Acclimation of leaf hydraulic conductance and stomatal conductance of Pinus taeda (loblolly pine) to long-term growth in elevated CO2 (free-air CO2 enrichment) and N-fertilization

We investigated how leaf hydraulic conductance (K_leaf) of loblolly pine trees is influenced by soil nitrogen amendment (N) in stands subjected to ambient or elevated CO₂ concentrations (CO₂^a and CO₂^e, respectively). We also examined how K_leaf varies with changes in reference leaf water potential (Ψ_leaf‐ref) and stomatal conductance (g_s‐ref) calculated at vapour pressure deficit, D of 1 kPa. We detected significant reductions in K_leaf caused by N and CO₂^e, but neither treatment affected pre‐dawn or midday Ψ_leaf. We also detected a significant CO₂^e‐induced reduction in g_s‐ref and Ψ_leaf‐ref. Among treatments, the sensitivity of K_leaf to Ψ_leaf was directly related to a reference K_leaf (K_leaf‐ref computed at Ψ_leaf‐ref). This liquid‐phase response was reflected in a similar gas‐phase response, with g_s sensitivity to D proportional to g_s‐ref. Because leaves represented a substantial component of the whole‐tree conductance, reduction in K_leaf under CO₂^e affected whole‐tree water use by inducing a decline in g_s‐ref. The consequences of the acclimation of leaves to the treatments were: (1) trees growing under CO₂^e controlled morning leaf water status less than CO₂^a trees resulting in a higher diurnal loss of K_leaf; (2) the effect of CO₂^e on g_s‐ref was manifested only during times of high soil moisture.     

Identification and functional characterization of effectors in expressed sequence tags from various life cycle stages of the potato cyst nematode Globodera pallida

In this article, we describe the analysis of over 9000 expressed sequence tags (ESTs) from cDNA libraries obtained from various life cycle stages of Globodera pallida . We have identified over 50 G. pallida effectors from this dataset using bioinformatics analysis, by screening clones in order to identify secreted proteins up-regulated after the onset of parasitism and using in situ hybridization to confirm the expression in pharyngeal gland cells. A substantial gene family encoding G. pallida SPRYSEC proteins has been identified. The expression of these genes is restricted to the dorsal pharyngeal gland cell. Different members of the SPRYSEC family of proteins from G. pallida show different subcellular localization patterns in plants, with some localized to the cytoplasm and others to the nucleus and nucleolus. Differences in subcellular localization may reflect diverse functional roles for each individual protein or, more likely, variety in the compartmentalization of plant proteins targeted by the nematode. Our data are therefore consistent with the suggestion that the SPRYSEC proteins suppress host defences, as suggested previously, and that they achieve this through interaction with a range of host targets.     

Population genetic analysis of a recent range expansion: mechanisms regulating the poleward range limit in the volcano barnacle Tetraclita rubescens

As range shifts coincident with climate change have become increasingly well documented, efforts to describe the causes of range boundaries have increased. Three mechanisms—genetic impoverishment, migration load, or a physical barrier to dispersal—are well described theoretically, but the data needed to distinguish among them have rarely been collected. We describe the distribution, abundance, genetic variation, and environment of Tetraclita rubescens, an intertidal barnacle that expanded its northern range limit by several hundreds of kilometres from San Francisco, CA, USA, since the 1970s. We compare geographic variation in abundance with abiotic and biotic patterns, including sea surface temperatures and the distributions of 387 co‐occurring species, and describe genetic variation in cytochrome c oxidase subunit I, mitochondrial noncoding region, and nine microsatellite loci from 27 locations between Bahia Magdalena (California Baja Sur, Mexico) and Cape Mendocino (CA, USA). We find very high gene flow, high genetic diversity, and a gradient in physical environmental variation coincident with the range limit. We infer that the primary cause of the northern range boundary in T. rubescens is migration load arising from flow of maladapted alleles into peripheral locations and that environmental change, which could have reduced selection against genotypes immigrating into the newly colonized portion of the range, is the most likely cause of the observed range expansion. Because environmental change could similarly affect all taxa in a region whose distributional limits are established by migration load, these mechanisms may be common causes of range boundaries and largely synchronous multi‐species range expansions.     

