RESUMEN El sitio Ramsar Humedales Chaco se caracteriza por su heterogeneidad ambiental y elevada diversidad de flora y fauna. Sin embargo, la fragmentación y homogeneización en estos ambientes tiende a afectar negativamente a taxones con baja abundancia o riqueza como los Thomisidae. En este trabajo se analiza la diversidad taxonómica de los ensambles de Thomisidae en ambientes con distintos grados de complejidad vegetal. Los muestreos se efectuaron durante los años 2013 a 2016 en pastizales, palmares, bosques abiertos y selvas de galería de siete localidades, mediante las técnicas de golpeteo de follaje, aspirado y observación directa. Se obtuvieron en total 464 individuos y 34 especies/morfoespecies pertenecientes a cinco subfamilias, siete tribus y diez géneros. Los ambientes boscosos mostraron baja diversidad taxonómica (Δ+) y altos valores de variación taxonómica (Λ +), ello refleja un árbol filogenético de Thomisidae poco uniforme debido a una sobrerrepresentación de Tmarus. La elevada riqueza de este género en los bosques sugiere que el mecanismo de ensamblaje del género posiblemente esté mediado por filtros ambientales, donde las condiciones bióticas favorecen la coexistencia de especies, los cuales les permiten sobrevivir en determinados hábitats. En los pastizales y palmares las especies estuvieron uniformemente representadas en el árbol filogenético. Los bosques degradados presentaron una estructura específica y taxonómica más cercana a los ambientes de pastizal y palmar. La inclusión de las relaciones filogenéticas en los análisis de diversidad podría ser clave a la hora de implementar planes de manejo y conservación.

ABSTRACT The Ramsar site Chaco Wetlands is characterized by its environmental heterogeneity and high diversity of flora and fauna. However, fragmentation and homogenization of environments tend to negatively affect taxa with low abundance or richness like the Thomisidae spiders. In this work, taxonomic diversity is analyzed for Thomisidae assemblages in those environments with varying degrees of plant complexity. The samples were carried out in grasslands, palm groves, open forests, and gallery forests of seven localities, during the years 2013 to 2016, by the techniques of foliage beating, vacuum sampling, and direct observation. A total of 464 individuals and 34 species/morphospecies were obtained. These samples belong to five subfamilies, seven tribes, and ten genera. Forested environments showed low taxonomic diversity (Δ +) and high values of taxonomic variation (Λ +), this reflects a phylogenetic tree of Thomisidae non-uniform due to an overrepresentation of species of the genus Tmarus. The high species richness of this genus in forests suggests that environmental filters possibly mediate the mechanism of assembly, where biotic conditions favor the coexistence of species, which allow them to survive in certain habitats. In the grasslands and palm groves, the species were uniformly represented in the phylogenetic tree. The degraded forests presented a specific and taxonomic structure closer to the grassland and palm grove environments. The inclusion of phylogenetic relationships in diversity analyzes could be key in implementing management and conservation plans.

The crab spider genus Uraarachne Keyserling 1880 currently comprises two species: U. longa Keyserling (type species, from Brazil, and herein newly recorded from Paraguay) and U. vittata (Caporiacco) from French Guiana. Uraarachne is herein proposed, on base of somatic and genitalic characters, as a senior synonym of Plancinus Simon 1886, which is known from three species from Uruguay: P. runcinioides Simon (type species), P. cornutus Simon, and P. brevipes Simon (all three transferred here to Uraarachne). Uraarachne runcinioides new comb., (type species of Plancinus), and U. cornuta new comb., are reported for the first time for Argentina and redescribed, based on the type specimens and new material, including the first known males. Four new species are described from Argentina: U. panthera n. sp., and U. ceratophrys n. sp. (from Misiones province, both on base of single male specimens), U. toro n. sp. (from Salta province, female only), and U. kapiity n. sp. (from the argentine provinces of Chaco, Corrientes, and Entre Ríos, and from Paraguay, on base of both sexes). Two additional species are transferred to Uraarachne: Runcinia plana Simon, previously known only from juveniles from Paraguay (adults described here for the first time, and distribution extended to central-eastern Argentina), and Misumenoides variegatus Mello-Leitão, known from the holotype male from Santa Fe (female described here for the first time, and distribution extended to Paraguay and Buenos Aires, Argentina). Platyarachne argentina Mello-Leitão and Erissoides argentinus Mello-Leitão are newly synonymized with Uraarachne runcinioides. The relationships of the genus are breafly discussed, proposing a close relationship with Runcinia Simon.

