Behavioural modification of a social spider by a parasitoid wasp

1. Manipulation of host behaviour by parasitoids has long captured the imagination of ecologists. Parasitoid wasps in the Polysphincta group of genera develop as external parasitoids of spiders. 2. In the present study, the previously undescribed interaction between a Zatypota sp. wasp (Ichneumonidae) and a social spider Anelosimus eximius (Theridiidae) is described. The larva of this Zatypota wasp is found to induce its host to disperse from their communal web and build an entirely enclosed web consisting of densely spun silk. 3. The wasp is observed to target primarily immature A. eximius individuals, with 37.5–44% of nests in a given area being parasitised. Of those nests, approximately 1.3–2.0% of individuals are hosts to the parasitoid larvae. Larger spider colonies had a significantly higher probability of harbouring parasitoids. 4. This interaction results in unusual behaviours for A. eximius induced by the parasitoid: (i) leaving the protection of the social nest and (ii) building a unique, altered web that it would not otherwise build. It is suggested that the wasp may be tapping into ancestral dispersal behaviours in its host and that a social species provides this wasp an evolutionary advantage by allowing a stable host source.     

A Bird’s Eye View of Discard Reforms: Bird-Borne Cameras Reveal Seabird/Fishery Interactions

Commercial capture fisheries produce huge quantities of offal, as well as undersized and unwanted catch in the form of discards. Declines in global catches and legislation to ban discarding will significantly reduce discards, but this subsidy supports a large scavenger community. Understanding the potential impact of declining discards for scavengers should feature in an eco-system based approach to fisheries management, but requires greater knowledge of scavenger/fishery interactions. Here we use bird-borne cameras, in tandem with GPS loggers, to provide a unique view of seabird/fishery interactions. 20,643 digital images (one min⁻¹) from ten bird-borne cameras deployed on central place northern gannets Morus bassanus revealed that all birds photographed fishing vessels. These were large (>15 m) boats, with no small-scale vessels. Virtually all vessels were trawlers, and gannets were almost always accompanied by other scavenging birds. All individuals exhibited an Area-Restricted Search (ARS) during foraging, but only 42% of ARS were associated with fishing vessels, indicating much ‘natural’ foraging. The proportion of ARS behaviours associated with fishing boats were higher for males (81%) than females (30%), although the reasons for this are currently unclear. Our study illustrates that fisheries form a very important component of the prey-landscape for foraging gannets and that a discard ban, such as that proposed under reforms of the EU Common Fisheries Policy, may have a significant impact on gannet behaviour, particularly males. However, a continued reliance on ‘natural’ foraging suggests the ability to switch away from scavenging, but only if there is sufficient food to meet their needs in the absence of a discard subsidy.     

Do pollen beetles need pollen? The effect of pollen on oviposition,survival, and development of a flower‐feeding herbivore

Abstract.  1. Pollen is considered to be an important dietary component for many species of flower-feeding herbivores. Its influence on oviposition site selection by the pollen beetle Meligethes aeneus , and on the development of its larvae was investigated.
2. The effects of pollen presence and absence on adult, egg, and larval incidence in the field, and on larval development in the laboratory were compared through the use of Synergy, a composite hybrid oilseed rape Brassica napus variety comprising male-fertile (with pollen) and male-sterile (without pollen) plants.
3. In the field, adult females were more abundant on male-fertile plants during flowering, and a greater proportion of male-fertile than male-sterile buds were accepted for oviposition. These data indicate a possible role of pollen in oviposition site selection by female pollen beetles.
4. The numbers of first instar larvae on the two plant lines did not differ; however, more second instars were found on male-fertile than on male-sterile flowers. This suggests a greater larval survival on male-fertile plants, possibly due to the more readily available food resources and better nutrition afforded by the presence of pollen.
5. Laboratory experiments confirmed that a diet which included pollen improved survival to adulthood and resulted in heavier pupae and adults; however, pollen was not obligatory for larval survival and development.
6. The pollen beetle, previously thought to be an obligate pollen feeder, is therefore more generalist in its requirements for development. These findings may relate to the nutritional and behavioural ecology of other flower-feeding herbivores.     

Detection of nuclear lamin B epitopes in oocyte nuclei from mice, sea urchins, and clams using a human autoimmune serum

Somatic nuclei typically contain two or three major proteins, the lamins A, B, and C or their antigenically related equivalents, interspersed between the chromatin and its attachment site, the inner nuclear membrane. The late oocyte nuclear envelopes of the previously investigated Xenopus and Spisula germinal vesicles, however, have no chromatin attached and only one lamin-like protein. Since mouse and sea urchin germinal vesicles have chromatin attached, we tested them for the possible presence of more than one lamin. In both species we found two different lamins incorporated in their nuclear envelope structure. One lamin is recognized by anti-lamin B and the other by anti-lamin AC antibodies. Spisula germinal vesicles were found to contain not only the nuclear envelope-bound lamin (clamin), but also a 65-kDa protein cross-reactive with anti-lamin B antibodies. This protein is present unattached to any structure and is apparently soluble. Our findings provide a possible explanation of the early presence of lamin B in pronuclei of mouse and sea urchin contrary to the late appearance of a lamin B equivalent in amphibian embryos. In Spisula, as in Xenopus, the presence of a lamin B equivalent could not be documented in the nuclear envelopes of early embryos, indicating that a separate lamin B equivalent is not essential for chromatin binding to the envelope in these species during early embryogenesis. The results also indicate that the nuclear complement of structural proteins might vary substantially in the same cell type of different species.     

