Adverse effects on pollen exposed to Atta texana and other North American ants: implications for ant pollination

Summary The effects of the surface secretions of eight species of ants on three types of pollen were bioassayed by exposure to the integument of undisturbed, living individuals for 20 min. Ant species included Atta texana which cultures fungi by means of various types of secretions. The frequency of grains showing membrane dysfunction, and therefore reduced viability, was quantified by means of a fluorochromatic test. Comparisons of treated and control samples showed that in 46 out of 50 bioassays there was a reduction in pollen viability following exposure to ants, 38 being statistically significant. Variation in the outcome of bioassays showed differential potency among ant species and differential vulnerability among pollen types. Ant pollination may be uncommon because surface secretions, often from the metapleural glands, cause membrane dysfunction in pollen. Ant species without metapleural glands may be pollinators, but ant pollinated plants may have pollen resistant to the secretion.     

Interaction between ants, extrafloral nectaries and insect herbivores in Neotropical coastal sand dunes: herbivore deterrence by visiting ants increases fruit set in Opuntia stricta (Cactaceae)

1. This study examines the anti-herbivore effect of ants visiting the extrafloral nectaries (EFNs) of Opuntia stricta (Cactaceae) and its possible influence on the plant's reproductive output in Mexican coastal sand dunes. Opuntia 's EFNs are located in the areoles of the developing tissue of emerging cladodes and flower buds.
2. Ants visited the EFNs of O . stricta on a round-the-clock basis. The associated ant assemblage was formed by nine species distributed in four subfamilies, and the species composition of the principal ant visitors changed markedly from day to night period.
3. Cladodes of control (ants present) and treatment (ants excluded) plants of Opuntia were equally infested by sucking bugs and mining dipterans. Damage to buds by a pyralid moth, however, was significantly higher on treatment than on control plants. Ant visitation to Opuntia 's EFNs translated into a 50% increase in the plant's reproductive output, as expressed by the number of fruits produced by experimental control and treatment branches. Moreover, fruit production by ant-visited branches was positively and significantly associated with the mean monthly rate of ant visitation to EFNs.
4. This is the first demonstration of ant protection leading to increased fruit set in the Cactaceae under natural conditions. Although the consequences of damage by sucking and mining insects remain unclear for Opuntia , the results show how the association of EFNs with vulnerable reproductive plant organs can result in a direct ant-derived benefit to plant fitness.     

Interaction between ants and seeds of a nonmyrmecochorous neotropical tree, Cabralea canjerana (Meliaceae), in the Atlantic forest of southeast Brazil

On the forest floor of two Atlantic forest sites in southeast Brazil, we recorded 26 ant species (12 genera) interacting with the seeds of Cabralea canjerana (Meliaceae), a typical ornithochorous tree whose seeds are covered by a lipid-rich aril. The ants treat the arillate seeds in three different ways: (1) the large ponerine ants Pachycondyla striata and Odontomachus chelifer individually remove the seeds to their nests, (2) many species (Pheidole spp.) recruit workers to remove the aril on the spot, or (3) Solenopsis spp. recruit nestmates and cover the seeds with soil before removing the aril on the spot. The ants remove the aril exceptionally rapidly, and removal greatly facilitates seed germination. Seed predation by insects below fruiting trees is severe, and field experiments using vertebrate exclosures showed that rodents also prey heavily upon seeds found near parent trees. Ponerine ants actively remove seeds from this predation-prone zone. By removing bird-manipulated and naturally fallen seeds, ants can play a key role in the fate of medium-sized seeds like those of C. canjerana.     

Interaction between cationic zinc porphyrin and lead ion induced telomeric guanine quadruplexes: evidence for end-stacking

The interaction between small molecules and telomeric quadruplex DNA has received great attention because of its importance in molecular recognition and anticancer drug design. Using UV/vis absorption titration, thermal melting, circular dichroism spectroscopy, and electrospray ionization mass spectrometry, we examined the formation of lead ion induced guanine quadruplexes (Pb-G4) from oligonucleotide AG₃(T₂AG₃)₃ and their interaction with a zinc derivative of 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (Zn-TMPyP). The binding of lead ion to the oligonucleotide was found to have an unusually high affinity and followed a 1:1 stoichiometry, and the resultant Pb-G4 structure was stabilized by Zn-TMPyP binding. Owing to the steric hindrance of the axial ligand of zinc and also the relatively rigid structure of Pb-G4, intercalation of Zn-TMPyP between adjacent guanine quartets is precluded, thus allowing the end-stacking binding mode to be characterized exclusively. In conjunction with a big redshift (more than 8 nm) in the absorption spectrum, we demonstrate that a conservative induced circular dichroism is an important signature for end-stacking of porphyrins on guanine quadruplexes.     