El género de arañas cangrejo Uraarachne Keyserling 1880, actualmente comprende dos especies: U. longa Keyserling (especie tipo, de Brasil y recientemente registrada en Paraguay) y U. vittata (Caporiacco) de Guayana Francesa. Aquí se propone Uraarachne -sobre la base de varios caracteres de morfología somática y genital- como sinónimo anterior de Plancinus Simon 1886, conocido hasta la fecha por tres especies de Uruguay: P. runcinioides Simon (especie tipo), P. cornutus Simon y P. brevipes Simon (las tres se transfieren aquí a Uraarachne). Uraarachne runcinioides n. comb. (especie tipo de Plancinus) y U. cornuta n. comb. se citan por primera vez para Argentina y son redescriptas en base a los especímenes tipo y a material recientemente encontrado en colecciones argentinas, incluyendo los primeros machos conocidos. Cuatro nuevas especies se describen para Argentina: U. panthera n. sp. y U. ceratophrys n. sp. (de la provincia de Misiones, ambas en base a especímenes machos), U. toro n. sp. (de la provincia de Salta, sólo una hembra), y U. kapiity n. sp. (de las provincias argentinas de Chaco, Corrientes y Entre Ríos, y de Paraguay, en base a los dos sexos). Adicionalmente, otras dos especies se transfieren a Uraarachne: Runcinia plana Simon, conocida previamente por juveniles de Paraguay (los adultos se describen por primera vez, y se extiende su distribución conocida hasta el centro-este de Argentina), y Misumenoides variegatus Mello-Leitão, conocida previamente por el macho holotipo de Santa Fe (la hembra se describe aquí por primera vez, extendiéndose su distribución conocida hasta Paraguay y Buenos Aires). Platyarachne argentina Mello-Leitão y Erissoides argentinus Mello-Leitão son sinonimizadas con Uraarachne runcinioides. Los parentescos probables del género son brevemente discutidos, proponiéndose una posible cercanía con Runcinia Simon.

ABSTRACT Urbanization has a great impact on the diversity of living organisms. Spiders, for example, have been shown to respond negatively (some orb weaving species) and positively (ground dwelling species) to urbanization. The effects of urbanization on crab spiders (Thomisidae) (sit-and-wait predators that generally ambush their prey on flowers and leaves) are not sufficiently known. This paper describes the Thomisidae community that inhabits green patches in a temperate Neotropical city, Cordoba, Argentina, and its surroundings, and ascertains whether there are differences in species richness, abundance and composition between urban and exurban sites. Samples were collected from 30 sites during the summer and spring of 2013 and 2014, using the garden-vacuum method. We compared the abundance, richness and composition of Thomisidae among three habitat categories (urban, suburban and external). Seven species in three genera, Misumenops, Wechselia and Tmarus, were detected. Misumenops was the most abundant genus in Córdoba, and Tmarus elongates Mello-Leitão, 1929 was collected in Argentina for the first time. The abundance, richness and composition of thomisid spiders did not differ between habitat categories, indicating that urbanization does not have a negative effect on the communities of these spiders in open green spaces. Site variability, on the other hand, does, suggesting that local factors may be more relevant than broad-scale factors to explain community patterns in this family.

Preys and capture sites used by crab spiders (Araneae: Thomisidae and Philodromidae) in a grassland of central Argentina. Distribution of predators and flowers influence on the selection of forage site of flower visitors. Predators, as crab spiders, can determine the structure of communities of flower visitors and influence on plant pollination. The objectives of this study were: (a) to evaluate the use of flowers or inflorescences (hereinafter units floral attraction, UFA) by crab spiders as capture sites; (B) to identify traits that may affect the use of capture sites; and (c) to assess the relationship between the size of the spiders and their prey. We surveyed two plots of one hectare in center of Pampas region (Buenos Aires, Argentina) recording all entomophilous flowering plants and their floral visitors. In addition, we captured all crab spiders with and without preys, recording the UFA they used as capture site. We estimate and evaluate the relationship between the size of the spiders and their prey. Crab spiders used as capture sites the most abundant UFA and with higher richness of floral visitors, regardless of whether they were flowers or inflorescences. On the other hand, the size of the spider could be determining the size of the preys. We found a positive association between the two variables, although this result was variable depending on the taxonomic orders of preys. Those results suggest that crab spiders can have a relevant role as modelers of the structure of plant - pollinator interaction.

