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Defense of Phalangid: Liquid Repellent Administered by Leg Dabbing
Abstract
The phalangid Vonones sayi has a pair of exocrine defensive glands that secrete quinones (2,3-dimethyl-1,4-benzoquinone and
2,3,5-trimethyl-1,4- benzoquinone). When distributed, the animal emits the secretion, dilutes it with aqueous regurgitated
fluid, and effects dosaged delivery of the mixture by brushing it on the assailant with the tips of its forelegs. Predators
such as ants are effectively repelled.
... Recent studies (Shear et al. 2014;Segovia et al. 2015;Raspoting et al. 2017) have indicated that the morphology of the ozopores and the chemical composition of the secretions may represent useful phylogenetic characters for assessing evolutionary relationships. Hara and Gnaspini (2003) noted three different mechanisms for the release of chemicals from the scent glands including the evaporation of secretions from the immediate vicinity of the ozopore, the production of a fine spray or liquid from the ozopore that spreads over the body (forming a chemical shield), or the specific direction of the scent gland secretions by jet emission or by leg dabbing (see Eisner et al. 1971Eisner et al. , 1977. Within the suborder Laniatores, some clades have evolved behaviors which correspond to specific ozopore morphology (Reviewed by Hara and Gnaspini 2003). ...
... In cosmetid harvestmen, the reduction or absence of cuticular channels that usually conduct the secretion over the dorsal surface of the scutum in other harvestmen as well as the presence of large coxal processes associated with legs I and II that partially block the external opening of the ozopore are together believed to represent adaptations that facilitate the formation of the droplet used in leg dabbing (Eisner et al. 1977;Gnaspini and Rodrigues 2011). Within the Laniatores, leg dabbing has only been observed in four species of cosmetid harvestmen, leading to the hypothesis that this behavior may represent a synapomorphy for the Cosmetidae (Caetano and Machado 2013;Eisner et al. 1971Eisner et al. , 1977Hara and Gnaspini 2003). Little is known about intraspecific variation in leg dabbing behavior, however, individuals of at least one species, Paecilaema sp., did not exhibit this behavior under laboratory conditions (Hara and Gnaspini 2003). ...
... In our study, we compared the frequency of emissions of enteric fluid and scent gland secretions by males, females and nymphs. Following the methods of previous studies of scent gland secretion and chemical defense in harvestmen (e.g., Eisner et al. 1971Eisner et al. , 1977Hara and Gnaspini 2003;Eisner et al. 2004;Machado and Pomini 2008; Moore and Townsend Jr 2019), we used forceps to simulate a predatory attack and seized individuals by femur IV and the body. In addition to behavioral obser vations, we also compared the morphology of the ozopores and associated structures of males, females and nymphs using scanning electron microscopy (SEM) to assess further the functional relationship be tween defensive behavior and morphology. ...
Relatively little is known about intraspecific variation in the use of chemical defenses by cosmetid harvestmen. In this study, we investigated sexual and ontogenetic variation in the emission of secretions from the scent glands and the morphology of the ozopores of Erginulus clavotibialis, a Neotropical species from Belize. Most individuals (> 94%) did not secrete when seized by leg IV, however, when the body was subsequently grasped firmly with forceps, 76% of the harvestmen (n = 96) responded by releasing enteric fluid (clear, no odor) or secretions from the scent glands (reddish-brown, distinct odor), most commonly in the form of globules near the ozopores. Adults and penultimate nymphs rarely (less than 5% of all trials) exhibited leg dabbing, an unusual behavior generally associated with cosmetid harvestmen. Males released enteric fluid (without scent gland secretions) significantly more than females or nymphs. Nymphs emitted secretions from scent glands at a significantly greater frequency than males or females. Using SEM, we examined the ozopores and the dorsal processes of coxae I and II and found that the morphology of these structures varies between adults and nymphs but not between males and females. The openings of the ozopores of nymphs are circular and are not obscured by the dorsal posterior process of coxa I and the dorsal anterior process of coxa II. In contrast, adults have subtriangular ozopores that are difficult to observe without dissection because they are partially blocked by the dorsal processes of coxae I and II.
