Resistance of spiders to Cretaceous-Tertiary extinction events

Throughout Earth history a small number of global catastrophic events leading to biotic crises have caused mass extinctions. Here, using a technique that combines taxonomic and numerical data, we consider the effects of the Cenomanian-Turonian and Cretaceous-Tertiary mass extinctions on the terrestrial spider fauna in the light of new fossil data. We provide the first evidence that spiders suffered no decline at the family level during these mass extinction events. On the contrary, we show that they increased in relative numbers through the Cretaceous and beyond the Cretaceous-Tertiary extinction event.     

Phylogenomic Resolution of Sea Spider Diversification through Integration of Multiple Data Classes

Despite significant advances in invertebrate phylogenomics over the past decade, the higher-level phylogeny of Pycnogonida (sea spiders) remains elusive. Due to the inaccessibility of some small-bodied lineages, few phylogenetic studies have sampled all sea spider families. Previous efforts based on a handful of genes have yielded unstable tree topologies. Here, we inferred the relationships of 89 sea spider species using targeted capture of the mitochondrial genome, 56 conserved exons, 101 ultraconserved elements, and 3 nuclear ribosomal genes. We inferred molecular divergence times by integrating morphological data for fossil species to calibrate 15 nodes in the arthropod tree of life. This integration of data classes resolved the basal topology of sea spiders with high support. The enigmatic family Austrodecidae was resolved as the sister group to the remaining Pycnogonida and the small-bodied family Rhynchothoracidae as the sister group of the robust-bodied family Pycnogonidae. Molecular divergence time estimation recovered a basal divergence of crown group sea spiders in the Ordovician. Comparison of diversification dynamics with other marine invertebrate taxa that originated in the Paleozoic suggests that sea spiders and some crustacean groups exhibit resilience to mass extinction episodes, relative to mollusk and echinoderm lineages.     

FOSSIL BLOOD DROPLETS IN MIOCENE DOMINICAN AMBER YIELD CLUES TO SPEED AND DIRECTION OF RESIN SECRETION

Abstract:  Two spiders (Filistatidae) in Miocene Dominican Republic amber, one newly identified and only the second known fossil of this family, have autospasized legs (detached at a predetermined locus of weakness when restrained by a non-self-induced source) at the patella-tibia joint. In both specimens, droplets of haemolymph (blood) are preserved exiting the patellae. The autospasized legs and the presence of haemolymph suggests that both spiders were engulfed in rapid-flowing resin seeps of relatively low viscosity, rather than having wandered onto a sticky exudate, becoming stuck and then covered by a subsequent resin flow. These are the first reported incidences of such fossilized blood droplets, the shape, size and position of which provide clues to preservational taphonomy, an understanding of which is necessary for reliable conclusions concerning fossil communities and ecosystems. In addition, haemolymph droplets may serve as reservoirs for fossil DNA.     

Oldest true orb-weaving spider (Araneae: Araneidae)

The aerial orb web woven by spiders of the family Araneidae typifies these organisms to laypersons and scientists alike. Here we describe the oldest fossil species of this family, which is preserved in amber from Alava, Spain and represents the first record of Araneidae from the Lower Cretaceous. The fossils provide direct evidence that all three major orb web weaving families: Araneidae, Tetragnathidae and Uloboridae had evolved by this time, confirming the antiquity of the use of this remarkable structure as a prey capture strategy by spiders. Given the complex and stereotyped movements that all orb weavers use to construct their webs, there is little question regarding their common origin, which must have occurred in the Jurassic or earlier. Thus, various forms of this formidable prey capture mechanism were already in place by the time of the explosive Cretaceous co-radiation of angiosperms and their flying insect pollinators. This permitted a similar co-radiation of spider predators with their flying insect prey, presumably without the need for a 'catch-up lag phase' for the spiders.     

