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PubMed1999

Hunger effects on foraging responses to perceptual cues in immature and adult wolf spiders (Lycosidae).

The wolf spider, Schizocosa ocreata (Hentz), varies foraging patch residence time in the presence of different sensory cues from prey, even without food rewards. This study examines the influence and interaction of hunger state, age and sex on the use of different types of sensory information to determine foraging patch sampling duration. In a series of two-chambered artificial foraging patches, I tested 26 S. ocreata once as immatures, and again as adults, under two hunger states (satiated and 7 days without food). Patches varied in the type of sensory information provided by live prey (crickets) as follows: visual cues alone; vibratory cues alone; combined visual/vibratory cues; and control (no prey). Without feeding in patches, the type of sensory stimuli available from prey strongly affected patch residence time, with spiders using primarily visual rather than vibratory cues. Hunger level as a main effect had no influence on residence time, but hunger state did mediate the importance of visual or vibratory information. Significant age- and sex-related differences in patch residence time in the presence of different sensory cues were found.These data suggest that ontogenetic and sex-specific foraging strategies are influenced by use of prefeeding perceptual cues rather than hunger state in wolf spiders. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Scanning and route selection in the jumping spider Portia labiata.

Jumping spiders Portia labiata were tested in the laboratory on three different kinds of detours. In one, both routes led to the lure. In the other variants, one of the routes had a gap, making that route impassable. When tested with only one complete route, Portia chose this route after visually inspecting both routes. An analysis of scanning showed that, at the beginning of the scanning routine, the spiders scanned both the complete and the incomplete route but that, by the end of the scanning routine, they predominantly scanned only the complete route. Two rules seemed to govern their scanning: (1) they would continue turning in one direction when scanning away from the lure along horizontal features of the detour route; and (2) when the end of the horizontal feature being scanned was reached, they would change direction and turn back towards the lure. These rules 'channelled' the spiders' scanning on to the complete route, and they then overwhelmingly chose to head towards the route they had fixated most while scanning. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2001

Wolf spider predator avoidance tactics and survival in the presence of diet-associated predator cues (Araneae: Lycosidae).

Some prey can distinguish between chemical cues from predators fed different diets. Here we document the first evidence of diet-based chemical discrimination of predators in a terrestrial arthropod and measure the survival value of behavioural responses to predator chemical cues. We tested activity level and avoidance behaviour of the wolf spider, Pardosa milvina, to faeces and silk associated with the predatory wolf spider, Hogna helluo, fed either P. milvina or crickets (Acheta domesticus). We then measured survival of Pardosa in the presence of Hogna when placed on blank paper or paper previously occupied by Hogna fed either crickets or Pardosa. Filter paper previously occupied by Hogna from each diet treatment or a blank control were simultaneously presented to adult female Pardosa among four treatment pairs (N=15/treatment): (1) blank paper/blank paper, (2) Hogna fed crickets/blank, (3) Hogna fed Pardosa /blank and (4) Hogna fed Pardosa / Hogna fed crickets. Cues from Hogna fed either crickets or Pardosa elicited significantly less activity relative to blank controls. Cues from Hogna fed Pardosa elicited a significantly greater reduction in activity than Hogna fed crickets. When given a choice, Pardosa initially chose the blank substrate significantly more often than either substrate with Hogna cues. Spiders survived longer in the presence of cues from either Hogna diet treatment relative to blank paper, but there was no significant effect of predator diet on survival. Results suggest diet-based predator cues elicit different levels of activity in Pardosa that reduce predation in the presence of Hogna. Copyright 2001 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Evidence from flagelliform silk cDNA for the structural basis of elasticity and modular nature of spider silks.

