On blocking rules for the bootstrap with dependent data

We address the issue of optimal block choice in applicationsof the block bootstrap to dependent data. It is shown that optimalblock size depends significantly on context, being equal ton^1/3, n^1/4 and n^1/5 in the cases of variance or bias estimation,estimation of a onesided distribution function, and estimationof a two-sided distribution function, respectively. A clearintuitive explanation of this phenomenon is given, togetherwith outlines of theoretical arguments in specific cases. Itis shown that these orders of magnitude of block sizes can beused to produce a simple, practical rule for selecting blocksize empirically. That technique is explored numerically.     

Characterization of microsatellite loci for the detection of temporal genetic shifts within a single cohort of the brown demoiselle,Neopomacentrus filamentosus

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.     

XENOPUS LAEVIS AND DEVELOPMENTAL BIOLOGY

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.     

Processing of calling songs by an L-shaped neuron in the prothoracic ganglion of the female cricket, Acheta domesticus

ABSTRACT. An L-shaped auditory intemeuron (LI) has been recorded from extracellularly and intracellularly, and identified morphologically (by Lucifer yellow or cobalt injection) in the prothoracic ganglion of mature female Acheta domesticus. The morphology of the LI is very similar to ascending, prothoracic acoustic interneurons that are most sensitive to higher carrier frequencies in both A. domesticus and other gryllid species. Its terminations in the brain are similar to ascending acoustic interneurons found in other gryllids. The LI neuron is most sensitive to 4–5 kHz model calling songs (CSs), the main carrier frequency of the natural call. Thresholds to high frequencies (8–15 kHz) are 15–20 dB higher. Increasing CS intensities of up to 15 dB above threshold at 4–5 kHz result in increased firing rates by the LI. More than 15 dB increase in intensity causes saturation with little increase in spiking rate until the intensity surpasses 80 dB. In response to 70 dB or higher stimulus intensities, the LI responds to the second and third CS syllables with one or two spikes, pauses, and then produces a burst of nerve impulses with the same or greater latency than for lower intensity stimuli. In response to CS syllables of changing duration (10–30 ms) this neuron responds with a rather constant duration burst of impulses. Syllable periods of the CS stimuli were accurately encoded by the LI. Progressively stronger injection of hyperpolarizing current reduces, and ultimately stops spiking of the LI in response to CS stimuli. More intense stimulation with reduced hyperpolarization shows an initial spike, pause and burst of spikes. Intracellular recording from axonal regions of the neuron shows large spikes, small EPSPs and a developing hyperpolarization through the response to a CS chirp. Inhibitory input to the LI is demonstrated at 4.5, 8 and 16 kHz. This probably explains the specialized response characteristics of the LI which enhanced its encoding of CS syllable period.     

A unifying theory for methods of systematic analysis

A unifying theory for systematic analysis states that a number of methods should be used jointly to cope with various kinds of data; also that groups should be as consistent as possible, be made with least information loss, and where needed, be polythetic. A test of relationship, homogeneity, can use various kinds of data. It can take account of the internal variation of aggregate items such as genera. It can give due emphasis to smaller clusters that have likely important contexts of external items. It helps in analysing trends, cores and hazes in dendrograms. A proposed detector for formal groups can be based on measures of isolation, identifiability and inclusiveness. Non-mathematical, inter-item reaction tests such as hybridization and serology can also be used in grouping. All relationship data are used polythetically to reveal natural groups. This leads to a unified informational concept for taxa. This is more useful than the biological species concept that is restricted to inter-breeding data. All the methods appear to be analogues of the powerful human grouping instinct. The resulting compatibility is important as precise methods are needed mainly when the data are too complex for the mind to use reliably. Cladograms can be made by self-graded deweighting of homogeneity and agglomerative clustering. Unlike classical cladistics this can reveal any polythetic group. Finding the derived states for making cladograms is often much too hypothetical for a fully cladistic approach to be properly precise. Instead, where the evidence is weak, a milder strength of graded deweighting is used for the cladistic properties, which help to show relationships along with the others. Axiomatic failures of other classes of grouping methods are discussed. Unavoidable remnants of instinctive processing lower the precision of all the methods. The Uniter computer program, based on the theory, is tested with finely graded values of artificially ‘evolved’ items and with coarsely coded cladistic data. The results show that with natural data, the program should act as a fairly sensitive probe of past evolutionary branching. Another test shows how specimens from species complexes can be grouped and how distinctions between groups are analysed.