Metabolism and anti-human immunodeficiency virus-1 activity of 2-halo-2',3'-dideoxyadenosine derivatives

Both 2',3'-dideoxyadenosine and 2',3'-dideoxyinosine have been shown (Mitsuya, H., and Broder, S. (1987) Nature 325, 773-778) to have in vitro activity against the human immunodeficiency virus-1 (HIV). However, these dideoxynucleosides may be catabolized by human T cells, even when adenosine deaminase is inhibited by deoxycoformycin. To overcome this problem, we have synthesized the 2-fluoro-, 2-chloro-, and 2-bromo-derivatives of 2',3'-dideoxyadenosine. The metabolism and anti-HIV activity of the 2-halo-2',3'-dideoxyadenosine derivatives and of 2',3'-dideoxyadenosine were compared. The 2-halo-2',3'-dideoxyadenosine derivatives were not deaminated significantly by cultured CEM T lymphoblasts. Experiments with 2-chloro-2',3'-dideoxyadenosine showed that the T cells converted the dideoxynucleoside to the 5'-monophosphate, 5'-diphosphate, and 5'-triphosphate metabolites. At concentrations lower than those producing cytotoxicity in uninfected cells (3-10 microM), the 2-halo-2',3-dideoxyadenosine derivatives inhibited the cytopathic effects of HIV toward MT-2 T lymphoblasts, and retarded viral replication in CEM T lymphoblasts. Experiments with a deoxycytidine kinase-deficient mutant CEM T cell line showed that this enzyme was necessary for the phosphorylation and anti-HIV activity of the 2-chloro-2',3'-dideoxyadenosine. In contrast, 2',3'-dideoxyadenosine was phosphorylated by the deoxycytidine kinase-deficient mutant and retained anti-HIV activity in this cell line. Thus, the 2-halo derivatives of 2',3'-dideoxyadenosine, in contrast to 2',3'-dideoxyadenosine itself, are not catabolized by T cells. Their anti-HIV and anti-proliferative activities are manifest only in cells expressing deoxycytidine kinase. The in vivo implications of these results for anti-HIV chemotherapy are discussed.     

The rat liver asialoglycoprotein receptor polypeptide must be inserted into a microsome to achieve its active conformation

Affinity chromatography on galactose-Sepharose has been utilized to demonstrate that rat liver asialoglycoprotein receptor synthesized in vitro in a reticulocyte lysate system is capable of binding carbohydrate ligand only when dog pancreas microsomes are present during translation. Analysis of receptor isolated from tunicamycin-treated rat hepatocytes indicates that glycosylation is not necessary for receptor activity. Genetically engineered receptor derivatives in which the natural membrane anchor is either deleted entirely or replaced with a cleavable signal sequence derived from dog preproinsulin have been used to demonstrate that: (a) inactive receptor made in the absence of membranes does not result from incorrect nucleation of folding around the hydrophobic portion of the polypeptide which is normally buried in the membrane and (b) the carbohydrate-binding domain of the receptor does not need to be tethered to the luminal side of the membrane to fold correctly. These results suggest that factors within the lumen of the microsomes are essential to establish the native conformation of the binding domain.     

Computer-assisted mathematical analysis of sigmoid biological events

A program in BASIC is described which allows accurate quantificationof some numerical parameters that can be objectively correlatedto biological indexes in sigmoid biological events. Attentionwas focused on the polymerization process of actin (a muscleprotein with a mol. wt of 42 000 daltons) studied as the variationin the OD₃₆₀ index with time. The experimental points, if plotted,can be well approximated by a rational function of the typeOD₃₆₀ = f(t), which passes through the origin and can be representedgraphically by a sigmoid curve. The program was very helpfulin comparing the experimental curves and in analysing significantparameters, such as maximum velocity and asymptote, that characterizethese curves and whose interpretation would otherwise be purelysubjective. Received on July 11, 1985; accepted on January 13, 1986     

Estimating denitrification rates in estuarine sediments: A comparison of stoichiometric and acetylene based methods

We compared denitrification rates obtained using an adaptation of the acetylene block technique to rates estimated from benthic flux nutrient stoichiometry in the subtidal sediments of Tomales Bay, California (USA). By amending whole cores with acetylene and saturating nitrate concentrations, we obtained potential denitrification rates, which ranged between 4 and 30 mmol N m^–2 d^–1. We determined the apparent Michaelis constant (K_app) and the maximum potential rate (V_mp) of the denitrifying community and used these constants in a rectangular hyperbola to estimatein situ denitrification rates. Both the K_app and V_mp of the denitrifying community exhibited significant variation over both depth in the sediment column and time of sampling.Estimates ofin situ denitrification obtained using our kinetic-fix adaptation of the acetylene block ranged between 1.8 (March) and 9 (Sept.) mmol N m^–1 d^–1. Denitrification rates obtained using benthic flux stoichiometry ranged between 0.7 and 4.1 mmol N m^–2 d^–1. Average denitrification rates obtained using the kinetic-fix acetylene block approach exceeded those obtained from net benthic flux stoichiometry; however, these differences were not significant. We conclude that our kinetic-fix adaptation of the acetylene block technique provides realistic estimates of denitrification in sediments, even when pore water nitrate concentrations are low and nitrification and denitrification are closely coupled.     

Blown away? Wind speed and foraging success in an acoustic predator

Mammal Research - Foraging animals must contend with fluctuating environmental variables that affect foraging success, including conditions like wind noise, which could diminish the usefulness of...