The effect of selection for desiccation resistance on cold tolerance of Drosophila melanogaster

Abstract.  Low temperature and desiccation stress are thought to be mechanistically similar in insects, and several studies indicate that there is a degree of cross-tolerance between them, such that increased cold tolerance results in greater desiccation tolerance and vice versa . This assertion is tested at an evolutionary scale by examining basal cold tolerance, rapid cold-hardening (RCH) and chill coma recovery in replicate populations of Drosophila melanogaster selected for desiccation resistance (with controls for both selection and concomitant starvation) for over 50 generations. All of the populations display a RCH response, and there is no effect of selection regime on RCH or basal cold tolerance, although there are differences in basal cold tolerance between sampling dates, apparently related to inter-individual variation in development time. Flies selected for desiccation tolerance recover from chill coma slightly, but significantly, faster than control and starvation-control flies. These findings provide little support for cross-tolerance between survival of near-lethal cold and desiccation stress in D. melanogaster .     

Glycolate Metabolism in Thallassiosira pseudonana

The kinetics and nature of glycolate uptake by the marine diatomThallassiosira pseudoncma were examined both in the light anddark. After a 2 h incubation with [1-₁₄C]lglycolate in the light,the major part of the radioactive label taken up was locatedin the protein fraction of the cells. The metabolic inhibitorsisonicotinic acid hydrazide (INH) and a-hydroxypyridyl methanesulphonate(-HPMS) reduced the total assimilation of 14C from [1-₁₄C]glycolateand reduced the percentage of radioactivity found in the proteinfraction. Short-term kinetic experiments showed that [1-₁₄C]lglycolatewas accumulated in the cells unchanged and after 30 s the glycolatepathway intermediates glycine and serine became labelled. After4 min serine was the dominant compound labelled, with smallquantities of labelled glycine also present. The enzyme glycolate:DCPIP oxidoreductase was shown to be present in high enoughconcentrations to account for the observed glycolate assimilation.These results substantiate the existence of the glycolic acidpathway in Th. pseudonana.     

The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology

The cranial osteology of the aquatic reptile Mesosaurus tenuidens is redescribed on the basis of new and previously examined materials from the Lower Permian of both southern Africa and South America. Mesosaurus is distinguished from other mesosaurs in exhibiting an absolutely larger skull and possessing relatively longer marginal teeth. The teeth gradually angle outwards as one progresses anteriorly in the tooth row and become conspicuously procumbent at the tip of the snout. The suggestion that mesosaurs used their conspicuous dental apparatus as a straining device for filter feeding is based upon erroneous reconstruction of a high number of teeth in this mesosaur. Reinterpretation of the morphology and the organization of the marginal teeth of Mesosaurus suggests that they were used to capture individually small, nektonic prey. General morphological aspects of the skull support the idea that Mesosaurus was an aquatic predator and that the skull was well adapted for feeding in an aqueous environment. The anatomical review permits critical reappraisal of several cranial characters that have appeared in recent phylogenetic analyses of early amniotes. Emendation of problematic characters and reanalysis of amniote phylogeny using a slightly modified data matrix from the literature strengthens the hypothesis that mesosaurs form a clade with millerettids, procolophonoids and pareiasaurs within Reptilia.  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 345–368.     

DNA Biosynthesis in Chloroplasts: II. DEVELOPMENTAL VARIATION IN TTP INCORPORATION INTO DNA BY PLASTID EXTRACTS

Incorporation of [³H]TTP into DNA by pea chloroplast extractswas highly dependent on the age of the tissue from which plastidswere prepared. Catalytic activity was greatest in samples from6- to 9-d-old plants; preparations from more mature tissueswere much less effective. Moreover, activity was 3 to 10 timesgreater in younger tissues regardless of whether chlorophyll,protein or plastid number was used as the index of comparison.Enzymes from the first (oldest), second, third, and fourth (youngest)leaves of the same plants were also studied. Again, activitywas 4 to 10 times greater in samples from the youngest tissues.When plastid extracts from older leaves were mixed with thosefrom younger tissues, they did not reduce synthesis. Thus, thedecline in activity does not appear to be due to the productionof an inhibitor during plant development. One explanation forthese data is that enzymes of ctDNA replication, such as DNApolymerase, vary in activity during leaf development; thereforechanges in enzyme levels may be an important factor in controllingchloroplast DNA replication during development. We have alsoexamined the incorporation of [³H]TTP into DNA by isolated intactpea chloroplasts; in general, labelled TTP was less readilyincorporated into chloroplast DNA than was [³H]thymidine. Key words: Chloroplast DNA replication, chloroplast DNA polymerase     

Synergistic effects of climate change and local stressors: CO2 and nutrient-driven change in subtidal rocky habitats

Climate-driven change represents the cumulative effect of global through local-scale conditions, and understanding their manifestation at local scales can empower local management. Change in the dominance of habitats is often the product of local nutrient pollution that occurs at relatively local scales (i.e. catchment scale), a critical scale of management at which global impacts will manifest. We tested whether forecasted global-scale change [elevated carbon dioxide (CO₂) and subsequent ocean acidification] and local stressors (elevated nutrients) can combine to accelerate the expansion of filamentous turfs at the expense of calcifying algae (kelp understorey). Our results not only support this model of future change, but also highlight the synergistic effects of future CO₂ and nutrient concentrations on the abundance of turfs. These results suggest that global and local stressors need to be assessed in meaningful combinations so that the anticipated effects of climate change do not create the false impression that, however complex, climate change will produce smaller effects than reality. These findings empower local managers because they show that policies of reducing local stressors (e.g. nutrient pollution) can reduce the effects of global stressors not under their governance (e.g. ocean acidification). The connection between research and government policy provides an example whereby knowledge (and decision making) across local through global scales provides solutions to some of the most vexing challenges for attaining social goals of sustainability, biological conservation and economic development.     

