Volatiles modulate the development of plant pathogenic rust fungi

Rust fungi are obligate biotrophic pathogens that differentiate a series of specialized cells to establish infection. One of these cells, the haustorium, which serves to absorb nutrients from living host cells, normally develops only in planta. Here, we show that the rust fungus Uromyces fabae (Pers.) Schroet. stimulates volatile emission of its host, broad bean (Vicia faba L.). Volatiles were identified and shown to be perceived by the fungus in in vitro assays that excluded the host. Three of them, nonanal, decanal, and hexenyl acetate promoted the development of haustoria on artificial membranes. In contrast, the terpenoid farnesyl acetate suppressed this differentiation. In assays using whole plants, farnesyl acetate reduced rust disease not only on broad bean but also on several cereals and legumes including soybean. This natural substance was effective against all rusts tested when directly applied to the host. This demonstrated that farnesyl acetate may serve as a powerful novel tool to combat rust fungi including Phakopsora pachyrhizi that currently threatens the production of soybeans world-wide.     

Three serine proteases from the latex of Euphorbia cyparissias

Three serine-centred proteolytic enzymes, euphorbains y-1, ?2 and ?3, were isolated from the latex of Euphorbia cyparissias. These proteases have different specific activities to azocoll and CBZ glycine p-nitrophenyl ester. The pIs and M_rs of y-1, ?2 and ?3 are 5.2 and 67 000, 5.2 and 33 000, and 6.3 and 67 000, respectively. The enzymes, which are glycoproteins, are immunologically distinct from euphorbain 1, but clearly related to that enzyme in amino acid composition.     

Pollinator-mediated interactions between a pathogenic fungus, Uromyces pisi (Pucciniaceae), and its host plant,Euphorbia cyparissias (Euphorbiaceae)

The plant Euphorbia cyparissias is commonly infected by rust fungi of the species complex Uromyces pisi. When infected, E. cyparissias is unable to flower, but instead is induced by the fungus to form pseudoflowers. Pseudoflowers are rosettes of yellow leaves upon which the fungus presents its gametes in a sweet-smelling fungal nectar. We hypothesized that the fungi, as they are heterothallic, are dependent on insect visitation to cross-fertilize their mating types. We confirmed that insects are required with an insect exclusion experiment. We further hypothesized that pseudoflowers of U. pisi interact with uninfected true host flowers through insects during their period of co-"flowering" in early spring. We conducted artificial array experiments in the field to test whether the two species share insects and whether they influenced each other's insect visitation. Insects moved between true flowers and pseudoflowers, but true flowers received more visits over all. Pseudoflowers and true flowers did not influence each other's visitation rates in mixtures. However, shorter visits were observed on pseudoflowers in mixtures than monocultures, suggesting that true flowers might be competitors for pseudoflowers. Further experiments are needed to determine whether the similarity of pseudoflowers to true flowers is adaptive.     

Testing non-additive effects of nectar-robbing ants and hummingbird pollination on the reproductive success of a parasitic plant

Nectar robbing may have an indirect negative effect on plant reproduction by discouraging legitimate pollinator species from visiting robbed flowers. In this study, we set up a 2 × 2 factorial design with nectar-robbing ants and hummingbird pollination to test for non-additive effects on fruit set, seed mass, and seed germination of the leafless mistletoe Tristerix aphyllus (Loranthaceae). Even though ants caused conspicuous damage at the base of the floral tubes, nectar availability was reduced by only 8 % in the presence of ants. The green-backed firecrown Sephanoides sephaniodes was insensitive to the presence of ants. Rather, the bird responded to flower number and the presence or the absence of damage, but not to the extent of damage within inflorescences. As hummingbirds were largely insensitive to variation in nectar robbing, the interaction ant × hummingbird had no effect on plant-reproductive success. Thus, the factorial experiment did not provide evidence for indirect negative effects of nectar robbing on plant reproduction. These results suggest that indirect effects of nectar robbers on pollinator behaviour may occur under a more restricted set of conditions than those previously considered. We suggest that the low amount of nectar removed by nectar-robbing ants was insufficient for hummingbirds to avoid robbed flowers, which restricted the potential for non-additive effects.     

