Leucauge, WHITE, 1841

Álvarez-Padilla, Fernando & Hormiga, Gustavo, 2011, Morphological and phylogenetic atlas of the orb-weaving spider family Tetragnathidae (Araneae: Araneoidea), Zoological Journal of the Linnean Society 162 (4), pp. 713-879 : 764-769

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https://doi.org/ 10.1111/j.1096-3642.2011.00692.x

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LEUCAUGE WHITE, 1841 View in CoL View at ENA ( FIGS 1C, E View Figure 1 , 41–50 View Figure 41 View Figure 42 View Figure 43 View Figure 44 View Figure 45 View Figure 46 View Figure 47 View Figure 48 View Figure 49 View Figure 50 )

Type species: Epeira venusta Walckenaer, 1841 (see Dimitrov & Hormiga, 2010). Linyphia (Leucauge) argyrobapta White, 1841 , is a junior synonym of Epeira venusta Walckenaer, 1841 . The type of Epeira venusta is an illustration by John Abbot (1792) from his unpublished manuscript on the spiders of Georgia ( USA). Abbot’s original illustration is in the library of The Natural History Museum in London. Walckenaer (1841) used Abbot’s manuscript (p. 13, fig. 113) to describe Epeira venusta . A photocopy of Abbot’s illustration, in the Museum of Comparative Zoology, was examined by Levi (1980) for his redescription of Leucauge venusta . The name venusta was published in 1841, before Whites’s argyrobapta , as can be seen from White’s (1841: 473) footnote about Walckenaer’s work.

Diagnosis: Leucauge species can be distinguished from all other tetragnathid genera by the following combination of characters: two parallel rows of feathered trichobothria on the IV femoral ectal surface ( Figs 1C View Figure 1 , 42E, F View Figure 42 , 47F View Figure 47 ); spermathecae walls translucent and weakly sclerotized ( Figs 43C View Figure 43 , 48C View Figure 48 ); fertilization ducts coiled around the copulatory ducts ( Figs 45D View Figure 45 , 50D View Figure 50 ); flagelliform embolus with an elongated base ( Figs 44D View Figure 44 , 50C View Figure 50 ); conductor apically projected ( Fig. 49F View Figure 49 ); and sperm duct with more than four switchbacks ( Figs 45B View Figure 45 , 50B View Figure 50 ).

Description: Female: body length from 3.2 to 10.3 mm. Cephalothorax fovea formed by two deep longitudinal pits ( Figs 42A View Figure 42 , 47B View Figure 47 ). Sternum as wide as long ( Figs 42H View Figure 42 , 47G View Figure 47 ). Labium trapezoidal, wider than long, and rebordered. Ocular area lower than carapace lateral margins ( Fig. 47A View Figure 47 ). Anterior surface of chelicerae smooth, boss present ( Figs 42D View Figure 42 , 47D View Figure 47 ). Secondary eyes with canoe-shaped tapetum ( Levi, 1980: figs 48, 49, 65, 66). Eyes subequal in size, lateral eyes slightly smaller, juxtaposed and on a tubercle. Clypeus one AME diameter high. Abdomen longer than wide, covered with silver guanine patches ( Fig. 1E View Figure 1 ). Booklung cuticle smooth ( Figs 41A View Figure 41 , 46A View Figure 46 ). Tracheal spiracle near the spinnerets ( Fig. 41B View Figure 41 ), internally covered with more than eight accessory glands ( Fig. 46B View Figure 46 ). Median tracheae not ramified, with rounded tips ( Figs 41C, D View Figure 41 , 46C–E View Figure 46 ). ALS with c. 65 piriform spigots. PMS with three to four aciniform spigots between the cylindrical and minor ampullate silk gland spigots but without any aciniform spigots over the anterior surface. PLS with c. 20 aciniform spigots roughly arranged in two parallel lines; distal end of the aggregate spigots embracing the distal end of the flagelliform spigot. Epigynal plate well sclerotized and flat in most species, ventrally projected in L. argyra ( Figs 43A View Figure 43 , 48A, B View Figure 48 ). Copulatory openings ventrally orientated, laterally displaced in L. argyra ( Fig. 50D View Figure 50 ). Copulatory ducts more than half the spermathecae length but less than its total length, cuticle sclerotization variable ( Figs 45D View Figure 45 , 50D View Figure 50 ). Fertilization duct sclerotization variable, distal section usually well sclerotized ( Fig. 43B–E View Figure 43 ). Accessory glands concentrated between the spermathecae and fertilization duct junction ( Fig. 43B–D View Figure 43 ). Accessory gland bases considerably enlarged giving them an inverted acorn form ( Figs 43F View Figure 43 , 48D View Figure 48 ).

