Rodrigo H. Willemart

Experimental demonstration of close-range olfaction and contact chemoreception in the Brazilian harvestman, Iporangaia pustulosa

We studied the ability to detect food by close‐range olfaction and contact chemoreception in the harvestman Iporangaia pustulosa Mello‐Leitão (Opiliones: Laniatores: Gonyleptidae). We first tested the reaction of individuals towards tasteless (pure agar), aversive (agar with salt), and food‐intake stimulating substrates (agar with saccharose). Only the substrate containing saccharose was consumed. Contact (mainly with legs II) was necessary for detection of the agar and, before ingestion, the stimulus was always tapped with legs I. In the second experiment, we observed the behavior of individuals in an arena with a screened plastic box containing pieces of Tenebrio molitor L. (Coleoptera: Tenebrionidae) larvae. Individuals spent more time on the box containing food than on the control. In the third experiment, in an arena identical to that used in Experiment 2, we introduced a live but motionless T. molitor larva in the box. There was no difference between experimental and control treatments. We also observed the behavior of I. pustulosa in an arena containing live isopods. In first capture attempts, isopods were only detected upon contact, mainly with legs I. Our results suggest that (i) I. pustulosa is capable of detecting food only by its chemical properties; (ii) food with weak odor may not be detected by close‐range olfaction; and (iii) legs I and II are important for food detection but, before ingestion, legs I are used to examine potential food items.

Spatial distribution‚ mobility‚ gregariousness‚ and defensive behaviour in a Brazilian cave harvestman Goniosoma albiscriptum (Arachnida‚ Opiliones‚ Gonyleptidae)

This study provides information on population dynamics and behaviour (gregariousness and defensive tactics) of the Brazilian cave harvestman Goniosoma albiscriptum (Goniosomatinae). Through a mark-recapture study, we observed that this species regularly uses the cave during the day, leaving it to forage on the vegetation after dusk (i.e., a trogloxene species). There were nine groups within the cave, composed of females and males, the latter being the only sex that moved from one group to another (although rarely). Distinct groups used distinct openings of the cave to leave the shelter after dusk. Goniosoma albiscriptum showed a variety of mechanical defensive behaviours, and also exuded scent gland secretions. During dryer and colder months (between April and August), adult and subadult harvestmen aggregated on the cave walls. The individuals that composed the aggregations were not always the same ones. Reproductive activity (detected by the presence of egg batches) was negatively correlated with formation of aggregations. We suggest that intolerance towards conspecifics during the reproductive period may inhibit the formation of aggregations.

Harvest-ironman: heavy armature, and not its defensive secretions, protects a harvestman against a spider

Natural selection has caused prey species to evolve distinct defensive mechanisms. One of such mechanisms was the evolution of noxious or distasteful chemicals, which have appeared independently in a number of vertebrates and invertebrates. In detailed analyses of arthropod behaviour, scent gland secretions have consistently been shown to be responsible for repelling specific predators. Because using such chemicals is costly, animals with alternative cheaper defences are expected not to release such secretions when alternative options exist. In this study, we sought to determine the defensive mechanisms of the harvestman Discocyrtus invalidus, a heavy bodied species that bears a pair of repugnatorial glands. The spider Enoploctenus cyclothorax was used as the predator, and the cricket Gryllus sp. was used as a control. In a first set of experiments, the harvestmen were preyed upon significantly less than the crickets. In two other experiments, we found that harvestmen did not use their scent gland secretions to deter the predator. Moreover, results of a fourth experiment revealed that these spiders are not repelled by defensive secretions. Discocyrtus invalidus has a thick cuticle on the entire body: scanning electron micrographs revealed that only the mouth, the articulations of appendages and the tips of the legs are not covered by a hard integument. In a fifth experiment, we found that these spiders had difficulty piercing the harvestmen body. This is the first experimental evidence that a chemically defended arachnid does not use its scent gland secretions to repel a much larger predator but instead relies on its heavily built body.