Forest use and vertical stratification in fruit-feeding butterflies of Sulawesi,Indonesia: impacts for conservation

Protected forest areas of Sulawesi are gradually being replaced by intensively used agroforestry systems and farmland, especially in lowland and sub-montane regions. Studies on the impact of these man-induced changes on biodiversity are of urgent conservation concern. We compared the fruit-feeding butterfly assemblage of a natural hill forest to that of a disturbed hill forest, representing a mosaic of old secondary forest and recently abandoned or active subsistence farms. Overall, species richness seemed highest in the disturbed site, but both abundance and diversity of endemic butterflies were significantly higher in the natural forest. Although the butterfly assemblage showed a clear vertical structure in the natural forest, vertical stratification was no longer pronounced at the disturbed site. Comparative studies based on diversity estimates from ground samples should consider not only the scale at which sampling is carried out and influences from nearby habitat patches in the surrounding landscape mosaic, but also possible behavioural changes in stratified species after forest modification. This study shows that higher overall species richness does not imply higher species distinctiveness, and indicates that the contribution of land-use systems to global biodiversity should be evaluated with caution, even when relatively high species richness estimates are found.     

Novel S-adenosyl-L-methionine:salicylic acid carboxyl methyltransferase,an enzyme responsible for biosynthesis of methyl salicylate and methyl benzoate,is not involved in floral scent production in snapdragon flowers

Using a functional genomic approach we have isolated and characterized a cDNA that encodes a salicylic acid carboxyl methyltransferase (SAMT) from Antirrhinum majus. The sequence of the protein encoded by SAMT has higher amino acid identity to Clarkia breweri SAMT than to snapdragon benzoic acid carboxyl methyltransferase (BAMT) (55 and 40% amino acid identity, respectively). Escherichia coli-expressed SAMT protein catalyzes the formation of the volatile ester methyl salicylate from salicylic acid with a K(m) value of 83 microM. It can also methylate benzoic acid to form methyl benzoate, but its K(m) value for benzoic acid is 1.72 mM. Snapdragon flowers do not emit methyl salicylate. The potential involvement of SAMT in production and emission of methyl benzoate in snapdragon flowers was analyzed by RNA gel blot analysis. SAMT mRNA was not detected in floral tissues by RNA blot hybridization, but low levels of SAMT gene expression were detected after real-time RT-PCR in the presence of SAMT-specific primers, indicating that this gene does not contribute significantly, if at all, in methyl benzoate production and emission in snapdragon flowers. Expression of SAMT in petal tissue was found to be induced by salicylic and jasmonic acid treatments.     

Interaction between echovirus 7 and its receptor, decay-accelerating factor (CD55): evidence for a secondary cellular factor in A-particle formation.

Soluble forms of decay-accelerating factor (DAF) (CD55), the receptor for echovirus 7, were synthesized in the yeast Pichia pastoris. Purified recombinant protein containing SCR domains 2, 3, and 4, but lacking the serine/threonine rich region, was shown to block infection of susceptible cells by echovirus 7. In contrast to the situation with poliovirus and its receptor, the neutralization of echovirus 7 by soluble DAF was completely reversible and did not lead to the formation of 135S A-particles. Binding of virus to susceptible cells, by contrast, did lead to the formation of A particles, mainly from virus that had been internalized. The data suggest that a secondary factor(s) may contribute to A-particle formation and uncoating of echovirus 7.     

