Trait-Specific Indirect Effects Underlie Variation in the Response of Spiders to Cannibalistic Social Partners.

AbstractIn cannibalistic species, selection to avoid conspecifics may stem from the need to avoid being eaten or to avoid competition. Individuals may thus use conspecific cues to modulate their behavior to such threats. Yet the nature of variation for such cues remains elusive. Here, we use a half-sib/full-sib design to evaluate the contribution of (indirect) genetic or environmental effects to the behavioral response of the cannibalistic wolf spider Lycosa fasciiventris (Dufour, 1835) toward conspecific cues. Spiders showed variation in relative occupancy time, activity, and velocity on patches with or without conspecific cues, but direct genetic variance was found only for occupancy time. These three traits were correlated and could be lumped in a principal component: spiders spending more time in patches with conspecific cues moved less and more slowly in those areas. Genetic and/or environmental components of carapace width and weight loss in the social partner, which may reflect the quality and/or quantity of cues produced, were significantly correlated with this principal component, with larger partners causing focal individuals to move more slowly. Therefore, environmental and genetic trait variation in social partners may maintain trait diversity in focal individuals, even in the absence of direct genetic variation.

The pest-specific effects of glyphosate on functional response of a wolf spider.

Although glyphosate is widely used for weed pest control, it might have negative side effects on natural enemies. Wolf spiders are one of the most representative predators found on soybean crops in Uruguay, preying on a wide variety of potential pests. However, the sublethal effects that pesticides might have on this group have been poorly explored for South American species. Herein, we explored the sublethal effects of glyphosate on the functional response of the wolf spider Hogna cf. bivittata against three potential pest insects, namely ant (Acromyrmex sp.), caterpillar (Anticarsia gemmatalis), and cricket (Miogryllus sp.). We contaminated residually adult females of the species Hogna cf. bivittata with glyphosate (Roundup®) and compared their functional response against non-contaminated spiders. We did not observe any mortality during the study. We found that overall Hogna cf. bivittata showed a functional response type II against crickets and caterpillars but no functional response to ants. Contaminated spiders killed less ants and caterpillars in comparison to the control group, probably as a consequence of the irritating effects of glyphosate. We did not observe differences in functional response to crickets at the evaluated densities, probably as a consequence of the low capture rate against this prey. Although glyphosate does not specifically target spiders, it might have negative sublethal effects on native predators such as Hogna cf. bivittata. Further studies should explore effect of glyphosate on other native predators from South American crops.

Koinobint life style of the spider wasp Minagenia (Hymenoptera, Pompilidae) and its consequences for host selection and sex allocation.

Spider wasps of the genus Minagenia have evolved koinobiontism as a relatively rare life strategy within the widely diversified hymenopteran family Pompilidae. In this study, we evaluated several aspects of the parasitic strategy of the wasp Minagenia sp. (hereafter, Minagenia) - namely host specificity, ontogeny, and sex determination as a function of host size. We found that Minagenia is highly host specific, being associated only with the genus Lycosa from the family Lycosidae, namely Lycosa u-album (Mello-Leitão, 1938), Lycosa erythrognatha (Lucas, 1836) and Lycosa poliostoma (Koch, 1847) with a parasitism incidence of 18.9%, 15.8% and 12.5%, respectively. Both ecological and taxonomical host traits determine the host selection and sex allocation of Minagenia female wasps. Charnov's host-size model explains Minagenia's host-size-dependent sex ratio in combination with the effect of host development stage, host species, and host foraging strategy. We also found that the final instar larva of Minagenia induces behavioural changes in spider hosts. The manipulated spider builds a protective silk chamber as a shelter for parasitoid pupation. Our results suggest that host manipulation seems to be narrowly connected with koinobiont life style throughout Hymenoptera. This study provides new information about the host-parasitoid koinobiont life strategy among spider wasps, which probably arose convergently in distant taxonomical groups within Pompilidae.

Author Correction: Silk physico-chemical variability and mechanical robustness facilitates intercontinental invasibility of a spider.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Silk physico-chemical variability and mechanical robustness facilitates intercontinental invasibility of a spider.

There are substantive problems associated with invasive species, including threats to endemic organisms and biodiversity. Understanding the mechanisms driving invasions is thus critical. Variable extended phenotypes may enable animals to invade into novel environments. We explored here the proposition that silk variability is a facilitator of invasive success for the highly invasive Australian house spider, Badumna longinqua. We compared the physico-chemical and mechanical properties and underlying gene expressions of its major ampullate (MA) silk between a native Sydney population and an invasive counterpart from Montevideo, Uruguay. We found that while differential gene expressions might explain the differences in silk amino acid compositions and protein nanostructures, we did not find any significant differences in silk mechanical properties across the populations. Our results accordingly suggest that B. longinqua's silk remains functionally robust despite underlying physico-chemical and genetic variability as the spider expands its range across continents. They also imply that a combination of silk physico-chemical plasticity combined with mechanical robustness might contribute more broadly to spider invasibilities.

