Fungal chemical defence alters density‐dependent foraging behaviour and success in a fungivorous soil arthropod

1. Aggregative behaviour in fungivorous soil arthropods is widespread; its adaptive value, however, is largely unknown. In this study, the spatial foraging behaviour of a collembolan, Folsomia candida, and the fitness consequences of feeding at different densities on the filamentous fungus Aspergillus nidulans were investigated. The effect of two fungal strains were compared; a wild‐type (wt) and a transgenic strain that lacks the ability to express the global secondary metabolite regulator LaeA (ΔlaeA). 2. In laboratory foraging tests, F. candida exhibited aggregated distributions of individuals across four distinct fungal colonies that were arranged in short distances from each other. By quantifying the extent of the feeding damage at each single colony, a more evenly distributed feeding activity was found among wt colonies than among chemical‐deficient colonies. 3. In a fitness experiment, where collembolans at different densities were restricted to feed on single A. nidulans colonies, mean growth rate of F. candida was positively related to density on the wt A. nidulans strain, but negatively related to density on the chemical‐deficient strain. 4. Depending on the fungus' ability to express secondary chemicals and availability of fungal food sources, F. candida may employ different foraging strategies: (i) avoidance of prolonged feeding on single colonies in a rich habitat (travel costs low), and (ii) intensified group feeding on single colonies in a resource‐limited habitat (travel costs high). It was hypothesised that flexibility in fungivore foraging behaviour (clumping vs. spreading feeding activity) is adaptive because it allows avoidance/overcoming induced fungal chemical defence.     

Divergence between passerine populations from the Malvinas – Falkland Islands and their continental counterparts: a comparative phylogeographical study

Bursts of speciation have followed colonization of remote oceanic islands by diverse taxa, a process evidenced by island endemics around the world. The present study explores whether the Malvinas – Falkland Islands (MFI), a relatively understudied archipelago off the South Atlantic coast of Patagonia, harbour endemic genetic lineages of passerine birds. Nine passerine species nest regularly in the MFI (Cinclodes antarcticus, Muscisaxicola maclovianus, Troglodytes cobbi, Cistothorus platensis, Turdus falcklandii, Anthus correndera, Melanodera melanodera, Sturnella loyca, and Carduelis barbata). Mitochondrial DNA (cytochrome c oxidase I sequences) are used to quantify and compare divergence between insular and continental populations, finding genetic patterns to vary across these nine species. Most MFI passerines do not show significant genetic differentiation from continental populations, whereas C. platensis, M. melanodera, and T. falcklandii are modestly diverged. Finally, T. cobbi differes markedly from its closest continental relative Troglodytes aedon, a result that is confirmed using nuclear and vocal data. The study also identifies broadly divergent lineages within continental populations of C. platensis and T. aedon. Taken together, these results suggest that the land bird populations of the MFI were established at different times. Troglodytes cobbi is the oldest MFI land bird, splitting from continental T. aedon during the Great Patagonian Glaciation of the Pleistocene. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, •• , ••–••.     

Disentangling the contributions of osmotic and ionic effects of salinity on stomatal,mesophyll, biochemical and light limitations to photosynthesis

There are conflicting opinions on the relative importance of photosynthetic limitations under salinity. Quantitative limitation analysis of photosynthesis provides insight into the contributions of different photosynthetic limitations, but it has only been applied under saturating light conditions. Using experimental data and modelling approaches, we examined the influence of light intensity on photosynthetic limitations and quantified the osmotic and ionic effects of salinity on stomatal (L_S), mesophyll (L_M), biochemical (L_B) and light (L_L) limitations in cucumber (Cucumis sativus L.) under different light intensities. Non‐linear dependencies of L_S, L_M and L_L to light intensity were found. Osmotic effects on L_S and L_M increased with the salt concentration in the nutrient solution (S_s) and the magnitude of L_M depended on light intensity. L_S increased with the Na⁺ concentration in the leaf water (S_l) and its magnitude depended on S_s. Biochemical capacity declined linearly with S_l but, surprisingly, the relationship between L_B and S_l was influenced by S_s. Our results suggest that (1) improvement of stomatal regulation under ionic stress would be the most effective way to alleviate salinity stress in cucumber and (2) osmotic stress may alleviate the ionic effects on L_B but aggravate the ionic effects on L_S.     