Interaction between sulphur mobilisation proteins SufB and SufC: evidence for an iron-sulphur cluster biogenesis pathway in the apicoplast of Plasmodium falciparum

The plastid of Plasmodium falciparum, the apicoplast, performs metabolic functions essential to the parasite. Various reactions in the plastid require the assembly of [Fe-S] prosthetic groups on participating proteins as well as the reductant activity of ferredoxin that is converted from its apo-form by the assembly of [Fe-S] clusters inside the apicoplast. The [Fe-S] assembly pathway involving sulphur mobilising Suf proteins has been predicted to function in the apicoplast with one component (PfSufB) encoded by the plastid genome itself. We demonstrate the ATPase activity of recombinant P. falciparum nuclear-encoded SufC and its localisation in the apicoplast. Further, an internal region of apicoplast SufB was used to detect PfSufB-PfSufC interaction in vitro; co-elution of SufB from parasite lysate with recombinant PfSufC on an affinity column also indicated an interaction of the two proteins. As a departure from bacterial SufB and similar to reported plant plastid SufB, apicoplast SufB exhibited ATPase activity, suggesting the evolution of specialised functions in the plastid counterparts. Our results provide experimental evidence for an active Suf pathway in the Plasmodium apicoplast.     

Ecological restoration, carbon sequestration and biodiversity conservation: The experience of the Society for Wildlife Research and Environmental Education (SPVS) in the Atlantic Rain Forest of Southern Brazil

Since 1999, SPVS has been involved in three projects that combine two fundamental goals over the course of 40 years: the conservation of one of Brazil's most important remnants of Atlantic Forest and the implementation of projects for carbon sequestration. In addition, there is an interest in replicating these projects in order to restore other degraded areas, protect the Brazilian biomes, and help to diminish deforestation and forest fire, therefore reducing carbon emissions. The acquisition of 19,000 ha of degraded areas of high biological importance in southern Brazil was the first step towards the implementation of the projects. These areas are owned by SPVS, a Brazilian NGO, and are being restored, conserved and transformed into Private Natural Reserves, in partnership with the NGO – The Nature Conservancy, and financed by the companies – American Electric Power, General Motors and Chevron Texaco. The process of forest restoration involves several stages: soil studies, surveying the region's native plants, planning for restoration by means of a Geographical Information System, production of seedlings, application of different techniques for planting (such as manual or mechanised planting with seedlings and stakes), and biomass and biodiversity monitoring. To guarantee the survival of the seedlings on the planted areas, during the first three years, there is a continuous and systematic maintenance programme including weeding of undergrowth, crowing and organic fertilisation. The three projects already planted around 500,000 seedlings of native species until September 2004, and aim to plant a further 300,000 until 2008.     

Genomic analysis reveals a duplication of eight rather than seven short consensus repeats in primate CR1 and CR1L: evidence for an additional set shared between CR1 and CR2

We report the discovery of previously unrecognised short consensus repeats (SCRs) within human and chimpanzee CR1 and CR1L. Analysis of available genomic, protein and expression databases suggests that these are actually genomic remnants of SCRs previously reported in other complement control proteins (CCPs). Comparison with the nucleotide motifs of the 11 defined subfamilies of SCRs justifies the designation g-like because of the close similarity to the g subfamily found in CR2 and MCP. To date, we have identified five such SCRs in human and chimpanzee CR1, one in human and chimpanzee CR1L, but none in either rat or mouse Crry in keeping with the number of internal duplications of the long homologous repeat (LHR) found in CR1 and CR1L. In fact, at the genomic level, the ancestral LHR must have contained eight SCRs rather than seven as previously thought. Since g-like SCRs are found immediately downstream of d SCRs, we suggest that there must have been a functional dg set which has been retained by CR2 and MCP but which is degenerate in CR1 or CR1L. Interestingly, dg is also present in the CR2 component of mouse CR1. The degeneration of the g SCR must have occurred prior to the formation of primate CR1L and prior to the duplication events which resulted in primate CR1. In this context, the apparent conservation of g-like SCRs may be surprising and may suggest the existence of mechanisms unrelated to protein coding. These results provide examples of the many processes which have contributed to the evolution of the extensive repertoire of CCPs.     

