Rhabdotubus, a Middle Cambrian rhabdopleurid hemichordate

Rhabdotubus johanssoni n.gen., n.sp., is described from the early Middle Cambrian Eccaparadoxides pinus Zone of Närke, southern Sweden. The colonies encrusted shells of inarticulate brachiopods, and occasionally trilobites, on otherwise soft substrates. The tubarium consists of repent and erect tubes. The former branch irregularly and produce a thecorhiza-like structure; the latter are erect and mostly isolated, up to 10 mm in length and widening gradually to about 1 mm width. Both repent and erect tubes are composed of fusellar bands, mostly irregularly arranged. Branching of repent tubes takes place through resorption or perforation of fusellar tissue in the parent tube. Branching of erect tubes occurs sporadically. There is no thecal dimorphism. No sclerotized stolon is present. Rhabdotubus is interpreted as the earnest known rhabdopleurid (Class Pterobranchia, Phylum Hemichordata). In general habitus it is similar to sessile graptolites of the Order Tuboidea. These similarities may well have phylogenetic significance, but further knowledge of the Tuboidea and other sessile orders of the Graptolithina is required to clarify the early evolution of graptolites.     

Hormonal Modulation of the Oscillatory System Involved in Polar Transport of Auxin

The amount of natural auxin collected in agar as a result of basipetal efflux from the cambial region of successive short sections of pine stem varies so that a wave-like pattern is formed. The wave-length is several times longer than the cell length in the cambial region, suggesting the existence of a supracellular oscillatory system, which forms a morphogenic field in the stem tissues, The amplitude of the auxin wave is amplified by apical application of IAA to the longer stem sections, particularly at she time of spring initiation of cambial activity. The wave of auxin disappears after simultaneous apical application of IAA and ABA. The modulatory effects of IAA and ABA are translocated along the investigated stem sections faster than known transport velocities of IAA molecules. This fact is considered as evidence of apical control of the morphogenic field by way of influence upon a supracellular system of conjugated oscillators in the tissue.     

Palaeobiology of a Biradiolites mooretownensis rudist lithosome: seasonality,reproductive cyclicity and population dynamics

Hennhöfer, D., Götz, S. & Mitchell, S.F. 2012: Palaeobiology of a Biradiolites mooretownensis rudist lithosome: seasonality, reproductive cyclicity and population dynamics. Lethaia, Vol. 45, pp. 450–461. During the Cretaceous, rudist bivalves were among the most important benthic carbonate producers on tropical to sub‐tropical carbonate platforms. Yet questions concerning the biology of rudist bouquets remain unanswered to a great extent. In this study a monospecific bouquet of the small radiolitid rudist Biradiolites mooretownensis has been evaluated from a palaeobiological angle. Three‐dimensional, high‐resolution, quantitative analysis provides a detailed evaluation of growth and reproduction in an in situ rudist association. A total of 1237 consecutive tomograms with a vertical spacing of 0.1 mm were produced of which 1150 have been digitally measured for total area, number of specimens, packing density, spat density, recruitment, survival time, mortality and accommodation space. The results show constant coverage of about 60%, a stable packing density of 3.2 specimens per cm² and constant reproduction throughout the bouquet. Time series analysis (spectral analysis) using PAST statistical software shows cyclic spat density every 14.9 mm of vertical growth. Combined with the results of the δ¹⁸O isotope analysis (showing cyclicities of 14 mm) one reproduction cycle appears to be annual. 46.4% of all counted specimens died before 3 mm of vertical growth. More than 93% of the initial spat does not exceed 15 mm shell height or 1 year respectively. Two mortality peaks in the juvenile’s life at 4 and 10–15 mm shell height either represent important obstacles in the ontogenetic development of the species or reflect external influences. □ Biradiolites, grinding tomography, palaeobiology, population dynamics, reproduction, rudists, sclerochronology, seasonality.     

