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1.
Neopomacentrus filamentosus, a common damselfish on the Indo–Australian archipelago, undergoes significant shifts in size and mitochondrial genetic structure upon larval settlement and metamorphosis to juvenile stages. We characterized five polymorphic microsatellite loci in order to study temporal genetic shifts within a single generation of N. filamentosus sampled first as larval settlers then again as demersal juvenile recruits. All loci were extremely polymorphic and exhibited high levels of heterozygosity. While all loci from the larval samples conformed to Hardy – Weinberg expectations, significant heterozygote deficiencies were seen in two loci in the juvenile samples, likely due to extreme size‐selective mortality imposed post‐settlement. 相似文献
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1. Because of the present popularity of Xenopus laevis for research in developmental biology, a review of the literature on this animal has been undertaken which emphasizes the anatomical, physiological and developmental features in which it differs from other anuran Amphibia. The need for caution in generalizing from observations on Xenopus to other vertebrates is stressed. 2. Earlier literature and the use of Xenopus for pregnancy testing have been surveyed briefly. Some of the peculiarities of this genus are: the prevalence of pulmonary rather than cutaneous or branchial respiration in the larva, with concomitant modifications of the vascular system; the larval filter-feeding mechanism; the unusual development of the forelimbs, outside the gill chamber; and a number of features of musculature and skeleton in the adult which may be regarded either as primitive or as neotenous, or as specializations for aquatic life. Urodele-like features of the morphology of the pituitary and pineal glands are also mentioned. 3. Recent work on the germ cells and their origin in Xenopus is reviewed in Section III. The germ plasm has been traced from early cleavage stages into germ cells whose identity and genetic characteristics may be traced by reciprocal transplants between anucleolate and normal Xenopus. This plasm is thought to contain redundant copies of DNA from the maternal oocyte, which may thus get passed on to the next generation. During oogenesis, yolk proteins originate from maternal liver protein, and both yolk platelets and pigment granules appear to form in association with mitochondria. The yolk platelets evidently contain both DNA and RNA, and the mitochondria also contain both DNA, of a circular form, and ribosomal RNA. In the oocyte nucleus, special interest has been focused recently on the extrachromo-somal DNA which arises from the nucleolar organizer regions of chromosomes. This DNA later forms the cores of the nucleoli. A number of synthetic processes can take place in the oocyte cytoplasm in the absence of the nucleus, and in the presence of foreign messenger-RNA. Ribosomal RNA synthesis shows at first an excess of 5 s over 18 s and 28 s forms. 4. Spermatogenesis has been studied little in Xenopus. Two unusual features are the absence of seminal vesicles for sperm storage and the spiral shape of the sperm head. By techniques involving destruction of the female pronucleus with ultraviolet light, or suppression of polar-body formation, androgenetic haploids, as well as triploids and tetraploids, have been produced in this species. Paternal genes begin to act at the onset of gastrulation, when nucleoli appear and major rRNA synthesis begins. This situation is sometimes presumed to typify events in all Amphibia -perhaps all vertebrates - but the assumption is unjustified, since in mammals there is much variation in the time of onset of rRNA synthesis, from the evidence so far available. 5. During cleavage in Xenopus, which appears to follow the same pattern as in other Amphibia, septate junctions may serve as channels of communication between the cells. Cytoplasmic DNA is a source for the nuclear DNA synthesis, and the total DNA per cell decreases. As shown by nuclear transplantation experiments, cleavage nuclei, like those of later embryonic stages, remain capable of initiating development in an enucleated egg. Egg cytoplasm can also initiate DNA and RNA synthesis in adult nuclei. 6. Gastrulation in Xenopus is unusual in that the mesoderm migrates forward below the surface and the dorsal lip is lined superficially by endoderm. Neural inductors have been extracted from the dorsal lip of Xenopus, but have not been analysed biochemically. By the end of gastrulation the induced ectoderm is synthesizing high-molecular-weight RNA and also shows increased quantities of three antigenic proteins. 7. In the early processes of differentiation of tissue primordia, regional differences in rates of yolk breakdown, proteolysis, amino-acid activation, tRNA characteristics and rates of incorporation of individual amino acids into protein may be demonstrated. There are also differences in antigens and in isoenzyme patterns. One peculiar morphological feature of early tissue development is the rotatory mode of somite-formation, not so far seem in any other vertebrate. 8. Among several organs whose development has been studied in some detail in Xenopus are: the granular skin glands, which arise from clones of cells; the lateral-line organs, which persist in the adult and are controlled by sensory and motor nerves; and the epidermal cells, which transmit electrical discharges, probably through their zonulae occludentes. In connexion with the filter feeding, the gut is ciliated in the larva: so also are the pronephric ducts. The growth of the pronephros appears to be controlled by a tissue-specific ‘chalone’. 