A contribution to the knowledge of liphistiid spiders

These spiders resemble fossil spiders of the Carboniferous. Although they are unique in retaining several primitive characters it is thought best to include them in the sub-Order Mygalomorphae and to abandon the special sub-Order Liphistiomorphae.
The family Heptathelidae to include those species with seven instead of eight spinnerets as in the Liphistiidae is also abandoned.
The species Liphistius thorelli Sim. from Sumatra is regarded as a synonym of the other Sumatran species L. sumatranus Thor.
Eight species of Liphistius and two of Heptathela are now recognized. Their distribution is confined, according to present knowledge, to Burma, Thailand, Vietnam, China, Japan, Malaysia and Sumatra. This may provide useful evidence in the question, as yet unsettled, of the origin of south-east Asia in terms of continental drift.
A special visit has been paid to Sumatra to rediscover Liphistius sumatranus (of which only one specimen was found and described in 1879) to establish with certainty that it is distinct from the Malaysian L. desultor . This was achieved and the species are now compared.
Some biological observations are provided.     

Calibrating the chelicerate clock: a paleontological reply to Jeyaprakash and Hoy

Divergence times inferred for major lineages of Chelicerata (scorpions, spiders, mites, pycnogonids and xiphosurans) in a recent paper on mitochondrial phylogeny by Jeyaprakash and Hoy are compared to the known stratigraphical occurrences of these groups. Erroneous statements concerning fossil date estimates in the original study are corrected. We emphasize that the fossil record of chelicerates is more complete than is sometimes assumed, and that paleontology plays a key role in dating cladogenesis by setting minimum divergence times, which can and do falsify molecular clock estimates where the inferred divergence is substantially younger than the known fossil record. The oldest representatives of each chelicerate order are documented here, together with similar data for the major mite lineages down to family level. Through these, we hope to provide a robust framework and reference points for future molecular systematic studies of this nature.     

Aerial web-weaving spiders: Linking molecular and organismal processes in evolution

Aerial web-weaving spiders display a wide variety of foraging behaviors that can be tied to the evolution of one family of proteins, the silks. In some cases, the physical structure and mechanical properties of silks alone determine the ecology of spiders: the habitats in which they forage, the prey they capture and their subsequent reproductive success. Future studies that integrate research on the physical structure of silks, the molecular genetics of silk synthesis and the foraging ecology of spiders in primitive and derived phylogenetic groups could reveal how molecular and organismal processes interact in evolution.     

Miocene spiders in Dominican amber (Oonopidae,Mysmenidae)

Oonops seldeni sp. nov. and Mysmenopsis lissycoleyae sp. nov. are described from male specimens preserved in Miocene amber from the Dominican Republic and are the first fossil records of these extant genera. Gamasomorpha incerta Wunderlich, 1988 is transferred to Stenoonops. Two females previously described as Orchestina dominicana? Wunderlich, 1981 are transferred to Orchestina sp. indet., and one new specimen of a male of Orchestina dominicana Wunderlich, 1988 is identified. Oonopidae is reported for the first time from Cretaceous ambers of Burma, Lebanon and New Jersey. These are the oldest records of this family, extending the known range from the Rupelian (Oligocene) to the Valanginian (Lower Cretaceous). Recent StenoonopsMysmenopsis are unknown from Hispaniola. The presence of these genera in amber suggests that they will be found. The presence of Mysmenopsis in amber is further evidence of kleptoparasitic/commensal spiders in the Miocene.     

On the Emsian (Lower Devonian) arthropods of the Rhenish Schiefergebirge: 1.Xenarachne, an enigmatic arachnid from Willwerath, Germany

A new fossil arachnid,Xenarachne willwerathensis n. gen., n. sp. is described from the Lower Devonian (upper Lower Emsian) Klerf-beds of Willwerath, Germany. This intriguing fossil has a pedicel and pygidium, indicating that it belongs to the tetrapulmonate arachnids, but cannot be referred with confidence to any particular order. It is placed as Tetrapulmonata incertae sedis, though has similarities to whip spiders (Amblypygi) and spiders (Araneae).Xenarachne could even represent a very early spider, though the Devonian arachnid fauna could have included taxa which did not belong in any currently recognised order.Xenarachne may be an example of just such a fossil.     