Orb-web weaving spiders rely on their aerial nets to entrap flying prey. A key mechanical feature of orb-web design is the high elasticity of the capture spiral. We report the cloning of substantial cDNA for flagelliform gland silk protein, which forms the core fiber of the catching spiral. Like all silks, the flagelliform protein is composed largely of iterated sequences. The dominant repeat of this protein is Gly-Pro-Gly-Gly-X, which can appear up to 63 times in tandem arrays. This motif likely forms Pro2-Gly3 type II beta-turns and the resulting series of concatenated beta-turns are thought to form a beta-spiral. We propose that this spring-like helix is the basis for the elasticity of silk. The variable fifth position of the motif (X) is occupied by a small subset of residues (Ala, Ser, Tyr, Val). Moreover, these X amino acids occur in specific patterns throughout the repeats. This ordered variation strongly suggests that with hydration, the beta-spirals form hydrogen-bonded networks that increase the elasticity of flagelliform silk. The self-assembly of flagelliform protein monomers into silk fibers may be promoted by beta-spiral/beta-spiral interactions. Additionally, the other two motifs in the flagelliform protein, Gly-Gly-X and a spacer that disrupts the glycine-rich regions, may contribute to the alignment of monomers into fibers. The flagelliform protein cDNA was compared to the other members of the spider silk gene family. We show that all spider silk proteins can be characterized as sets of shared structural modules. The occurrence of these modules among the proteins is inconsistent with the phylogenetic relationships inferred from the C-terminal regions. This observation, along with the high level of variation among individual flagelliform protein repeats, but striking lack of such variation in the other silk proteins, suggests that unusual homogenization processes are involved in silk protein evolution.

Amino Acid Sequence↗
PubMedDate not supplied

SPIDER and WEB: processing and visualization of images in 3D electron microscopy and related fields.

The SPIDER system has evolved into a comprehensive tool set for image processing, making use of modern graphics interfacing in the VMS and UNIX environment. SPIDER and WEB handle the complementary tasks of batch processing and visualization of the results. The emphasis of the SPIDER system remains in the area of single particle averaging and reconstruction, although a variety of other application areas have been added. Novel features are a suite of operations relating to the determination, modeling, and correction of the contrast transfer function and the availability of the entire documentation in hypertext format.

Animals↗
PubMed1999

Collective decision-making in social spiders: dragline-mediated amplification process acts as a recruitment mechanism

Amplification mechanisms involved in group cohesion and coordination of several individuals' activities are a major research topic in social arthropod biology. In this paper, we investigate how recruitment processes can be mediated by the use of silk draglines in the case of social spiders. Our intent is to demonstrate how a behavioural feature common to all spider species can induce positive feedback, potentially leading to collective decision-making in a social context. Dragline-mediated amplification mechanisms are investigated in a simulated "Y" choice set-up. Numerical experiments involve two distinct models: a simplified one, devoted to the exploration of the most basic amplifying properties of the system, and a more complex simulation platform, taking into account the geometrical properties of a growing network (two-dimensional web). The effect of hypothetical subpopulations, as well as variations in silk attractivity in the case of mixed populations (originating from multiple nests) are also discussed. Results fit experimental data and demonstrate that spiders' behaviour exhibits very strong amplifying properties that can play a crucial part in the organization of social life. Copyright 1999 Academic Press.

Journal Article↗
PubMed2002

Vasa expression and germ-cell specification in the spider mite Tetranychus urticae.

The specification of germ cells is an important process during the development of all animals. Expression of an evolutionarily conserved gene such as vasa can be used as a marker for germ cell fate. We have isolated a vasa-related gene from the two-spotted spider mite (Tetranychus urticae) and used it to examine the segregation of germ cells in this animal. In spider mites, vasa expression first appears in a group of cells that do not join the initial blastoderm surface. Instead, these cells remain in the interior of the blastoderm and then migrate to posterior regions of the embryo, where they form a cluster that appears in regions of the embryo consistent with the gonads. The expression pattern of this spider mite vasa homologue implies a novel process acts to specify germ cells in this species and that the specification of germ cells is an evolutionarily labile process.

Amino Acid Sequence↗
PubMed1997

Acetylcholine and histamine are transmitter candidates in identifiable mechanosensitive neurons of the spider Cupiennius salei: an immunocytochemical study.