Analysis of the human replication protein A:Rad52 complex: evidence for crosstalk between RPA32, RPA70, Rad52 and DNA

The eukaryotic single-stranded DNA-binding protein, replication protein A (RPA), is essential for DNA replication, and plays important roles in DNA repair and DNA recombination. Rad52 and RPA, along with other members of the Rad52 epistasis group of genes, repair double-stranded DNA breaks (DSBs). Two repair pathways involve RPA and Rad52, homologous recombination and single-strand annealing. Two binding sites for Rad52 have been identified on RPA. They include the previously identified C-terminal domain (CTD) of RPA32 (residues 224-271) and the newly identified domain containing residues 169-326 of RPA70. A region on Rad52, which includes residues 218-303, binds RPA70 as well as RPA32. The N-terminal region of RPA32 does not appear to play a role in the formation of the RPA:Rad52 complex. It appears that the RPA32CTD can substitute for RPA70 in binding Rad52. Sequence homology between RPA32 and RPA70 was used to identify a putative Rad52-binding site on RPA70 that is located near DNA-binding domains A and B. Rad52 binding to RPA increases ssDNA affinity significantly. Mutations in DBD-D on RPA32 show that this domain is primarily responsible for the ssDNA binding enhancement. RPA binding to Rad52 inhibits the higher-order self-association of Rad52 rings. Implications for these results for the "hand-off" mechanism between protein-protein partners, including Rad51, in homologous recombination and single-strand annealing are discussed.     

Molecular evidence for hybridization between two Australian desert skinks, Ctenotus leonhardii and Ctenotus quattuordecimlineatus (Scincidae: Squamata)

Australian scincid lizards in the genus Ctenotus constitute the most diverse vertebrate radiation in Australia. However, the evolutionary processes that have generated this diversity remain elusive, in part because both interspecific phylogenetic relationships and phylogeographic structure within Ctenotus species remain poorly known. Here we use nucleotide sequences from a mitochondrial locus and two nuclear introns to investigate broad-scale phylogeographic patterns within Ctenotus leonhardii and C. quattuordecimlineatus, two geographically widespread species of skinks that were found to have a surprisingly close genetic relationship in a previous molecular phylogenetic study. We demonstrate that the apparent close relationship between these ecologically and phenotypically distinct taxa is attributable to mitochondrial introgression from C. quattuordecimlineatus to C. leonhardii. In the western deserts, Ctenotus leonhardii individuals carry mtDNA lineages that are derived from C. quattuordecimlineatus mtDNA lineages from that geographic region. Coalescent simulations indicate that this pattern is unlikely to have resulted from incomplete lineage sorting, implicating introgressive hybridization as the cause of this regional gene-tree discordance.     

Major histocompatibility complex class I associations in iron overload: evidence for a new link between the HFE H63D mutation, HLA-A29, and non-classical forms of hemochromatosis

 The present study is an analysis of the frequencies of HFE mutations in patients with different forms of iron overload compared with the frequencies found in healthy subjects from the same region. The frequencies of HLA-A and -B antigens and HLA haplotypes were also analyzed in the same subjects. The study population included: 71 healthy individuals; 39 genetically and clinically well-characterized patients with genetic hemochromatosis (HH); and 25 patients with non-classical forms of iron overload (NCH), excluding secondary hemochromatosis. All subjects were HLA-typed and HFE-genotyped by the oligonucleotide ligation assay (OLA). The gene frequencies found for the C282Y and H63D mutations of HFE were respectively: 0.03 and 0.23 in healthy individuals, 0.86 and 0.04 in HH patients, and 0.08 and 0.48 in NCH patients. An expected significant association between HH and HLA-A3 was observed, which was found to be in linkage disequilibrium with the C282Y mutation. A new association was seen, however, between HLA-A29 and NCH, in linkage disequilibrium with the H63D mutation. Again as expected, the HLA-B antigen B7 was associated with HH in linkage disequilibrium with HLA-A3. In addition, the HLA-B antigen B44 was found to be associated with NCH but not in linkage disequilibrium with either A29 or the H63D mutation. In conclusion, a new association of the HFE H63D mutation with forms of hemochromatosis other than HH and a new association between the HLA phenotype A29 and the HFE H63D mutation were found in the same patients. These findings reinforce evidence for the involvement of the major histocompatibility class I in iron metabolism, supporting the notion of a physiological role for the immunological system in the regulation of iron load. Received: 11 June 1997 / Revised: 29 October 1997