Matching global and regional distribution models of the recluse spider Loxosceles rufescens: to what extent do these reflect niche conservatism?

The Mediterranean recluse spider, Loxosceles rufescens (Dufour, 1820) (Araneae: Sicariidae) is a cosmopolitan spider that has been introduced in many parts of the world. Its bite can be dangerous to humans. However, the potential distribution of this alien species, which is able to spread fairly quickly with human aid, is completely unknown. Using a combination of global and regional niche models, it is possible to analyse the spread of this species in relation to environmental conditions. This analysis found that the successful spreading of this species varies according to the region invaded. The majority of populations in Asia are stable and show niche conservatism, whereas in North America this spider is expected to be less successful in occupying niches that differ from those in its native region and that do not support its synanthropic way of living.

The influence of hunger and breeding temperature on the venom production of the spider Cupiennius salei (Araneae, Ctenidae).

The venom production of the free hunting neotropic spider Cupiennius salei was tested under different breeding conditions. Three groups kept at different temperatures (17, 21 and 25 degrees C) showed that venom production remained stable within this temperature range, only at a temperature of 15 degrees C the spiders stopped feeding and venom synthesis. Hunger periods do not have a direct effect on the released venom quantity. Two groups of spiders--the first group after a four and the second after an eight weeks hunger period--were compared and no difference in venom production was found. Such long fasting periods are a natural situation for spiders. In this case Cupiennius salei reduces its body weight but not venom supply. This means that body weight is a parameter only of short-term fitness which changes with the actual living conditions (temperature, feeding intervals) of each individual. Long-term fitness is best described by the prosoma length, which was formed during the juvenile growth of each spider and is rather invariable in adulthood. It was shown that the quantity of released venom is better correlated with the length of the prosoma than with the weight of the animal. This means that venom production is mostly an indicator of long-term fitness.

Immobilizing and lethal effects of spider venoms on the cockroach and the common mealbeetle.

Immobilizing and lethal effects of the venoms obtained from six spider species (Brachypelma albopilosum, Atrax robustus, Cupiennius salei, Selenops mexicanus, Tegenaria atrica, Argiope bruennichi) were tested on Blatta orientalis (cockroach) and Tenebrio molitor (common mealbeetle). The immobilizing effects were quantified by measuring insect locomotor activity in circle arenas observed over 72 hr after venom injection. Both insect species showed cramps, quivering and jerking of the limbs as well as flaccid paralysis after venom injection. Through relative toxicity of the venoms tested is the same in T. molitor and B. orientalis, T. molitor is absolutely less sensitive to spider venoms. The effects on locomotor activity show time characteristics specific for each venom. A dependence of the venom paralyzing effects on insect locomotor activity, low intensity of the initial excitatory phase of the venom effects and partial recovery of the insects was found with A. bruennichi and T. atrica venom. The maximal venom yields of A. bruennichi and S. mexicanus are not lethal to B. orientalis, indicating that the mere immobilizing effects of spider venoms are far more crucial to prey capture than their lethal effects. The contribution of a variety of differently acting neurotoxic components in spider venoms to the observed venom effects on insects and the significance of the venoms in spider nutrition, hunting behaviour and ecology are discussed.

Purification of toxic peptides and the amino acid sequence of CSTX-1 from the multicomponent venom of Cupiennius salei (Araneae:Ctenidae).

The venom of the wandering spider Cupiennius salei was analysed biochemically by gel filtration, cation exchange chromatography, RP-HPLC, IEF, SDS-PAGE and TLC-electrophoresis. The native venom contains high levels of Na+, K+, Ca2+, histamine and taurine. It shows considerable activity of hyaluronidase, but not proteolytic activity. Thirteen peptides (CSTX-1 to CSTX-13) with an apparent mol. wt between 2.6 and 12.5 kDa causing differently strong toxic, effects were purified. Toxicity data of the crude venom (insects and mouse) are given and compared with the toxicity of CSTX-1, which causes most of the crude venom's toxicity. CSTX-1 has a mol. wt of 8352.6 and its amino acid sequence of 74 amino acids is given.

Quantity and quality of venom released by a spider (Cupiennius salei, Ctenidae).

The amount of venom injected by the spider Cupiennius salei depended on the efficiency of the mechanical defence of the prey species. Spiders were milked for the first venom (i.e. the first microlitre of venom emitted) versus remaining venom, and for venom regenerated from emptied glands. HPLC gel filtration and IEF electrophoresis showed that the protein content of the first venom was only half as compared to that of the remaining venom, and that this was due to a dilution of all proteins. Venom regeneration came in two speeds. The amount of venom was regenerated more rapidly than the protein concentration. Newly regenerated venom as compared to older venom was characterized by a lower concentration of all proteins and by a higher total concentration of free amino acids, whereas histamine and taurine did not follow this trend. K+ concentration and pH remained similar during venom regeneration. Crickets injected with the venoms showed less acute symptoms when the protein concentration was lower, namely with the first venom and with newly regenerated venom. Consequently, a spider which modulates the quantity of venom injected into a prey also directly changes the venom quality. The ecological consequences of this are discussed. This paper also discusses which region of a gland (ampulla, extracellular and intracellular parts of the glandular sac) is involved in the changes of the venom quality.