Histochemical and indirect immunocytochemical techniques were used to search for neuroactive substances and transmitter candidates in identified sensory neurons of two types of cuticular mechanoreceptors in the spider Cupiennius salei Keys.: (1) in lyriform slit-sense organ VS-3 (comprising 7-8 cuticular slits each innervated by 2 bipolar neurons), and (2) in tactile hairs (each supplied by 3 bipolar sensory cells). All neurons are mechanosensitive. A polyclonal antibody against choline acetyltransferase (ChAT) strongly labeled all cell bodies and afferent fibers of both mechanoreceptor types. Western blot analysis using the same antibody against samples of spider sensory hypodermis and against samples from the central nervous system demonstrated a clear band at 65 kDa, corresponding to the molecular mass of ChAT in insects. Moreover, staining for acetylcholine esterase (AChE) revealed AChE activity in one neuron of each mechanoreceptor type. Incubation with a polyclonal antibody against histamine clearly labeled one neuron in each set of sensilla, whereas activity in the remaining one or two cells was near background. All mechanoreceptor preparations treated with a polyclonal antiserum against serotonin tested negative, whereas sections through the central nervous system of the same spiders were clearly labeled for serotonin. The presence of ChAT-like immunoreactivity and AChE implicates acetylcholine as a transmitter candidate in the two mechanoreceptive organs. We assume that histamine serves as a mechanosensory co-transmitter in the central nervous system and may also act at peripheral synapses that exist in these sensilla.

Journal Article↗
PubMed2003

Temperature and sex allocation in a spider mite.

Although temperature is the most important environmental factor regulating arthropod development and reproduction, its influence on sex allocation in haplodiploid arthropods remains largely unexplored. We investigated under laboratory conditions how maternal age and temperature mediate offspring sex ratio of the spider mite Tetranychus mcdanieli (Acari: Tetranychidae). Over nine temperature regimes, female-biased sex ratios were consistently observed, varying from 57 to 87% among progeny produced over lifetime. Spider mite sex ratio was affected by maternal age: more male progeny were produced at both the beginning and the end of the female lifespan, yielding a dome shaped curvilinear relationship. This pattern of variation with age probably results from constraints on using sperm at young ages and sperm depletion or viability at older ages. We found a significant curvilinear relationship between temperature and sex ratio. The proportion of female offspring was lowest at intermediate temperatures and highest at extreme temperatures. We suggest that increased female-biased sex ratio at extreme temperatures is an evolutionary response of spider mites to deteriorating habitats as, in the Tetranychidae, females have better capacities than males to disperse and survive under harsh conditions.

Aging↗
PubMed2006

Spider monkey, Muriqui and Woolly monkey relationships revisited.

The taxonomic relationships among the four genera of the Atelidae family, Alouatta (Howler), Ateles (Spider), Lagothrix (Woolly) and Brachyteles (Muriqui), have been the subject of great debate. In general, almost all authors agree with the assignment of Howler monkeys as the basal genus, either in its own tribe Alouattini or in the subfamily Alouattinae, but they disagree on the associations among the other members of the family. Muriquis have been grouped with Spider monkeys based on the fact that they share various behavioral and morphological characteristics. Cladistic analyses using morphological, biochemical, karyotype and behavioral characteristics depicted a phylogenetic tree that places Howler as the basal genus and the remaining genera in an unresolved politomy. More recent studies using molecular data have suggested that Muriqui and Woolly monkeys are sister groups. However, a recent study based on nuclear and mtDNA argued that politomy is what best represents the relationships among Spider, Woolly and Muriqui. To contribute to this debate we have added new data from two nuclear genes, Transferrin and von Willebrand Factor, and using an alignment of 17,997 bp we demonstrate that a total analysis strongly supports the Muriqui-Woolly clade. A gene-to-gene approach showed that four of the eight nuclear genes provide support for the Muriqui-Woolly clade, two strongly and two moderately, while none of the eight genes provide support for any alternative arrangement. The mitochondrial genes were not able to resolve the politomy. A possible reason for the difficulty in resolving atelid relationships may be the short period of time separating each cladogenetic event in the evolutionary process that shaped this family.

Animals↗
PubMed2004

Predation risk affects diapause induction in the spider mite Tetranychus urticae.

Whenever diapause induction triggers movement into another microhabitat or the development of protective morphological structures, this may also alter predation risk. If the risk of being eaten is lower in the diapause phase, then there may be selection favouring diapause induction in response to predators or their cues. In this article, we studied the effect of the predatory mite Typhlodromus pyri on diapause induction in the spider mite Tetranychus urticae. We used a Greek strain because under long-night photoperiods and low temperature only part of the population enters diapause, thereby leaving room for the impact of another factor. In spider mite groups under predation, the percentage diapause induction increased whenever night-lengths were such that diapause was induced (13-16 h of night). Given this diapause induction in response to predation risk, the question arises whether entering diapause helps spider mites to escape from predation and contribute more offspring to the spring generation next year.

