Stereological Studies of the Effects of α-MSH and cAMP on Melanosomes in Melanoma Cells

The effects of α-MSH and cAMP on melanosomes in Cloudman S91 melanoma cells were investigated by modern stereological techniques. Cells were cultured for 4 days in medium containing α-MSH or cAMP harvested at 24 hour intervals; some were frozen for melanin assay and the reminder embedded in Epon for light and electron microscopy. Cellular and melanosomal parameters were estimated by new stereological probes. We found that both stimulators induced increases in nuclear volume, cell volume, and the volume fractions and volumes of premelanosomes (V_Vpm,cell’V_pm) and mature melanosomes (V_Vmm,cell’V_mm) and the number of mature melanosomes (N_mm). Both stimulators also caused declines in the volume of individual mature melanosomes (_Vimm) the melanin content per mature melanosome unit volume and the melanin content per individual mature melanosome. The increases in the volume of individual premelanosomes and the number of premelanosomes were only induced by cAME The effect cAMP on some parameters occurred 24 hours prior to α-MSH and was more marked. The response of premelanosomes to the stimulators was more sensitive than mature melanosomes. These results suggest that both stimulators enchanced melanogenesis by increasing the V_Vpm,cell’V_Vmm,cell’V_pm, V_mm and N_mm. The melanogenic level did not depend on the _Vimm and melanin concentration in melanosomes. The maturation of premelanosomes was involved in melanogenesis induced by both stimulators, but, de novo synthesis and enlargement of premelanosomes were only stimulated by cAME It imply that exogenous cAMP may affect melanosomes, and hence melanogenesis in quantitatively or qualitatively different ways to α-MSH.     

Direct Measurements of Turgor Pressure Potentials of Guard Cells: II. THE MECHANICAL ADVANTAGE OF SUBSIDIARY CELLS, THE SPANNUNQSPHASE, AND THE OPTIMUM LEAF WATER DEFICIT

Evidence of the mechanical advantage of subsidiary cells wasobtained by simultaneous measurements of turgor pressure potentialsin adjacent subsidiary and guard cells using injection circuitswith two separate needles. In Tradescantia virginiana the mechanicaladvantage approaches two. Using the same technique evidencewas obtained that the Spannungsphase is, in the first place,a turgor relations phenomenon due to the mechanical advantageof epidermal or subsidiary cells. In addition, the evidenceindicated that the elastic properties of guard cell walls mayundergo changes during the Spannungsphase when potassium iontransport commences. During these measurements it was confirmedthat the optimum leaf water deficit for maximum stomatal openingoccurs when the epidermal turgor is near zero. Under these conditionsthe width of the stomatal pore is a function of the turgor pressureof the guard cells, since at zero turgor of the subsidiary cellstheir mechanical advantage has disappeared.     

Ecological influences on larval chironomid communities in shallow lakes: implications for palaeolimnological interpretations

1. To correctly interpret chironomid faunas for palaeoenvironmental reconstruction, it is essential that we improve our understanding of the relative influence of ecosystem variables, biotic as well as physicochemical, on chironomid larvae. To address this, we analysed the surface sediments from 39 shallow lakes (29 Norfolk, U.K., 10 Denmark) for chironomid head capsules, and 70 chironomid taxa (including Chaoborus) were identified. 2. The shallow lakes were selected over large environmental gradients of aquatic macrophytes, total phosphorus (TP) and fish communities. Redundancy analysis (RDA) identified two significant variables that explained chironomid distribution: macrophyte species richness (P < 0.001) and TP (P < 0.005). Generalised linear models (GLM) identified specific taxa that had significant relationships with both these variables. Macrophyte percentage volume infested (PVI) and species richness were significant in classifying the lake types based on chironomid communities under twinspan analysis, although other factors, notably nutrient concentrations and fish communities, were also important, illustrating the complexities of classifying shallow lake ecosystems. Lakes with plant species richness >10 all had relatively diverse (Hill’s N2) chironomid assemblages, and lakes with Hill’s N2 >10 all had TP <250 μg L⁻¹ and total fish densities <2 fish per m². 3. Plant density (PVI), and perhaps more importantly species richness, were primary controls on the distribution of chironomid communities within these lakes. This clearly has implications for palaeoenvironmental reconstructions using zoobenthos remains (i.e. chironomids) and suggests that they could be used to track changes in benthic/pelagic production and could be used as indicators of changing macrophyte habitat. 4. Measuring key biological gradients, in addition to physicochemical gradients, allowed the major controls on chironomid distribution to be assessed more directly, in terms of plant substrate, food availability, competition and predation pressure, rather than implying indirect mechanisms through relationships with nutrients. Many of these variables, notably macrophyte abundance and species richness, are not routinely measured in such studies, despite their importance in determining zoobenthos in temperate shallow lakes. 5. When physical, chemical and ecological gradients are considered, as is often the case with palaeo‐reconstructions rather than training sets chosen to maximise one gradient, complex relationships exist, and attempting to reconstruct a single trophic variable quantitatively may not be appropriate or reliable.     