Effects of transmitters on the reproductive success of Tufted Puffins

ABSTRACT.   Although radiotelemetry is useful for monitoring nest attendance and the foraging ranges and distribution of breeding birds, attachment of transmitters may affect reproductive behavior. In 2003, we captured 25 adult Tufted Puffins ( Fratercula cirrhata ) at two colonies in Chiniak Bay, Kodiak Island, Alaska, and fitted them with subcutaneously anchored radiotransmitters (<1.2% of body mass). We determined the presence of radio-marked birds at each study site using automated, remote radiotelemetry systems, and compared rates of nestling growth, fledging mass, and fledging success for chicks with and without (control group) a radio-marked parent. Although most radio-marked adults continued to attend nests after capture and attachment of transmitters, nestlings with a radio-marked parent had lower mean growth rates (6.9 g/d vs. 14.4 g/d) and fledging success (33% vs. 84%) than control chicks. These results suggest that colony attendance by adult puffins fitted with transmitters declined sharply or completely and this led to high nestling mortality. Given the negative effects of transmitters on Tufted Puffins in our study and in other studies of alcids, we suggest delaying the attachment of transmitters until well after the brooding period. In addition, we recommend pilot studies be undertaken to distinguish the possible effects of capture and handling from those of actually carrying the device.     

Effects of electromagnetic fields on the reproductive success of American kestrels

Reduced reproductive success of birds nesting near power lines has been documented but never directly attributed to electromagnetic fields (EMFs). Laboratory studies have identified EMF effects on embryonic development, but reproductive success of wild birds is dependent on additional factors, including fertility, egg size, hatching, and fledging success. We tested whether EMFs affect reproductive success of birds. Captive American kestrels (Falco sparverius) were bred for one season per year for 2 yr under either controlled or EMF conditions. EMF exposure was equivalent to that experienced by wild reproducing kestrels and was weakly associated with reduced egg laying in 1 yr only. In both years fertility was higher, but hatching success was lower in EMF pairs than control pairs. Fledging success was higher in EMF pairs than control pairs in 1995 only. Egg composition and embryonic development were examined in 1 yr only, but hatchlings were measured in both years. EMF eggs were larger, with more yolk, albumen, and water, but had thinner egg shells than control eggs. Late-term EMF embryos were larger and longer than control embryos, although hatchlings were similar in body mass and size. EMF exposure affected reproductive success of kestrels, increasing fertility, egg size, embryonic development, and fledging success but reducing hatching success.     

Additions to the rust fungi of Argentina

A contribution is made to the rust fungus flora of Argentina: Puccinia baccharidis-boliviensis, P. cordyceps, P. pucarae, and Aecidium hypseocharidicola are described as new species. Cionothrix praelonga, Fromme?lla mexicana var. mexicana, Phakopsora compressa, Prospodium peruvianum, Puccinia amphiospora, P. chaetochloae, P. liabi, P. pappophori, P. sanguinolenta, P. subaquila, Ravenelia havanensis, Uredo leonuri, Uromyces orbicularis, and U. cnidoscoli are new reports for Argentina. New observations on already known species were made: the aecia of Puccinia subaquila and aecia and uredinia of Uromyces cnidoscoli are described for the first time. Senecio hieronymi is a new host for Puccinia lagenophorae. Uredo leonuri belongs to the genus Coleosporium. Melilotus albus is a new host of Uromyces anthyllidis in Argentina.     

