The effects of phylogenetic relatedness on invasion success and impact: deconstructing Darwin's naturalisation conundrum

Darwin's naturalisation conundrum describes the paradox that the relatedness of exotic species to native residents could either promote or hinder their success through opposing mechanisms: niche pre‐adaptation or competitive interactions. Previous studies focusing on single snapshots of invasion patterns have provided support to both sides of the conundrum. Here, by examining invasion dynamics of 480 plots over 40 years, we show that exotic species more closely related to native species were more likely to enter, establish and dominate the resident communities, and that native residents more closely related to these successful exotics were more likely to go locally extinct. Therefore, non‐random displacement of natives during invasion could weaken or even reverse the negative effects of exotic–native phylogenetic distances on invasion success. The scenario that exotics more closely related to native residents are more successful, but tend to eliminate their closely related natives, may help to reconcile the 150‐year‐old conundrum.     

The effect of oxygen on fatty acid composition of soil micromycetes

The aim of this work was to describe changes in fatty acid profiles of fungi growing under artificial conditions of oxygen depletion. In total, 133 fungal strains belonging to eight orders were isolated from cattle impacted soils and tested. The analysis of the ten most frequent fatty acids revealed significant shift in fatty acids composition as a result of decreasing oxygen level. Taxonomic- as well as aeration-dependent changes in the amounts of fungal biomarker fatty acids (18:1ω9 and 18:2ω6,9) were found. Therefore, the ratio of these two fatty acids could be considered as an indicator of anaerobic, microaerobic or aerobic conditions in soil. Moreover, fatty acid-based estimation of fungal biomass in soils should be performed as a sum of both biomarker fatty acids and with respect to the soil characteristics as well as to the composition of fungal community.     

Apparent competition: an impact of exotic shrub invasion on tree regeneration

Invasion of habitats by exotic shrubs is often associated with a decrease in the abundance of native species, particularly trees. This is typically interpreted as evidence for direct resource competition between the invader and native species. However, this may also reflect indirect impacts of the exotic shrubs through harboring high densities of seed predators––known as apparent competition. Here I present data from separate seed predation experiments conducted with two shrub species exotic to North America; Rosa multiflora, an invader of abandoned agricultural land, and Lonicera maackii, an invader of disturbed or secondary forest habitats. Both experiments showed significantly greater risks of seed predation for tree seeds located under shrub canopies when compared to open microhabitats within the same site. These results indicate the potential importance of indirect impacts of exotic species invasions on native biota in addition to the direct impacts that are typically the focus of research.     

Minimal YopB and YopD translocator secretion by Yersinia is sufficient for Yop-effector delivery into target cells

Pathogenic Yersinia sp. utilise a common type III secretion system to translocate several anti-host Yop effectors into the cytosol of target eukaryotic cells. The secreted YopB and YopD translocator proteins are essential for this process, forming pores in biological membranes through which the effectors are thought to gain access to the cell interior. The non-secreted cognate chaperone, LcrH, also plays an important role by ensuring pre-secretory stabilisation and efficient secretion of YopB and YopD. This suggests that LcrH-regulated secretion of the translocators could be used by Yersinia to control effector translocation levels. We collected several LcrH mutants impaired in chaperone activity. These poorly bound, stabilised and/or secreted YopB and YopD in vitro. However, these mutants generally maintained stable substrates during a HeLa cell infection and these infected cells were intoxicated by translocated effectors. Surprisingly, this occurred in the absence of detectable YopB- and YopD-dependent pores in eukaryotic membranes. A functional type III translocon must therefore only require minuscule amounts of secreted translocator proteins. Based on these observations, LcrH dependent control of translocation via regulated YopB and YopD secretion would need to be exquisitely tight.     

Apoptosis of Dedifferentiated Hepatoma Cells is Independent of NF-κB Activation in Response to LPS

Dedifferentiated hepatoma cells, in contrast to most other cell types including hepatoma cells, undergo apoptosis when treated with lipopolysaccharide (LPS) plus the protein synthesis inhibitor cycloheximide (CHx). We recently reported that the dedifferentiated hepatoma cells also exhibit a strong and prolonged NF-κB induction phenotype upon exposure to LPS, suggesting that NF-κB signaling may play a pro-survival role, as reported in several other cell systems. To test the role of NF-κB in preventing LPS-mediated apoptosis, we examined the dedifferentiated cell line M38. Results show that antioxidants strongly inhibited LPS + CHx-mediated cell death in the M38 cells, yet only modestly inhibited NF-κB induction. In addition, inhibition of NF-κB translocation by infection of the M38 cells with an adenoviral vector expressing an IκBα super-repressor did not result in LPS-mediated cell death. These results suggest that unlike TNFα induction, the cell survival pathway activated in response to LPS is independent of NF-κB translocation in the dedifferentiated cells. Addition of inhibitors of JNK, p38 and ERK pathways also failed to elicit LPS-mediated apoptosis similar to that observed when protein synthesis is prevented. Thus, cell survival pathways other than those involving NF-κB inducible gene expression or other well-known pathways appear to be involved in protecting the dedifferentiated hepatoma variant cells from LPS-mediated apoptosis. Importantly, this pro-apoptotic function of LPS appears to be a function of loss of hepatic gene expression, as the parental hepatoma cells resist LPS-mediated apoptosis in the presence of protein synthesis inhibitors.     

