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.     

COMPARATIVE SPERMATOLOGY OF FOUR SYMPATRIC SPECIES OF SIPHONARIA (PULMONATA: BASOMMATOPHORA)

The fine structure of the modified sperm and spermatogenesisof four sympatric species of Siphonaria is described. The morphologyof the sperm of all species is very similar. The head, whichis about 6 µm long, is composed of a nucleus with fibrouschromatin capped by an acrosome (about 1 µm long) comprisedof an acrosomal pedestal and apical vesicle. The midpiece hasa mitochondrial derivative which surrounds a single glycogenhelix, posterior to which is a glycogen piece. Although differencesbetween each species exist, the value of sperm morphology forpurposes of taxonomy in this genus is questioned. Comparisonwith other basommatophorans however suggests that sperm morphologymay be of value at a higher taxo-nomic level. The morphologicalchanges that occur during spermatogenesis are similar to thosedescribed for other molluscs with modified sperm, except thatduring early spermiogenesis the Golgi body and smooth endoplasmicreticulum become highly developed. This proliferation of theSER and Golgi occurs at the same time as elongation of the spermatid.Throughout spermatogenesis, the germ cells are closely associatedwith a somatic cell which, because of structural similaritieswith the somatic cell of mammalian seminiferous epithelium,has been termed a Sertoli cell. After the spermatids have beenreleased from the Sertoli cells of the testis, maturation continuesin the hermaphrodite duct where the acrosome reaches its finalsize and glycogen accumulates in the glycogen compartment ofthe mid-piece. (Received 25 April 1990; accepted 1 September 1990)     

Courtship feeding in Ospreys Pandion haliaetus: a criterion for mate assessment?

In many bird species males provision their mates prior to egg-laying. Courtship feeding has been suggested to function in several ways: to advance laying date by improving female condition, to induce a female to copulate or to allow a female to assess her mate. The role of courtship feeding in Ospreys Pandion haliaetus was investigated in British Columbia, Canada. Courtship feeding rate affected the probability of a pair initiating a clutch. Pairs that laid eggs had higher rates of courtship feeding than pairs that did not lay eggs in both 1991 and 1992. Male courtship feeding rate also correlated negatively with the duration of the courtship period. Experimentally increasing the amount of food available to females prior to egg-laying resulted in a nonsignificant reduction in the duration of the courtship period. This study found no evidence to support the suggestion that female Ospreys trade copulations for food during the courtship period; only 63 of 385 copulations observed were associated with feeds, and courtship feeding rate did not correlate with the copulation rate of a pair. Male provisioning rates, however, were predictable; courtship feeding rate correlated with both male delivery rate to the nest when chicks were 1–2 weeks old and mean brood growth rate. Female Ospreys therefore may be able to predict the quality of subsequent paternal care using courtship feeding rate. As predicted if optimal hatching asynchrony is dependent on food availability, mean brood growth rate, an indirect measure of male parental care, was negatively correlated with hatching asynchrony. This suggests that female Ospreys may manipulate hatching asynchrony in response to male courtship feeding rate, thereby maximizing the productivity of their brood at predicted food levels.     

Studies on the occurrence of tomato bushy stunt virus in English rivers

Tomato bushy stunt virus (TBSV) of unknown source was isolated from water of the River Thames, near Oxford. The isolate designated TBSV-T was mechanically transmissible to several tomato (Lycopersicon esculentum) cvs and to other species including Petunia hybrida, pepper (Capsicum annuum). eggplant (Solanum melongena), Nicotiana clevelandii, Chenopodium amaranticolor and C. quinoa in which it caused systemic symptoms. It caused no infection of globe artichoke (Cynara scolymus) or Pelargonium domesticum. The virus was not adsorbed to soil and could be isolated from leachate of soil in which systemically-infected tomato or C. quinoa plants were grown. Tomato plants became infected when grown in soil watered with virus suspensions. TBSV-T was infective after 10 min at 80°C but not at 90°C and when diluted to 10^-5 but not to 10^-6. Purified virus preparations contained C. 30 nm isometric particles. In gel-diffusion serological tests, TBSV-T reacted with homologous anti-serum and with antiserum to petunia asteroid mosaic virus but not to pelargonium leaf curl virus. Seed-borne infection (50–65%) of TBSV was demonstrated in plants grown from seed of symptomlessly-infected tomato fruit. TBSV was isolated from symptomlessly-infected tomato fruit imported from Morocco during October-April 1981. One of the isolates (TBSV-M) was indistinguishable from TBSV-T in host range, symptomatology and serological reactions. TBSV was also found in tomato plants growing extraneously in primary settlement beds at sewage works; such plants having been derived from undigested seeds in sewage. Because of its ‘alimentary-resistance’ in man, it is possible that one ecological route whereby TBSV enters rivers is by man's consumption of TBSV-infected tomatoes and eventual sewage dispersal into rivers.     

