Cues guiding uloborid construction behavior support orb web monophyly

Behavior can provide useful traits for testing phylogenetic hypotheses, and some details of orb web construction behavior have been especially useful in characterizing higher-level groups in spiders. The cues used to guide construction behavior and behavioral responses to these cues hold similar promise, but have never been used in phylogenetic studies. Here we use several techniques to test the hypothesis that orb webs in the two major branches of orb-weaving araneomorph spiders (Araneoidea and Deinopoidea) are monophyletic, using both the cues that guide orb construction and the spiders’ responses to these cues. If orb webs evolved only once, the expectation is that these traits should be similar in members of both evolutionary lines. This prediction was supported: species in the two groups use several of the same cues, and respond to them in similar ways. These cues include two identical reference stimuli for positioning sticky spiral lines; supplies of silk available in their glands that affect the positioning of sticky spiral loops; and at least one stimulus related to the size of the available space for the orb, which is used to trigger similar modifications of seven independent orb design traits. Neither group used tension-related cues to guide sticky spiral placement. These comparisons reinforce previous conclusions supporting orb web monophyly that were derived from morphological, molecular, and behavioral traits.Smithsonian Tropical Research Institute, Panama, USAUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

The hub as a launching platform: rapid movements of the spider Leucauge mariana (Araneae: Tetragnathidae) as it turns to attack prey

artículo (arbitrado)--Universidad de Costa Rica. Escuela de Biología, 2011Spiders are effectively blind with respect to the lines in their webs, and they commonly use exploratory leg movements to find lines, just as a blind man finds objects using a cane. Nevertheless, a mature female Leucauge mariana (Keyserling 1881), which spins a relatively open, sparsely-meshed hub and whose legs I and II hold widely-spaced radii rather than dense hub lines, turns precisely and rapidly when prey strike her orb. She can turn . 90u, finding and grasping new lines with all her legs, in as little as 0.1 s and can reach a prey several body lengths away in as little as 0.23 s after impact. The hub design and resting postures of the spider’s legs allow her to sense where the prey strikes the web, generate the force necessary to turn her body rapidly, and find lines to grasp. The spider may move most (if not all) of her legs, without obtaining further guidance information once the leg has begun to move until it nears the site where it will grasp a line. The order in which legs are moved is relatively consistent, and each tarsus moves to a site where lines are relatively abundant; some then make small, quick searching movements to find and grasp lines there. When radial lines were experimentally cut near the hub in a sector in which a prey was subsequently introduced, legs I and II first made small searching movements, and then executed much larger searching movements. The rapid leg movements directed toward specific areas where lines are abundant, and the small searching movements employed at these sites suggest that the spider modifies her behavior when she is at the hub of an orb.Universidad de Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

The mystery of how spiders extract food without masticating prey

Standard accounts of how spiders obtain food without masticating their prey are probably largely wrong. Species in the families Uloboridae, Thomisidae, Araneidae and Theridiidae do not inject digestive fluid into the prey’s interior, nor do they suck fluids directly from its interior. Rather they regurgitate fluid onto the surface of the prey, and then suck it back up from there. Philoponella vicina and other uloborids are extreme in this respect: they wet the entire outer surface of the prey package simultaneously with digestive fluid, and their mouthparts often never touch the prey. Capillarity (along with digestion of prey membranes in Philoponella) is apparently responsible both for the dispersion of digestive fluid into the prey, and the exit of liquids from inside the prey.Instituto Smithsoniano de Investigaciones Tropicales (STRI)Universidad de Costa RicaSmithsonian Tropical Research Institute, Panama, USAUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Functional aspects of genital differences in Leucauge argyra and L. mariana (Araneae: Tetragnathidae)

Morphological studies have documented the tendency for male genitalia to diverge rapidly compared to other body parts in many animal groups, including spiders. But documentation of how differences in genital structures of closely related species correlate with differences in the behavior of their genitalia during copulation is rare. This study describes how the genitalia of the spider Leucauge argyra (Walckenaer 1841), a species in which both male and female have unusual derived structures, are used during copulation and compares their sexual behavior with previous descriptions of genital behavior in the congener L. mariana (Taczanowski 1881) and the genital morphology of other Leucauge species. Males of L. argyra have two prominent derived genital structures, both of which interact directly with the female; one of them apparently locks against a modified female structure, while the other is inserted into the female atrium. On the other hand, the most prominent derived female structure does not lock against or receive any male structure and may serve to sense movements of the male palp, perhaps to trigger deposition of a strong copulatory plug by the female. The female atrium is unusual in that it receives insertions of both the male’s conductor and his cymbial hook. Both derived male structures of L. argyra may have evolved to stabilize the male’s genitalia during intromission, perhaps in response to violent and dangerous female resistance or to perforate the strong plug that is probably produced or at least moved into place by the female. The rotating and projecting movements executed by male genitalia in L. argyra, which as in other spiders are presumably produced by the hydraulic unfolding of complex membranes in the palp, are quite different from the movements of the male genitalia of L. mariana. We speculate that in spiders in general, changes in palpal sclerites are often accompanied by changes in the movements of the sclerites, and thus by changes in the unstudied internal membranes of the palp.The Smithsonian Tropical Research Institute (STRI)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Vestiges of an orb-weaving ancestor? The “biogenetic law” and ontogenetic changes in the webs and building behavior of the black widow spider Latrodectus geometricus (Araneae Theridiidae)