9. The development of the eye in Xenopus normally entails induction of the lens by the eye-cup, as in other vertebrates, but independent ‘free lenses’ may form, by aggregation of epidermal cells instead of invagination from a placode, when the eye-cup rudiment is removed. In the development of the retina there is little evidence of the large-scale cell death described in other vertebrates. Topographical relations between retina and tectum appear to be established long before the full complement of cells is present in either organ. This and other recent experimental evidence suggests that there are no specific point-to-point retinotectal connexions. 10. Studies of the development of motor and sensory elements in the spinal cord of Xenopus showed that there were some early sensory cells lying dorsomedially, and also that the proximal regions of the motor roots were orientated longitudinally: both features are unique to Xenopus. As in Urodela, ablation of the limb causes reduction in size of the lumbar motor horns: in Xenopus it has been shown that there is also increased cell death in the sensory ganglia. 11. Like other Amphibia, Xenopus can regenerate central nervous system, limbs and the lens of the eye. Limb regeneration is somewhat better than in other Anura but gradually declines with increasing age after metamorphosis and also with increasingly proximal levels of amputation. The lens may regenerate from the cornea, the neural retina or the iris, and the regenerates soon acquire lens antigens. 12. Events at metamorphosis in Xenopus are controlled by interactions between the anterior pituitary and the thyroid, as in other Amphibia: cells secreting thyroid-stimulating hormone and thyroid-releasing factor have been identified in the anterior lobe. In response to thyroxine, the isolated tail regresses in organ culture, and this regression is accompanied by increases in the activities of lytic enzymes. 13. Some physiological features of metamorphosis peculiar to Xenopus are: the continued increase in serum proteins for some time afterwards; the more gradual changes in haemoglobin than in other Anura; and the continued excretion of more ammonia than urea. Under conditions of dehydration, however, carbamyl phosphatase activity in the liver increases and a higher proportion of urea is produced. 14. It is concluded that the preferential use of Xenopus for research in developmental biology since the 1950s has led to some important advances in knowledge, but that there is now a need to use other species in order to find out to what extent the same mechanisms operate in them as in Xenopus. 相似文献
4.
ELIZABETH A. NESBITT 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2005,38(1):17-25
Large cassid gastropods found in close association with Oligocene mysticete whale skeletons in a deep water setting indicate a novel trophic relationship. Bones of early mysticetes are preserved in close association with a recurring assemblage of bivalve taxa that are common components of fossil and recent hydrothermal vent and cold methane seep localities. Living members of these bivalve groups harbor sulfide-oxidizing autotrophic bacteria and comparisons with recent whale-falls indicate that they utilized bone-oil seepage. But unlike recent whale-falls, this fossil invertebrate assemblage is volumetrically dominated by large individuals of the cassid gastropod Liracassis apta that are preserved with their apertures adhering to the bone surfaces. Comparisons with recent cassoidean taxa and their ecological settings suggests that Liracassis apta belongs to the subfamily Oocorythinae, not Cassininae, and was an opportunistic scavenger in deep water, low oxygen environments. Oocorythine gastropods radiated rapidly on the northeastern Pacific margin during the Late Eocene and Oligocene to become the most commonly recorded gastropod in shelf and slope settings. 相似文献
5.
ELIZABETH M. CHADD 《Medical and veterinary entomology》1990,4(1):97-104
The Electrodyn sprayer was compared with a compression sprayer (Hudson X-pert) for residual application of cypermethrin, a pyrethroid insecticide, to control the malaria vectors Anopheles arabiensis Patton and An. funestus Giles in experimental huts at Magugu in Tanzania. The time taken for hut spraying, 2-2.5 min per hut, was similar for both types of sprayer. Two or three huts were treated internally with cypermethrin at 40 or 80 mg a.i./m2 using Electrodyn formulation for comparison with 80 mg a.i./m2 using wettable powder formulation. Each of the twelve huts (including five untreated controls) was fitted with window exit traps and either louvre or verandah traps for mosquito sampling. The Electrodyn sprayer was fitted with a pair of elbowed deflectrodes to direct the positively charged spray droplets onto walls and ceiling. All treatments gave 94-100% mortality-rates of indoor-resting anophelines throughout the evaluation period of 11 weeks post-spray. Reductions of An.arabiensis and An.funestus females by 10-42% and 62-91%, respectively, in rooms and by 72% and 51% in exit traps indicated that cypermethrin deterred mosquitoes from entering the huts. Overall mortality-rates of mosquitoes were 66% of both species in huts treated with 40 mg/m2 Electrodyn, 43% An.funestus and 71% An.arabiensis due to 80 mg/m2 Electrodyn formulation and 49% An.funestus and 64% An.arabiensis due to 80 mg/m2 WP formulation (no significant differences). It is concluded that the Electrodyn sprayer with deflectrodes is a convenient and effective means of residual house-spraying with pyrethroid insecticide for malaria vector control. 相似文献
6.