Ultrastructure of Tricornia muhezae N. G., N. Sp. (Microspora, Thelohaniidae), a Parasite of Mansonia africana (Diptera: Culicidae) from Tanzania

ABSTRACT. Collections of Mansonia africana mosquito larvae were made at one site in N.E. Tanzania in 1985 and 1987 and from two additional sites, both within about 2 mi of the original one in 1987. An octosporous microsporidian, present at all three sites, was found in both years infecting from 7 to 22% of larvae. Spores (stained in Giemsa) measured 3.0 μ m × 0.25 μ m × 2.25 μ m × 0.26 μ m. Ultrastructurally, spores were seen to have an anterior rim surrounding a depressed area where the endospore was at its thinnest. In transmission electron microscopy section, the rim appeared as two processes into which all layers of the wall extended. At the posterior end all layers of the wall extended into a simple knob-like structure which could be interpreted as a section through a crest running longitudinally around the spore. The polar filament was anisofilar, with two anterior coils of greater diameter than the three posterior coils. Although most closely resembling the genera Amblyspora and Parathelohania in the family Thelohaniidae, the species in M. africana differs from the former, which has oval spores, broadly rounded at the ends, and from the latter, which has a prominent, ridged posterior extension to the spores. The new species has been placed in a new genus and the name Tricornia muhezae proposed.     

The feeding and ranging behaviour of Galapagos giant tortoises (Geochehne elephantopus) The Cambridge and London University Galapagos Expeditions, 1972 and 1973

Field observations on the behaviour of adult Galapagos giant tortoises ( Geochehne elephantopus ) on the islands of Santa Cruz (Indefatigable) and Pinzon (Duncan) were made by the 1972 Expedition, and on Santa Cruz by the 1973 Expedition. The animals (in all 14 on Santa Cruz and three on Pinzon) were observed continuously throughout the day for periods of 3–14 days so that their main non-reproductive activities (feeding and walking) could be quantitatively recorded. The period of potential activity was between about 08.00 hrs and 16.00–18.00 hrs, but the pattern of behaviour was extremely variable, both in a given individual and between one individual and another; it seemed little influenced by the relatively slight fluctuations of temperature and climate which occurred during the period of study (July-September) on Santa Cruz. The tortoises on Pinzon, a much more arid island, were less active, and one showed a strongly bimodal activity pattern with a resting period during the middle of the day. The animals studied in 1972 showed a strong disposition to return after several days to the same sleeping place, but this homing tendency was not observed in 1973. This discrepancy can perhaps be attributed to the fact that the two expeditions worked in different areas under different weather conditions. Observations on the plants eaten, on the association between tortoises and certain birds, and on some other aspects of tortoise behaviour such as walking speed and responses to sounds are also described.     

Genus Pleistophora Gurley, 1893: An Assemblage of at Least Three Genera1

Until recently, pansporoblastic microsporidia that produce a variable and large number of sporoblasts from a sporont have been included in a single genus, namely Pleistophora Gurley, 1893. Ultrastructural studies have been used to determine whether the resemblance of these species is fundamental or superficial. The results indicated that the multisporous pansporoblastic forms belong to at least three genera and, thus, that Pleistophora is a “composite genus.” The term pansporoblast was originally used for stages in myxosporidian development. The term sporophorous vesicle adopted from Gurley is suggested for the spore-containing vesicle in the Microspora. Three species were studied: Pleistophora typicalis, the type-species; Pleistophora culicis, for which a new genus Vavraia has already been proposed; and Pleistophora simulii. P. typicalis and V. culicis have isolated nuclei throughout their development, and the sporophorous vesicle wall enveloping the sporoblasts is derived from amorphous secretions laid down during merogony external to the plasmalemma. Pleistophora and Vavraia are differentiated principally in terms of the structure of the sporophorous vesicle wall and mode of division of the sporogonial plasmodium. The nuclei of young sporonts of P. simulii are in diplokaryon arrangement and undergo meiosis to give haploid nuclei in the sporoblasts. The sporophorous vesicle wall is membranoid and is laid down external to the plasmalemma at the onset of sporogony. A new genus, Polydispyrenia n. g., is suggested for this species, the affinities of which are closer to the dimorphic species of microsporidia than to Pleistophora or Vavraia. The terms “merontogenetic sporophorous vesicle” and “sporontogenetic sporophorous vesicle” are used to distinguish between the two groups.     

Methane bubbles in surface peat cores: in situ measurements

The quantification of greenhouse gas sources and sinks is important to understanding the impact of climate change. Methane (CH₄) is a potent greenhouse gas, which, on a global scale, is released largely as a product of anaerobic microbial decomposition and predominantly from wetlands. A zone of intense CH₄ production just below the water table is thought to contribute significantly to the overall flux from peat bogs. We describe the use of membrane inlet quadrupole mass spectrometry (QMS) to confirm the existence of bubbles, their gaseous concentrations and their localization at a fine spatial resolution within intact peat cores. We use the distribution of the noble gas argon (Ar) and the distinct QMS responses to dissolved and gaseous (bubble) phases to identify trapped bubbles with a resolution of 0.6 mm. Bubbles with CH₄ concentrations of up to 20 kPa were widely distributed in the upper 300 mm of the cores with ～11% of all profiles comprising bubbles. The dissolved concentrations responsible for the bubbles were on average 83±80 μm , indicating lower concentrations relative to other QMS studies. We suggest that if the distinction between dissolved and gaseous phases is not made in studies of CH₄ within peat profiles then the prominence of bubbles is likely to result in overestimates of dissolved CH₄ concentrations. Fluxes of CH₄ from peat as a result of drawdown or other perturbation are likely to be large, rapid and short lived because of bubble burst, and also larger than from peat without bubbles. We suggest that the dynamics of fluxes need to be modelled taking into account both gaseous and dissolved phases. Estimates of potential fluxes that assume CH₄ is dissolved are likely to overestimate fluxes if the gaseous phase has not been taken into account.