Sean E. Walker

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.

The effects of hunger on locomotory behaviour in two species of wolf spider (Araneae, Lycosidae).

We compared the influence of recent feeding history on locomotory behaviour in two species of wolf spiders, Hogna helluo (Walckenaer) and Pardosa milvina Hentz, in the laboratory. Both species are cursorial hunters. We maintained the spiders in the laboratory on satiation and stringent feeding regimes and measured their locomotory activity levels for 1 h using a digital activity recording device. We subjected H. helluo to either ad libitum feeding for 14 days or no food for 14 days. We subjected P. milvina to ad libitum feeding or fasting treatments for 7 and 14 days. We found that H. helluo showed a shift in locomotory activity depending on feeding regime, whereas P. milvina did not. Food-limited H. helluo travelled further than satiated H. helluo, and did so by moving more frequently. Pardosa milvina was in general much more active than H. helluo. We propose that P. milvina is an active forager compared with the sit-and-wait strategy of H. helluo. This difference in foraging strategy is correlated with differences in body size and habitat use. Copyright 1999 The Association for the Study of Animal Behaviour.

A TEST FOR A DIFFERENTIAL COLONIZATION AND COMPETITIVE ABILITY IN TWO GENERALIST PREDATORS

Spatial subdivision of the landscape can reduce the intensity of interspecific interactions, whether they be predation or competition. Recent models examining the ways in which spatial pattern in the landscape will influence the outcome of species interactions assume a trade-off between colonization ability and competitive ability in the interacting species. We tested for differential colonization and competitive ability in two interacting species of wolf spider (Hogna helluo and Pardosa milvina) which co-occur in agricultural and early successional habitats in the eastern USA. We conducted our research in replicated experimental soybean plots in which we created islands of enhanced habitat by supplementing natural litter and enhancing weed growth. Our experimental manipulations were repeated once for each of the two spider species: (1) spiders added, (2) prey attractants (composted vegetable waste) added, (3) spiders and prey attractants added, and (4) one control, for a total of eight subplots. We replicated the experiment six times, three times each in conventionally tilled fields and conservation tilled fields. We censused these plots at the end of the summer and found that conspecific addition significantly elevated numbers of one species (H. helluo) but not the other (P. milvina). These findings were consistent with our predictions that H. helluo is limited in colonization ability when compared to P. milvina. The addition of prey attractants significantly elevated numbers of both species, but the effect was far stronger for the superior colonist (P. milvina). This indicates that P. milvina is able to track resource abundance (both habitat structure and prey), a trait correlated with colonization ability. We found no strong evidence for a negative effect of H. helluo addition on numbers of P. milvina, as would be predicted if H. helluo strongly competed with or significantly preyed upon P. milvina. Body condition of P. milvina was lowest in subplots with higher numbers of H. helluo, indicating that H. helluo may have influenced the foraging success of P. milvina. We also found a strong and unexpected effect of the context of the plots (background tillage regime) on numbers of P. milvina, with there being approximately twice the P. milvina in the subplots in conventionally tilled fields.

Leg Autotomy in the Wolf Spider Pardosa milvina: A Common Phenomenon with Few Apparent Costs

Abstract A number of animals escape predation by sacrificing a body part. Spiders commonly lose legs in encounters with predators or conspecifics. We investigated the frequency of leg loss and its affect on locomotion and prey capture activities of the wolf spider, Pardosa milvina (Araneae; Lycosidae). In addition, we determined if Pardosa were easier to subdue by the larger wolf spider predator, Hogna helluo (Araneae; Lycosidae), once they had experienced leg loss. A field census demonstrated that Pardosa autotomized members of all pairs of legs with equal frequency but overall leg loss was high and increased significantly late in the season. Laboratory experiments revealed that leg loss had no effect on locomotory behavior or prey capture. However, injured spiders tended to take smaller prey. The ability of Hogna, to attack and subdue 7 or 8-legged Pardosa was not different, although 8-legged Pardosa tended to lose multiple legs as they were killed whereas 7-legged Pardosa only lost one. These data suggest that the costs of autotomizing one leg are marginal for Pardosa females and, thus, support the “spare leg hypothesis” that has been proposed for other arachnids.

Sexual Dimorphism in Functional Response and Trophic Morphology in Rabidosa rabida (Araneae: Lycosidae)

Abstract We investigated sexual dimorphism in feeding behavior and morphological characteristics associated with prey capture in the wolf spider, Rabidosa rabida (Araneae, Lycosidae). Female R. rabida attack and consume more prey than do males. In addition to behavioral differences between males and females, morphological features such as chelicerae size and venom gland size are also larger in females. These morphological differences are significant even after accounting for their positive correlation with body size. These data suggest that differences between the sexes in the relationship between fitness and foraging result in a dichotomy between male and female foraging behavior and differences in morphology associated with prey capture.