... In many laniatorean harvestmen, individuals release clear, odorless enteric fluids that mix with and dilute the aromatic secretions emitted from the scent glands, enabling the formation of an effective chemical shield on the dorsum (Acosta, Poretti, & Mascarelli, 1993;Eisner, Rossini, González, & Eisner, 2004;Gnaspini & Cavalheiro, 1998;Hara & Gnaspini, 2003). Hara and Gnaspini (2003) noted three mechanisms for the release of scent gland secretions including the evaporation of chemicals from the immediate vicinity of the ozopore, the production of a fine spray or liquid from the ozopore that spreads over the body (forming a chemical shield), or the specific direction of the scent gland secretions by jet emission or by leg dabbing (see Eisner, Jones, Hicks, Silberglied, & Meinwald, 1977;Eisner, Kluge, Carrel, & Meinwald, 1971). Recent studies have found that the frequency of the use of scent gland secretions vary between ovigerous and non-ovigerous females (Nazareth & Machado, 2015) and that at least some species of harvestmen exhibit intraspecific variation with respect to the mechanism of secretion (Moore & Townsend Jr., 2019;Segovia, Hara, Pagoti, & Sannomiya, 2015). ...
... In contrast to other laniatoreans, members of the family Cosmetidae exhibit the defensive behavior known as "leg dabbing" (Caetano & Machado, 2013), an unusual behavior known only from one other lineage of harvestmen, the suborder Cyphophthalmi (Gnaspini & Hara, 2007). In cosmetid harvestmen, this secondary defense mechanism begins with the accumulation of scent gland secretions that mix with enteric fluids at the base of coxa II (Eisner et al., 1971(Eisner et al., , 1977. The cosmetid harvestman dips the tip of tarsi I or II into the fluid and presents the tarsus in the direction of the aggressor (Eisner et al., 1971(Eisner et al., , 1977. ...
... In cosmetid harvestmen, this secondary defense mechanism begins with the accumulation of scent gland secretions that mix with enteric fluids at the base of coxa II (Eisner et al., 1971(Eisner et al., , 1977. The cosmetid harvestman dips the tip of tarsi I or II into the fluid and presents the tarsus in the direction of the aggressor (Eisner et al., 1971(Eisner et al., , 1977. This behavior has been observed for adults of four species including Vonones sayi, Paecilaemella eutypa, P. quadripunctata, and Cynorta astora (Eisner et al., 1971(Eisner et al., , 1977. ...
The ozopores of cosmetid harvestmen rest upon lateral projections of the carapace, have simple or highly reduced channels, and are partially obscured by enlarged dorsal processes associated with coxae I and II. Rather than use scent gland secretions to form a chemical shield on the dorsum, the cosmetid harvestman exhibits a unique defensive behavior known as “leg dabbing” in which the distal tip of tarsus I or II is dipped into fluid that accumulate at the base of coxa II and the droplet on the tarsus is pointed toward the predator. Relatively little is known about interspecific variation in ozopore morphology among cosmetid harvestmen. In this study, we used scanning electron microscopy to examine the ozopores of males and females of nine species as well as those of antepenultimate nymphs for two species. Among adults, we found differences between species in the shapes of the ozopores (round or subtriangular), the morphology of the dorsal and lateral channels (if present), and the relative size, shape and armature of the dorsal posterior process (dpp) of coxa I and the dorsal anterior process (dap) of coxa II. Our observations suggest that the morphology of dpp I and dap II could be sources for systematic characters in future phylogenetic studies of the Cosmetidae. We observed ontogenetic differences but relatively little intersexual variation in the morphology of the ozopore. The ozopores of nymphs are generally more oval than those of adults and the opening of the ozopore of the nymph is less obstructed, if at all, by the dorsal coxal processes of legs I–II. These morphological differences suggest that nymphs may use scent gland secretions in a manner different from that of adults. The morphology of the ozopores of cosmetid harvestmen vary between species as well as between nymphs and adults. Unobstructed opening of the ozopore of a nymph of the cosmetid harvestman Paecilaema inglei revealing relative size and position of the dorsal coxal processes of legs I–II.
