Early Stages in the Differentiation of Gametocytes of Haemoproteus columbae Kruse*

SYNOPSIS The sexes of mature gametocytes of Haemoproteus columbae Kruse circulating in the blood of the domestic pigeon can be identified in the electron microscope by the same criteria that distinguish them in the light microscope. The microgametocyte has a large nucleus and pigment granules restricted to the 2 extremities of its halter-shaped cells. The macrogametocyte has dense granular cytoplasm with scattered pigment granules and a small central nucleus. The sex of young gametocytes cannot yet be recognized. When blood containing mature gametocytes is cooled outside the body of the host visible signs of gametogenesis appear within 30 seconds. The earliest signs are increasing electron lucidity of the cytoplasm and separation of the outer membrane from the body of the parasite. The membrane may form vesicles or whorls or lie free in the erythrocyte's cytoplasm. The middle membrane of the parasite becomes the plasma membrane. Axonemes and microtubules appear in the cytoplasm and nucleoplasm of the microgametocyte. The macrogametocyte lags slightly behind the microgametocyte in development. With the first signs of differentiation, the host cell cytoplasm begins to disappear. The fate of the outer membrane and the erythrocyte's cytoplasm suggests the release of a lytic substance by the parasite.     

Emergence and survival of herbaceous seedlings in temperate grassy woodlands: Recruitment limitations and regeneration niche

Abstract Field experiments examined herbaceous seedling emergence and survival in temperate grassy woodlands on the New England Tablelands of New South Wales. Effects of intensity of previous grazing, removal of ground cover by fire or clearing, burial of seeds, grazing and seed theft by ants on seedling emergence and survival were studied in two field experiments. Thirteen species with a range of traits were used in the experiments and their cumulative emergence was compared with laboratory germination studies. Field emergence correlated to laboratory germination but all species had lower emergence in the field. Little natural emergence of native species was observed in the field in unsown treatments. Short‐lived forbs had the highest emergence, followed by perennial grasses; rhizomatous graminoids and perennial forbs had the lowest emergence. Soil surface and cover treatments did not markedly enhance emergence suggesting that intertussock spaces were not prerequisites for forb emergence. No consistent pattern of enhanced emergence was found for any treatment combination across all species. Seedling survival varied among species, with perennial grasses and short‐lived forbs having the highest seedling mortality. Low mortality rates in the graminoids and rhizomatous forbs appeared partially to compensate for lower seedling emergence. All perennial grasses and some short‐lived forbs showed increased risk of mortality with grazing. Differences in emergence and survival of species were related to ground cover heterogeneity, soil surfaces and, to some extent, herbivory. The complexity of these patterns when superimposed on temporal variability suggests that no generalizations can be made about the regeneration niche of herbaceous species groups. Strong recruitment limitation and partitioning of resources in the regeneration niche may reduce competition among native species and explain the high species richness of the herbaceous layer in the temperate grassy communities of eastern Australia.     

Combined phylogenetic analysis of a new North American fossil species confirms widespread Eocene distribution for stem rollers (Aves,Coracii)

We report a nearly complete skeleton of a new species of stem roller (Aves, Coracii) from the early Eocene Green River Formation of North America. The new species is most closely related to two species‐depauperate lineages, Coraciidae (rollers) and Brachypteraciidae (ground rollers), that form a monophyletic crown clade (Coracioidea) with an exclusively Old World extant distribution. Phylogenetic analysis utilizing a matrix of 133 morphological characters and sequence data from three genes (RAG‐1, c‐myc, and ND2) identifies the new species as a stem member of the Coracii more closely related to the crown clade than the only previously identified New World taxon, Primobucco mcgrewi. The phylogenetic placement of the new species and Primobucco mcgrewiindicates a widespread northern hemisphere distribution in the Eocene with subsequent restriction to Africa, Madagascar, Australia, and temperate to tropical parts of Europe and Asia. It provides evidence of further ecological diversity in early stem Coracii and convergence on crown morphologies. The new species contributes to mounting evidence that extant distributions for major avian subclades may be of comparatively recent origin. Further late Palaeogene sampling is needed to elucidate potential drivers for shifting avian distributions and disappearance of Coracii from North America. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 157 , 586–611.     