Lipid and reproductive cycles of bluegills (Lepomis macrochirus) exposed to 35 years of elevated environmental temperatures

1. We studied bluegills to compare how thermal perturbation affected lipid dynamics and reproductive cycles of fish from heated (Pond C) and normothermic (Par Pond) sites.

2. Bodies of bluegills contained over 90%, and gonads and livers 10% of the non-polar lipids.

3.Overall, the percent body lipids of bluegills from the heated pond was twice as high (12.4%) as that of Par Pond bluegills (6.6%).

4. During a prolonged reactor down period, when both ponds were normothermic, body lipids of bluegills from Pond C and Par Pond increased at a rate of approximately 3 and 1% of body mass per week, respectively.

5. Juveniles from Pond C had higher percent stored lipids than did adult males or females.

6. Lipid cycling in Par Pond bluegills was seasonal, whereas Pond C bluegill lipid cycles corresponded to long reactor down periods.     

A Structural Comparison of the Acidic Extracellular Polysaccharides from Rhizobium trifolii Mutants Affected in Root Hair Infection

The structures of the acidic extracellular polysaccharides (EPSs) from several R. trifolii mutants were compared by examining their compositions and their sugar linkages as determined by methylation analysis. These mutant strains were derived from the wild-type R. trifolii ANU843 and were unable to induce normal root hair curling (Hac- phenotype) or nodulation response (Nod- phenotype) in clover plants. These strains included several transposon Tn5-induced Nod-mutants, strain ANU871, which possesses a 40 to 50 kilobase deletion of the resident Sym plasmid, and strain ANU845 which is missing the Sym plasmid (pSym-). Strains ANU845(pSym-) containing either plasmid pRt150 or pBR1AN were also used. The recombinant plasmid pRt150 restores only root hair curling capacity to ANU845 while plasmid pBR1AN (an R. trifolii pSym) restores both root hair curling and nodulation capacity to this strain. Our composition and methylation results show that the EPSs from all these strains have the same glycosyl and pyruvyl linkages. Thus we suggest that neither the nod genes involved in root hair curling nor the entire pSym encodes for the arrangement of glycosyl or pyruvyl residues in these EPSs. Whether or not the nod genes dictate the location of acetyl or β-hydroxybutyrate substituent groups remains to be determined.     

Detection and identification of cyanogenic glucosides in six species of Acacia

The presence of prunasin in Acacia deanei ssp. paucijuga, sambunigrin in Acacia cunninghamii, and acacipetalin in Acacia giraffae has been established by both chromatographic and NMR spectral evidence. Mandelonitrile glucosides of unknown configuration in Acacia parramattensis and Acacia pulchella and (an) as yet unidentified glycoside(s) in Acacia farnesiana are also reported.     

Locomotory mechanisms in Antarctic pycnogonids

Patterns of walking, modes of joint movement, and individual limb diversity were analysed with the aid of ciné film of several living Antarctic pycnogonids, including the 8-legged Colossendeis australis, C. angusta, Pallenopsis patagonica , and Nymphon sp., the 10-legged Decolopoda australis , and the 12-legged Dodecolopoda mawsoni. Appendage musculature of several of these species and also of the 10-legged Pentapycnon charcoti and Pentanymphon antarcticurn was dissected. At least two distinct morphotypes were identified: a short-legged, crawling variety ( P. charcoti ); and the more typical long-legged, large bodied, walking forms. No gross differences in musculature of joints were noted in the species examined. All joints are, at least superficially, hinge joints. The coxa-body joint is largely immobile, the coxa 1-coxa 2 joint alone exhibits promotion-remotion and all other joints are flexion-extension joints. The 8-legged forms move in an imprecise manner, there being irregularity of leg raising and lowering and where legs touch down in relation to the body and to other legs. The 10- and 12-legged forms exhibit more precise patterns of metachronal leg movements. Although legs move in a basic promotion-remotion, extension-flexion mode, there is a certain degree of twisting of a leg as it is picked up, brought forward, and set down; models indicating how such joint movement occurs were constructed. The possibility that hydrostatic pressure is employed in extension is considered and is found to be remote. Lateral placement of legs, orientated in almost all directions in the horizontal plane of the trunk, achieves a versatility of movement similar to that in crabs. Comments on pycnogonid taxonomic affinities are offered.