Ontogenetic shifts in competitive interactions and intra‐guild predation between two wolf spider species

Abstract. 1. The wolf spiders (Araneae: Lycosidae) Hogna helluo (Walckenaer) and Pardosa milvina Hentz co‐occur in soybean fields of south‐west Ohio, U.S.A. As adults, Hogna is the larger species and has the competitive advantage in most interactions; due to differing phenologies, however, their size‐classes frequently overlap and as such there is potential for shifts in competitive ability and intra‐guild predation. The hypothesis that competitive interactions and intra‐guild predation will favour Pardosa when Pardosa is similar‐sized, or has a size advantage over Hogna, was tested in laboratory and field experiments.

Courtship and mating behavior in the brown house snake Lamprophis fulginosus

Courtship behavior in snakes may serve several roles, including species identification, timing of gamete production, and evaluation of fitness of the partner (Ford and Burghardt, 1993). The behavioral acts involved in species identification could be of potential use in taxonomy and systematics (Secor, 1987). However, most accounts of mating in snakes are qualitative and lack descriptions that are sufficiently accurate to examine species specific traits. The most useful descriptions of courtship patterns for evolutionary comparisons utilize sequence analysis of the data (Gillingham, 1987) and for snakes those reports are limited to Elaphe (Gillingham, 1979), Lampropeltis (Secor, 1987), Agkistrodon (Schuett and Gillingham, 1988), and Thamnophis (Rossman et al., 1996). In this paper, we describe the courtship behavior of the brown house snake, Lamprophis fulginosus, a wide-spread south African colubrid snake of the subfamily Boodontinae and compare it to the courtship behavior described for other colubrids.

The use of multimodal communication in mate choice decisions by female house crickets, Acheta domesticus

Females of various animal taxa benefit from mating with large males, and size is often communicated through different signal modalities. In male house crickets, Acheta domesticus, size is positively correlated with heritable immunocompetence and the proportion of three-pulse chirps in the male’s calling song. Although females can use these acoustic signals to choose desirable males, little is known about how these acoustic signals interact with other signal modalities. We investigated whether females prefer large males in the absence of acoustic signals. In tournament style two-choice tests, wing-clipped males that were mounted first on consecutive trials had a significantly larger mass on average than wing-clipped males that were not mounted first in both trials. We also used 100 two-choice tests to verify female acoustic preferences. Female house crickets spent significantly more time near speakers playing the calling song of a large male than the calling song of a small male. Finally, we pre-exposed females to a calling song recording from a small or large male and then presented the female with a small or large wing-clipped male to determine whether calling song or nonacoustic signals were weighed more heavily by females. Females had a lower latency to mount when presented with a large male, regardless of the quality of the calling song to which females had been pre-exposed. However, a high-quality calling song still decreased females’ latency to mount small males. These results suggest that females assess size using long-range acoustic signals, but also reassess size using more proximate nonacoustic signals.

SEXUAL DIMORPHISM IN THE METABOLIC RATE OF TWO SPECIES OF WOLF SPIDER (ARANEAE, LYCOSIDAE)

Abstract Spiders have long been noted as classic examples of extreme sexual dimorphism and adaptations to the lifestyle of a sit-and-wait predator. We examined sex-based differences in the metabolic rate of two species of wolf spider that differ in their degree of sexual dimorphism and predatory strategy. Pardosa milvina (Hentz 1877) is a small active wolf spider that does not exhibit a large degree of sexual dimorphism in body size. Hogna helluo (Walckenaer 1837) is a large, strongly sexually dimorphic wolf spider with large, sedentary females and smaller, active males. We found that P. milvina had a higher mass-specific metabolic rate than H. helluo. Also, P. milvina males had a higher metabolic rate than P. milvina females but there was no difference in mass-specific metabolic rate between H. helluo males and females. Our data demonstrate that an actively foraging species, P. milvina, exhibits a higher metabolic rate than species with a sit-and-wait strategy, H. helluo. This suggests that activity levels may be correlated with metabolic rates. In addition, we hypothesize that sexual selection and selection for specific reproductive roles may have resulted in species differences in sexual dimorphism for metabolic rate.

Heads up: sexual dimorphism in house crickets (Acheta domesticus)

Many species are sexually dimorphic because of differential selection on each sex. In many species, males tend to have exaggerated traits or larger body size compared with females. In house crickets (Acheta domesticus L., 1758), the males defend resources and compete for mates by engaging in a striking visual display sequence that includes mandible flaring, where males spread their mandibles wide open. This behavior presumably acts only in males as a visual signal of body size and as an indicator of the willingness to fight, as females do not exhibit this behavior. We tested the hypothesis that sex differences in the signals used for aggressive interactions will lead to sex differences in the morphology of the head in house crickets. To test this hypothesis we made linear measurements of body and head sizes on males and females and utilized geometric morphometric methods to reconstruct sex differences in shape. We also compared the total pigmented area of the faces of males and females. Males had larger h...