The Fine Structure of Microgametogenesis in Haemoproteus columbae Kruse*

SYNOPSIS. The structural changes leading to the formation of motile microgametes from a single immobile intracellular gametocyte have been examiued in the electron microscope. After pigeon blood infected with Haemoproteus columbae was exposed to the air at room temperature for a few minutes axonemes appeared in the parasite's cytoplasm and the cytoplasm itself appeared less dense. The axonemes were connected with bundles of intranuclear microtubules that were perhaps spindle fibers. No conventional kinetosomes or centrioles have been observed. After the microgametocyte left the erythrocyte, it assumed the shape of a polarized slug or a dumb-bell. Half of the organism was surrounded by a single membrane and filled by part of the nucleus. The other half was surrounded by the remains of the multiple membranes of the gametocyte and contained pigment granules, mitochondria, axonemes and nuclear extensions. The axonemes and nuclear extensions were segregated at the periphery of the cell, exterior to the gametocyte's inner membrane, and were assembled in situ into microgametes. The mature microgamete appeared to peel off from the gametocyte, leaving a residual body.     

The Fine Structure of the Mature Gametes of Haemoproteus columbae Kruse*

SYNOPSIS. The filiform microgamete of Haemoproteus columbae consists of an elongate double-walled nucleus paralleled by 2 axonemes embedded in a homogeneous matrix. At one end of the gamete, the axonemes are sharply flexed back on themselves, but no conventional kinetosome has been recognized. No mitochondria have been seen. Single-walled vesicles occur in the matrix, and the entire gamete is surrounded by a single membrane. The large round macrogamete has a conspicuous central nucleus with its outer membrane drawn out into anastomosing evaginations which extend to the periphery of the cell. A moderately electron dense material fills the space between the 2 nuclear membranes and the lumina of the evaginations. Nucleolar material may occur in scattered masses within the nucleus. One or 2 axonemes appear to arise endogenously next to the nuclear membrane. The cytoplasm is filled with ribosomes and perhaps glycogen granules. Typical protozoan mitochondria and vesicles containing pigment retained from the erythrocytic stage are found in the peripheral cytoplasm. Accumulations of dense-walled vesicles occur in the cytoplasm in conjunction with evaginations of the nuclear membrane. Amid these vesicles triple-ringed discs resembling the cytostomes of merozoites are frequently seen. Several distinct layers of dense material surround the micro-gamete.     

Size, shape and the distribution of organic matter in the Recent Antarctic brachiopod Liothyrella uva

The living terebratulid articulate brachiopod Liothyrella uva (Jackson 1912) was sampled from a shallow water population at Signy Island, South Orkney Islands, Antarctica. Neither shell height nor shell breadth were directly proportional to length and as a result there was a change in shell shape with size (and hence age); this change was small but statistically significant. The proportion of the total organic matter found in the shell and internal (mantle) tissues also changed with size. In small (5–7 mm length) brachiopods 70–80% of the total organic matter was located within the shell; this fraction decreased with increasing size until above about 25 mm length the proportion of organic matter in the shell was constant at 30–45%. Variability in this measure was influenced by infection with endolithic red algae. Punctal density was independent of size with a mean value of 95.7 per mm² [SE (standard error) ± 2.2], which was greater than in populations sampled from higher latitudes. With increasing shell length there was a slight increase in the size of puncta close to the shell edge. In all morphometric measures the range of variation observed was similar to that described from populations of Liothyrella from other areas of the Southern Ocean.     

The metazoan food webs from six Bornean Nepenthes species

Abstract.

• 1 Two contrasting hypotheses concerning patterns in food web structure within pitchers of Nepenthes are tested using new information from six species of Nepenthes from Borneo.
• 2 In general, predictions that webs will be more complex, and the food chains they contain will be longer, the closer they are to the centre of Nepenthes species diversity, are supported.
• 3 For Nepenthes albomarginata, a widespread species with a distinctive north Bornean form, a contrasting pattern is evident explicable in terms of the morphology of the pitchers and local habitat preferences.
• 4 General explanations for food web patterns will always be susceptible to exception, reflecting nuances of natural history.