Comparison of the capture efficiency, prey processing, and nutrient extraction in a generalist and a specialist spider predator.

Predators are traditionally classified as generalists and specialists based on the presence of adaptations that increase efficiency of prey capture and consumption and selection of particular prey types. Nevertheless, empirical evidence comparing foraging efficiency between generalist and specialist carnivores is scarce. We compared the prey-capture and feeding efficiency in a generalist and a specialist (araneophagous) spider predator. By using two related species, the generalist Harpactea rubicunda (Dysderidae) and the specialist Nops cf. variabilis (Caponiidae), we evaluated their fundamental trophic niche by studying the acceptance of different prey. Then, we compared their predatory behavior, efficiency in capturing prey of varying sizes, feeding efficiency, and nutrient extraction. Nops accepted only spiders as prey, while Harpactea accepted all offered prey, confirming that Nops is stenophagous, while Harpactea is euryphagous. Further, Nops displayed more specialized (stereotyped) capture behavior than Harpactea, suggesting that Nops is a specialist, while Harpactea is a generalist. The specialist immobilized prey faster, overcame much larger prey, and gained more mass (due to feeding on larger prey) than the generalist. Both the specialist and the generalist spider extracted more proteins than lipids, but the extraction of macronutrients in the specialist was achieved mainly by consuming the prosoma of the focal prey. We show that the specialist has more efficient foraging strategy than the generalist.

Local trophic specialisation in a cosmopolitan spider (Araneae).

Trophic specialisation can be observed in species with long-term constant exploitation of a certain prey in all populations or in a population of a species with short-term exploitation of a certain prey. While in the former case the species would evolve stereotyped or specialised trophic adaptations, the trophic traits of the latter should be versatile or generalised. Here, we studied the predatory behavioural adaptations of a presumed myrmecophagous spider, Oecobius navus. We chose two distinct populations, one in Portugal and the other in Uruguay. We analysed the actual prey of both populations and found that the Portuguese population feeds mainly on dipterans, while the Uruguayan population feeds mainly on ants. Indeed, dipterans and springtails in Portugal, and ants in Uruguay were the most abundant potential prey. In laboratory trials O. navus spiders recognised and captured a wide variety of prey. The capture efficiency of the Portuguese population measured as components of the handling time was higher for flies than for ants, while that of the Uruguayan population was higher for ants. We found phenotypic plasticity in behavioural traits that lead to increased capture efficiency with respect to the locally abundant prey, but it remains to be determined whether the traits of the two populations are genetically fixed. We conclude that O. navus is a euryphagous generalist predator which shows local specialisation on the locally abundant prey.

[Sexual behavior of Alpaida veniliae (Araneae: Araueidae)]. / Comportamiento sexual de Alpaida veniliae (Araneae: Araneidae).

Studies in transgenic soybean crops in Buenos Aires province, Argentina, revealed that Alpaida veniliae is one of the most abundant species in the guild of orb web spiders. This species is an effective natural enemy of insect pests affecting this crop. In the present study we carried out a descriptive and quantitative analysis of sexual behavior (courtship, mating and post-mating) of A. veniliae. The spiders were collected in transgenic soybean crops located in Chivilcoy (35 degrees 01' S - 60 degrees 06' W), Buenos Aires, Argentina, and reared under laboratory conditions. Based on observations of 20 couples (with virgin females), behavioral units of male and female in terms of postures and movements, including details on duration and frequency, were described at all stages of sexual activity (courtship, mating and post-mating). Courtship exhibited the greatest number and duration of behavioral units in both sexes. Male and female had a sequence of 16 and nine units, respectively, being the frequency of repetitions of the units significantly higher in the male. Mating was brief and males used a single palp to fill only one of the female spermathecae, after which the female became unreceptive. Mating had two behavioral units in the male and only one in the female. During post-mating males had three and females two behavioral units. The average duration of the whole sexual behavior was 541.90 +/- 123.1 seconds for the male and 338.20 +/- 74.1 seconds for the female. Alpaida veniliae females rarely accept a second mating with the same or another male (remating), indicating a strict monogamy. In 46% of observed mating, the female cannibalized the male after it. Females became unattractive after mating, since stop producing sex pheromones, causing a reduction of the male vibratory courtship. The high cost of courtship, including the risk of cannibalism, would reinforce the selectivity of males towards receptive virgin females.