Spiders are special: fear and disgust evoked by pictures of arthropods

Because all spiders are predators and most subdue their prey with poison, it has been suggested that fear of spiders is an evolutionary adaptation. However, it has not been sufficiently examined whether other arthropods similarly elicit fear or disgust. Our aim was to examine if all arthropods are rated similarly, if only potentially dangerous arthropods (spiders, bees/wasps) elicit comparable responses, or if spiders are rated in a unique way. We presented pictures of arthropods (15 spiders, 15 beetles, 15 bees/wasps, and 15 butterflies/moths) to 76 students who rated each picture for fear, disgust, and how dangerous they thought the animal is. They also categorized each animal into one of the four animal groups. In addition, we assessed the participants' fear of spiders and estimates for trait anxiety. The ratings showed that spiders elicit significantly greater fear and disgust than any other arthropod group, and spiders were rated as more dangerous. Fear and disgust ratings of spider pictures significantly predicted the questionnaire scores for fear of spiders, whereas dangerousness ratings of spiders and ratings of other arthropods do not provide any predictive power. Thus, spider fear is in fact spider specific. Our results demonstrate that potential harmfulness alone cannot explain why spiders are feared so frequently.     

Diversity of insects captured by weaver spiders (Arachnida: Araneae) in the cocoa agroecosystem in Tabasco, Mexico

The aim of this work was to know the diversity of insects captured by weaver spiders in a plantation of cocoa (Theobroma cacao L.) of 6 ha in the State of Tabasco, Mexico. The study was carried out from July 2004 to June 2005 by means biweekly samples of the insects captured on the spiders webs. The total of 3,041 webs of 54 species of spiders belonging to seven families (Araneidae, Theridiidae, Tetragnathidae, Uloboridae, Pholcidae, Dyctinidae and Linyphiidae) were revised. We found 1,749 specimens belonging to 10 orders of insects, represented by 93 families, the majority of Coleoptera, Diptera and Hemiptera that constituted 74% of the identified families. The biggest number of specimens of all orders was captured by Araneidae, except of Isoptera, whose specimens were captured mainly by the family Theridiidae. The index of diversity (H'), evenness (J') and similarity (Is), applied to know the diversity of families of insects captured among families of spiders, varied from 0.00 to 3.24, 0.00 to 0.81, and 0.04 to 0.522, respectively. We conclude that there is a wide diversity of insects predated by the weaver spiders in the cocoa agroecosystem, and that there are species that can be promising for the biological control of pests.     

Spiders of soybean crops in Santa Fe province, Argentina: influence of surrounding spontaneous vegetation on lot colonization.

Trials during two consecutive soybean cycles were performed in central Santa Fe in order to determine the main spider families present in the crop and to determine the influence of spontaneous margin flora on colonization towards the lot. Samplings were done by sweeping net and pitfall traps. It was concluded that:1. Oxyopidae was the most frequent family in the herbaceous layer of both the margins and the soybean crop, and Lycosidae in the lower layer; 2. Margin strips in a soybean lot contribute to the colonization of the crop by spiders of aerial habits and also promote re-colonization following pesticide applications, since they act as shelters. The influence on spiders of terrestrial habits was somewhat lower; 3. The distribution of the populations of spiders of terrestrial habits was homogeneous in a soybean crop seeded directly and these predators had a greater capacity to control pests at all points of the lot.     