Adaptation, Physiological↗
PubMed2006

Does the number of diapausing eggs laid on bark affect the population dynamics of the spider mite Panonychus mori?

We studied the relationship between number of diapausing eggs produced by the spider mite Panonychus mori and the subsequent population trend for a period of 3 years. Panonychus mori showed a single population density peak on its host plant moonseed, Cocculus trilobus. The position and height of this peak were correlated with the density of diapausing eggs around the moonseed leaf buds produced the winter before. In 1994 the density of diapausing eggs measured in February was 4.3/bud, which was 6-14 times higher than the density of diapausing eggs for the same period in 1995 (0.3/bud) and 1996 (0.7/bud). The subsequent population density peak in 1994 occurred in mid June and was about 2.5 times higher than the peaks in 1995 and 1996, which both occurred early September. Thus, the present study showed a positive correlation between the density of diapausing eggs on the host plant and the start and the extend of the population increase the next growing season. Predators associated with the spider mite population were phytoseiid mites, especially Amblyseius eharai was well synchronized with the spider mite density in 1994. Field observations revealed that P. mori produced diapausing eggs in response to short photoperiod in early October each year, which corresponded with the timing predicted by the critical photoperiod around 13 h at 18 degrees C, as assessed in laboratory trials. Diapause ended by early April when egg hatchability attained about 50% and eggs took 9 days to hatch at 25 degrees C and a 16L:8D photoperiod. Hatching in early April was twice faster than in late February.

Analysis of Variance↗
PubMed2006

Odour-mediated responses of a predatory mirid bug and its prey, the two-spotted spider mite.

It has been shown that many natural enemies of herbivorous arthropods use herbivore induced plant volatiles (HIPVs) to locate their prey. Herbivores can also exploit cues emitted by plants infested with heterospecifics or conspecifics. A study was conducted to test whether green bean HIPVs as well as odours emitted directly by spider mites influenced the orientation behaviour of the predatory mirid bug, Macrolophus caliginosus and its prey, Tetranychus urticae in a Y-tube olfactometer. Our results show that both spider mites and M. caliginosus preferred spider mite infested green bean plants to uninfested plants. For M. caliginosus this response was mediated by HIPVs whereas for T. urticae it was mediated through a composite response to both HIPVs and odours emitted directly by the conspecifics (and their associated products). The results may be of use in practical biocontrol situations, through e.g., plant breeding for improved HIPV production, conditioning of mass-reared predators to appropriate cues, and employment of "push-pull-strategies" by using HIPVs.

Animals↗
PubMed1993

Walking behaviour and population density of adult linyphiid spiders in relation to minimizing the plot size in short term pesticide studies with pyrethroid insecticides.

Temporal changes in spatial distribution and population density of linyphiid spiders were studied in relation to physical factors and deltamethrin spraying in the field. The results of the study have been used to set the conditions necessary when plot size is reduced in field trials. The results showed independence of observations at 7 m from an unsprayed reservoir, with respect to migration, in the week following pesticide application. Soil moisture had a positive effect on trapping success, without having apparent effect on trapping success, without having was found for deltamethrin spraying on wet and dry soil. Shifts in the spatial distribution of spider activity showed a close correlation with crop microclimatic conditions. The effect of trapping on population density was shown to be limited. The results suggest that small plots surrounded by a border of 7 m are appropriate for assessing short term pesticide effects on adult linyphiid spiders in winter wheat.

Journal Article↗
PubMed2006

Seasonal variations of fecal progesterone and 17beta-estradiol in captive female black-handed spider monkeys (Ateles geoffroyi).

A number of studies in free-ranging and captive spider monkeys (Ateles spp.) have shown that this genus is able to reproduce throughout the entire year. Nonetheless, it is still controversial whether births, and therefore conceptions, tend to be more frequent during certain seasons. In the present study, we monitored changes in fecal 17beta-estradiol and progesterone for approximately 1 years in five female black-handed spider monkeys (Ateles geoffroyi) kept in captivity in Mexico City. The objective was to determine whether hormone concentrations and menstrual cycles of summer and autumn accounted for a greater chance of conception than those of winter and spring, consistent with birth patterns previously reported. We collected fecal samples from the five monkeys almost daily for 1 year (March 2004 to February 2005) and used radioimmunoassay of fecal extracts to determine concentrations of 17beta-estradiol and progesterone. Concurrently, menstrual cycle phases were determined by cytological evaluation of vaginal swabs. Periovulatory 17beta-estradiol concentrations were significantly higher in autumn than in winter, spring or summer. Moreover, as evidenced by progesterone peaks, most of the summer-autumn menstrual cycles were ovulatory; in contrast, most of the winter and spring cycles were anovulatory. In conclusion, our data supported the notion that, although not a strictly seasonal reproducer, the black-handed spider monkey is more likely to conceive at the end of the rainy season and throughout autumn.