La distribución de los depredadores y flores son factores importantes que influyen sobre la elección del sitio de forrajeo por los visitantes forales. Los depredadores como las arañas cangrejo pueden determinar la estructura de las comunidades de visitantes forales y afectar la polinización de las plantas. Los objetivos de este trabajo fueron (a) evaluar el uso por las arañas cangrejo de flores o inflorescencias (en adelante unidades de atracción foral, UAF) como sitios de captura; (b) determinar características que pueden afectar el uso de los sitios de captura; y (c) evaluar la relación entre el tamaño de las arañas y el de sus presas. Recorrimos dos parcelas de una hectárea en el centro de la región Pampeana (Buenos Aires, Argentina) registrando todas las plantas entomófilas en flor y sus visitantes forales. Además, capturamos todas las arañas cangrejo con y sin presa registrando las UAF que utilizaron como sitio de captura. Medimos y evaluamos la relación entre el tamaño de las arañas y de sus presas. Las arañas cangrejo utilizaron como sitios de captura las UAF más abundantes y con mayor riqueza de visitantes forales, independientemente de si eran flores o inflorescencias. Por otro lado, el tamaño de la araña podría determinar el tamaño de su presa. Encontramos una asociación positiva entre ambas variables, aunque este resultado fue variable dependiendo de los órdenes taxonómicos de las presas. Estos resultados sugieren que las arañas cangrejo pueden tener un papel relevante modelando la estructura de las interacciones planta-polinizadores.

Um evento de predação sobre Tropidurus hispidus (Tropiduridae) pela aranha caranguejeira Lasiodora klugi (Theraphosidae) foi observado em área de caatinga arbórea no nordeste do Brasil. Artrópodes são potenciais predadores de pequenos vertebrados e pesquisadores têm relatado eventos de predação envolvendo aranhas e herpetofauna em regiões neotropicais. Portanto, a presente comunicação breve é o segundo caso de predação de aranha sobre lagartos do gênero Tropidurus no Brasil e o primeiro para as caatingas semiáridas, reforçando a argumentação de que grandes aranhas possuem um papel relevante como predadores desses animais.

A predation event on Tropidurus hispidus (Tropiduridae) by the crab spider Lasiodora klugi (Theraphosidae) was observed in an arboreal caatinga area in northeastern Brazil. Arthropods are potential predators of small vertebrates and researchers have reported predation events involving spiders and herpetofauna in Neotropical regions. As such, the present short communication is the second case of predation of spiders on Tropidurus lizards in Brazil, and the first for the semiarid caatinga, reinforcing the argument that large spiders have relevant roles as predators of these animals.

Ainda que aranhas Thomisidae sejam comumente encontradas em flores, as associações desses aracnídeos a espécies de plantas e às suas características florais foram pouco registradas na região neotropical. Observações do hábito das plantas, visitantes florais, e também das características florais, tais como antese, odor, forma, cor e recursos da flor, foram assinaladas para espécies floridas de uma área de cerrado presentes em uma trilha de 2 km de extensão. Misumenops argenteus e Misumenops pallens representaram 62,86% das aranhas habitantes de 22 espécies de plantas floridas. As plantas Senna rugosa (Fabaceae), Styrax ferrugineus (Styracaceae) e Banisteriopsis campestris (Malpighiaceae) abrigaram, individualmente, cerca de 10 a 17% do total das aranhas e, nestas plantas, a antese diurna; flores de coloração atrativa a abelhas, como amarela (S. rugosa), branca (S. ferrugineus) e rosa (B. campestris) e as anteras poricidas, bem como a visita das flores por abelhas reforçou a evidência de síndrome de polinização para melitofilia. Este é o primeiro levantamento de espécies de aranhas Thomisidae associadas a plantas do cerrado brasileiro.

Although crab spiders are common in flowering plants, their relations with plant species and its floral traits have been poorly known in the Neotropics. Observations regarding plant habits, floral visitors and also floral characteristics such as anthesis, odour, shape, colour and floral resources were recorded in flowering plant species of an area of "Cerrado" on a 2 km long trail. Misumenops argenteus and Misumenops pallens accounted for 62.86% of the spiders captured on 22 flowering plant species. The plants Senna rugosa (Fabaceae), Styrax ferrugineus (Styracaceae) and Banisteriopsis campestris (Malpighiaceae), hosted, each one, about 10 to 17% of the total spiders collected and these plants had diurnal anthesis, bee-attractive flower colours such as yellow (S. rugosa), white (S. ferrugineus), and pink (B. campestris), poricidal anthers as well as being visited by bees which evidenced bee-pollination syndrome. This study is the first survey regarding crab spiders and their associations with plant species of the "Cerrado".

