Sieve Element of Impatiens Sultanii: 2. Developmental Aspects

The sieve elements arise from vacuolate cells, and enlargementof one or more slime bodies increases the volume of cytoplasmrelative to that of the vacuole. The slime finally dispersesthroughout the region once occupied by the vacuole. A new term,mictoplasm, is proposed for the resulting mixture of non-membranouscytoplasmic material, including slime, with the contents ofthe vacuole. The nucleus disappears during development, butbefore losing its chromaticity, it apparently releases one ormore nucleoli into the cytoplasm. The extruded nucleoli areprominent during development but usually disappear with thetonoplast, nucleus, and dictyosomes as the cell matures. Atmaturity, small vesicles, plastids containing spherical starchgrains, and sparsely distributed mitochondria deficient in tubulesare attached to the plasmalemma. The sieve-plate connectingstrand develops in a pore site bearing a pair of callose plateletsand penetrated in the centre by a plasmodesms. The callose cylinderwhich surrounds the mature connecting strand is followed sothat the shape of a connecting strand in cross section is stellate.Mictoplasm and the plasmalemma are continuous from one cellto the next through the sieve-plate connecting strands.     

Phylogeny of Australasian agamid lizards based on nuclear and mitochondrial genes: implications for morphological evolution and biogeography

Recent mtDNA phylogenies of Australasian agamid lizards are highly incongruent with existing morphological views. To resolve this discrepancy we sequenced two nuclear gene regions, c- mos and brain-derived neurotrophic factor (BDNF). These were highly concordant with each other and the mtDNA phylogeny, but not the morphology. A combined molecular analysis reveals substantial hidden support (additional phylogenetic signal that emerges only when the data sets interact in a combined analysis). Bayesian posteriors, and a partitioned bootstrap procedure introduced here, indicate strong support for most nodes. The resultant tree implies extensive morphological homoplasy, with many genera emerging as non-monophyletic ( Amphibolurus , Rankinia , Ctenophorus , Physignathus , Diporiphora ). The water and forest dragons ( Physignathus and Hypsilurus ) form a paraphyletic basal assemblage to the more derived Australian forms such as Amphibolurus and Ctenophorus , which include almost all the xeric taxa. However, the thorny devil Moloch horridus is a basal lineage and not closely related to the other arid forms. Tree topology, inferred divergence dates, palaeogeographical and palaeoclimatic data are all consistent with Miocene immigration into Australia from the north by mesic forest ecomorphs, followed by initial diversification in mesic habitats before radiation into xeric habitats facilitated by increasing aridity.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 343–358.     

A molecular phylogenetic analysis of the bloodroot and kangaroo paw family, Haemodoraceae: taxonomic, biogeographic and conservation implications

A phylogenetic analysis of plastid DNA sequences from the trn L-F region corroborates the hypothesis that Haemodoraceae, a small monocotyledonous family centred in southwestern Australia, are monophyletic with relationships to Philydraceae, Pontederiaceae and Comme–linaceae. It also supports the long-standing recognition of two subfamilies. In Conostylidoideae Tribonanthes falls in an isolated position, thus supporting its segregation as a recently recognized monogeneric tribe. Tribal status for Phlebocarya is not supported as this taxon is unexpectedly placed in Conostylideae as sister to Conostylis–Blancoa. Macropidia falls as sister to Anigozanthos . The DNA tree permits continued recognition of Macropidia and Blancoa as distinct genera, contrary to a recent morphological cladistic analysis. Haemodoroideae fall into two clades: ( Dilatris(Lachnanthes+Haemodorum )) and ( Xiphidium(Schiekia+Wachendofia )). It is unlikely that Haemodoraceae are of Gondwanan origin, and the phylogenetic pattern indicates a largely relictual distribution with a recent radiation in Western Australia.     

Charles Darwin's correspondence with David Moore of Glasnevin on insectivorous plants and potatoes

Recently discovered correspondence between Charles Darwin and David Moore shows the latter's role in providing fresh material of importance to Darwin's studies on insectivorous plants. One letter relates to Moore's experimental work on potatoes. This research, probably concerned with resistance of selected varieties of potato to blight, is apparently not supported by Glasnevin Botanic Garden (Dublin) records or contemporary literature.     

Regeneration of Rapid Escape Reflex Pathways in Earthworms

SYNOPSIS. The medial and lateral giant nerve fibers in the earthworm,Eisenia foetida, regenerate cell-specific connections and recoverthrough-conduction capabilities in as little as 1–2 daysafter ventral nerve cord (VNC) transection Similar cell-specificreconnections between giant fibers occur approximately 4–10days after grafting together two posterior pieces of worms ortransplanting lengths of VNC from donor to recipient worms fromwhich a comparable length of VNC has been removed In the lattercase, touch-sensory and giant motor neurons within the transplantedVNC also regenerate, leading to restoration of escape reflexfunction in segments receiving the transplant Results from heterotopicallytransplanted VNC indicate that both central and peripheral regenerationis cell-specific, but specificity is sufficiently broad to includesegmentally homologous target cells from body regions otherthan those of the transplant origin E. foetida and related speciesmay be useful for studying the extent to which differentiatednervous systems, composed of serially homologous neuronal networks,can be remodelled by experimental manipulations such as graftsand transplants.     