Interactions between citrus psylla,Trioza erytreae (Hem. Triozidae), and spiders in an unsprayed citrus orchard in the transvaal lowveld

During a two year survey, a total of 3,054 spiders represented by 21 families were sampled in an unsprayed citrus orchard in the Transvaal Lowveld. Numerically the Salticidae was the dominant family (34.4%) followed by the Theridiidae (21.9%), Thomisidae (11.9%), Araneidae (7.9%), Clubionidae (7.0%) and the Tetragnathidae (3.7%). Eighteen species of spiders were observed to prey on citrus psylla,Trioza erytreae (Del Guercio) (Hemiptera: Triozidae), while six species trap nymphs and adults under their retreats and webs. There were significant positive correlations between the weekly psylla populations and the weekly populations of web-building spiders and wandering spiders present one to four weeks later but no significant correlation between the weekly spider populations and the weekly psylla populations present one to five weeks later. This seems to indicate that while spiders are unable to keep citrus psylla populations at acceptable low levels, they may contribute in reducing their numbers.      

Microanatomy of Early Devonian book lungs

The book lungs of an exceptionally preserved fossil arachnid (Trigonotarbida) from the Early Devonian (approx. 410 Myr ago) Rhynie cherts of Scotland were studied using a non-destructive imaging technique. Our three-dimensional modelling of fine structures, based on assembling successive images made at different focal planes through the translucent chert matrix, revealed for the first time fossil trabeculae: tiny cuticular pillars separating adjacent lung lamellae and creating a permanent air space. Trabeculae thus show unequivocally that trigonotarbids were fully terrestrial and that the microanatomy of the earliest known lungs is indistinguishable from that in modern Arachnida. A recurrent controversy in arachnid evolution is whether the similarity between the book lungs of Pantetrapulmonata (i.e. spiders, trigonotarbids, etc.) and those of scorpions is a result of convergence. Drawing on comparative studies of extant taxa, we have identified explicit characters (trabeculae, spines on the lamellar edge) shared by living and fossil arachnid respiratory organs, which support the hypothesis that book lungs were derived from a single, common, presumably terrestrial, ancestor.     

Leg autotomy in a spider has minimal costs in competitive ability and development

A number of species have the ability to autotomize limbs voluntarily, but animals that have lost limbs often face substantial costs. We examined the frequency of leg loss and its effects on competitive ability and development in the spider Holocnemus pluchei (Araneae: Pholcidae), a family of spiders known for its readiness to autotomize legs. Leg loss was common in field populations, with 7.5% of all surveyed spiders missing at least one leg, most commonly one of the anterior pair. More spiders were missing multiple legs than expected by chance, suggesting that leg loss events are not independent. Large adult spiders were missing legs more frequently than were small spiders. The competitive ability of injured males was tested in three contexts. In the field, no effect of leg loss was found on the ability of spiders to remain in webs into which they were introduced. In the laboratory, no effect of leg loss was found on the ability to fight with a single opponent over a prey, except that injured spiders were more likely to lose high-intensity fights. There was no difference between intact and injured males in their ability to compete with three females for limited prey. Leg loss significantly affected development time. The moult interval during the instar in which the injury occurred increased by approximately 15%. However, the growth rate for injured spiders was slightly but not significantly faster in the instar following leg loss, and total development time of the two instars together did not differ significantly between treatments. No spider showed any signs of regeneration. We conclude that, although there were some statistically significant differences between intact and injured males, these are unlikely to have major impacts on fitness, in contrast to findings in other species. Copyright 1999 The Association for the Study of Animal Behaviour.     

Heydenius araneus n.sp. (Nematoda: Mermithidae), a parasite of a fossil spider, with an examination of helminths from extant spiders (Arachnida: Araneae)

Abstract. A mermithid, a parasite of a spider (Araneae: Thomisidae) in Baltic amber (40 mya), is described as Heydenius araneus n.sp. (Nematoda: Mermithidae) and represents the first fossil record of a nematode parasite of an arachnid. After a critical examination of reports of naturally occurring helminths of extant spiders, I conclude that although mermithid parasitism is well established in this host group, previous reports of hairworm parasites of spiders are "nomina dubia," putative records, or refer to mermithid nematodes.