Elizabeth M. Jakob

Rearing environment affects behaviour of jumping spiders

We tested the effect of rearing conditions on the behaviour of jumping spiders, Phidippus audax. Spiders were assigned randomly to either small or large cages that either were empty or contained a painted dowel. Laboratory-reared spiders were raised from second instar to adult in these environments. Field-caught adults also were randomly assigned to these containers and were held for approximately 4 months prior to testing. We presented spiders with three tests designed to examine a range of behaviours. Field-caught spiders were more likely than laboratory-reared spiders to (1) react to videotaped prey, (2) progress further on a detour test, and (3) be less stereotactic and more active in an open field. Larger cage size and the presence of the dowel also improved performance in several tests. Our results suggest that the rearing conditions we used, which are commonly employed by behavioural researchers, may profoundly influence the behaviour of adult spiders. Copyright 2000 The Association for the Study of Animal Behaviour.

Leg autotomy in a spider has minimal costs in competitive ability and development

A number of species have the ability to autotomize limbs voluntarily, but animals that have lost limbs often face substantial costs. We examined the frequency of leg loss and its effects on competitive ability and development in the spider Holocnemus pluchei (Araneae: Pholcidae), a family of spiders known for its readiness to autotomize legs. Leg loss was common in field populations, with 7.5% of all surveyed spiders missing at least one leg, most commonly one of the anterior pair. More spiders were missing multiple legs than expected by chance, suggesting that leg loss events are not independent. Large adult spiders were missing legs more frequently than were small spiders. The competitive ability of injured males was tested in three contexts. In the field, no effect of leg loss was found on the ability of spiders to remain in webs into which they were introduced. In the laboratory, no effect of leg loss was found on the ability to fight with a single opponent over a prey, except that injured spiders were more likely to lose high-intensity fights. There was no difference between intact and injured males in their ability to compete with three females for limited prey. Leg loss significantly affected development time. The moult interval during the instar in which the injury occurred increased by approximately 15%. However, the growth rate for injured spiders was slightly but not significantly faster in the instar following leg loss, and total development time of the two instars together did not differ significantly between treatments. No spider showed any signs of regeneration. We conclude that, although there were some statistically significant differences between intact and injured males, these are unlikely to have major impacts on fitness, in contrast to findings in other species. Copyright 1999 The Association for the Study of Animal Behaviour.

Plasticity, Learning and Cognition

As is becoming increasingly clear, spiders are not entirely instinct driven and inflexible in their behaviour. Here we review evidence for behavioural plasticity, learning and other cognitive processes such as attentional priming and memory. We first examine these attributes in several natural contexts: predation, interactions with conspecifics and potential predators, and spatial navigation. Next we examine two somewhat more artificial experimental approaches, heat aversion and rearing in enriched versus impoverished environments. We briefly describe the neurobiological underpinnings of these behaviours. Finally, we point to areas where our knowledge gaps are greatest, and we offer advice for researchers beginning their own studies of spider learning. Overview The history of the study of spider learning parallels that of insect learning, but lags well behind. At the start of the twentieth century, the general view was that insect learning was generally guided by instinct, but a steady accumulation of data has transformed our view of the importance of learning in their daily lives (reviewed in Dukas, 2008). In spite of their tiny brains, insects are capable of learning a multitude of tasks related to foraging, anti-predatory behaviour, aggression, social interactions, courtship and mate choice (Dukas, 2008). The study of spider behaviour is undergoing a similar transformation. Beginning over a century ago, researchers have periodically delved into the question of whether spider behaviour is primarily instinctual or can be modified with experience.

EFFECTS OF MATERNAL BODY SIZE ON CLUTCH SIZE AND EGG WEIGHT IN A PHOLCID SPIDER (HOLOCNEMUS PLUCHEI)

Abstract The pholcid spider Holocnemus pluchei (Scopoli 1763) competes for food with conspecifics, and spiders reared on high food levels are generally larger. In this study, we examined whether larger female body size (as estimated by tibia-patella length) translated into increased reproductive success in the form of increased clutch size, clutch weight, and average egg weight. Larger spiders had more eggs and thus heavier clutches, but there was no relationship between maternal size and average egg weight. We also looked for a tradeoff between average egg weight and egg number, and we found a weak relationship in which average egg weight was highest for intermediate-sized clutches. Larger female body size thus translates into increased reproductive success in terms of egg number and clutch weight, but not weight of individual eggs.

Jumping Spiders Associate Food With Color Cues In A T-Maze

Abstract Salticid spiders are a tractable group for studies of learning. We presented Phidippus princeps Peckham & Peckham 1883 with the challenging task of associating prey with color cues in a T-maze. Experimental spiders were given the opportunity to learn that a cricket was hidden behind a block of a particular color. To eliminate the use of other cues, we randomly assigned both block position within the maze, and maze location within the room. For control spiders, no cues predicted the location of prey. We gave spiders two blocks of trials. Each block consisted of four training trials followed by a probe trial in which no prey was present. Trials lasted an hour, and spiders were given one trial per day. Not all spiders were successful in finding the prey during training trials. In the first probe trial, there was no evidence of learning: there was no effect of treatment, the number of successful training trials, or their interaction on which block the spiders chose first. In the second probe trial, there was a significant interaction between treatment and number of successful training trials: experimental-group spiders with a greater number of successful training trials were more likely to choose the correct block in the probe trial. This study demonstrates that P. princeps can learn the location of prey by color cues alone, a challenging task, and adds to the growing literature on learning in spiders.

