Morphogenetic Transitions and Cytoskeletal Elements of the Stalked Zooid and the Telotroch Stages in the Peritrich Ciliate Vorticella convallaria

ABSTRACT. A method is described for obtaining large numbers of telotrochs from mass cultures of Vorticella convallaria . These free-swimming cells contract slightly along the aboral-oral plane when extracted with Triton X-100, and thus appear more similar in shape to zooids than unextracted telotrochs. Cytoskeletal structures associated with feeding, such as the infudibulum and the cytopharynx, are visible in cytoskeletal preparations of these non-feeding telotrochs and thus appear not to be disassembled during telotroch formation. The telotroch to stalked-zooid transition proceeds rapidly through a set series of morphogenetic stages. After telotroch attachment, the aboral cilia cease beating and are resorbed. Within 7 min the cell is inverted bell-shaped and the zooid begins feeding. Stalk elongation begins about 15–20 min after attachment, lengthening at the rate of 0.5 μ/min for the first hour and more slowly (0.1 μm/min) after that. Interestingly, these developmental stages are essentially the same as those described for the telotroch to zooid transition in the colonial peritrich Zoothamnium . This evolutionary conservation suggests that the precise sequence and timing of these events are critical for their successful completion. Furthermore, the facts that the telotroch to zooid transition occurs very rapidly, that the feeding structures are maintained throughout the transformation, and that basic cytoskeletal architecture is relatively unchanged is consistent with the hypothesis that the transformation occurs through controlled cytoskeletal rearrangements rather than by changes in gene expression.     

Growth limitation of submerged aquatic macrophytes by inorganic carbon

1. This study determined the effects of CO₂ and HCO₃- enrichment on in situ growth of two submerged macrophytes, Elodea canadensis and Callitriche cophocarpa, in two Danish lakes: Lake Hampen and Lake Væng. Lake Hampen is an oligotrophic low-alkaline lake (0.4 meq ^?1) and Lake Væng is mesotrophic with an alkalinity of 1.1 meq 1-^?1. In Lake Hampen experiments were carried out throughout the growth season, whereas experiments in Lake Væng were restricted to late summer. The CO₂ and HCO₃-enrichment procedures used increased the concentration of free-CO₂ by 500–1000 μM and the concentration of HCO₃- by about 80 μM. 2. The concentration of free-CO₂ in Lake Hampen was about five times atmospheric equilibrium concentration (55 μM) in early summer declining to virtually zero at the end of summer. 3. Under ambient conditions Callitriche, which is restricted to CO₂ use, was unable to grow and survive in both lakes. In contrast, Elodea, which has the potential to use HCO₃- in photosynthesis, grew at rates varying from 0.046 to 0.080 day^?1 over the season. 4. Under CO₂ enrichment the growth rate of Callitriche varied from 0.089 to 0.124 day^?1 and for Elodea from 0.076 to 0.117 day^?1 over the season. Enrichment with HCO₃-affected Elodea only and only to a limited extent. This may be a result of insufficient increase in [HCO₃-] upon enrichment or to a limited capacity of the plants to take up HCO₃-. 5. The substantial stimulation of in situ growth of Elodea and Callitriche by enhanced concentrations of free-CO₂ shows that inorganic carbon is an important determinant of growth of submerged macrophytes and that inorganic carbon limitation of in situ growth may be a common phenomenon in nature, even in lakes with an alkalinity as high a 1 meq 1-^?1. Inorganic carbon, however, is only one of many parameters important for growth, and the growth rates of Elodea at both ambient and high free-CO₂ were closely coupled to day length and photon irradiance, indicating that light had an ultimate control on growth.     

