes. It was therefore assumed earlier that sex was determined by haploidy or diploidy. But the above results show that larvae from fertilized as well as from unfertilized eggs of imagines have 5 chromosomes in the soma, but are females, and the female paedogenetic offspring of larvae from unfertilized eggs have either 5 or 10 chromosomes in their somatic cells. Therefore sex determination is not by haploidy-diploidy but by some other, unknown, mechanism. The cytological events associated with paedogenetic, bisexual, and parthenogenetic reproduction in Heteropeza pygmaea are compared (Fig. 37). The occurrence and meaning of the small nuclei which are found in the eggs of most gall midges are discussed. It has been shown here that these nuclei function to restore the chromosome number in fertilized eggs; it is suggested that they function similarity in certain other gall midges. Consideration of the mode of restoration of the germ-line chromosome number leads to the conclusion that in Heteropeza few, if any, of the chromosomes are limited to the germ-line, i.e. can never occur in somatic cells (p. 124).     

Combinative stimulation inactivates sex pheromone production in the silkworm moth, Bombyx mori.

Mating results in a strong suppression of sex pheromone (bombykol) production in the female silkworm moth, Bombyx mori. The mechanical stimulation from the insertion of a penis, inflation of the bursa copulatrix (BC), or copulation with the sterile male whose penis was removed in order to prevent ejaculation (pr-male) induced only a partial decline in bombykol production. Artificial insemination stimulates oviposition of fertilized eggs as does normal mating. However, bombykol production did not decline in artificially inseminated females. When females were artificially inseminated before or after mating with pr-males, some females had a small amount of bombykol, similar to females mated with normal males, while other females had a large amount of bombykol similar to virgin females. The former usually laid fertilized eggs, while the latter laid only unfertilized eggs though semen filled their spermatophores and spermathecae. The mechanical stimulation caused by mating with a pr-male could be replaced by covering the abdominal tip with melted paraffin. Neither implantation of the BC obtained from mated females, nor injection of the spermatophore extract, into a female mated with a pr-male could inactivate bombykol production. Injection of hemolymph from a mated female into a virgin also failed to affect bombykol production These results indicate that a combination of both the tactile stimulation of the abdominal tip and the arrival of fertile spermatozoa in the vestibulum trigger a neural inactivation mechanism of bombykol production after mating.     

Inhibition of chromosome separation in fertilized starfish eggs by kalihinol F, a topoisomerase I inhibitor obtained from a marine sponge

Kalihinol F, a naturally occurring diterpene from a marine sponge, Acanthella sp., inhibited chromosome separation in fertilized starfish (Asterina pectinifera) eggs but allows the first cleavage to occur, thereby forming unseparated metaphase chromosomes which were elongated between the two daughter cells. The chromosomes were eventually torn off in the embryonic cells. Most of the cells gradually lost the chromosomes during the cell cycle progression. The embryonic development halted at the morula stage just before the onset of blastulation. The mitotic failure occurred when kalihinol F was applied to a fertilized egg during the second meiotic process, but not after the completion of the second meiotic division. Kalihinol F inhibited topoisomerase I activity in vitro, but had no effects on activities of DNA polymerases alpha, beta, and gamma, and of topoisomerase II. These results suggest that the topoisomerase I plays an essential role in meiosis II in this species.     

Crossing over and Diploid Egg Formation in the Elongate Mutant of Maize

Rhoades (1941) found recombination in the proximal regions of chromosome 5 to be higher in male than in female flowers. Two explanations were proposed to account for the lower female values, namely: (1) there is a basic difference in rates of crossing over in mega- and microsporocytes, or (2) selective orientation of the chromosome 5 bivalent on the meiotic spindle leads to the preferential segregation of noncrossover chromatids to the basal megaspore. These alternatives have been tested by carrying out a half-tetrad analysis of the diploid eggs produced by plants homozygous for the recessive elongate (el) allele. The A2-Bt crossover values determined from the diploid eggs of elongate plants were much lower than those calculated from haploid sperm of both El el and el el plants. Since male and female flowers should have similar cross-over values if the orientation hypothesis were correct, it was concluded that the amount of crossing over in the A2-Bt region of chromosome 5 is intrinsically higher in male than in female meiocytes. In the analysis of diploid eggs the use of the Bt locus, which marks the centric region of chromosome 5, provided information on the origin of diploid eggs. The genotypic constitution of 425 diploid eggs was ascertained. Of these, 20.4% were Bt bt. They could not be accounted for by failure of the second meiotic division or by replication during the interphase between the two meiotic divisions, but are expected if there is a single division with an equational separation of the centromere regions of chromosome 5. The Bt Bt and bt bt genotypes arise from a disjunctional separation. It is proposed that diploid eggs are produced by an abnormal meiosis in which there is one division with either disjunctional or equational separation. Disjunctional separation is more frequent but the ratio of the two types varies from ear to ear. Recombination in the A2-Bt-Pr region of chromosome 5 was found to be higher in the haploid gametes of elongate homozygotes than in El El and El el plants. On the other hand, crossing over was reduced in the Sh-Bz segment of chromosome 9 in elongate plants, but the adjacent Bz-Wx interval was unaffected.     

Proximate Factors Regulating Maternal Options in the Eggplant Lace Bug, Gargaphia solani (Heteroptera: Tingidae)

The eggplant lace bug, Gargaphia solani, was used to investigate the proximate factors regulating maternal care and a noncaring, condition dependent strategy called egg dumping. We hypothesize that the act of delaying oviposition while searching for a dumping opportunity suppresses oogenesis and triggers guarding behavior. We examined several predictions of this hypothesis by measuring: (1) whether females do delay oviposition in the absence of dumping stimuli, (2) whether females in transition between egg dumping and egg guarding are capable of expressing either reproductive option, (3) the effect of nymphal interactions and antennal ablation on the duration of maternal care, and (4) oogenesis in guarding and dumping females. We found that females without a dumping opportunity wait, on average, 30 h longer to oviposit than females exposed to a dump mass. Females that had initiated their own egg mass could resume eggdumping if they had laid less than half of their eggs but were unlikely to abandon their eggs when most had been laid. Maternal care in G. solani can be prolonged if interactions with nymphs are artificially prolonged. Females require antennae to maintain maternalcare. Presumably antennae transduce cues from eggs and nymphs. Dissections of dumping and guarding females 72 h after their first oviposition demonstrated that dumpers continue to produce primary oocytes after a dumping event but guarders terminate oogenesis whilecaring for their first brood. We interpret all of these results within the context of the hypothesis that juvenile hormone titers regulate the expression of both egg dumping and egg guarding.