... Typically, chemicals flow to the latero-dorsal region of the body (e. g, Acosta et al. 1993;Gnaspini and Cavalheiro 1998). In Cosmetidae, chemicals flow to the ventral region of the body, accumulating in the surroundings of the mouth (Eisner et al. 1971). The individuals collect the droplets with the tip of their legs and apply the secretion on the aggressor or spread it onto their own body, a behaviour known as leg-dabbing that, among laniatorids, is only known in cosmetids (Eisner et al. 1971;Gnaspini and Hara 2007). ...
... In Cosmetidae, chemicals flow to the ventral region of the body, accumulating in the surroundings of the mouth (Eisner et al. 1971). The individuals collect the droplets with the tip of their legs and apply the secretion on the aggressor or spread it onto their own body, a behaviour known as leg-dabbing that, among laniatorids, is only known in cosmetids (Eisner et al. 1971;Gnaspini and Hara 2007). Cosmetids and other laniatorids usually secrete methyl ketones, benzoquinones, and phenols among other chemicals (e.g., Eisner et al. 1977;Hara et al. 2005;Rocha et al. 2013), known to be repellents to several predators (Eisner et al. 2004;Machado et al. 2005;Silva et al. 2018). ...
Pedipalps in laniatorid harvestmen are usually cylindrical and raptorial, but species in Cosmetidae are exceptional in that adults, but not immature, have pedipalps flattened as a spoon. These have never been addressed with a functional approach. We have investigated possible roles of the pedipalps in Cosmetidae in exploration, social interactions and defence. Concerning exploration, we would expect the individuals to tap the substrate with the pedipalps, as species in the suborders Eupnoi and Dyspnoi do, but this was not observed. In social interactions, pedipalps could be used for holding females during mating or to fight other males but we could not relate the spoon-shape with any of the behaviours observed. For defence, we hypothesised that the pedipalp of adults would act as a barrier preventing the potentially noxious secretion from contacting the mouth when the individual performs 'leg-dabbing'. This is typical in adult cosmetids but not in other laniatorids. Because immature cosmetids have cylindrical pedipalps, we predicted that they would not perform 'leg-dabbing'. However, immature also performed leg-dabbing and the secretion did contact the mouth. We also found no evidence of pedipalps being used for digging, drinking or self-grooming. Although we have made progress, the question remains open.
... In harvestmen, there is also considerable phylogenetic variation with respect to the mechanism of emission of chemicals from the scent glands (Hara & Gnaspini 2003;Caetano & Machado 2013). Secretions by harvestmen may be released as a globule near the ozopore (Hara & Gnaspini 2003), displaced as a fluid along lateral grooves on the dorsal scutum (Acosta, Poretti & Mascarelli 1993;Hara & Gnaspini 2003;Eisner et al. 2004), emitted as a jet ("squirting"), usually upwards and backwards or sideways (Gnaspini & Cavalheiro 1998;Hara & Gnaspini 2003), or presented as droplets on the tips of leg I following leg dabbing (Eisner et al. 1971). In several species of harvestmen, individuals release clear, odourless enteric secretions that mix with and dilute opaque, aromatic secretions from the scent glands (Acosta, Poretti & Mascarelli 1993;Gnaspini & Cavalheiro 1998;Eisner et al. 2004). ...
... Jet emission has been observed for triaenonychines, multiple gonyleptid species, the cranaid harvestman Phareicranaus calcariferus, and the Manaosbiidae (reviewed by Gnaspini & Hara 2007). In contrast, leg dabbing has only been reported for a few cosmetid species (Eisner et al. 1971) and this unusual behaviour has been proposed as a synapomorphy for the family Cosmetidae (Caetano & Machado 2013). The chemical composition of secretions from the scent gland exhibit considerable interspecific variation and may contain benzoquinones, vinyl-ketones and alkyl-phenols (Eisner et al. 1977;Duffield et al. 1981;Acosta, Poretti & Mascarelli 1993;Hara et al. 2005;Caetano & Machado 2013;Raspotnig et al. 2015). ...