Monoclonal antibodies specific for potato mop-top virus, and some properties of the coat protein

A method was devised which gave consistent yields (1–2 mg/kg leaves) of potato mop-top furovirus (PMTV) particles. Monoclonal antibodies (MAbs) were produced and some properties of 10 of them were studied. Four MAbs readily detected PMTV isolates from six countries in Northern Europe and Japan when the isolates were trapped with polyclonal antibody; and diagnostic tests based solely on MAbs (SCR 68 to coat plates and biotin- or enzyme-labelled SCR 69 to detect trapped virus) were devised. The pattern of reactions of the MAbs in ELISA and immunoblots suggested that they react with at least five different epitopes. PMTV coat protein preparations were analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Three bands of 23.9 kd, 21.5 kd and 20.5 kd were visible in silver-stained gels and all three reacted with PMTV specific MAbs. The relative amounts of the three bands varied between different virus preparations, but the 21.5 kd band was usually the most abundant. The three bands were probably not produced by anomalous behaviour in SDS-PAGE. Moreover PMTV protein was readily degraded by trypsin treatment giving a band of 20.5 kd. Therefore the results suggest that PMTV coat protein sub-units are sensitive to degradation by plant proteases. At least two degraded forms were found when purified preparations were analysed by SDS-PAGE, and the undegraded protein was estimated to be 23.9 kd. The PMTV MAbs did not react in immunoblots with SDS-treated coat protein preparations of beet necrotic yellow vein furovirus or Indian peanut clump furovirus.     

Production and properties of monoclonal antibodies to Solanum nodiflorum mottle sobemovirus

Black raspberry necrosis virus (BRNV) reaches only very low concentrations in herbaceous plants and is difficult to maintain in culture. However, in a mixed culture with an unrelated virus, Solanum nodiflorum mottle (SNMV), in the genus Sobemovirus, the concentration of BRNV particles increases about 1000‐fold. In attempts to produce monoclonal antibodies (MAbs) to BRNV for diagnostic use, purified virus particles from the mixed virus culture were used as immunogen and the resultant antibodies screened against cultures of SNMV alone, BRNV+SNMV and healthy plant extracts. None of the virus‐specific MAbs obtained in this way was specific to BRNV but six were specific to SNMV. Although the original objective was not achieved, the SNMV MAbs were characterised and used to study serological properties of SNMV and other Sobemoviruses. Characterisation of the six SNMV MAbs showed that four were IgG3, one IgG1 and the other IgG2b. SNMV was detected by all six MAbs in ELISA, by five in Western blotting, by three in agarose gel double diffusion tests, but only one was suitable for trapping virus particles in immuno‐electron microscopy (IEM). In Western blotting using virus in sap extracts of Nicotiana clevelandii, each of the five MAbs detected a single major band of Mc. 31 000 in sap containing SNMV, and additional bands of lower mass attributed to degradation of coat protein. In various serological tests, no cross‐reactions were detected between SNMV and seven other viruses from the genus Sobemovirus. However, in IEM but not in Western blotting, significant cross‐reactions were observed between SNMV and Velvet tobacco mottle virus, another species from the genus Sobemovirus. The significance of these different findings is discussed.     

Drought mortality of bush elephants in Hwange National Park, Zimbabwe

African bush elephants inhabiting the undeveloped Kalahari Sands region of Hwange National Park, Zimbabwe are subject to episodic mortality during droughts. We monitored the drought‐related mortality of elephants in Hwange National Park over the course of an extended drought between 1993 and 1995. The drought‐related mortality of elephants was higher during 1994 than 1995, despite significantly higher rainfall in 1994 than 1995. We found significant differences in the age‐specific mortality of elephants during 1994 and 1995. The cumulative mortality profile from this study differed significantly from previous die‐offs at this site, with a higher mortality among adult age classes than that reported from earlier studies in Hwange National Park. The effective duration of the rainy season, not total annual precipitation, appears to be the best predictor for the potential severity of drought mortality among elephants in the Kalahari Sands habitats of Hwange National Park.