Fat frogs,mobile genes: unexpected phylogeographic patterns for the ornate chorus frog (Pseudacris ornata)

The southeastern coastal plain of the United States is a region marked by extraordinary phylogeographic congruence that is frequently attributed to the changing sea levels that occurred during the glacial‐interglacial cycles of the Pleistocene epoch. A phylogeographic break corresponding to the Apalachicola River has been suggested for many species studied to date that are endemic to this region. Here, we used this pattern of phylogeographic congruence to develop and test explicit hypotheses about the genetic structure in the ornate chorus frog (Pseudacris ornata). Using 1299 bp of mtDNA sequence and seven nuclear microsatellite markers in 13 natural populations of P. ornata, we found three clades corresponding to geographically distinct regions; one spans the Apalachicola River (Southern Clade), one encompasses Georgia and South Carolina (Central Clade) and a third comprises more northerly individuals (Northern Clade). However, it does not appear that typical phylogeographic barriers demarcate these clades. Instead, isolation by distance across the range of the entire species explained the pattern of genetic variation that we observed. We propose that P. ornata was historically widespread in the southeastern United States, and that a balance between genetic drift and migration was the root of the genetic divergence among populations. Additionally, we investigated fine‐scale patterns of genetic structure and found the spatial scale at which there was significant genetic structure varied among the regions studied. Furthermore, we discuss our results in light of other phylogeographic studies of southeastern coastal plain organisms and in relation to amphibian conservation and management.     

New microsatellite loci for the European bushcricket,Ephippiger ephippiger (Orthoptera: Tettigoniidae)

Ephippiger ephippiger is a model organism for studies of sexual selection and phylogeography but little is known about fine‐scale population structure. Available microsatellite loci have null allele problems so we used an enrichment technique to isolate 21 new microsatellite loci for E. ephippiger. We present primer pairs for 10 polymorphic loci (3–11 alleles per locus). Observed heterozygosities at polymorphic loci ranged from 0.118 to 0.787, but several were significantly lower than expected.     

Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil

Soil moisture affects microbial decay of SOM and rhizosphere respiration (RR) in temperate forest soils, but isolating the response of soil respiration (SR) to summer drought and subsequent wetting is difficult because moisture changes are often confounded with temperature variation. We distinguished between temperature and moisture effects by simulation of prolonged soil droughts in a mixed deciduous forest at the Harvard Forest, Massachusetts. Roofs constructed over triplicate 5 × 5 m² plots excluded throughfall water during the summers of 2001 (168 mm) and 2002 (344 mm), while adjacent control plots received ambient throughfall and the same natural temperature regime. In 2003, throughfall was not excluded to assess the response of SR under natural weather conditions after two prolonged summer droughts. Throughfall exclusion significantly decreased mean SR rate by 53 mg C m^?2 h^?1 over 84 days in 2001, and by 68 mg C m^?2 h^?1 over 126 days in 2002, representing 10–30% of annual SR in this forest and 35–75% of annual net ecosystem exchange (NEE) of C. The differences in SR were best explained by differences in gravimetric water content in the Oi horizon (r²=0.69) and the Oe/Oa horizon (r²=0.60). Volumetric water content of the A horizon was not significantly affected by throughfall exclusion. The radiocarbon signature of soil CO₂ efflux and of CO₂ respired during incubations of O horizon, A horizon and living roots allowed partitioning of SR into contributions from young C substrate (including RR) and from decomposition of older SOM. RR (root respiration and microbial respiration of young substrates in the rhizosphere) made up 43–71% of the total C respired in the control plots and 41–80% in the exclusion plots, and tended to increase with drought. An exception to this trend was an interesting increase in CO₂ efflux of radiocarbon‐rich substrates during a period of abundant growth of mushrooms. Our results suggest that prolonged summer droughts decrease primarily heterotrophic respiration in the O horizon, which could cause increases in the storage of soil organic carbon in this forest. However, the C stored during two summers of simulated drought was only partly released as increased respiration during the following summer of natural throughfall. We do not know if this soil C sink during drought is transient or long lasting. In any case, differential decomposition of the O horizon caused by interannual variation of precipitation probably contributes significantly to observed interannual variation of NEE in temperate forests.     

A comparative study of cannibalism and predation in seven species of flour beetle

Abstract 1. The present study quantified egg and pupal cannibalism, and interspecific predation on eggs and pupae, by larvae and adults of seven species of flour beetle (Tribolium spp.) under laboratory conditions: T. anaphe, T. brevicornis, T. castaneum, T. confusum, T. destructor, T. freemani, and T. madens. 2. Variation among species in cannibalism and predation propensities did not reflect taxonomic affinities within the genus, indicating that these behaviours were shaped by ecology at species level. 3. Within species, larvae and adults displayed different propensities for cannibalism and predation, leading to the conclusion that these behaviours evolve independently in the two life stages. 4. All species behaved as intraguild predators to some degree, especially in the adult stage. 5. Three general patterns of cannibalism and predation were described by principal component mapping and cluster analysis. 6. The first group comprised three cosmopolitan pest species that were more voracious as adults than as larvae: T. castaneum, T. confusum, and T. destructor. It is proposed that stored product environments select for high adult voracity because the costs associated with emigration from such rare, but resource‐rich, habitats intensifies interference competition among adults. 7. The second group consisted of species that inhabit natural environments and that were more voracious as larvae: T. anaphe, T. freemani, and T. madens. Habitats for these species are probably numerous, but generally poor in quality, a situation that intensifies larval competition, while favouring earlier adult emigration. 8. The largest species, T. brevicornis, demonstrated inconsistent voracity between life stages and was the only species with chemically defended pupae. 9. It is proposed that consumption of eggs provides primarily nutritional benefits, whereas consumption of pupae has a more important role in interference competition.     