Most harvestmen emit secretions from scent glands as a secondary defence mechanism. Prior studies of Phareicranaus calcariferus described the general morphology of the ozopore, noted jet emission as the mechanism for the release of secretions, but did not investigate intraspecific variation in emissions or the morphology of the ozopore. In this study, we compared the modes of emission by adult females and alpha males and found that when seized by forceps, approximately 50% of adults emitted enteric fluids (colourless, odourless), globules of secretions near the ozopores, or jets of fluid that were directed upwards and backwards or laterally. Individuals that used jet emissions usually released secretions from one scent gland and in a single burst. We observed considerable intersexual variation with respect to the type of emissions. Females emitted jets 32% of the time (n = 28), whereas males produced jets in only 4% of our observations (1 out of 26). Males more frequently produced enteric fluid (31%) in comparison to females (14%). Our SEM-based investigation of ozopore morphology did not reveal intersexual differences in microanatomy. However, we observed intraspecific variation in the morphology of the dorsal openings and dorsal channels of the ozopores.
... After an acclimation period of 2 min on the experimental rock covered by a 20 cm diameter x7 cm height box, we released the animal. The animals were then subjected to the simulated predator attack by pinching the right femur IV once for three seconds, always by the same person, with tweezers covered with rubber on the extremities (see similar protocols in Eisner et al., 1971Eisner et al., , 1977Hara and Gnaspini, 2003;Segovia et al., 2015). We recorded the trial for three minutes or until the animal moved onto the water, which was defined as having no more contact with the rock. ...
Animals that live by rivers may benefit from being able to cross them, but behavioral adaptations are needed. Additionally, being able to remain submerged is also important if the animal moves under water. Here we asked whether the harvestman Heteromitobates discolor (Opiliones), that lives by rivers, (a) can propel itself across the water surface, (b) moves into the water if disturbed and (c) can survive for long periods when submerged. Heteromitobates discolor exhibited two gaits on water, whereas a strictly terrestrial species was not able to propel itself. When experimentally submitted to simulated predator attack on a rock on the river, H. discolor walked onto the water, while a strictly terrestrial species did not. Finally, it was able to survive for 6 h under water, presumably due to the conspicuous air film that formed around its body, which was also observed in a strictly terrestrial species. Altogether, these observations suggest that the aquatic environment is not a barrier for regular activity and can be used as an extension of the terrestrial environment for H. discolor.
... During this nocturnal activity period, these harvestmen are more likely to encounter generalist predators such as ctenid spiders, scorpions, anurans and mammals that rely upon olfactory or tactile stimuli, rather than strictly visual cues (Cook et al. 2013). In these encounters with nocturnal predators, harvestmen may use one or more secondary defenses, including the relative thickness of the exoskeleton (Souza & Willemart 2011;Dias & Willemart 2013), the release of noxious chemicals from defensive glands (Eisner et al. 1971(Eisner et al. , 2004Pomini et al. 2010), or stridulation (Gnaspini & Hara 2007;Pomini et al. 2010). Additional laboratory studies are needed to determine how individuals respond to predators, specifically to assess the frequencies and efficacies of different secondary defenses, such as stridulation. ...