Characterisation of antibacterial activity of peptides isolated from the venom of the spider Cupiennius salei (Araneae: Ctenidae).

The characterisation of the antimicrobial activity of five antibacterial peptides, isolated from the venom of the neotropical wandering spider Cupiennius salei is reported here. The peptides have a molecular mass, determined by electrospray ionisation-mass spectrometry, between 3-4 kDa. Minimal inhibitory concentrations against five different bacteria species were determined by a liquid growth inhibition assay. All five peptides showed minimal inhibitory concentrations that are comparable to those of other known antibacterial peptides, like insect defensins and cecropins, found in the last years in a large diversity of animals. The peptides are supposed to lyse the cells by formation of either distinct channels or pores, but their mode of action is not yet revealed.

The importance of human ecology at the threshold of the next millennium: how can population growth be stopped?

Ecology is defined as the set of complex interactions between the biotic and abiotic environments. Human ecology concerns principally the population ecology "only" of Homo sapiens, but it also includes all aspects of global ecology because humans are the most important species. Human demography is characterized by a recent decline in mortality and fertility rates. These demographic transitions have largely been completed in industrialized countries, but not in the 140 developing countries. Approximately 100 countries are following the same demographic pattern as industrialized countries, however with a time delay of several generations. China has effectively reduced its population increase by means that would be unacceptable in Western democracies. Some 44 developing countries still show increasing population growth and no detectable demographic transition in birth rate. Thus one part of the world shows limited (and, in the long run, shrinking) population growth, and another continues with a strong increase. All populations are limited in their development by their sustainability by their environment, for example, food and energy resources, and the extent of pollution which the use of these resources produces. It is argued that in the case of human population the limits of sustainability have already been reached with the 6 billion humans alive today, since at least 20% of these suffer from hunger, natural resources are overexploited, and biodiversity is threatened. In the coming 200 years it is more likely that the total population will substantially oscillate rather than approach the predicted 12 billion. The most important goal of human ecology should therefore be to slow population growth as far as possible.

Recent habitat fragmentation due to roads can lead to significant genetic differentiation in an abundant flightless ground beetle.

Although habitat fragmentation is suspected to pose a major threat to biodiversity, its impact on abundant invertebrate species has been little investigated. We assessed the genetic population structure of the flightless ground beetle Abax parallelepipedus in a forest fragmented by two main roads and a highway using five microsatellite loci. We detected low levels of genetic differentiation, which was concordant with the high population densities of 632-1707 individuals/ha estimated with a mark-recapture method. A Mantel test detected a highly significant increase of pairwise F(ST)-values with the number of roads between sampling locations. As expected, the most pronounced effect of the isolation due to roads was observed in the sample from the smallest fragment (highway exit loop), which was differentiated significantly from most other locations. However, no signs of a recent bottleneck or a loss of genetic variability were detected in this population, indicating a still relatively large effective population size (N(e)). Computer simulations confirmed that the observed F(ST)-values were indeed compatible with a N(e) of a few hundred individuals in this fragment, assuming strong or absolute isolation since the construction of the roads. We discuss the implications of our findings for the conservation of abundant but poorly dispersing species in fragmented habitats.

Degradation of the Cry1Ab protein within transgenic Bacillus thuringiensis corn tissue in the field.

Large quantities of Bacillus thuringiensis (Bt) corn plant residue are left in the field after harvest, which may have implications for the soil ecosystem. Potential impacts on soil organisms will also depend on the persistence of the Bt toxin in plant residues. Therefore, it is important to know how long the toxin persists in plant residues. In two field studies in the temperate corn-growing region of Switzerland we investigated degradation of the Cry1Ab toxin in transgenic Bt corn leaves during autumn, winter and spring using an enzyme-linked immunosorbent assay (ELISA). In the first field trial, representing a tillage system, no degradation of the Cry1Ab toxin was observed during the first month. During the second month, Cry1Ab toxin concentrations decreased to approximately 20% of their initial values. During winter, there was no further degradation. When temperatures again increased in spring, the toxin continued to degrade slowly, but could still be detected in June. In the second field trial, representing a no-tillage system, Cry1Ab toxin concentrations decreased without initial delay as for soil-incorporated Bt plants, to 38% of the initial concentration during the first 40 days. They then continued to decrease until the end of the trial after 200 days in June, when 0.3% of the initial amount of Cry1Ab toxin was detected. Our results suggest that extended pre- and post-commercial monitoring are necessary to assess the long-term impact of Bt toxin in transgenic plant residues on soil organisms.

Effects of transgenic Bt corn litter on the earthworm Lumbricus terrestris.