Climatic characteristics of heat waves and their simulation in plant experiments

Extreme events such as heat waves are emerging as a key facet of climate change, but to date, experiments on the impacts on plants are scarce. Experimental simulation of heat waves requires knowledge of regional heat wave characteristics, as plant responses depend heavily on meteorological conditions. We analysed nine Western European meteorological datasets, and found that heat waves occurring during the growing season in this region encompass more sunshine (+ 69%), lower precipitation (?78%) and a larger vapour pressure deficit (VPD) (+ 111%) compared with normal conditions. Possible consequences for plant responses are discussed, with emphasis on the likely seasonal variation of heat wave impacts. We explain why infrared heating (which typically increases VPD) is an appropriate technique for heat wave simulation. Finally, we advocate experiments to take into account the smaller nighttime compared with daytime temperature increases observed during heat waves, and the precipitation deficits before and during heat waves.     

The genetics of colour-patterns in the grasshopper Chorthippus brunneus

Several alleles were found to determine the colour of the dorsal pronotum in Chorthippus brunneus; there was evidence for at least two loci (C and V). Brown (C^B)was the universal recessive and green (C^C) was dominant to all other colours. The white allele (C^W)was codominant with green(C^G)and purple (C^P). Wing-patterns were determined by a separate, probably linked locus (W). A dominant plain wing-pattern (W^P) was associated with colours other than brown. Striped(W^S)and mottled(W^mo) were codominant and a plain recessive allele (W^P) was also found. All three alleles were associated with the brown phenotype. A purple-sided allele (S^Pu) was sometimes obmd with C^pu.. S^Pu was dominant to brown sides (S^B), A series of markings on the dorsal and lateral pronotum (linea intermedia, fascia postocularis, linea media, carina media and zona lateralis) were investigated and found to be controlled at separate loci which may be linked to W. These characters were expressed by dominant alleles. Epistatic effects by modifier loci were shown to have an important effect on the determination of wing phenotype. Allele Wo⁺, for example, suppressed the stripe-wing pattern, linea media, carina media and zona lateralis. It was concluded that colour patterns appear to be under genetic control and that dominant alleles were rare in the wild. Changes in shades of colours were shown to be age-dependent and minor.     

Theileria gilberti n. sp. (Apicomplexa: Theileriidae) in the Gilbert's Potoroo (Potorous gilbertii)

ABSTRACT. The morphology and genetic characterisation of a new species of piroplasm identified in the blood of the Gilbert's potoroo ( Potorous gilbertii ) from the Two Peoples Bay Nature Reserve near Albany, Western Australia, is described from blood and tissue samples from 16 Gilbert's potoroos. Microscopy of blood showed these parasites are highly pleomorphic with a mean length of 1.8 μm and mean width of 0.85 μm. Phylogenetic analysis of 18S rRNA sequence data identified the piroplasm as a new species of Theileria that is closely related to other Australian marsupial piroplasm species. Based on biological and molecular data, it is proposed that the parasite from Gilbert's potoroo be given the name Theileria gilberti n. sp.     

Reproductive ecology of the jacky dragon (Amphibolurus muricatus): an agamid lizard with temperature‐dependent sex determination

Abstract The jacky dragon, Amphibolurus muricatus (White, ex Shaw 1790) is a medium sized agamid lizard from the southeast of Australia. Laboratory incubation trials show that this species possesses temperature‐dependent sex determination. Both high and low incubation temperatures produced all female offspring, while varying proportions of males hatched at intermediate temperatures. Females may lay several clutches containing from three to nine eggs during the spring and summer. We report the first field nest temperature recordings for a squamate reptile with temperature‐dependent sex determination. Hatchling sex is determined by nest temperatures that are due to the combination of daily and seasonal weather conditions, together with maternal nest site selection. Over the prolonged egg‐laying season, mean nest temperatures steadily increase. This suggests that hatchling sex is best predicted by the date of egg laying, and that sex ratios from field nests will vary over the course of the breeding season. Lizards hatching from eggs laid in the spring (October) experience a longer growing season and should reach a larger body size by the beginning of their first reproductive season, compared to lizards from eggs laid in late summer (February). Adult male A. muricatus attain a greater maximum body size and have relatively larger heads than females, possibly as a consequence of sexual selection due to male‐male competition for territories and mates. If reproductive success in males increases with larger body size, then early hatching males may obtain a greater fitness benefit as adults, compared to males that hatch in late summer. We hypothesize that early season nests should produce male‐biased sex ratios, and that this provides an adaptive explanation for temperature‐dependent sex determination in A. muricatus.     