Stridulatory organs have not been previously investigated for harvestmen in the family Cosmetidae. During a field study, we observed the infrequent production of vibrations by adult Cynorta marginalis Banks, 1909. Using SEM, we examined the surfaces of several appendages for potential stridulatory organs. Our observations indicate that C. marginalis has denticles on the mesal surfaces of the basichelicerites that when rubbed together may function as an isomorphous stridulatory organ. In addition, there are denticles on the ectal surfaces of the basichelicerites and furrowed ridges on the femora of the pedipalps that may represent heteromorphous stridulatory organs. We did not observe any sexual dimorphism in morphology at either anatomical location. We also examined the appendages of two additional cosmetid harvestmen: Paecilaema inglei Goodnight & Goodnight, 1947, a species that also stridulates when held and Erginulus clavotibialis (Pickard-Cambridge, 1905), a species that has not been observed to produce vibrations. As in C. marginalis, we observed denticles on mesal and ectal surfaces of the basichelicerites and a furrowed ridge on the mesal surfaces of the femora of the pedipalps of adult P. inglei. In contrast, the basichelicerites of E. clavotibialis had relatively fewer and smaller denticles on the external surfaces of the chelicerae and the mesal surface of the femora of the pedipalps lacked ridges and were relatively smooth. Our comparative morphological data supports the hypothesis that there are cosmetid harvestmen that may use surface features on the chelicerae and pedipalps to produce vibrations which may function as a secondary defense mechanism.
... Regarding scent gland secretions, the chemical composition of exudates appears to reflect the phyletic lineages among opilionids. In detail, suborders are characterized by the presence of (1) naphthoquinones and methyl-ketones in the Cyphophthalmi (Raspotnig et al. 2005Jones et al. 2009); (2) naphthoquinones, anthraquinones, and certain acyclic ketones in the Dyspnoi (Raspotnig et al. , 2014; (3) naphthoquinones and ethyl-ketones in the Eupnoi (Blum and Edgar 1971;Meinwald et al. 1971;Jones 1 3 et al. 1976Jones 1 3 et al. , 1977Wiemer et al. 1978;Ekpa et al. 1985;Raspotnig et al. 2015), and (4) phenols, benzoquinones, terpenes, vinyl-ketones and nitrogen-containing compounds in the Laniatores (e.g., Eisner et al. 1971;Segovia et al. 2015;summarized in Raspotnig 2012). ...
The homologous and phylogenetically old scent glands of harvestmen—also called defensive or repugnatorial glands—represent an ideal system for a model reconstruction of the evolutionary history of exocrine secretion chemistry (“phylogenetic chemosystematics”). While the secretions of Laniatores (mainly phenols, benzoquinones), Cyphophthalmi (naphthoquinones, chloro-naphthoquinones, methyl-ketones) and some Eupnoi (naphthoquinones, ethyl-ketones) are fairly well studied, one open question refers to the still largely enigmatic scent gland chemistry of representatives of the suborder Dyspnoi and the relation of dyspnoan chemistry to the remaining suborders. We here report on the secretion of a nemastomatid Dyspnoi, Nemastoma triste, which is composed of straight-chain methyl-ketones (heptan-2-one, nonan-2-one, 6-tridecen-2-one, 8-tridecen-2-one), methyl-branched methyl-ketones (5-methyl-heptan-2-one, 6-methyl-nonan-2-one), naphthoquinones (1,4-naphthoquinone, 6-methyl-1,4-naphthoquinone) and chloro-naphthoquinones (4-chloro-1,2-naphthoquinone, 4-chloro-6-methyl-1,2-naphthoquinone). Chemically, the secretions of N. triste are remarkably reminiscent of those found in Cyphophthalmi. While naphthoquinones are widely distributed across the scent gland secretions of harvestmen (all suborders except Laniatores), methyl-ketones and chloro-naphthoquinones arise as linking elements between cyphophthalmid and dyspnoan scent gland chemistry.
... The significance of leg loss to the individual may depend greatly on the relative position of the injured appendage. In at least one species of cosmetid harvestman, Vonones sayi, the tips of leg I are dabbed into the defensive chemical secretion released from the ozopores and presented toward the potential predator (Eisner et al., 1971). This behavior could result in an increased risk of injury to leg I. ...