Climate niche shift in invasive species: the case of the brown anole

Anolis sagrei, a Cuba and Bahama native lizard, is a successful invader in Florida and adjacent areas. Herein, we focus on conservatism in its climate niche axes and possible congruencies with its natural history properties. The not mutually exclusive hypotheses of the present study explaining its northern range limit are: (1) climatic conditions within species' native and invasive ranges are identical; (2) the species is pre‐adapted to novel conditions as a result of historical climate variations; and (3) only some niche axes limit the species' invasive distribution and the observed pattern is explained by an interplay between the potential niche within its native range and life‐history. Species distribution models for native and invasive distributions were built on ten bioclimatic variables. Using Schoener's niche overlap index, the degree of niche conservatism among variables was identified. Significances of hypothesis (1) were tested using null‐model approaches. Possible climatic pre‐adaptations were evaluated by comparing its actual tolerance within its invasive range with that of the Last Glacial Maximum (LGM) within its native range (hypothesis 2). Results of (1) and (2) are discussed in relation to natural history, approaching hypothesis 3. We detect varying overlaps in niche axes, indicating that natural history properties are associated with conservative niche axes. Climatic comparisons with LGM of native and current conditions of invasive range suggest that pre‐adaptations are unlikely. Possible shifts in the fundamental niche of the species may have been facilitated by enhanced genetic diversity in northern invasive populations. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 943–954.     

Few parasites,and no evidence for Wolbachia infections,in a freshwater ostracod inhabiting temporary ponds

Biological systems with asexual reproduction have often attracted research on parasites and host immune defence, because parasites are expected to be better able to exploit genetically less diverse populations. In addition, maternally inherited parasitic microorganisms such as Wolbachia can directly alter the reproductive systems of their hosts and induce parthenogenesis. In the freshwater ostracod Eucypris virens, both sexual and asexual reproduction is known, and we speculated that parasite pressures might help to explain their co‐existence. This species complex inhabits shallow, often eutrophic temporary water bodies, conditions that should provide ample opportunities for parasite infections. We surveyed natural populations of E. virens throughout its Europe‐wide range for natural parasites, and particularly tested for the presence of intracellular Wolbachia bacteria. Surprisingly, the results indicate that very few E. virens populations support parasite infections. We also found no evidence for the presence of Wolbachia in the populations screened. The results therefore show that parasitic infections do not play a role in the maintenance of sex in this system. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 207–216.     

Static and dynamic bending has minor effects on xylem hydraulics of conifer branches (Picea abies,Pinus sylvestris)

The xylem hydraulic efficiency and safety is usually measured on mechanically unstressed samples, although trees may be exposed to combined hydraulic and mechanical stress in the field. We analysed changes in hydraulic conductivity and vulnerability to drought‐induced embolism during static bending of Picea abies and Pinus sylvestris branches as well as the effect of dynamic bending on the vulnerability. We hypothesized this mechanical stress to substantially impair xylem hydraulics. Intense static bending caused an only small decrease in hydraulic conductance (?19.5 ± 2.4% in P. abies) but no shift in vulnerability thresholds. Dynamic bending caused a 0.4 and 0.8 MPa decrease of the water potential at 50 and 88% loss of conductivity in P. sylvestris, but did not affect vulnerability thresholds in P. abies. With respect to applied extreme bending radii, effects on plant hydraulics were surprisingly small and are thus probably of minor eco‐physiological importance. More importantly, results indicate that available xylem hydraulic analyses (of conifers) sufficiently reflect plant hydraulics under field conditions.     

Ascorbate promotes emission of mercury vapour from plants

Mercury vapour (Hg°) emission from plants contributes to the atmospheric mercury cycle. Although a part of this Hg° emission originates from Hg(II) uptake by the roots, the question how terrestrial plants reduce Hg(II) has not been addressed so far. Young barley plants grown on a hydroponic cultivation containing Hg(II) increased the Hg° emission significantly. Homogenates of barley leaves added to dissolved Hg(II) induced a powerful volatilization at alkaline but not at acidic pH. The same pH dependence and emission kinetic together with the highest reduction capacity was observed for ascorbic acid as compared to other phytoreductants. The electrochemical potentials of the reactions involved suggest an electron transfer from NADPH via GSH and ascorbate to Hg(II). The results support the assumption of a novel mechanism how plants transfer reduction equivalents from the antioxidative defense system via ascorbate to reduce Hg(II) ions, thus counteracting mercury toxicity by volatilizing the metal. This effect appears to be assisted by other light-dependent processes such as transpiration and ascorbate synthesis.