Comportamiento sexual de Alpaida veniliae (Araneae: Araneidae) / Sexual behavior of Alpaida veniliae (Araneae: Araneidae)

Studies in transgenic soybean crops in Buenos Aires province, Argentina, revealed that Alpaida veniliae is one of the most abundant species in the guild of orb web spiders. This species is an effective natural enemy of insect pests affecting this crop. In the present study we carried out a descriptive and quantitative analysis of sexual behavior (courtship, mating and post-mating) of A. veniliae. The spiders were collected in transgenic soybean crops located in Chivilcoy (35º01’ S - 60º06’ W), Buenos Aires, Argentina, and reared under laboratory conditions. Based on observations of 20 couples (with virgin females), behavioral units of male and female in terms of postures and movements, including details on duration and frequency, were described at all stages of sexual activity (courtship, mating and post-mating). Courtship exhibited the greatest number and duration of behavioral units in both sexes. Male and female had a sequence of 16 and nine units, respectively, being the frequency of repetitions of the units significantly higher in the male. Mating was brief and males used a single palp to fill only one of the female spermathecae, after which the female became unreceptive. Mating had two behavioral units in the male and only one in the female. During post-mating males had three and females two behavioral units. The average duration of the whole sexual behavior was 541.90±123.1 seconds for the male and 338.20±74.1 seconds for the female. Alpaida veniliae females rarely accept a second mating with the same or another male (remating), indicating a strict monogamy. In 46% of observed mating, the female cannibalized the male after it. Females became unattractive after mating, since stop producing sex pheromones, causing a reduction of the male vibratory courtship. The high cost of courtship, including the risk of cannibalism, would reinforce the selectivity of males towards receptive virgin females.

Estudios realizados en cultivos de soja transgénica en la provincia de Buenos Aires, Argentina, revelaron que Alpaida veniliae es una de las especies más abundantes dentro del gremio de arañas orbiculares. Esta especie es un eficaz enemigo natural de las plagas de insectos de este cultivo. En el presente estudio se llevó a cabo un análisis descriptivo y cuantitativo de la conducta sexual (cortejo, cópula y post-cópula) de A. veniliae. Las arañas fueron recolectadas en cultivos de soja transgénica ubicados en Chivilcoy (35º01’ S - 60º06’ W), (Buenos Aires, Argentina) y criadas en condiciones de laboratorio. A partir de la formación de 20 parejas (con hembras vírgenes), se observaron las unidades de comportamiento de machos y hembras, en términos de posturas y movimientos, incluyendo los detalles de su duración y frecuencia en todas las etapas del apareamiento. El cortejo exhibió el mayor número y la mayor duración de las unidades de comportamiento en ambos sexos. La secuencia de unidades fue 16 en el macho y nueve en la hembra, siendo la frecuencia de repeticiones de las unidades significativamente mayor en el macho. La cópula fue breve y el macho usó un solo palpo transfiriendo esperma a una sola espermateca de la hembra. Hubo dos unidades de comportamiento en el macho y una en la hembra. Durante la post-cópula el macho tuvo tres y la hembra dos unidades de comportamiento. La duración media de todo el comportamiento sexual fue 541.90±123.1 segundos para el macho y 338.20±74.1 segundos para la hembra. La hembra de A. veniliae sólo excepcionalmente aceptó una segunda cópula con el mismo u otro macho, lo que indica una monogamia estricta. En el 46% de las cópulas observadas la hembra canibalizó al macho al terminar la misma. Debido a que a partir de este momento dejan de producir feromonas sexuales, se vuelven no receptivas y provocan una reducción del cortejo del macho. El alto costo del cortejo del macho, incluyendo el riesgo de canibalismo, reforzaría la selectividad de éstos hacia las hembras receptivas vírgenes.

Infección intrahospitalaria por rotavirus en salas generales de pediatría del Centro Hospitalario Pereira Rossell

