PHYLOGENY OF THE CONJUGATING GREEN ALGAE (ZYGNEMOPHYCEAE) BASED ON rbc L SEQUENCES

Sequences of the gene encoding the large subunit of RUBISCO (rbcL) for 30 genera in the six currently recognized families of conjugating green algae (Desmidiaceae, Gonatozygaceae, Mesotaeniaceae, Peniaceae, and Zygnemataceae) were analyzed using maximum parsimony and maximum likelihood; bootstrap replications were performed as a measure of support for clades. Other Charophyceae sensu Mattox and Stewart and representative land plants were used as outgroups. All analyses supported the monophyly of the conjugating green algae. The Desmidiales, or placoderm desmids, constitute a monophyletic group, with moderate to strong support for the four component families of this assemblage (Closteriaceae, Desmidiaceae, Gonatozygaceae, and Peniaceae). The analyses showed that the two families of Zygnematales (Mesotaeniaceae, Zygnemataceae), which have plesiomorphic, unornamented and unsegmented cell walls, are not monophyletic. However, combined taxa of these two traditional families may constitute a monophyletic group. Partitioning the data by codon position revealed no significant differences across all positions or between partitions of positions one and two versus position three. The trees resulting from parsimony analyses using first plus second positions versus third position differed only in topology of branches with poor bootstrap support. The tree derived from third positions only was more resolved than the tree derived from first and second positions. The rbcL‐based phylogeny is largely congruent with published analyses of small subunit rDNA sequences for the Zygnematales. The molecular data do not support hypotheses of monophyly for groups of extant unicellular and filamentous or colonial desmid genera exhibiting a common cell shape. A trend is evident from simple omniradiate cell shapes to taxa with lobed cell and plastid shapes, which supports the hypothesis that chloroplast shape evolved generally from simple to complex. The data imply that multicellular placoderm desmids are monophyletic. Several anomalous placements of genera were found, including the saccoderm desmid Roya in the Gonatozygaceae and the zygnematacean Entransia in the Coleochaetales. The former is strongly supported, although the latter is not, and Entransia's phylogenetic position warrants further study.     

Low incidence of extra-pair paternity in the colonially nesting common swift Apus apus

The frequency of extra-pair paternity in a wild colony of swifts Apus apus was determined by multilocus DNA fingerprinting in two successive breeding seasons. The data were used to examine the expectation that extra-pair paternity is frequent in colonial-nesting species, either for proximal reasons such as the increased opportunity for extra-pair matings, or because extra-pair matings are important in the evolution and maintenance of coloniality. Forty-two broods containing 88 chicks were analysed. The genetic analysis revealed four cases of extra-pair paternity (4.5% of chicks) from four (9.5%) nests. Rapid mate-switching was considered unlikely to be the cause of extra-pair paternity since three of the cases were in the nests of previously established breeding pairs. Extra-pair copulations were not observed, but were assumed to be the cause of extra-pair paternity. The data show that high levels of extra-pair paternity are not an inevitable feature of high-density nesting.     

Seasonal diapause development and diapause termination in the European skipper, Thymelicus lineola (Ochs.)

Eggs of the European skipper, Thymelicus lineola, containing pharate first-instar larvae were brought into the laboratory at the beginning of each month from September to May and maintained at 20°C, 14L:10D. No emergence was observed within 40 days of collection before December. From that time on, while total emergence was similar, the duration of the emergence period decreased over the season from > 120 days in December to < 14 days in May. There was however no marked change in the seasonal supercooling point values of diapausing larvae.The rate of emergence from eggs collected in March was influenced by photoperiod, being slower under short-day conditions. However for any given photoperiod tested, the rate of emergence increased with an increase in temperature. The possible adaptive significance of a two-phase diapause, where diapause termination is photoperiodically controlled in species that overwinter as an egg or as a pharate first-instar larva within the egg chorion in exposed habitats, is discussed.     

The positive correlation between avian species richness and human population density in Britain is not attributable to sampling bias

Aim  To assess whether spatial variation in sampling effort drives positive correlations between human population density and species richness.
Location  British 10 × 10 km squares.
Methods  We calculated three measures of species richness from atlas data of breeding birds in Britain: total species richness, species richness standardised for sampling effort, and the number of species only recorded in supplementary casual records in a manner not standardised for survey effort. We then assessed the form of the relationship between these richness estimates and human population density, both with and without taking spatial autocorrelation into account.
Results  Both total and standardised species richness exhibit similar species richness–human population density relationships; species richness generally increases with human population density, but decreases at the very highest densities. Supplementary species richness is very weakly correlated with human population density.
Main conclusions  In this example, sampling effort only slightly influences the form of species richness–human population density relationships. The positive correlation between species richness and human population density and any resultant conservation conflicts are thus not artefactual patterns generated by confounding human density and sampling effort.     