Young juveniles of L. geometricus fit the strong trend for “ontogeny to repeat phylogeny” previously documented in other web-building spiders; younger spiders were less likely to build the derived silk retreats that occur at the edges of webs of adults. Younger individuals also consistently builtç more highly organized webs, with radial lines that converge on a central, horizontal disc and that support regularly spaced, sticky “gumfoot” lines. Some details of how radial and gumfoot lines were built suggest that the radial and gumfoot lines and the behavior involved in their construction may be homologous with traits associated with radii and sticky spirals in aranoid orb webs. The numerous convergences between the webs and building behavior of young L. geometricus and the highly modified webs and building behavior of genera of the orb weaving families Theridiosomatidae (Wendilgarda) and Anapidae (Comaroma), which have independently replaced orbs with webs designed to capture prey on surfaces near the web, suggest a new hypothesis for how gumfoot theridiid webs may have evolved from orbs.Smithsonian Tropical Research InstituteUniversidad de Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Seasonal patterns of parasitism of the tropical spiders Theridion evexum (Araneae, Theridiidae) and Allocyclosa bifurca (Araneae, Araneidae) by the wasps Zatypota petronae and Polysphincta gutfreundi (Hymenoptera, Ichneumonidae)

Las tasas de parasitismo de Theridion evexum por la avispa parasitoide Zatypota petronae y de Allocyclosa bifurca por Polysphincta gutfreundi fueron estudiadas durante dos años. El parasitismo en T. evexum fue muy bajo (promedio 1.39+1.8%) y restringido a aproximadamente siete meses del año. El parasitismo en A. bifurca fue más alto (promedio 7.8+7.6%) y no mostró un claro patrón estacional. La reproducción de la araña hospedera T. evexum fue muy estacional, con solamente una generación por año, mientras que los adultos de A. bifurca estuvieron presentes todo el año. Autocorrelaciones de las tasas de parasitismo entre censos consecutivos en diferentes sitios sugiere que P. gutfreundi tiende a retornar a los mismos sitios para parasitar las arañas hospederas durante algunas semanas.The rates of parasitism of Theridion evexum by the parasitoid wasp Zatypota petronae, and Allocyclosa bifurca by Polysphincta gutfreundi, were followed for two years. Parasitism of T. evexum was very low (mean 1.39+1.8%), and restricted to nearly seven months of the year. Parasitism of A. bifurca was higher (mean 7.8+7.6%), and did not show a seasonal pattern. Reproduction of the host spider T. evexum was highly seasonal, with only one, highly coordinated generation per year, while adults of A. bifurca were present year round. Short-term autocorrelation on parasitism rates over time at different sites suggest that P. gutfreundi tend to return to the same sites to hunt hosts over periods of a few weeks.Universidad de Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Courtship behavior of different wild strains of Ceratitis Capitata (Diptera: Tephritidae)

Este estudio documenta diferencias en el comportamiento de cortejo de cepas silvestres de Ceratitis capitata (Wied.) provenientes de Madeira (Portugal), Hawaii (Estados Unidos de Norte América), Costa Rica y Patagonia (Argentina). Algunas características mostraron grandes variaciones y traslape substancial. Los ángulos a los cuales los machos miraron hacia las hembras cambiaron muy poco en el momento de la transición de la vibración continua al zumbido intermitente durante el curso del cortejo en todo las cepas, pero los machos de Madeira tendieron a enfrentar más directamente a la hembra que otros machos. Los ángulos de las hembras disminuyeron claramente durante el cortejo en todas las cepas. La distancia entre el macho y la hembra tendió a disminuir conforme el cortejo continuaba en todas las cepas, pero las distancias a las cuales los machos iniciaron la vibración continua, el zumbido intermitente, y el salto sobre la hembra eran relativamente menos variables entre cepas excepto la cepa de Costa Rica. Moscas de Madeira cortejaron más tiempo y el macho movió su cabeza y zumbaba sus alas mas prolongadamente que las otras cepas.This study documents differences in the courtship behavior of wild strains of Ceratitis capitata (Wiedemann) from Madeira (Portugal), Hawaii (U.S.A.), Costa Rica, and Patagonia (Argentina). Some traits showed large variations and others substantial overlaps. The angle at which the male faced toward the female at the moment of transition from continuous wing vibration and intermittent buzzing changed very little during the course of courtship in all strains, but males from Madeira tended to face more directly toward the female than other males. Females tended to look more, and more directly, toward the males as courtship progressed in all strains. The distance between male and female tended to decrease as courtship proceeded in all strains, but the distances at which males initiated continuous vibration, intermittent buzzing, and jumped onto the female were relatively less variable between strains, except for the strain from Costa Rica. Flies of Madeira courted for longer and the male moved his head and buzzed his wings longer than the other strains.Universidad de Costa Rica, Smithsonian Tropical Research Institute, Costa Rica. Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales Universidad de Buenos Aires. Technical Cooperation Division, IAEA, Wagramerstrasse. USDA/APHIS/CPHSTUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Egg sac construction by folding dead leaves in Pozonia nigroventris and Micrathena sp. (Araneae: Araneidae)

