Web damage during prey capture in Hyptiotes paradoxus (C.L.KOCH 1834) (Uloboridae)

H. paradoxus - well known for its characteristic triangular web - has frequently been described to always completely collapse its web when catching prey. The aim of the present article is to show that this is not the case, and to discuss how the myth of the obligate complete collapse of the web has arisen and why it survived so well.Es wurde oft beschrieben, dass das charakteristische, dreieckige Netz von H. paradoxus beim Fang einer Beute vollständig zerstört wird. Diese Arbeit zeigt auf, dass dies meist nicht der Fall ist und diskutiert, wie sich der Mythos der obligaten vollständigen Netzzerstörung bildete, und wieso er sich soweit verbreiten konnte

Distorted Sex Ratio at Birth in the Captive Pygmy Hippopotamus, Hexaprotodon Liberiensis

The total captive population of the pygmy hippopotamus Hexaprotodon (=Choeropsis) liberiensis has a highly female-biased sex ratio at birth (41% males), which exceeds most of the other known distorted sex ratios in captive mammals. Deviation from an even sex ratio was not compensated by a higher juvenile mortality in females. I examined the possible causes of that deviation and could not find any association between offspring sex and inbreeding, parity, or mother's age. I found, however, a significant difference in sex ratios among different zoological gardens, suggesting that husbandry influenced sex at birth in the pygmy hippopotamus. Further analysis suggested that high feeding intensity and "hands-on” husbandry favored production of daughters. However, not all the observed patterns and relationships could be explained by classic sex ratio theorie

Asymmetry in Orb-Webs: An Adaptation to Web Building Costs?

Orb-web spiders build vertically asymmetric webs, in which the lower part is larger than the upper part. One hypothesis explaining this asymmetry suggests that the spider's mass imposes higher building costs in the upper part of the web, causing the spider to reduce this part of the web. We tested this hypothesis by assessing building costs of different parts of the web. We found that the specific time-cost of building (i.e. the time required to build a certain length of silk) differed between the two parts of the web and that the difference in time-costs influenced web asymmetry. Contrary to predictions, however, building costs were larger in the lower part of the web, suggesting that additional factors affect the spider's decisions while building the web, which are likely to be prey-capture consideration

First records and data about the biology of Cyclosa oculata (Araneae: Araneidae) in Switzerland

Die Radnetzspinne Cyclosa oculata (Walckenaer, 1802) wurde an elf Orten in der Nordwestschweiz nachgewiesen. Alle Fundorte lagen in Buntbrachen mit relativ hohem Anteil abgestorbener Vegetation vom Vorjahr, relativ niedriger Vegetationshöhe und geringem Anteil von Gräsern an der Vegetation. C. oculata baute ihr kleines Radnetz in Bodennähe, tief in der Vegetation. Unter den ecribellaten Radnetzspinnen Mitteleuropas ist C. oculata einzigartig, da sie manchmal ein rudimentäres Netze baut und verwendet, da sie ihre Kokons in das Netz einbaut, und da sie ein dauerhaftes Detritus-Stabiliment baut. Aufgrund unserer Beobachtungen nehmen wir an, dass das Stabiliment C. oculata zur Tarnung dient.The orb-web spider Cyclosa oculata (Walckenaer, 1802) was found at eleven localities in north-western Switzerland. All records were from wildflower strips ("Buntbrachen") with a relatively high proportion of dried vegetation from the previous year, a relatively low vegetation height and a low proportion of grasses in the vegetation. C. oculata built its vertical orb-web near the ground, deep in the vegetation. Among ecribellate orb-web spiders in Central Europe, C. oculata is unique because it sometimes builds rudimentary webs on which it stays, because it builds its cocoons into the web, and because its stabilimentum is long-lasting and consists largely of debris. Based on our observations, we deduce that the stabilimentum of C. oculata serves as camouflage

Spider orientation and hub position in orb webs

Orb-web building spiders (Araneae: Araneoidea, Uloboridae) can be considered as territorial central place foragers. In territorial central place foragers, the optimal foraging arena is circular, with the forager sitting in its centre. In orb webs, the spider's orientation (head up or head down) whilst waiting for prey on the hub of its web and the downwards-upwards asymmetry of its running speeds are the probable causes for the observed deviation of the hub from the web's centre. Here, we present an analytical model and a more refined simulation model to analyse the relationships amongst the spider's running speeds, its orientation whilst waiting for prey and the vertical asymmetry of orb webs. The results of our models suggest that (a) waiting for prey head down is generally favourable because it allows the spider to reach the prey in its web on average quicker than spiders waiting head up, (b) the downwards-upwards running speed asymmetry, together with the head-down orientation of most spiders, are likely causes for the observed vertical asymmetry of orb webs, (c) waiting head up can be advantageous for spiders whose downwards-upwards running speed asymmetry is small and who experience high prey tumbling rates and (d) spiders waiting head up should place their hub lower than similar spiders waiting head dow