Rhacophyton from the Upper Devonian of West Virginia

A new species of Rhacophyton, R. ceratangium , is described from Upper Devonian rocks of West Virginia, U.S.A.; this is synonymous with R. incertum (Dawson) Krausel and Weyland but reasons are cited to indicate that the latter species name is not appropriate.
The collections include: stems up to 2 cm in diameter bearing bipinnate, non-laminate vegetative fronds; abundant well preserved fertile fronds that show clearly the distinctive morphology of their sterile and fertile pinnae; fragments of axes with woody tissues petrified.
The sporangia are particularly distinctive with their long slender tip; they dehisced longitudinally and contained several hundred spores; all available evidence indicates that the plant was homosporous. All petrified axes have a slender bar-shaped strand of primary wood swollen at either end and surrounded by strongly developed secondary wood consisting of scalariform tracheids and rays.
R. ceratangium is closely related to the Belgian R. zygopteroides Leelercq. A comparison with other Devonian and Carboniferous pteridophytes suggests that Rhacophyton is probably a primitive member of the Progymnospermopsida or immediately ancestral to that group.     

Does reduction of the eggshell occur concurrently with or subsequent to the evolution of viviparity in phrynosomatid lizards?

Viviparity and placentation have evolved many times within squamate reptiles, but the sequence in which the attendant morphological modifications occur remains unclear. In particular, it is unknown whether a reduction of the egg shell occurs concurrently with longer periods of egg retention (i.e. increasingly advanced stages of embryogenesis at oviposition) or whether such thinning occurs after viviparity has evolved. To investigate this question, we evaluated the prediction that shell morphology and permeability vary systematically with the capacity to support embryonic development in utero (as judged by the maximum embryonic stage attainable in utero) in five species of oviparous sccloporine lizards and one lizard species in the sister genus Urosuarus. Despite major differences among species in the capacity to support embryogenesis, shell morphology (structure, thickness) and physiology (permeability to water vapour) did not vary as predicted. These results raise the intriguing possibility that other features associated with simple placentation (e.g. increased oviductal and chorioallantoic vascular density) evolve concurrently with longer periods of egg retention and viviparity and that shell thinning may occur subsequent to the evolution of viviparity, at least in sceloporine lizards.     

Revision of Trigonostomum Schmidt, 1852 (Platyhelminthes, Typhloplanoida, Trigonostomidae) with the description of seven new species

A morphological and taxonomic account of the genus Trigonostomum is provided. All known species are discussed and briefly re-described where necessary. Seven new species are described: T. franki from Curaçao, Florida (USA), the East African Coast and New Caledonia, T. nataschae from the French sub-Antarctic island Kerguelen, T. spinigerum from New Caledonia and T. watsoni from the Australian East Coast and New Caledonia. T. tori and T. galapagoensis , both formerly enclosed in T. setigerum , are considered new species, while T. australis also belongs to the same species group. Proxenetes denhartogi is transferred to Trigonostomum . Based on a comparison of old and new material, T. marki is synonymized with T. penicillatum , while T. prytherchi and T. divae are regarded as junior synonyms of T. lilliei ; T. intermedium and T. quadrifolium are considered synonyms of T. coronatum . Three species are considered species inquirendae : T. brunchorsti , T. piriforme and Marinellia lingulifera . Similarities and differences of the 17 valid species are discussed and summarized in an identification key.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 141 , 271–296.     

Chemosensory Behaviour of Strombidium purpureum, an Anaerobic Oligotrich with Endosymbiotic Purple Non-Sulphur Bacteria

ABSTRACT. Strombidium purpureum Kahl, is an anaerobic oligotrichous ciliate with endosymbiotic phototrophic bacteria. Like other anaerobic ciliates, S. purpureum reacts to O₂-pressure. In the light, the ciliates avoid even traces of O₂ (< 1% atmospheric saturation). In the dark, however, the ciliates accumulate in water with a pO₂ of 1–4% atmospheric saturation. Experiments show that ciliates which have accumulated in the dark under microaerophilic conditions react when the light is turned on, and their ability to escape is enhanced by steep O₂-gradients. The ciliates orient themselves in O₂-gradients by a series of phobic responses. They tumble whenever they swim towards a higher O₂-tension and thus they eventually all swim in the direction of lower pO₂. The ecological implications of such behaviour are discussed.     