Animals↗
PubMed2006

Artificial insemination in black-handed spider monkey (Ateles geoffroyi).

Artificial insemination (AI) was performed in spider monkeys; these primates are vulnerable to extinction and usually do not reproduce spontaneously in captivity. Uterine cycles were followed by daily assessment of vaginal cytology, and corroborated a posteriori by concentrations of 17-beta estradiol and progesterone, measured by radioimmunoassay (RIA), in fecal samples collected once daily. Five females between 13 to 27 years old were inseminated intravaginally (with fresh semen) twice each during the periovulatory phase (Days 9-12 of the menstrual cycle; Day 0, first day of menstrual bleeding), from September to the first 3 weeks of November (most fertile months). Transcervical AI was not useful in this primate because the liquid portion of the semen completely solidified instead of liquefying as in other primates. Pregnancies were apparently achieved in 5 of 14 attempts. One female became pregnant after the first round of inseminations, delivered a healthy infant, was inseminated and got pregnant again (subsequently aborted). One female aborted, apparently due to an intramural uterine leiomyoma. Another two females stopped menstruating for a few months, then restarted menstruating (these females may have been pregnant and aborted). In conclusion, in spider monkeys: (1) captivity-induced stress did not inhibit reproduction; (2) fecal steroid hormones were useful to assess cyclicity; (3) the semen coagulum, which apparently is a tightly packed and large reservoir of spermatozoa, must not be discarded but used in AI; (4) old female spider monkeys did not have cessation of reproductive function.

Abortion, Veterinary↗
PubMed2003

Experimental evidence for a non-clock role of the circadian system in spider mite photoperiodism.

In the spider mite Tetranychus urticae photoperiodic time measurement proceeds accurately in orange-red light of 580 nm and above in light/dark cycles with a period length of 20 h but not in 'natural' cycles with a period length of 24 h. To explain these results it is hypothesized that the photoperiodic clock in the spider mite is sensitive to orange-red light, but the Nanda-Hamner rhythm (a circadian rhythm with a free-running period tau of 20 h involved in the photoperiodic response) is not and consequently free runs in orange-red light. To test this hypothesis a zeitgeber was sought that could entrain the Nanda-Hamner rhythm to a 24-h cycle without inducing diapause itself, in order to manipulate the rhythm independently from the orange-red sensitive photoperiodic clock. A suitable zeitgeber was found to be a thermoperiod with a 12-h warm phase and a 12-h cold phase. Combining the thermoperiod with the long-night orange-red light/dark regime, both with a cycle length of 24 h, resulted in a high diapause incidence, although neither regime was capable of inducing diapause on its own. The conclusion is that the Nanda-Hamner rhythm is necessary for the realization of the photoperiodic response, but is not part of the photoperiodic clock, because photoperiodic time measurement takes place in orange-red light whereas the rhythm is not able to 'see' the orange-red light. It is speculated that the Nanda-Hamner rhythm is involved in the timely synthesis of a substrate for the photoperiodic clock in the spider mite.

Animals↗
PubMed1997

Evolutionary Relationship between Diapause and Cold Hardiness in the House Spider, Achaearanea tepidariorum (Araneae: Theridiidae).

The relationship between diapause and cold hardiness of the house spider, Achaearanea tepidariorum, differed geographically. In a cool-temperate population, enhanced chilling tolerance and supercooling ability were observed in diapause individuals, whereas a subtropical population showed only chilling tolerance. Because this spider is considered to be of tropical origin, it would follow that the ancestral diapause of this spider was equipped with chilling tolerance, but not with an increased supercooling ability. It seems that the ability to lower the supercooling point evolved through natural selection in the course of expansion of this species to the northern climates. Copyright 1997 Elsevier Science Ltd. All rights reserved

Journal Article↗