Resumen Introducción: los rotavirus son causa importante de diarrea en el mundo, siendo la causa más frecuente en los países desarrollados. En países en desarrollo, como el nuestro, son importante causa de morbilidad y responsables de diarrea intrahospitalaria. Objetivo: describir los casos de diarrea intrahospitalaria ocurridos en los primeros ocho meses después de la incorporación de la investigación de rotavirus al estudio de las infecciones intrahospitalarias. Métodos: del 1º de abril al 31 de diciembre de 2002 se estudiaron los pacientes de 0 a 14 años denunciados como casos de diarrea intrahospitalaria al Comité de Infecciones Intrahospitalarias del HP-CHPR. La muestra para el diagnóstico de rotavirus fue de materia fecal, que se procesó en el Laboratorio de Virología del Departamento de Bacteriología y Virología del Instituto de Higiene, Facultad de Medicina. Las muestras positivas se estudiaron en la Sección Virología de la Facultad de Ciencias donde se realizó la caracterización electroferotípica en gel de poliacrilamida. Se analizaron los siguientes datos: edad, sexo, estado nutricional, enfermedad que motivó el ingreso, momento de instalación de la diarrea, servicio de origen, evolución y complicaciones y días de hospitalización. Resultados: todos los rotavirus detectados tenían patrón electroferotípico largo. El porcentaje de diarrea intrahospitalaria asociada a rotavirus en el HP-CHPR en el período estudiado fue de 40%. La edad promedio de los pacientes fue de 10,9 meses; la mitad de los pacientes tenían buen estado nutricional. El 50% de los niños afectados presentaban una infección respiratoria aguda baja de probable etiología viral al ingreso. La diarrea apareció en promedio a los 7 días de internación y tuvo una duración promedio de 4 días. La duración promedio de la internación fue de 13 días y 5 niños presentaron complicaciones no graves. Discusión: el riesgo de infección nosocomial aumenta cuanto más prolongada es la internación y tiene una no despreciable morbilidad tanto en el presente estudio como en otros trabajos. Es necesario mejorar la notificación de los casos de diarrea intrahospitalaria y continuar estudios que permitan la caracterización genotípica de estas cepas. Se recomienda: lavado frecuente de manos, aislamiento de los niños con gastroenteritis, altas tempranas y educar al personal de salud. Futuros estudios permitirían establecer con más precisión los serotipos y genotipos de las cepas de rotavirus de los niños asistidos en el ámbito público y privado y así poder discutir la potencial eficacia de las vacunas que tal vez estén disponibles en los próximos años.

Summary Introduction: rotavirus is a common cause of worldwide diarrhea being the first cause of this disease in developed countries. In developing countries like ours, is an important cause of communitarian and nosocomial diarrhea. Objective: to describe nosocomial diarrhea cases which took place in the first eight-month period after the incorporation of rotavirus investigation into the nosocomial infections study. Methods: from April first to December 31, 2002, patients between 0 to 14 years old were included as cases of nosocomial diarrhea to the 'Nosocomial Infections Committee' from the Centro Hospitalario Pereira Rossell. Stool sample was used for the diagnosis, which was processed at the virology section of the Bacteriology and Virology department from the Hygiene Institution. Positive samples were processed at the Virology section from the Science University where the electrophoretic characterization in poliacrilamide gel was realized. The following data was analyzed: age, nutritional status, cause of hospitalization, duration of disease, evolution and complications, and hospitalization time. Results: all rotavirus detected had long electrophoretic pattern. The percentage of nosocomial diarrhea associated to rotavirus at Pereira Rossell Hospital in the period studied was 40%. Average age was 10,9 months, half of them with a good nutritional status. 50% of the affected children had an acute viral respiratory tract infection since the beginning. Diarrhea appeared approximately after a week and lasted four days. Hospitalization lasted an average of 13 days and 5 children had mild complications. Discussion: the risk of nosocomial infections increases with the duration of hospitalization and has an important morbidity shown in this study as in other studies as well. It is necessary to improve the notification of the cases and continue studying the genotype. It is recommended: frequent handwashing, patients grouping, early delays, and health personnel education. Future studies will establish serotypes and genotypes of different rotavirus at different institutions in order to establish the potential efficacy of the vaccine in the next years.

The prey capture behaviour of Metepeira gressa (Araneae, Araneidae) on mealworms, flies and ants

The prey-capture behavioral repertoire of females and juveniles of the araneid spider Metepeira gressa (Keyserling, 1892) was analyzed using mealworm larvae, flies, and ants as prey of the same size. Flies and ants are frequently encountered by the spider species, but the beetle larvae are not. During the experimental period each type of prey was offered only once to each spider. The first unit of immobilization is very important to subdue the prey. When capturing mealworms and ants, spiders performed “Wrap”as the first unit of the Immobilization phase, and while capturing flies the spiders used “Bites”. “Wrap”seems to be a discriminatory initial behavior on dangerous prey, such as ants. The discrimination between ants and mealworms was tested using the observed behavioral units in spite of both generated similar capture patterns. The only difference detected was the occurrence of the unit “Other Locomotion”, more frequently on mealworm. The spider has many difficulties in mealworm capture because of the large size of the prey and the strength and the peculiar defensive tactic (“wriggling”) that progressively destroys the spider web. In disagree with the expectations, the spiders spent more time and energy in the capture of mealworms