Costly sexual harassment in a beetle

Abstract The optimal number of mating partners for females rarely coincides with that for males, leading to sexual conflict over mating frequency. In the bruchid beetle Callosobruchus maculatus, the fitness consequences to females of engaging in multiple copulations are complex, with studies demonstrating both costs and benefits to multiple mating. However, females kept continuously with males have a lower lifetime egg production compared with females mated only once and then isolated from males. This reduction in fitness may be a result of damage caused by male genitalia, which bear spines that puncture the female’s reproductive tract, and/or toxic elements in the ejaculate. However, male harassment rather than costs of matings themselves could also explain the results. In the present study, the fitness costs of male harassment for female C. maculatus are estimated. The natural refractory period of females immediately after their first mating is used to separate the cost of harassment from the cost of mating. Male harassment results in females laying fewer eggs and this results in a tendency to produce fewer offspring. The results are discussed in the context of mate choice and sexual selection.     

Why are birds' eggs colourful? Eggshell pigments co‐vary with life‐history and nesting ecology among British breeding non‐passerine birds

The colourful appearance of bird eggshells has long fascinated biologists and considerable research effort has focused on the structure and biochemistry of the avian eggshell matrix. The presence of tetrapyrrole pigments was identified nearly a century ago. Surprisingly, how the concentrations of avian eggshell pigments vary among related species, and whether this variability is associated with either eggshell appearance and/or species life‐history traits, remains poorly understood. We quantified the concentrations of the two key eggshell pigments, protoporphyrin IX and biliverdin, from a diverse sample of eggshells stored at the Natural History Museum, Tring, UK. We explicitly tested how these two pigments are associated with physical measures of eggshell coloration and whether the pigment concentrations and colour diversity co‐vary with phylogenetic affiliations among species. We also tested a series of comparative hypotheses regarding the association between the concentrations of the two pigments and specific life‐history and breeding ecology traits. Across species, the average concentrations of protoporphyrin and biliverdin were positively correlated, and both strongly co‐varied with phylogenetic relatedness. Controlling for phylogeny, protoporphyrin concentration was associated with a higher likelihood of cavity nesting and ground nesting, whereas biliverdin concentration was associated with a higher likelihood of non‐cavity nesting habit and bi‐parental provisioning. Although unlikely to be explained by a single function, the breeding ecology and life history‐dependence of eggshell pigment concentrations in these comparative analyses implies that related species share pigment strategies, and that those strategies relate to broad adaptive roles in the evolution of variation in avian eggshell coloration and its underlying mechanisms. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 657–672.     

The effect of long‐term repeated burning and fire exclusion on above‐ and below‐ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

We used a long‐term fire experiment in south‐east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soil‐stored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 1971–1972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil‐stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 3–7.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil‐stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.     

Is stomatal conductance optimized over both time and space in plant crowns? A field test in grapevine (Vitis vinifera)

Crown carbon gain is maximized for a given total water loss if stomatal conductance (g_s) varies such that the marginal carbon product of water (?A/?E) remains invariant both over time and among leaves in a plant crown, provided the curvature of assimilation rate (A) versus transpiration rate (E) is negative. We tested this prediction across distinct crown positions in situ for the first time by parameterizing a biophysical model across 14 positions in four grapevine crowns (Vitis vinifera), computing optimal patterns of g_s and E over a day and comparing these to the observed patterns. Observed water use was higher than optimal for leaves in the crown interior, but lower than optimal in most other positions. Crown carbon gain was 18% lower under measured g_s than under optimal g_s. Positive curvature occurred in 39.6% of cases due to low boundary layer conductance (g_bw), and optimal g_s was zero in 11% of cases because ?A/?E was below the target value at all g_s. Some conclusions changed if we assumed infinite g_bw, but optimal and measured E still diverged systematically in time and space. We conclude that the theory's spatial dimension and assumption of positive curvature require further experimental testing.