Previous studies of leg injuries in har-vestmen have focused on the fitness consequences for individuals that use autospasy (voluntary detachment of the leg) as a secondary defense mechanism. Leg damage among non-autotomizing species of laniatorean harvestmen has not been investigated. Under laboratory conditions, we damaged femur IV of Cynorta mar-ginalis and observed with scanning electron microscopy (SEM) the changes in these wounds over ten days. We also used SEM to examine leg damage from individuals of three species of cosmetid harvestmen that were collected in the field. On the basis of changes in the external surface of the hemolymph coagulum, we classified these wounds as fresh (coagulum forming), recent (coagulum with smooth surface), older (coagulum is scale-like with visible cell fragments), and fully healed (scale replaced by new cuticle growth on the terminal stump). Our observations indicate that wound healing in harvestmen occurs in a manner comparable to that of other chelicerates. Leg injuries exhibited interspecif-ic variation with respect to the overall frequency of leg wounds and the specific legs that were most commonly damaged. In addition, we measured walking and climbing speeds of adult C. marginalis and found that individuals with fresh injuries (lab-induced) to femur IV walked at speeds significantly slower than uninjured adults or individuals collected from the field that had fully healed wounds to a single leg. J. Morphol. 000:000–000, 2016. V C 2016 Wiley Periodicals, Inc.
Arachnida represent a hyperdiverse group of terrestrial arthropods. Although arachnids are mostly predators, they often fall prey to other predators. Here, the diversity of enemies and the defences of arachnids which are used against their predators is reviewed. The main predators of arachnids are other arachnids, followed by insects, mammals and birds. Almost all types of defences has evolved in this class, but countershading, and elusiveness await to be discovered in Arachnida. Overall, empirical evidence is rare but has slowly been accumulating over the last decade. Anachoresis is used most frequently across all orders; only in Acari, Araneae, Opiliones, and Solifugae it is rivalled by background matching, and Batesian mimicry. The number of different types of defences used by an order is positively correlated with the number of predatory groups preying on it. The major gaps are identified and future avenues for investigation – cases which deserve special attention because these may reveal completely new phenomena – are proposed. It is concluded that this group offers a very diverse array of defences which has not been sufficiently studied; thus, this review aims to stimulate further research.
Mastigoproctus giganteus possesses a pair of voluminous glands, the secretion of which consists of 84 per cent acetic acid, 5 per cent caprylic acid, and 11 per cent water. The secretion is ejected forcibly as a finely dispersed spray that can be aimed accurately in almost all directions. It acts as a strong deterrent to predator attack, being repellent to arthropods and vertebrates alike.The presence of caprylic acid adds considerably to the effectiveness of the weapon as it is used against arthropods. By acting as a wetting agent, caprylic acid promotes the spread of the spray droplets over the cuticle of the predator, hence increasing the effective area of contact of the poison. In addition, caprylic acid exerts a marked accelerating effect on the penetration of the secretion, presumably by increasing the permeability of the epicuticular lipid barrier.
The major component of the antibiotic gonyleptidine, a yellow pigment from the secretion of a South American arachnid, was identified by isolation of the hydroquinone diacetate as 2,3-dimethyl-1,4-quinone. Because of correspondence of infrared absorption bands with those of gonyleptidine, and because of even higher bacteriostatic potency, 2,5-dimethyl-1,4-quinone and 2,3,5-trimethyl-1,4-quinone seemed likely minor companions, and various methods of fractionation were tested on known mixtures of the three synthetic quinones. That finally applied to 115 mg. of gonyleptidine involved, in the first step, reaction with 2,3-dimethylbutadiene for selective conversion of 2,3-dimethyl-1,4-quinone to an adduct, which remained in the neutral fraction when the unreacted quinones were reduced with hydrosulfite and extracted with alkali. After reoxidation, the quinone mixture was submitted to Thiele acetoxylation. The 2,5-dimethyl-1,4-quinone present yielded the non-steam-volatile 2,5-dimethyl-1,3,4-triacetoxybenzene, and 2,3,5-trimethyl-1,4-quinoue was isolated from the steam distillate. Thioacetic and β-thiopropionic acid derivatives of the alkyl-1,4-quinone were prepared incidentally and some of them have been found to be bacteriostatic. New observations concerning the scope of the Thiele reaction are presented.
Insects, millipedes, and some of their relatives, discharge noxious secretions that repel predators.