Published descriptions of egg sac construction behavior in araneids are scarce. We describe egg sac construction and oviposition in one individual of the poorly known araneid Pozonia nigroventris (Bryant 1936) and two individuals of Micrathena sp. These spiders folded dead leaves to protect their eggs. All individuals pulled up and hung a dead leaf above the forest floor, oviposited on the leaf, and then folded the leaf around the egg sac. They then deposited the enclosed egg sac in the leaf litter below. The use of dead leaves in this way probably evolved convergently, since these genera are only distantly related.Smithsonian Tropical Research Institute, Panama, USAUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

The function of female resistance behavior: Intromission by male coercion vs. female cooperation in sepsid flies (Diptera: Sepsidae)

Female resistance behavior that occurs prior to intromission does not by itself imply forced copulation. Such behavior may function instead as a test of the male in order to favor some males over others, or to induce the male to desist. Thus, male persistence and forcefulness may sometimes be better described as persuasion rather than coercion. Under the persuasion hypothesis, the male only gains intromission due to an active response of the female. Under the coercion hypothesis, male and female are opposed in a physical battle which the female loses if copulation occurs. In species in which males are morphologically incapable of forcing intromission without active female cooperation (I argue here that this is probably a very common situation), data on the behavioral and ecological context in which resistance occurs can distinguish between the two possibilities. Partially congruent functions of resistance, seen from the female point of view, are female resistance to screen (male persuasion), and female resistance to avoid males non-selectively (male coercion). Sepsid flies illustrate these ideas. Females often struggle energetically in apparent attempts to dislodge mounted males and to prevent intromission, and males grasp females with powerful species-specific structures on their front legs and genitalia. This suggests the possibility of coerced intromission. But behavioral and morphological evidence demonstrate that active female cooperation occurs at the moment of intromission, and that males are probably dependent on this cooperation because they are not morphologically equipped to force their genitalia into those of an uncooperative female. Despite the impression from previous publications, male insects in general may seldom be able to achieve intromission by genitalic force. The species-specific forms of the grasping genitalia of male sepsids are probably not the result of an evolutionary arms race between coercive males and unselectively resistant femalesEste artículo intenta organizar algunas ideas teóricassobre posibles conflictos entre machos y hembras en cuantoa la cópula. Las ideas se ilustran con datos nuevos de unafamilia de moscas (Sepsidae), y con otros datos ya publicadossobre otros insectos. El hecho de que una hembra oponeresistencia a la penetración por el macho no implica ensí mismo que la cópula es forzada, ya que la resistencia dela hembra también puede funcionar como una prueba delmacho, para así tamizar entre diferentes machos y conseguirhijos superiores. Se contrastan dos hipótesis para elmacho, la de la cópula por coerción vs. la de la cópula porpersuasión; también se contrastan, desde la perspectiva dela hembra, dos hipóteses relacionadas, la resistencia paraevitar a todo macho en forma no selectiva vs. la resistenciapara tamizar entre machos. Cuando la morfología de la genitaliade los dos sexos es tal que el macho no es físicamentecapaz de forzar la intromisión, como es el caso en lasmoscas sépsidas y probablemente en muchos otros insectos(a pesar de algunas publicaciones que sugieren lo contrario),las hipótesis contrastantes para cada sexo pueden resolversecon datos sobre el contexto ecológico en el cualocurre la interacción macho-hembra. Se realizó un análisisde esta clase con los sépsidos. Parece más probable que laresistencia energética que la hembra pone al macho sea unesfuerzo para tamizar entre machos que un esfuerzo paraevitar la cópula en forma no selectiva

Niche expansion in the spider Wendilgarda galapagensis (Araneae, Theridiosomatidae) on Cocos Island

Wendilgarda galapagensis, a species endemic to Cocos Island, shows an unusually wide variation in habitat choice, web design, and construction behavior. Differences between W. galapagensis and close relatives are probably derived rather than vestiges of characters of a common ancestor. Cocos lsland has an impoverished fauna, and the derived characters of W. galapagensis may have evolved in response to reduced interspecific competition, reduced predation, or increased intraspecific competition