CHEMOSENSORY RESPONSE TO PREY IN PHIDIPPUS AUDAX (ARANEAE, SALTICIDAE) AND PARDOSA MILVINA (ARANEAE, LYCOSIDAE)

Abstract Many predators exploit the chemical signatures of prey when foraging. We present a comparative study designed to test if the foraging behavior of Phidippus audax (Hentz 1845) is manipulated by substrate-borne chemicals left by prey. Our findings suggest that foraging P. audax do not use chemical cues left by prey, while the wolf spider Pardosa milvina (Hentz 1844) in the same experimental setup does respond to chemical cues. However, further examination into the role of chemical cues on prey detection in salticids is required.

Firefly flashing and jumping spider predation

Bioluminescent flashing in fireflies, while primarily a sexual signal, is known to deter some predators while attracting others. We tested whether flashing serves an antipredator function against two species of diurnal, visually hunting jumping spiders, Phidippus princeps and Phidippus audax. To confirm anecdotal reports that fireflies flash during the day in a nonmating context, we documented that adult fireflies (Photuris sp.) of both sexes flash when disturbed in daylight. We also confirmed that activity periods of Phidippus and fireflies overlap, and that spiders attack fireflies and elicit flashing behaviour. We conducted three experiments to examine the influence of flashing on spider behaviour. (1) We tested whether the sudden onset of a flashing LED startled spiders that had initiated attacks on crickets, and found no evidence that it did so. (2) We used choice tests to determine whether flashing lights attracted or deterred spiders from attacking palatable prey. Spiders more often attacked crickets positioned next to a flashing LED versus an LED that was either off or glowed steadily. (3) Many firefly species are distasteful. Therefore, we tested whether flashing lights facilitate avoidance of unpalatable prey with experience. Spiders were given seven encounters with unpalatable prey (nonluminescent Ellychnia corrusca fireflies) associated with either flashing or unlit LEDs. Spiders in the two treatments were equally likely to attack the prey during their first encounter, but spiders exposed to flashing LEDs were significantly less likely to attack unpalatable prey by their seventh trial. Spiders tested with palatable prey showed no decline in attacks after exposure to flashing LEDs. We conclude that, although bioluminescent flash signals may increase attack rates by predatory jumping spiders, they may also facilitate learning about unpalatable prey. Thus, the costs and benefits of flashing may depend on the prevalence of firefly palatability.

Competitive interactions between a native spider (Frontinella communis, Araneae: Linyphiidae) and an invasive spider (Linyphia triangularis, Araneae: Linyphiidae)

There are numerous reports of spiders that have become established outside of their native ranges, but few studies examine their impact on native spiders. We examined the effect of the European hammock spider Linyphia triangularis (Araneae, Linyphiidae) on the native bowl-and-doily spider Frontinella communis (Araneae, Linyphiidae) in Acadia National Park, Maine, USA. First, we added L. triangularis to established plots of F. communis. Significantly more F. communis abandoned their webs when L. triangularis were added compared to control plots. Second, we tested whether F. communis were deterred from building webs in areas where L. triangularis was established. Significantly fewer F. communis built webs on plots with L. triangularis than on control plots. In both experiments, L. triangularis sometimes took over webs of F. communis or incorporated F. communis webs into their own webs, but F. communis never took over or incorporated L. triangularis webs. Competition between L. triangularis and F. communis for both webs and web sites may contribute to the decline of F. communis.

Ontogenetic Shifts in the Costs of Living in Groups: Focal Observations of a Pholcid Spider (Holocnemus pluchei)

Abstract Holocnemus pluchei spiders (Family Pholcidae) facultatively live in groups: sometimes they live alone and sometimes they share webs. In the field groups vary in size and composition and include spiders of all ages and either sex. Group membership is flexible and individuals move frequently among groups. To understand group formation and maintenance it is necessary to understand the costs of group membership. We used focal animal sampling to investigate the cost of group living for spiders of different ages across a range of group sizes. Both spider age and group size affected the costs incurred by group-living spiders. There was no variation among groups of different sizes in the percentage of time focal small or large spiders spent in costly behaviors (moving, web maintenance, bouncing or interactions with conspecifics), but medium-sized spiders spent more time engaged in costly behaviors with increasing group size. Medium and large spiders also had more interactions with greater numbers of different conspecifics when they were in groups larger than three, whereas small spiders interacted rarely with conspecifics regardless of group size. These results suggest that there are significant ontogenetic shifts in the costs of group living in H. pluchei.

Competition between introduced and native spiders (Araneae: Linyphiidae)

The European sheet-web spider Linyphia triangularis (Araneae: Linyphiidae) has become established in Maine, where it often reaches very high densities. Two lines of evidence from previous work suggest that L. triangularis affects populations of the native linyphiid spider Frontinella communis. First, F. communis individuals are relatively scarce in both forest and coastal habitat where L. triangularis is common, but more common where L. triangularis is at low density. Second, in field experiments, F. communis species are less likely to settle in experimental plots when L. triangularis is present, and F. communis disappears from study plots when L. triangularis is introduced. Here we test two mechanisms that may underlie these patterns. First, we tested whether L. triangularis invades and usurps the webs of F. communis. When spiders were released onto webs of heterospecifics, L. triangularis was more likely to take over or share webs of F. communis than the reverse. We also observed natural takeovers of F. communis webs. Second, we explored the hypothesis that L. triangularis reduces prey availability for native species. We sampled flying prey in areas with L. triangularis and those where it had been removed, and found no effect of spider presence on measured prey density. We also found no effect of prey supplementation on web tenacity in F. communis, suggesting that F. communis movements are not highly dependent on prey availability. We conclude that web takeover is likely more important than prey reduction in driving negative effects of L. triangularis on F. communis.