Sexually Dimorphic Tegumental Gland Openings in Laniatores (Arachnida, Opiliones), With New Data on 23 Species

Sexually dimorphic glands often release sexual pheromones both in vertebrates and invertebrates. Species of Laniatores (Arachnida, Opiliones) seem to depend on chemical communication but few studies have addressed this topic. In this study, we review the literature for the Phalangida and present new data for 23 species of Laniatores. In 16 taxa, we found previously undescribed sexually dimorphic glandular openings on the femur, patella, metatarsus, and tarsus of legs I and metatarsus of legs III and IV. For the other species, we provide scanning electron micrographs of previously undescribed sexually dimorphic setae and pegs located on swollen regions of the legs. We also list additional species in which males have swollen regions on the legs, including the tibia, metatarsus, and tarsus of legs I, trochanter and tibia of legs II, femur, metatarsus, and tarsus of legs III, and metatarsus and tarsus of legs IV. The function and biological role of the secretions released by these glands are discussed. J. Morphol., 2010.

Breeding biology of the cavernicolous harvestman Goniosoma albiscriptum (Arachnida, Opiliones, Laniatores): sites of opposition, egg batches characteristics and subsocial behaviour

Summary We present field data on seasonality, mating behaviour, sites of oviposition, characteristics of egg batches, and parental care of a cavernicolous population of the Brazilian harvestman Goniosoma albiscriptum. We also tested if guarding females became more aggressive than non-guarding ones by allowing a potential predator to approach G. albiscriptum females. Field work was conducted in several visits to a cave, from September 1999 to April 2001. Reproductive activity was detected almost the whole year, with a minor peak in the spring (October-November) and a major peak in the summer (February-March). Average sex ratio throughout the year was female biased. Proportionally, guarding females were found significantly more often in exposed places than females without eggs. No significant difference was detected between the number of eggs laid in exposed and non-exposed places. The mean number of eggs per batch was 69.58±26.96, and the average minimum time of embryonic development was 33.26±9.78 days. Twenty-nine females produced two egg batches, with no significant difference between the number of eggs laid in the first and second batch. Intervals between the two ovipositions ranged from 3 to 17 months. Laboratory tests showed that conspecifics and other cave inhabitants, such as other harvestmen species and crickets, preyed on G. albiscriptum eggs. Guarding females reacted aggressively to a non-conspecific approaching harvestman. Non-guarding females never reacted aggressively. Con-specific males near females during the day attacked conspecifics males but not males of another species. Once, a male was seen standing next to eggs and immatures, possibly guarding them.

Caves as a Winter Refuge by a Neotropical Harvestman (Arachnida, Opiliones)

Organisms may respond to regular and predictable environmental changes by migrating to regions where resources are available and/or the conditions are more favorable (Dingle and Drake 2007). Although migration is usually associated with long-distance displacements, like those of some birds and butterflies, less vagile animals may also migrate through considerably shorter distances (Kraus and Morse 2005). In fact, the term migration covers a wide range of population displacements (Dingle and Drake 2007), and includes seasonal movements into shelters where the environmental conditions are expected to be less affected by the external environmental changes. Caves are a good example of seasonal shelter, generally with a permanently high humidity and stable temperature even during the winter (Culver and Pipan 2009). Several species do indeed use caves as winter refuges, including insects (e.g. Tercafs 2000), arachnids (Holmberg et al. 1984; Novak et al. 2004), and vertebrates like bats (Lewis 1995), baboons (Barrett et al. 2004), snakes (Sexton and Hunt 1980), and frogs (Resetarits 1986). We highlight, however, that all these examples are from animals living in temperate regions. As far as we know, there is so far no record of the use of caves as winter refuges by animals that are not from temperate regions. This is probably related to the less stressful climatic conditions of the cold period when compared to the harsh winter of temperate regions. J Insect Behav (2011) 24:393–398 DOI 10.1007/s10905-011-9264-x

Comparative Density of Hair Sensilla on the Legs of Cavernicolous and Epigean Harvestmen (Arachnida: Opiliones)

To allow an animal to behave appropriately, the location of sensorial structures is expected to be related to their function. As the different leg pairs of arachnids may have different functions (probing x supporting the body), one could expect them to have a different density of sensilla. Moreover, different regions of the same leg (dorsal, lateral, and ventral) would also be expected to have different densities of sensilla, according to the use of each region (e.g., the ventral part is often in contact with the substrate while the dorsal part is not). As caverni- colous animals are expected to be more sensitive than their epigean relatives, one could also expect a different density of sensilla when comparing cavernicolous and epigean animals. Using three epigean and three caverni- colous species of harvestmen (Arachnida, Opiliones), this study aimed at describing the morphology of hair sensil- la on the legs and answering three questions: (1) Are there differences in the density of hair sensilla between the dorsal, lateral and ventral regions of each leg pair of the same individual? (2) Are there differences in the density of hair sensilla between the leg pairs of the same individual? (3) Are there differences in the density of hair sensilla when comparing the leg pairs of individuals of cavernicolous and non-cavernicolous species? The tarsi and metatarsi of all right legs of the six studied species were analyzed under a scanning electron microscope. The results (P < 0.05) showed that, in general: the ventral region of the tarsus was denser in sensilla trichodea than the lateral and dorsal regions, particularly on legs I and II; the density of sensilla chaetica did not differ on legs III and IV, but was greater on the dorsal region of legs I and II; the ventral part of legs I had the higher density of sensilla trichodea of the four pairs, whereas the second pair had the lower density; Holcobunus citrinus (Eupnoi) was the species with higher density of sensilla trichodea, on all legs; the cavernicolous species had a lower density of sen- silla than the epigean species. The results are tentatively related to harvestmen behavior.