Cladistic analysis of the Cirripedia Thoracica

We present a cladistic analysis of the Cirripedia Thoracica using morphological characters and the Acrothoracica and Ascothoracida as outgroups. The list of characters comprised 32 shell and soft body features. The operational taxonomic units (OTUs) comprised 26 well-studied fossil and extant taxa, principally genera, since uncertainty about monophyly exists for most higher ranking taxonomic units. Parsimony analyses using PAUP 3.1.1 and Hennig86 produced 189 trees of assured minimal length. We also examined character evolution in the consensus trees using MacClade and Clados. The monophyly of the Balanomorpha and the Verrucomorpha sensu stricto is confirmed, and all trees featured a sister group relationship between the ‘living fossil Neoverruca and me Brachylepadomorpha. In the consensus trees the sequential progression of ‘pedunculate‘sister groups up to a node containing Neolepas also conforms to current views, but certain well-established taxa based solely on plesiomorphies stand out as paraphyletic, such as Pedunculata (= Lepadomorpha); Eolepadinae, Scalpellomorpha and Chthamaloidea. The 189 trees differed principally in the position of shell-less pedunculates, Neoverruca, the scalpelloid Capitulum, and the interrelationships within the Balanomorpha, although the 50% majority rule consensus tree almost fully resolved the latter. A monophyletic Sessilia comprising both Verrucomorpha and Balanomorpha appeared among the shortest trees, but not in the consensus. A tree with a monophyletic Verrucomorpha including Neoverruca had a tree length two steps longer than the consensus trees. Deletion of all extinct OTUs produced a radically different tree, which highlights the importance of fossils in estimating cirripede phylogeny. Mapping of our character set onto a manually constructed cladogram reflecting die most recent scenario of cirripede evolution resulted in a tree length five steps longer than any of our shortest trees. Our analysis reveals that several key questions in cirripede phylogeny remain unsolved, notably the position of shell-less forms and the transition from ‘pedunculate‘to ‘sessile‘barnacles. The inclusion of more fossil species at this point in our understanding of cirripede phylogeny will only result in even greater levels of uncertainty. When constructing the character list we also identified numerous uncertainties in the homology of traits commonly used in discussing cirripede evolution. Our study highlights larval ultrastructure, detailed studies of early ontogeny, and molecular data as the most promising areas for future research.     

Spatial and temporal response of stream bacteria to sources of dissolved organic carbon in a blackwater stream system

1. We hypothesized that changes in bacterial colony growth would be correlated to shifts in riparian vegetation (via leachate quality) along a river continuum of a south-eastern, blackwater stream (U.S.A.). Spatially, we expected bacterial assemblages from downstream reaches to utilize more sources of leachate and at higher concentrations than bacteria collected from headwater reaches. Temporally, we predicted higher colony growth on leachate from autumn-shed (senescent) leaves compared with leachate from fresh, green leaves.
2. We examined spatial differences in assemblage growth by culturing bacteria sampled along the stream continuum on gradient plates using leachates from four common riparian species ( Taxodium distichum , Carya spp., Acer rubrum and Decumaria barbara ). Bacteria from the lowest site were able to use all sources provided and at all concentrations, whereas bacteria from upper reaches could not. Colony density was correlated to relative leachate concentration at all sites along the continuum.
3. Leachates from fresh and senescent A. rubrum leaves were used to determine temporal differences. Winter assemblages of bacteria could not grow on fresh leaf leachate at any concentration but grew well on autumn leaf leachate at higher concentrations. Differential response of bacterial assemblages indicated local adaptation to potential sources of dissolved organic matter.
4. Growth response of stream bacterial colonies appeared to be dependent on the timing and source of leachate as well as on sources of dissolved organic carbon from further upstream. Growth of bacterial assemblages exhibited 'generalist' characteristics in headwater reaches and 'specialist' characteristics at the mouth of our study stream drainage. Thus, our findings lend support to the argument that variable resource habitats favour a small, generalist assemblage, while environments with stable resource supplies allow for highly diverse assemblages dominated by specialists.