Male: slightly smaller than females; no significant sexual size dimorphism has been reported for Leucauge species. Male somatic morphology as in female except for having the cheliceral anterior surface macrosetae thicker and lacking the cheliceral boss ( Figs 42C, H View Figure 42 , 47C View Figure 47 ). Epiandrous plate well sclerotized, fusules immersed in a transverse groove. This groove can be continuous or subdivided ( Figs 41E View Figure 41 , 46G View Figure 46 ). Epiandrous fusules not immersed in pits and with their bases wider than the fusule shaft. PLS triplet reduced to nubbins ( Figs 41F View Figure 41 , 46F View Figure 46 ). Male palpal patella with one long macroseta, palpal tibia more than twice as long as wide ( Figs 42H View Figure 42 , 49F View Figure 49 ). Cymbium dorsal surface can be either smooth ( Fig. 44B View Figure 44 ) or with processes and modified macrosetae; the cymbium of L. argyra has an enormous modified macroseta and a cymbial dorsobasal process ( Fig. 49C View Figure 49 ). Paracymbium hookshaped, without apophyses, and considerably shorter than the cymbium length ( Figs 44C View Figure 44 , 49E View Figure 49 ). Tegulum roughly oval, with a mesal depression produced by the displaced subtegulum ( Figs 44F View Figure 44 , 49F View Figure 49 ). Conductor rigid, although some parts are weakly sclerotized, its attachment to the tegulum membranous and originating at the ventral edge of the tegulum. The part of the tegulum where the embolus and conductor arise is membranous in L. venusta and other leucaugine genera, in the former species the embolus and tegulum attachment are close together. Usually the conductor’s base apex and margins are more sclerotized and can bear distal apophyses ( Figs 44A, E, F View Figure 44 , 45A View Figure 45 , 49D, F View Figure 49 , 50A View Figure 50 ). Embolus base rectangular, longer than wide. Embolus flagelliform, considerably narrower than its base ( Figs 44D View Figure 44 , 45C View Figure 45 , 50C View Figure 50 ), flexible and weakly sclerotized. Sperm duct path convoluted with several coils ( Figs 45B View Figure 45 , 50B View Figure 50 ). Although Archer (1951: fig. 7) mentioned that L. argyra has a median apophysis we have not found any tegular apophyses, other than the conductor, in any of the tetragnathid species that we have studied, including L. argyra . This species has a huge macroseta on the dorsal surface of the cymbium ( Fig. 49B, C View Figure 49 ) not homologous to the cymbial dorsobasal process by the conjunction test ( Patterson, 1982).

Natural history: This genus includes 170 species and eight subspecies with a worldwide geographical distribution, except western Europe ( Platnick, 2009). Many Leucauge species build horizontal webs with more than 30 radii and spirals, an open hub, and a barrier web below the orb ( Fig. 3F View Figure 3 ; Levi, 1980: plates 4–5; Eberhard, 1982, 1987, 1988a, 2001). Their webs are usually found on low vegetation in a diversity of habitats and are often built in open sunny spots, such as patches of secondary growth along roads and forest gaps, and in gardens and orchards. Some species prefer habitats along the shores of fresh water bodies whereas other species are found in pristine primary forests. Many studies have been published on a diversity of aspects of the biology of a few Leucauge species , to the extent that these spiders can be referred as to model organisms for spider biology. For example, studies of Leucauge mariana (Taczanowski, in Keyserling, 1881b) include those of the early and late stages of web building behaviours ( Eberhard, 1982, 1988a, b, 1990a; Zschokke, 2002), internal anatomy ( Palmgren, 1979), effects of gravity on web architecture, the behaviour involved in dispersal by airborne silk lines ( Eberhard, 1987), mating behaviour and sexual selection in relation to genitalic development ( Eberhard & Huber, 1998a, b), kleptoparasitic associations, and predation rates and preferences ( Hénaut, 2000). Leucauge venusta has been studied for capture silk stickiness ( Opell, 1997), variations in web construction ( Hénaut, García-Ballinas & Alauzet, 2006), web architecture variations either in solitary or aggregations ( Buskirk, 1986), kleptoparasitic interactions ( Hénaut et al., 2005), community structure ( Peck, 1966; Post & Riechert, 1977), variations in the material properties of dragline silk across many spiders including L. venusta ( Swanson et al., 2006) , amongst many others. Other works on American species include the study of the effects of parasitoid toxins in the web building behaviour of L. argyra ( Eberhard, 2001) . In addition, a considerable number of studies has been conducted with some Palaeotropical Leucauge species such as the predatory behaviour of Leucauge magnifica ( Yoshida, 2000) or web architecture in relation to predation in Leucauge decorata ( Blackwall, 1864; Li & Lee, 2004), amongst others.

Taxonomy: Leucauge has never been revised except for treatments of some North American ( Levi, 1980) and Asian species ( Yaginuma, 1954; Kim, Kim & Lee, 1999; Song, Zhu & Chen, 1999; Hu, 2001; Namkung, 2003; Zhu et al., 2003). The specimens that we have studied for the description and diagnosis of this genus belong to L. venusta ( Walckenaer, 1841) and L. argyra ( Walckenaer, 1841) , two of the species that have been most intensively studied. The current number of described species of Leucauge in the Neotropics represents a small fraction of the total number of species found in museum collections. A phylogenetic analysis that included four Leucauge species recovered this genus as monophyletic and sister to a clade that includes Okileucauge , Tylorida , and Mesida ( Tanikawa, 2001; Fig. 141B View Figure 141 ). In Tanikawa’s analysis Leucauge monophyly was supported by a single synapomorphy, the presence of parallel trichobothria rows with more than ten pairs on femur IV. It is likely that the genus Leucauge as currently delimited is either polyphyletic or paraphyletic. Leucauge argyra , which has been previously recognized as belonging to a different genus ( Plesiometa F. O. P. Cambridge, 1903 ; e.g. see Eberhard, 2001 and Levi, 2005b), was recovered in our analysis as sister to L. venusta . The genera Alcimosphenus Simon, 1895 and Opas O. P. Cambridge, 1896 , previously included in Leucauge , have been recently recognized as different genera ( Levi, 2005c, 2008). The analyses of both data sets (morphology plus behaviour and morphology plus behaviour plus DNA sequences) recover L. venusta and L. argyra as sister taxa ( Figs 143A, B View Figure 143 , 144 View Figure 144 ). In order to test whether L. argyra could belong to a separate genus (and whether the remaining species in Leucauge form a clade), a larger sample of Leucauge species and representatives from closely genera would be required. Both data sets suggest that Leucauge is sister to the Palaeotropical genus Opadometa .


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