Sexual coercion does not exclude luring behavior in the climbing camel-spider Oltacola chacoensis (Arachnida, Solifugae, Ammotrechidae)

Sexual coercion in the form of forced copulation has been used as a typical example to illustrate the conflict of interests between females and males. Among arthropods, forced copulation has been reported for some groups of insects and crustaceans, but not for arachnids. In the present work, we analyse and describe the behavioral patterns of mating behavior of the climbing camel-spider, Oltacola chacoensis, relating it to relevant morphological features, In this species, the male forcefully clasps the female’s genital region with his chelicerae and locks her fourth pair of legs with his pedipalps. In some cases, the cuticle of the female’s abdomen was damaged by this cheliceral clasping. In contrast to other camel-spiders, the female O. chacoensis never remained motionless during mating, but continuously shook her body, opening her chelicerae notably towards the male. Despite this coercive context, males performed copulatory courtship (tapping with pedipalps) and females showed an apparent cooperative behavior (they remained still during a short period of the sperm transfer phase). These results strengthen the idea that sexual coercion (in the form of forced copulation) and luring behavior (in the form of copulatory courtship) are not two mutually-exclusive male’s strategies during a single copulation.

First experimental evidence that a harvestman (Arachnida: Opiliones) detects odors of non-rotten dead prey by olfaction

Harvestmen feed on live, dead and fresh, or decomposing animals, fungi, and plant matter, being very dependent on chemoreception to find food. Herein we performed an experiment to test if individuals of Discocyrtus pectinifemur Mello-Leitao, 1937 (Gonyleptidae) (n = 23) behave differently when in contact with olfactory cues from different sources (rotten prey, non-rotten prey and a control). Using dead crickets in a box covered with a mesh, and recording the time the harvestmen spent in the vicinities of the box, we show that D. pectinifemur detects non-rotten prey and stays longer on it than on the other two treatments. Our results contrast with a previous study on another species, showing that we should not generalize results obtained for one species. Our data also suggest that olfactory receptors occur on the legs of these harvestmen and that D. pectinifemur might choose dietary items based on olfaction.

The effectiveness of post-contact defenses in a prey with no pre-contact detection

Most empirical and theoretical papers on prey-predator interactions are for animals with long-range detection, animals that can detect and react to predators long before these touch the prey. Heavy-bodied and chemically defended harvestmen (Arachnida, Opiliones) are an exception to this general pattern and rely on contact to detect arthropod predators. We examined the interactions between the Brazilian wandering spider Ctenus ornatus with harvestmen (Mischonyx cuspidatus) or control prey (Gryllus sp. and M. cuspidatus immature, both with soft integuments). Considering a prey-predator system in which fleeing from or reacting to a predator at a distance is not possible, we predicted both a high survival value of near-range defense mechanisms and that mortality would be higher in the absence of such defense mechanisms. We also expected the predator to behave differently when interacting with harvestmen or with a control prey without such defense mechanisms. Our results from laboratory experiments partially matched our predictions: First of all, histological sections showed that the integument of adult harvestmen is thicker than that of immature harvestmen and that of crickets. Adult harvestmen were less preyed upon than the control prey; the heavy armature increases the survival rate but the secretions from the scent glands do not. The predator did behave differently when attacking harvestmen compared to crickets. Despite the large size difference between predator and harvestmen, the protection provided by the armature allowed some of the harvestmen to survive encounters without pre-contact detection, thus greatly reducing the reliance on long-range detection to survive encounters with predators. Harvestmen call for theoretical and empirical work on prey-predator interactions that take into account the possibility that prey may not detect the predator before contact is established.