Oren Hasson

Pursuit-deterrent signals: communication between prey and predator

When encountering predators, prey animals often expose themselves by loud vocalization, by repeated movements or by revealing conspicuous colors. The more elaborate displays were often considered to be warning signals directed to other prey, and the less obvious displays to be intention movements. During the last decade, there has been increasing evidence that, in fact, prey display is aimed at the predator, apparently to deter further pursuit. This communication between two seemingly unlikely partners, prey and predator, appears to be based upon a common interest - satisfying the predators need for further information.

Initiation and resolution of jumping spider contests: roles for size, proximity, and early detection of rivals

Abstract. Animals are commonly expected to assess each other during contests in order to economically identify relative status. Escalated or long contests are expected to arise mainly when rivals have difficulty discriminating small differences. Results of the present study of male-male contests in Plexippus paykulli, a jumping spider (Salticidae) with acute vision, are not in accord with this widely held view. Despite the typical finding that size-advantaged rivals are more likely to win contests and that this tendency increases with size disparity, contest dynamics suggest that these tendencies are achieved in the absence of direct size assessment. In contests between different-sized spiders, maximum escalation and overall duration were predicted by the absolute size of the size-disadvantaged spider (usually the loser) rather than the size difference between the rivals. This result suggests that spiders base decisions of persistence on their own size, such that size-disadvantaged rivals usually reach their limits first, and then retreat. This interpretation is further supported by findings that maximum escalation and total duration were both positively related to size in contests between size-matched spiders. Spiders were more likely to win if they oriented and displayed first, and longer, more escalated, contests ensued if the size-disadvantaged spider was the first to orient and display. Proximity of rivals at contest outset also influenced contest dynamics, but not outcome.

Body postures and patterns as amplifiers of physical condition.

The question of why receivers accept a selfish signallers message as reliable or ‘honest’ has fuelled ample controversy in discussions of communication. The handicap mechanism is now widely accepted as a potent constraint on cheating. Handicap signals are deemed reliable by their costs: signallers must choose between investing in the signal or in other aspects of fitness. Accordingly, resources allocated to the signal come to reflect the signallers fitness budget and, on average, cheating is uneconomic. However, that signals may also be deemed reliable by their design, regardless of costs, is not widely appreciated. Here we briefly describe indices and amplifiers, reliable signals that may be essentially cost free. Indices are reliable because they bear a direct association with the signalled quality rather than costs. Amplifiers do not directly provide information about signaller quality, but they facilitate assessment by increasing the apparency of pre–existing cues and signals that are associated with quality. We present results of experiments involving a jumping spider (Plexippus paykulli) to illustrate how amplifiers can facilitate assessment of cues associated with physical condition without invoking the costs required for handicap signalling.

The predatory response of a stalking spider,Plexippus paykulli, to camouflage and prey type

When approaching prey, a stalking predator should consider trade-offs between the probabilities of early detection (by the prey, before the strike), spontaneous departure (of prey, before the strike), prey escape (following the strike) and interference (by rivals or predators). In this study we tested the response of a jumping spider, Plexippus paykullito a background with two different camouflaging properties, and two different prey types (maggots versus adult house flies). Spiders jumped towards adult house flies from greater distances on a non-camouflaging background, but background colour had no effect on jumping distance when the prey were maggots. Spiders stalking both prey types approached more slowly when camouflaged. Our experiments suggest that jumping spiders may be responding to changes in the trade-off relationships between the probabilities of early detection, spontaneous departure, escape and interference.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Providing or hiding information: On the evolution of amplifiers and attenuators of perceived quality differences

In many coevolutionary systems members of one party select members of a second party based on quality differences existing among members of the latter (e.g., predators and prey, pollinators and flowers, etc.). We examined the fate of characters that increase (amplifiers) or decrease (attenuators) the perceived amplitude of differences in the quality upon which choice of the selecting party is based. We found that the evolution of such characters depends on (i) the relationship between the cost of the character and the relative benefit it gives to the high quality individuals (if an amplifier) or low quality individuals (if an attenuator), and (ii) the frequency, among members of the selected party, of the quality sought by the selecting party.

A fly in spider’s clothing: what size the spider?

Many flies of the family Tephritidae have stripes on their wings and black markings on their thorax which make them look like jumping spiders (Salticidae), especially when they display their wings horizontally. Previous studies have shown that salticid spiders respond to tephritids by displaying and retreating, arguing that tephritids evolved as mimics of salticids to protect them from predation by the latter. Here I show that the jumping spiders’ reaction to a tephritid fly, the Mediterranean fruit fly (medfly) Ceratitis capitata, depends on the spider’s size, age and sex. Large, adult female jumping spiders seem to be the least confused or intimidated by the medfly. This reduces the benefits that may derive from the resemblance of tephritids’ wing and thorax patterns and displays to salticids, and leaves some doubt whether these flies’ special characteristics solely evolved to confuse spiders.

Frequency-dependent host selection by parasitic mites: a model and a case study

Previous studies on frequency-dependent food selection (changing food preferences in response to changes in relative food abundance) have focused on predators and parasitoids. These organisms utilize several victims during their lifetime. We introduce the case of parasites which, having accepted a host, do not change it. We propose two alternative models to explain the biased occurrence of parasites on different host types: (1) through the option of rejecting less-preferred hosts prior to accepting one of them; (2) by differential parasite survival on different host types. These models predict that host rejection, but not differential survival, can create frequency-dependent parasitism (FDP). Unlike previously described factors responsible for frequency dependence of food selection, which act through changing the foraging behaviour of individual predators or parasitoids, FDP involves no adjustment of parasite foraging strategy according to previous feeding experience. The mite Hemisarcoptes coccophagus is an obligate parasite of armoured scale insects (Homptera: Diaspididae). Our field data show that H. coccophagus is found more frequently on ovipositing than on young host females. Our model, combining the effects of host rejection and differential survival, is used to estimate the relative contribution of these factors to parasite biased occurrence on different hosts. The contribution of differential survival was dominant in H. coccophagus, and overode any effect of host rejection. Nevertheless, our prediction that FDP may be found in parasites is supported by literature data about a parasitic water mite.