ACTIN AND MYOSIN REGULATE PSEUDOPODIA OF PORPHYRA PULCHELLA (RHODOPHYTA) ARCHEOSPORES1

Archeospores of Porphyra pulchella Ackland, J. A. West et Zuccarello (Rhodophyta) display amoeboid and gliding motility. Time‐lapse videomicroscopy revealed that amoeboid cells extend and retract pseudopodia as they translocate through the media. We investigated the involvement of actin and myosin in generating the force for amoeboid motility using immunofluorescence, time‐lapse videomicroscopy, and cytoskeletal inhibitors. Actin filaments were seen as short and long rodlike bundles around the periphery of spores. The actin inhibitors cytochalasin D (CD) and latrunculin B (Lat B), and the myosin inhibitor butanedione monoxime (BDM) disrupted the actin filament network and reversibly inhibited pseudopodial activity, resulting in the rounding and immobilization of spores. It was uncertain whether forward translocation of archeospores resumed following drug removal. These results demonstrate that actin and myosin have a role in generating force for pseudopodial activity. This is the first report of cytoskeletal involvement in red algal cell movement. The involvement of actin and myosin in forward translocation of amoeboid archeospores can only be speculated upon.     

Song is a reliable signal of bill morphology in Darwin's small tree finch Camarhynchus parvulus, and vocal performance predicts male pairing success

The shape and movement of the vocal tract are known to influence bird song. Current theory predicts that large bill and body size are correlated with low frequency song and slow trill rate. It is also widely accepted that song characteristics are important for mate choice by females. We investigated the relationship between bill morphology, song characteristics, and pairing success in Darwin's small tree finch Camarhynchus parvulus , on the Galapagos Islands. Contrary to predictions from a previous cross-species study on Darwin's finches, we found that individuals with larger bill size produced songs with slow trill rate, high dominant frequency, and broad frequency bandwidth, indicating that song is a reliable signal of bill morphology. Vocal performance as indicated by the deviation from an upper performance limit was higher in paired than unpaired males. Pairing was not skewed in favour of a particular bill size, and both small and large billed males that sang high performance song had high pairing success. The reliable signalling function of song has implications for female choice and territorial defence, given that both females and conspecific competitors can assess the relative size of males' bills through song, while females may use vocal performance as a signal of male quality.     

LIPID COMPOSITION OF CHLORARACHNIOPHYTES (CHLORARACHNIOPHYCEAE) FROM THE GENERA BIGELOWIELLA,GYMNOCHLORA, AND LOTHARELLA1

The Chlorarachniophyceae are unicellular eukaryotic algae characterized by an amoeboid morphology that may be the result of secondary endosymbiosis of a green alga by a nonphotosynthetic amoeba or amoeboflagellate. Whereas much is known about the phylogeny of chlorarachniophytes, little is known about their physiology, particularly that of their lipids. In an initial effort to characterize the lipids of this algal class, four organisms from three genera were examined for their fatty acid and sterol composition. Fatty acids from lipid fractions containing chloroplast‐associated glycolipids, storage triglycerides, and cytoplasmic membrane‐associated polar lipids were characterized. Glycolipid‐associated fatty acids were of limited composition, principally eicosapentaenoic acid [20:5(n‐3)] and hexadecanoic acid (16:0). Triglyceride‐associated fatty acids, although minor, were found to be similar in composition. The polar lipid fraction was dominated by lipids that did not contain phosphorus and had a more variable fatty acid composition with 16:0 and docosapentaenoic acid [22:5(n‐3)] dominant along with a number of minor C₁₈ and C₂₀ fatty acids. Crinosterol and one of the epimeric pair poriferasterol/stigmasterol were the sole sterols. Several genes required for synthesis of these sterols were computationally identified in Bigelowiella natans Moestrup. One sterol biosynthesis gene showed the greatest similarity to SMT1 of the green alga, Chlamydomonas reinhardtii. However, homologues to other species, mostly green plant species, were also found. Further, the method used for identification suggested that the sequences were transferred to a genetic compartment other than the likely original location, the nucleomorph nucleus.     

CELL DIVISION AND MORPHOGENESIS OF THE CENTRIC DIATOM CHAETOCEROS DECIPIENS (BACILLARIOPHYCEAE) II. ELECTRON MICROSCOPY AND A NEW PARADIGM FOR TIP GROWTH

Valve morphogenesis starts when the silica deposition vesicle (SDV) expands across a cleavage furrow covered by an unidentified layer, which may aid in its shaping. A labiate process (LP) is present only in the outer valve of terminal cells in the filament. Before these particular cells form setae, a layered "labiate process apparatus" (LPA) appears on the SDV in the exact center of the forming valve, near the microtubule center arising after cleavage. The LPA thereafter surmounts the lips of the LP as it forms. After the girdle bands separate slightly, two lateral protrusions develop in the corners of the cell. These nascent setae are lined internally by a cylindrical, fibrous band (sleeve), which assembles immediately ahead of the expanding edge of the SDV, very close to the plasmalemma. Then these protrusions, lined by the fibrous band, the SDV, and the forming silica wall, grow through two gaps in the girdle bands. The cytoplasm at the tip of the growing seta is naked. Immediately behind the tip, this fibrous band is adpressed to the plasmalemma and thereby apparently defines the diameter of the seta; it extends to internally ensheath the tipmost edge of the SDV for a short distance, like a tight-fitting inner sleeve. This structure is considered the major organelle involved in seta morphogenesis. Microtubules (MTs), while present, are variable in extent and disposition within the seta. Turgor pressure is considered irrelevant in driving seta growth. Instead, a new paradigm proposed for tip-growing cells generally, may apply to seta morphogenesis, as follows. If, as is suspected, the fibrous band contains actin, cycling of this actin (as in animal cells undergoing ruffling or filopodial extension) could drive seta extension via attachment of the band to the just-formed silica wall. The band is visualized as a molecular treadmill whose support base, the new wall, is being continually extended; extension is controlled and generated strictly at the tip.