Impacts of Argentine ants on avian nesting success

Biological invasions can have severe and widespread impacts on ecological communities. A few species of ants have become particularly damaging invaders but quantitative data of their impacts on many taxa is still lacking. We provide experimental evidence using artificial nests baited with quail eggs that the invasive Argentine ant (Linepithema humile) can be a significant avian nest predator – Argentine ants recruited to more nests and in higher abundance than the native ant species they displace. However, at a site invaded by Argentine ants, we monitored over 400 nests of a ground-nesting species, the Dark-eyed Junco (Junco hyemalis), and found that less than 2% of nests failed as a result of Argentine ant predation/infestation. A review of the literature also suggests that Argentine ants may not be a serious threat to bird nests relative to other predators or parasites. However, invasive ants with the capability of overwhelming prey though stinging (specifically the red-imported fire ant, Solenopsis invicta), may have a higher impact on avian nesting success. Received 14 January 2005; revised 28 April 2005; accepted 12 May 2005.     

Effects of extra-pair and within-pair reproductive success on the opportunity for selection in birds

The number of mates, their fecundity, and the number of extra-pairfertilizations can all affect male reproductive success in biparentalspecies. Extra-pair mating in birds has been of particular interest,because it could generate strong levels of sexual selectioneven when a species is socially monogamous. We examined howextra-pair fertilizations affect the opportunity for selectionin the sexually dimorphic common yellowthroat (Geothlypis trichas)and the sexually monomorphic house wren (Troglodytes aedon).We were able to identify sires for at least 95% of all nestlings,and, thus, we were able to make a nearly complete accountingof male reproductive success. Although extra-pair fertilizationswere common in yellowthroats (26% of young) it contributed little(21%) to the total variance in male reproductive success. Mostof the variance in reproductive success (58%) was attributableto the male's within-pair success, which was influenced primarilyby the number of young produced by each mate and the proportionof within-pair young sired. Despite a moderate level of extra-pairfertilizations (10% of young) in house wrens, almost all ofthe variance in male reproductive success (97%) was attributableto within-pair success, particularly the number of social mates.Although extra-pair fertilizations generally increase the variancein male reproductive success, within-pair reproductive successmay be the major source of variation in male reproductive success.Thus, sexual dimorphism in monogamous birds may be influencedmore by the number of mates and their fecundity than by extra-pairmatings.     

Additions to the rust fungi of South Africa

This paper presents new species, combinations, national reports and host records for the South African rust fungi (Uredinales/Pucciniales). Endophyllum mpenjatiense on cf. Hibiscus sp. (Malvaceae), Phakopsora combretorum (anamorph Uredo combreticola) on the new host Combretum apiculatum (Combretaceae) and Uredo sekhukhunensis on Ziziphus mucronata (Rhamnaceae) are described as new species. Dietelia cardiospermi and E. metalasiae are proposed as new combinations to replace Aecidium cardiospermi on Cardiospermum halicacabum (Sapindaceae) and A. metalasiae on Metalasia spp. (Asteraceae), respectively. Four species are new records for South Africa: Crossopsora antidesmae-dioicae on Antidesma venosum (Euphorbiaceae), Phakopsora ziziphi-vulgaris on Z. mucronata, and Uromyces cypericola and Puccinia subcoronata, both on a new host, Cyperus albostriatus (Cyperaceae). The record of P. subcoronata is the first one from outside the New World. Puccinia scirpi is reported as a possible addition to the South African rust fungi. New host records and observations are presented for Pucciniastrum agrimoniae that is recorded on two new host genera and species, Cliffortia odorata and Leucosidea sericea (Rosaceae), Uromyces cypericola whose urediniospores are described for the first time, Phakopsora stratosa in that spermogonia and Uredo-like aecia were discovered, and for Sphaerophragmium dalbergiae in that characters of the urediniospores are re-evaluated. A lectotype is selected for Aecidium garckeanum and spermogonia are reported for this rust for the first time. The rust fungi of Ehrharta (Poaceae) are discussed and critically evaluated in the light of spore morphology and host species.     