Microclimatic factors associated with elevational changes in army ant density in tropical montane forest

Abstract.  1. The density (rate of encountering foraging raids) and species richness of army ants (Formicidae: Ecitoninae, and behaviourally convergent Ponerinae) was measured in montane tropical forest. Above-ground and subterranean army ant raids were sampled using standard protocols at four sites across an elevational gradient (1200–1650 m above mean sea level) in and near cloud forest in the area of Monteverde, Costa Rica.
2. Mean ambient temperature differed among sites, and decreased with elevation. For the above-ground foraging army ant species, raid rates also declined with elevation. Surface army ant raid rates, however, were not affected by day to day weather variation within sites (temperature, cloud cover, or precipitation).
3. For the underground foraging army ant species, raid rates did not vary directionally with elevation, and subterranean raid rates were not affected by day to day weather variation within sites.
4. Army ant species richness was not directionally related to elevation, and species sharing among sites was generally high.
5. Army ant community structure changes with elevation in Neotropical montane forest, and the results suggest that the strongest effects are of temperature regimes on the density of raids. These findings provide a baseline against which to detect changes in army ant communities that may accompany directional climate change in tropical cloud forests.     

Prey protein influences growth and decoration building in the orb web spider Argiope keyserlingi

Abstract. 1. Protein is important for a foraging animal to consume, as it promotes growth and enhances survival, particularly in web‐building spiders, which need to invest considerable protein into web building and may trade‐off growth for web investment. 2. The influence of dietary protein uptake on growth and web investment was tested in the orb web spider Argiope keyserlingi, by feeding them flies reared on three different media: (1) high protein, (2) low protein, and (3) standard (control) media. There was a negative correlation between protein and energy content of the flies across treatments; flies reared on the high protein media had the highest protein, but lowest energy, while flies reared on the low protein media had the lowest protein but highest energy. 3. It was found that silk investment and web architecture in A. keyserlingi was not affected by diet. Growth and decoration building were both enhanced when spiders were fed a high protein diet. 4. It was concluded that protein intake, rather than energy, influenced both growth and decoration building because: (1) protein intake enhances growth in other animals, (2) protein is essential for silk synthesis, especially aciniform silk, and (3) protein is a limiting factor actively sought by foraging animals in natural environments.     

Laboratory incubations reveal potential responses of soil nitrogen cycling to changes in soil C and N availability in Mojave Desert soils exposed to elevated atmospheric CO2

Elevated atmospheric carbon dioxide (CO₂) has the potential to alter soil carbon (C) and nitrogen (N) cycling in arid ecosystems through changes in net primary productivity. However, an associated feedback exists because any sustained increases in plant productivity will depend upon the continued availability of soil N. We took soils from under the canopies of major shrubs, grasses, and plant interspaces in a Mojave Desert ecosystem exposed to elevated atmospheric CO₂ and incubated them in the laboratory with amendments of labile C and N to determine if elevated CO₂ altered the mechanistic controls of soil C and N on microbial N cycling. Net ammonification increased under shrubs exposed to elevated CO₂, while net nitrification decreased. Elevated CO₂ treatments exhibited greater fluxes of N₂O–N under Lycium spp., but not other microsites. The proportion of microbial/extractable organic N increased under shrubs exposed to elevated CO₂. Heterotrophic N₂‐fixation and C mineralization increased with C addition, while denitrification enzyme activity and N₂O–N fluxes increased when C and N were added in combination. Laboratory results demonstrated the potential for elevated CO₂ to affect soil N cycling under shrubs and supports the hypothesis that energy limited microbes may increase net inorganic N cycling rates as the amount of soil‐available C increases under elevated CO₂. The effect of CO₂ enrichment on N‐cycling processes is mediated by its effect on the plants, particularly shrubs. The potential for elevated atmospheric CO₂ to lead to accumulation of NH₄⁺ under shrubs and the subsequent volatilization of NH₃ may result in greater losses of N from this system, leading to changes in the form and amount of plant‐available inorganic N. This introduces the potential for a negative feedback mechanism that could act to constrain the degree to which plants can increase productivity in the face of elevated atmospheric CO₂.     

Extreme,continuous variation in an island snail: local diversification and association of shell form with the current environment

On Rosemary Island, a small continental island (11 km²) in the Dampier Archipelago, Western Australia, snails of the genus Rhagada have extremely diverse morphologies. Their shells vary remarkably in size and shape, with the latter ranging from globose to keeled‐flat, spanning the range of variation in the entire genus. Based primarily on variation in shell morphology, five distinct species are currently recognized. However, a study of 103 populations has revealed continuity of shell form within a very closely‐related group. A phylogenetic analysis of specimens from Rosemary Island, and other islands in the Dampier Archipelago, indicates that much of the morphological variation has evolved on the island, from within a monophyletic group. Within the island, snails with distinct shell morphologies could not be distinguished based on variation in mitochondrial DNA or their reproductive anatomy. The shell variation is geographically structured over a very fine scale, with clines linking the extreme forms over distances less than 200 m. Although there is no evidence that the different forms have evolved in isolation or as a consequence of drift, there is a strong association between keeled‐flat shells and rocky habitats, suggesting that shell shape may be of adaptive significance. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 756–769.