Applying the results of ecological studies to land-use policies and practices

Summary

• 1. 

  Good progress has been made in bringing the importance of high-nature-conservation-value farming systems to the attention of a wider audience. However, simply having a broad appreciation of which farming systems are good for certain species or species assemblages is of little use without a detailed understanding of how each particular farming system functions and integrates with the species reliant upon that system as a whole.
• 2. 

  Many species have intimate and complex interactions with the annual farming cycle, and their presence on any one piece of farmland is determined not only by the farm management occurring at that time but also by the management practised over the previous weeks and months. Since their exact farm management requirements are not fully understood, it would currently be difficult (if not impossible) to put in place the exact set of conditions necessary to ensure the continued occurrence of many desired species.
• 3. 

  Consequently, a detailed understanding of the ecological relationships involved is essential before advice can be provided on how best to develop any individual farming system (and the associated policies) so that the ecological characteristics of the system of value to the wildlife assemblages are maintained.
• 4. 

  These issues are highlighted and illustrated with reference to the findings from research into the ecology and requirements of the chough Pyrrhocorax pyrrhocorax and the effects of farm management practices on ground beetles (Coleoptera: Carabidae) and leatherjackets (Diptera: Tipulidae), which together can form important prey items for birds associated with grassland habitats.

     

Effects of climate change on labile and structural carbon in Douglas-fir needles as estimated by δ13C and Carea measurements

Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO₂ but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of labile carbon between years for evergreen foliage. Here, we combined changes in foliar C_area (C concentration on an areal basis) as needles aged with changes in foliar isotopic composition (δ¹³C) caused by inputs of ¹³C‐depleted CO₂ to estimate labile and structural C in needles of different ages in a four‐year, closed‐chamber mesocosm experiment in which Douglas‐fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were exposed to elevated temperature (ambient + 3.5 °C) and CO₂ (ambient + 179 ppm). Declines in δ ¹³C of needle cohorts as they aged indicated incorporation of newly fixed labile or structural carbon. The δ ¹³C calculations showed that new C was 41 ± 2% and 28 ± 3% of total needle carbon in second‐ and third‐year needles, respectively, with higher proportions of new C in elevated than ambient CO₂ chambers (e.g. 42 ± 2% vs. 37 ± 6%, respectively, for second‐year needles). Relative to ambient CO₂, elevated CO₂ increased labile C in both first‐ and second‐year needles. Relative to ambient temperature, elevated temperature diminished labile C in second‐year needles but not in first‐year needles, perhaps because of differences in sink strength between the two needle age classes. We hypothesize that plant‐soil feedbacks on nitrogen supply contributed to higher photosynthetic rates under elevated temperatures that partly compensated for higher turnover rates of labile C. Strong positive correlations between labile C and sugar concentrations suggested that labile C was primarily determined by carbohydrates. Labile C was negatively correlated with concentrations of cellulose and protein. Elevated temperature increased foliar %C, possibly due to a shift of labile constituents from low %C carbohydrates to relatively high %C protein. Decreased sugar concentrations and increased nitrogen concentrations with elevated temperature were consistent with this explanation. Because foliar constituents that vary in isotopic signature also vary in concentrations with leaf age or environmental conditions, inferences of c_i/c_a values from δ ¹³C of bulk leaf tissue should be done cautiously. Tracing of ¹³C through foliar carbon pools may provide new insight into foliar C constituents and turnover.     

Environmental variation and behaviour: resource availability during ontogeny and feeding performance in salamander larvae (Ambystoma texanum)

1. The effects of resource availability during ontogeny on subsequent feeding performance were investigated in larvae of the small-mouthed salamander ( Ambystoma texanum ).
2. Salamander larvae were reared individually in either high or low prey density treatments for 7 weeks prior to intermediate prey density foraging trials. Larvae from the low prey density treatment were on average 35% smaller in body size than individuals from the high prey density treatment.
3. Resource availability during development influenced larval feeding rates and altered the relationship between body size and three feeding performance measures (attack rates, capture success and feeding rates). Feeding rates in predation trials were also positively correlated with growth rate early in the larval period (until the end of week 5).
4. These results suggest that the environment to which developing organisms are exposed can have significant effects on subsequent behaviour, and that small-mouthed salamander larvae may show state-dependent changes in feeding behaviour in response to differences in long-term feeding history. Additionally, differences in feeding performance may influence the probability of survival to the adult stage for organisms that utilize ephemeral habitats.