Effects of neolignans from the stem bark of Magnolia obovata on plant pathogenic fungi

Aims:  To characterize antifungal principles from the methanol extract of Magnolia obovata and to evaluate their antifungal activities against various plant pathogenic fungi.
Methods and Results:  Four neolignans were isolated from stem bark of M. obovata as antifungal principles and identified as magnolol, honokiol, 4-methoxyhonokiol and obovatol. In mycelial growth inhibition assay, both magnolol and honokiol displayed more potent antifungal activity than 4-methoxyhonokiol and obovatol. Both magnolol and honokiol showed similar in vivo antifungal spectrum against seven plant diseases tested; both compounds effectively suppressed the development of rice blast, tomato late blight, wheat leaf rust and red pepper anthracnose. 4-Methoxyhonokiol and obovatol were highly active to only rice blast and wheat leaf rust respectively.
Conclusions:  The extract of M. obovata and four neolignans had potent in vivo antifungal activities against plant pathogenic fungi.
Significance and Impact of the Study:  Neolignans from Magnolia spp. can be used and suggested as a novel antifungal lead compound for the development of new fungicide and directly as a natural fungicide for the control of plant diseases such as rice blast and wheat leaf rust.     

Indices of reproductive skew depend on average reproductive success

Several indices of reproductive skew, which quantify the degree of unequal partitioning of reproductive output among members in an animal society, have been proposed. Here we point out the drawbacks of these indices. The most serious problem is the dependence of the indices on mean reproductive success: skew values tend to be larger, as average numbers of offspring decrease, due to random sampling error in numbers of offspring. Thus it is difficult to compare societies with different average lifetime reproductive success using these indices, even though we have presented methods to calculate the expected reproductive skew caused by random sampling error, especially when average numbers of offspring are small, as is often the case with cooperatively breeding vertebrates. As an alternative, we propose using the spatial dispersion indices of population ecology (Morisita's index or its standardized version) for the measurement of reproductive skew. These indices are almost independent of average fecundity and have their own method of testing for random variation in offspring numbers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of population size on reproductive success of the endangered and endemic species Primula merrilliana

The reproductive ability related to the population size of the endangered and endemic species Primula merrilliana Schltr.was investigated.In 26 populations observed,only four contain more than 500 flowering individuals,whereas most of them(53.8%) consist of less than 100 flowering individuals.Though the ratio of pin and thrum plants keeps its balance at 1:1 for all populations,the frequency of pin and thrum flowers was significantly biased in most small populations.Population size strongly affected reproductive success; plants in small populations produced significantly fewer flowers and fruits per plant and fewer seeds per fruit,and therefore fewer seeds per plant.The floral density was another important factor that influenced the reproductive success of P.merrilliana,because four main reproductive success parameters (fruits per plant,seeds per fruit,seeds per plant,and the proportion of flowers setting fruit) were all positively correlated with floral density.The size of plants and the number of leaves per plant (measure of habitat quality) were not influenced by the variation of population size,suggesting that the reduced fecundity in small populations may not be a consequence of lower habitat quality,inbreeding depression and pollen limitation as a result of less attractiveness in small populations are therefore likely explanations for these patterns.     

Effects of mate removal on the behaviour and reproductive success of Reed Warblers Acrocephalus scirpaceus

The Reed Warbler Acrocephalus scirpaceus is a largely monogamous insectivorous passerine in which males and females provide equal care by day to eggs and chicks. Polygyny occurs occasionally, with males leaving one female unaided. When females were temporarily removed from three recently-completed clutches their males deserted and resumed the high song levels typical of unmated males. Males may desert either because they are physically incapable of incubation or because the energy expenditure needed for a male to return to an equivalent stage in the breeding cycle is much lower than for a female to do so. Widowed females ( n = 7 ), however, continued the breeding attempt alone, with similar incubation levels but higher provisioning rates than those of control females. In three out of four mid-season broods raised by lone females all fertile eggs were reared to healthy fledglings (in the fourth brood the female died), while only one of four late-season nests produced any fledglings (which were underweight). Late-season control nests were as successful as earlier ones. Loss of male help led to starvation of chicks, but caused no adverse effects during incubation. This explains the small changes in widows' sitting levels during incubation, but much greater effects after hatching. Females may need male help to rear late broods (but not early broods) as days are shorter and food is scarcer. Males may normally help at nests, even those in the mid-season, because in stressful spells (even for a few days) such help is vital for successful breeding but in good periods it costs the male little.