Na literatura tem sido amplamente registrado que aranhas Thomisidae predam visitantes florais de várias espécies de planta. Neste estudo nós apresentamos observações de Croton selowii Baill. (Euphorbiaceae), uma espécie monóica, abrigando aranhas Thomisidae em uma área de restinga de Pernambuco, Brasil. A espécie é visitada por invertebrados de várias ordens e vários deles são predados pelas aranhas, principalmente espécies de Diptera. As aranhas apresentaram um comportamento de esfregar as pernas dianteiras dentro das flores, o que pode ser interpretado como uma estratégia de camuflagem das pernas. Croton selowii parece representar um bom sítio de forrageamento para essas aranhas, pois possui um sistema de polinização generalista, sendo visitado por ampla gama de invertebrados e floresce em um período de baixa disponibilidade de flores na área.

In the literature it has been extensively mentioned that crab spiders (Araneae: Thomisidae) prey on floral visitors of several plant species. Here we present observations of Croton selowii Baill. (Euphorbiaceae), a monoecious species harboring individuals of crab spiders in an area of coastal vegetation of Pernambuco state, Brazil. The species is visited by several invertebrate orders, and some of them were preyed upon by the spiders, mainly Diptera species. The spiders rubbed the forelimbs within the flowers, which may constitute a strategy to camouflage these structures. Croton selowii seems to represent a suitable foraging site for the spiders, because it has a generalist pollination system (thus being visited by a wide range of invertebrate species) and blooms in a period of low flower resource availability in the area.

Frente al manejo tradicional, el cultivo ecológico proporciona una alternativa a los problemas de aparición de resistencias, residuos y contaminación ambiental, además de favorecer un aumento de la biodiversidad del ecosistema por el efecto beneficioso sobre la fauna auxiliar. En los agroecosistemas, la acción conjunta de los enemigos naturales de los fitófagos puede mantener a las poblaciones de muchos de ellos por debajo del umbral económico de daño. Uno de los grupos de depredadores menos conocidos en los estudios de control natural de las plagas del algodón son las arañas (Orden Araneae), de modo que se realizaron prospecciones en parcelas de algodón orgánico situadas en el sur de España: Córdoba, Sevilla y Cádiz. Los ejemplares se recolectaron mediante la batida directa de las plantas. La especie más abundante resultó ser Cheiracanthium sp. (Miturgidae), seguida de otras especies como Philodromus sp. (Philodromidae), los tomísidos Thomisus onustus, Runcinia grammica y Synema globosum (Thomisidae), Salticus sp. (Salticidae) y Larinia lineata (Araneidae). Además se recogieron individuos de las familias Theridiidae y Linyphiidae. Este trabajo, por tanto, es una primera aproximación en el conocimiento de las especies y su abundancia en el cultivo ecológico del algodón, lo que supone una base para futuras investigaciones en el marco del control de fitófagos mediante arañas.

Compared to traditional management, organic farming provides an alternative to the problems of the appearance of resistance, residues and environmental pollution, as well as favoring an increase in ecosystem biodiversity through beneficial effects on other fauna. In agroecosystems, the combined action of natural enemies on phytophages can maintain populations of many of them below economic damage thresholds. One of the least known groups of predators in studies on the natural control of cotton pests are the spiders (Order Araneae), therefore surveys were conducted in plots of organic cotton situated in southern Spain: Córdoba, Sevilla and Cádiz. Specimens were collected by beating the plants. The most abundant species was Cheiracanthium sp. (Miturgidae), followed by other species such as Philodromus sp. (Philodromidae), the crab spiders Thomisus onustus, Runcinia grammica andSynema globosum (Thomisidae), Salticus sp. (Salticidae) and Larinia lineata (Araneidae). In addition, individuals were collected from the families Theridiidae and Linyphiidae. This work, therefore, is a first step in understanding the species and their abundance in organic cotton crops, and will be the basis for future research in the area of phytophage control by spiders.