Highly Purified Micro- and Macronuclei from Tetrahymena thermophila Isolated by Percoll Gradients1

ABSTRACT. A new procedure is described that utilizes Percoll gradients for purifying micronuclei (MIC) and macronuclei (MAC) from Tetrahymena thermophila. Separation of MIC from MAC during certrifugation in Percoll gradients occurs as a result of their difference in size rather than density. Three kinds of tests were used to evaluate the purity of the nuclei: visualization of the nuclei by light microscopy; examination of the nuclei by electron microscopy; and Southern blots of MIC and MAC DNA probed with the 5s rRNA genes or a fragment from the MAC extrachromosomal rDNA molecule. When examined under the light microscope, the isolated MIC and MAC have much lower nuclear cross contamination levels than previous methods have reported. MIC's contaminated with less than 1 MAC in 1000 MIC and MAC's contaminated with less than 1 MIC in 500 MAC can be routinely prepared. Quantitative analyses of electron micrographs gave higher estimates of cross contamination in our purified nuclei, which may, in part, be explained by the difficulty in identifying small MIC or MAC fragments. Southern blots of MIC and MAC DNA probed with 5s rDNA confirmed the level of MAC contamination in the MIC estimated by light microscopy during purification of the nuclei. The level of nucleolar contamination in the MIC was estimated at 10% by Southern blots of MIC and MAC DNA, derived from a heterokaryon with distinctive MIC and MAC Bam HI sites, using an rDNA probe.     

Phylogeography of Camassia quamash in western North America: postglacial colonization and transport by indigenous peoples

Recent human activities have spread numerous plant species across the globe, yet it is unclear to what degree historical human activities influenced plant dispersal. In western North America, Camassia quamash was one of the most important food plants for indigenous peoples, who transported its propagules either intentionally or accidentally. We investigated how human and natural dispersal might have contributed to the current pattern of spatial genetic structure in C. quamash by performing phylogeographical surveys at two geographical scales. We sequenced two noncoding regions of chloroplast deoxyribonucleic acid (DNA) in 226 individuals from 53 populations of C. quamash as well as 126 individuals from 21 populations of the non-food plant Zigadenus venenosus . Contrary to the expectation of anthropogenic transport, C. quamash populations did not exhibit weaker genetic structure than Z. venenosus populations. We also failed to find convincing evidence for signatures of transport. Instead, our data showed strong effects of past glaciation and geographical barriers of the mountains in the Cascade Range, Olympic Peninsula and Vancouver Island. West of the Cascades, the species appears to have largely migrated northward from a southern refugium after deglaciation, whereas few populations having a highly divergent haplotype might have survived in southwestern Washington. Our data suggest that despite substantial ethnobotanical evidence for anthropogenic transport, the current pattern of genetic structure of C. quamash does not show any detectable signatures of transport by indigenous peoples and is better understood as the result of natural dispersal processes.     

Evidence of a sex-linked diapause response in Papilio glaucus subspecies and their hybrids

ABSTRACT. Pupal diapause in the eastern tiger swallowtail. Papilio glaucus L., is obligatory or facultative depending on subspecies. The southern subspecies, P. g. glaucus has a facultative diapause, induced by a larval exposure to short photoperiods. In the northern subspecies. P.g. canadensis , diapause is obligatory, occurring in each generation. F*** hybrids inherit the diapause response of their father or respond differently from either parent. The incidence of diapause in hybrids was associated with sex, indicating that the diapause response may be determined by an X-linked gene.     

PREDATOR VIGILANCE AND GROUP SIZE IN MAMMALS AND BIRDS: A CRITICAL REVIEW OF THE EMPIRICAL EVIDENCE

One commonly cited benefit to animals that forage in groups is an increase in the probability of detecting a predator, and a decrease in the time spent in predator detection. A mathematical model (Pulliam 1973) predicts a negative relationship between group size and vigilance rates. Over fifty studies of birds and mammals report that the relationship at least partly explains why individuals forage in groups. This review evaluates the strength of these conclusions based on their evidence. Those variables that may confound the relationship between vigilance and group size are outlined, and their control is assessed for each study. The variables I consider to be important include the density and type of food; competition between individuals; the proximity to both a safe place and the observer; the presence of predators; the visibility within the habitat; the composition of the group; the ambient temperature and the time of day. Based on these assessments, most of the studies fail to adequately demonstrate an unambiguous relationship between vigilance behavior and group size. Nevertheless, many studies reveal interesting features of the relationship between vigilance and group size that should provide fruitful avenues for future research.