Untangling the Tangle-Web: Web Construction Behavior of the Comb-Footed Spider Steatoda triangulosa and Comments on Phylogenetic Implications (Araneae: Theridiidae)

Theridiidae typically construct a three-dimensional web often described as "irregular.” The web consists of a supporting structure and lines under tension termed gumfooted lines. We used automated methods to observe web construction in the theridiid Steatoda triangulosa under laboratory conditions. Web construction lasted several nights. After orientation, spiders built a three-dimensional structure of several threads radiating sideways and downward from the retreat. To build gumfooted lines, they started from the retreat, moved along a structural thread, then dropped down to attach the thread to the lower substrate. On returning, they coated the lowest part of the thread with viscid silk before moving up along the same thread back to the structural thread. They then continued moving along the same structural thread to drop down again to build the next gumfooted line. This behavior was continued until the spiders had built a series of gumfooted lines (a bout). There were regular intervals between the construction of two bouts. Thus, a single web included many bouts built in different stages. We show that gumfooted lines are not homologues to sticky web elements of orb-weavers and present new synapomorphic characters that support the monophyly of Theridiidae + Nesticidae and the monophyly of araneoid sheet web weavers. Further, the time allocation pattern for different behavioral stages and the fine structure of a gumfooted line are presente

P.A. Sebastian & K.V. Peter (Hrsg.) (2009): Spiders of India [Rezension] : Universities Press, Hyderabad. 614 S. & 96 Tafeln mit 170 Farbfotos. ISBN 978-81-7371-641-6. Fester Einband, Format: 22 x 15 cm. Preis inkl. Porto 3201 Indische Rupien (ca. 50 Euro). Bestellung: http://www.universitiespress.com

Dieses Buch (mit einem Vorwort des leider verstorbenen Jean-Pierre Maelfait) wurde von einem Kollektiv von 10 Autoren verfasst und besteht aus zwei Teilen. Der erste Teil, welchem eine Liste aller im Buch vorgestellten Gattungen und Arten vorangestellt ist, enthält eine kurze allgemeine Einleitung in die Biologie der Spinnen, mit Beschreibungen von Anatomie, Physiologie, Reproduktion und des Netzbaus (S. 1-63), sowie eine Einführung in das Sammeln von Spinnen (S. 64-69). Zusätzlich sind dort noch zwei Schlüssel zu Spinnenfamilien, einer basierend auf morphologischen Merkmalen und ein zweiter basierend auf den Netztypen, vorhanden

Genetic structure of the wild populations of the Indian Rhinoceros (Rhinoceros unicornis)

The Indian (or Greater One-horned) rhinoceros, Rhinoceros unicornis is one of only five extant rhinoceros species. In the wild it occurs exclusively in India (mainly in Assam) and in Nepal. These two populations have been completely separated for at least a few centuries. In addition, both populations experienced a bottleneck during the 20th century. These observations suggest the questions how genetically distinct and how diverse the two populations are. In the present study I review two molecular genetic studies on these aspects, as well as three studies, mainly based on the worldwide R. unicornis zoo population, assessing the consequences of inbreeding and outbreeding (i.e. Assam x Nepal matings) on juvenile mortality. In addition, I present the results of an analysis of the effects of inbreeding and outbreeding based on the latest studbook data. In this analysis - in contrast to earlier studies - I no longer found a negative effect of outbreeding on offspring mortality, but still a higher mortality in primiparous offspring and still no negative effect of inbreeding on juvenile mortality. These results suggest that outbreeding between the two populations is not as problematic as it was once suggested to be, but it also confirms that inbreeding avoidance may not be as important in the Indian rhinoceros as it is in other species

Radius construction and structure in the orb-web of Zilla diodia (Araneidae)

In orb-webs, the tension of the sticky spiral produces a centripetal force on the radii, resulting in an increase in tension along each radius from the centre of the web to the periphery. Zilla diodia (Walckenaer, 1802) atypical of araneids, was found to adapt the structure of its radii to this tension gradient by building radii that are double stranded at the periphery of the web and single stranded near the centre. Furthermore, the proportion of each radius that is doubled was found to be larger in the upper part of the web - where the overall tensions in the radii are known to be higher - than in the lower part of the web, suggesting that the spider adjusts the proportion of each radius that is doubled to the overall tension in the radius