Estimates of gene flow, genetic substructure and population heterogeneity in bracken (Pteridium aquilinum) 总被引:1,自引:0,他引:1
PAUL G. WOLF ELIZABETH SHEFFIELD F.L.S. CHRISTOPHER H. HAUFLER 《Biological journal of the Linnean Society. Linnean Society of London》1991,42(4):407-423
Bracken [ Pteridium aquilinum (L.) Kuhn] is a cosmopolitan species and is a noxious weed in many areas. Because of its abundance, particularly in Britain, bracken affords an ideal system for investigating various aspects of population genetics and evolution. High mobility of dispersal units (spores) suggests that rates of gene flow among distant populations should be high. Gene flow is a major evolutionary force that influences the genetic structure of populations. To examine the effects of gene flow on population heterogeneity and population substructuring in bracken, starch gel electrophoresis of enzymes was used to provide the necessary genetic database. Allele frequency data at 21 loci were obtained for seven British populations, one Majorcan and one from the eastern United States. A model was employed to estimate the amount of gene flow ( Nm ) at several levels. Gene flow among British populations was extremely high ( Nm = 36.51), one of the highest estimates reported for plants. Among eight European populations gene flow was lower (but still considered high) at Nm = 2.47. Trans-Atlantic gene flow was low ( Nm = 0.0926).
F -statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.
The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing species. 相似文献
F -statistics were used to assess population heterogeneity and substructuring. The data indicate that, compared with other species, there is very little genetic differentiation among British populations of bracken. Indeed, it appears that the whole island is behaving as a single randommating population. This result is consistent with high levels of gene flow. Only one population (on the Isle of Arran) showed statistically significant genetic substructuring. Habitat heterogeneity on the island and age structure are hypothesized as possible causes of this result.
The data reported here support previous studies demonstrating that bracken is genetically polymorphic and is an outcrossing species. 相似文献
7.
Plants of berseem clover (Trifolium alexandrinum L.) cv. Taborwere raised under conditions inhibiting the acquisition of coldhardiness (non-hardened) or inducing cold hardiness (hardened).All non-hardened plants developed an elongated shoot and exhibitedconsiderable frost sensitivity, as measured by the extent ofthe reduction in yield of variable chlorophyll fluorescenceafter exposure to sub-zero temperature. Hardened plants developeda shorter shoot, with fewer leaves and a greater percentageof dry matter in the root system. These parameters were associatedwith a marked increase in frost resistance. Exogenous applicationof ABA to plants effected similar morphological modificationsin both hardening and non-hardening temperature regimes; plantsdeveloped a shorter primary shoot axis and leaves exhibiteda marked increase in frost hardiness. In berseem clover ABAcan thus substitute, at least partially, for the low temperaturetreatment required to induce cold hardiness. Spraying plantsraised under hardening conditions with gibberellic acid reversedthe effects of the hardening treatment, since they developedan elongated shoot and exhibited frost sensitivity comparableto non-treated plants grown under non-hardening conditions.It is concluded that these endogenous hormones are directlyinvolved in triggering changes in morphogenesis which accompanyphysiological and metabolic events associated with the inductionof plant cold hardiness. Key words: Frost resistance, morphogenesis, abscisic acid, giberellic acid, Trifolium alexandrinum 相似文献
8.
Constant Production of Type C Virus Particles in a Continuous Tissue Culture derived from Pleural Effusion Cells of a Lymphoma Patient 总被引:5,自引:0,他引:5
ELIZABETH S. PRIORI LEON DMOCHOWSKI BROOKS MYERS J. R. WILBUR 《Nature: New biology》1971,232(28):61-62
PARTICLES resembling viruses were first observed in organs of mice with spontaneous leukaemia and in thin sections of a biopsy specimen from a lymph node of a patient with acute lymphocytic leukaemia by Dmochowski and Grey1. They also found them in some biopsy specimens of lymph nodes and bone marrows before and after growth in tissue culture2,3,8. Recent reports have described the presence of type C virus particles in other human tumours including liposarcoma4, osteosarcoma5,6, giant cell tumour9, rhabdomyosarcoma (unpublished results of L. D. and E. S. P.) and breast carcinoma7. 相似文献
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10.
The activity of glutamine synthetase (GS) extracted from chickpeasgrown under different nitrogen and temperature regimes was examined.Cytosolic GS (GS1) was much less temperature sensitive thanchloroplastic GS (GS2). There was no change in the ratio ofthe two isoforms from plants with different growth temperatures.Specific activity of GS appeared to be independent of growthtemperature and was little affected by nitrogen supply. In vitro studies were performed on the heat stability of GS2in the presence of glycine betaine, proline, and myoinositol.The latter was most effective in preventing loss of enzyme activityat high temperatures. Glycine betaine was also effective asa heat protectant but enzyme activity in the presence of prolinewas lower than the control at temperatures above 30 ?C. Theimportance of myo-inositol protection of metabolism is discussedin relation to the accumulation in chickpeas of another cyclitol,pinitol. Key words: Chickpeas, high temperature stress, glutamine synthetase 相似文献