A 200-day study was carried out to investigate the impact of transgenic Bacillus thuringiensis (Bt) corn on immature and adult Lumbricus terrestris in the field and in the laboratory. Another objective of this study was to develop test methods that could be used for standard testing of the impact of transgenic plants on different earthworm species in the field and in the laboratory. For this purpose two different experiments were involved, a laboratory experiment with adult L. terrestris and a field experiment with immature L. terrestris. No lethal effects of transgenic Bt corn on immature and adult earthworms were observed. Immature L. terrestris in the field had a very similar growth pattern when fed either (Bt+) or (Bt-) corn litter. No significant differences in relative weights of (Bt+) and (Bt-) corn-fed adult L. terrestris were observed during the first 160 days of the laboratory trial, but after 200 days adult L. terrestris had a significant weight loss of 18% of their initial weight when fed (Bt+) corn litter compared to a weight gain of 4% of the initial weight of (Bt-) corn-fed earthworms. Further studies are necessary to see whether or not this difference in relative weight was due to the Bt toxin or other factors discussed in the study. Degradation of Cry1Ab toxin in corn residues was significantly slower in the field than at 10 degrees C in the laboratory. Enzyme-linked immunosorbent assay results indicated that earthworms in both experiments were exposed to the Bt toxin throughout the whole experimental time.

Effects of size, motility and paralysation time of prey on the quantity of venom injected by the hunting spider Cupiennius salei.

Previous experimental studies have shown that neotropical wandering spiders (Cupiennius salei) inject more venom when attacking larger crickets. It has been postulated that this is a consequence of predator-prey interactions during envenomation, which increase in intensity with the size of a given prey species. The present study was designed to test this hypothesis using anaesthetized crickets of different sizes that were moved artificially. Cupiennius salei was found (1) to inject more venom the greater the intensity of the struggling movement of the crickets (prey size kept constant); (2) to inject more venom the longer the duration of the struggling movement of the crickets (prey size and intensity of movement kept constant); and (3) to inject equal amounts into crickets of different size (duration and intensity of movement kept constant). These results indicate that C. salei alters the amount of venom it releases according to the size and motility of its prey. Venom expenditure depends mainly on the extent of the interactions with the prey during the envenomation process, whereas prey size is of minor significance. The regulation of venom injection in concert with behavioural adaptations in response to various types of prey minimizes the energetic cost of venom production, thus increasing the profitability of a given prey item.

A lysine rich C-terminal tail is directly involved in the toxicity of CSTX-1, a neurotoxic peptide from the venom of the spider Cupiennius salei.

CSTX-1 (74 amino acids, 8,352.62 Da) is a potent neurotoxin from the venom of Cupiennius salei. With the monoclonal antibody 9H3 against CSTX-1, we identified two similar peptides by Western blot analysis. These two peptides were purified by RP-HPLC: CSTX-2a (61 amino acids, 6865.75 Da) and CSTX-2b (60 amino acids, 6709.57 Da). Using ESI-MS analysis and sequencing we verified that CSTX-2a is a truncated version of CSTX-1. CSTX-2b differs from CSTX-2a by the absence of Arg61. Toxicity of CSTX-1, CSTX-2a, and CSTX-2b to Drosophila melanogaster showed that the absence of the last 13 amino acids of CSTX-1 results in a seven-fold activity loss. CSTX-2b, which lacks Arg61 is 190-fold less toxic. We conclude that the C-terminal part of CSTX-1, especially Arg61, is essential for the expression of toxicity. CSTX-1 is degraded to CSTX-2a and CSTX-2b by proteases that are released from venom gland cells by apocrine secretion.

CSTX-9, a toxic peptide from the spider Cupiennius salei: amino acid sequence, disulphide bridge pattern and comparison with other spider toxins containing the cystine knot structure.

CSTX-9 (68 residues, 7530.9 Da) is one of the most abundant toxic polypeptides in the venom of the wandering spider Cupiennius salei. The amino acid sequence was determined by Edman degradation using reduced and alkylated CSTX-9 and peptides generated by cleavages with endoproteinase Asp-N and trypsin, respectively. Sequence comparison with CSTX-1, the most abundant and the most toxic polypeptide in the crude spider venom, revealed a high degree of similarity (53% identity). By means of limited proteolysis with immobilised trypsin and RP-HPLC, the cystine-containing peptides of CSTX-9 were isolated and the disulphide bridges were assigned by amino acid analysis, Edman degradation and nanospray tandem mass spectrometry. The four disulphide bonds present in CSTX-9 are arranged in the following pattern: 1-4, 2-5, 3-8 and 6-7 (Cys6-Cys21, Cys13-Cys30, Cys20-Cys48, Cys32-Cys46). Sequence comparison of CSTX-1 with CSTX-9 clearly indicates the same disulphide bridge pattern, which is also found in other spider polypeptide toxins, e.g. agatoxins (omega-AGA-IVA, omega-AGA-IVB, mu-AGA-I and mu-AGA-VI) from Agelenopsis aperta, SNX-325 from Segestria florentina and curtatoxins (CT-I, CT-II and CT-III) from Hololena curta. CSTX-1/CSTX-9 belong to the family of ion channel toxins containing the inhibitor cystine knot structural motif. CSTX-9, lacking the lysine-rich C-terminal tail of CSTX-1, exhibits a ninefold lower toxicity to Drosophila melanogaster than CSTX-1. This is in accordance with previous observations of CSTX-2a and CSTX-2b, two truncated forms of CSTX-1 which, like CSTX-9, also lack the C-terminal lysine-rich tail.