Molecular taxonomy in pholcid spiders (Pholcidae, Araneae): evaluation of species identification methods using CO1 and 16S rRNA

Old World Micropholcus spiders, with first records of acrocerid parasitoids in Pholcidae (Araneae)

Micropholcus Deeleman-Reinhold & Prinsen, 1987 is one of only two Pholcidae genera known to occur both in the Old and New Worlds. However, there are major morphological and ecological differences among geographically separate groups of species, and it was mainly molecular data that have resulted in our current view of uniting all these species into a single genus. In the Old World, only four species have previously been described. Here, current knowledge about Old World Micropholcus is reviewed, redescribing three of the four previously known species, and describing twelve new species, originating from Saudi Arabia (M.dhahran Huber, sp. nov., M.harajah Huber, sp. nov., M.alfara Huber, sp. nov., M.abha Huber, sp. nov., M.tanomah Huber, sp. nov., M.bashayer Huber, sp. nov., M.maysaan Huber, sp. nov.), Oman (M.darbat Huber, sp. nov., M.shaat Huber, sp. nov.), Morocco (M.ghar Huber, sp. nov., M.khenifra Huber, Lecigne & Lips, sp. nov.), and the Philippines (M.bukidnon Huber, sp. nov.). We provide an exploratory species delimitation analysis based on CO1 barcodes, extensive SEM data, and first records of Acroceridae (Diptera) larvae in Pholcidae, extracted from book lungs.

Castaways: the Leeward Antilles endemic spider genus Papiamenta (Araneae: Pholcidae)

Ninetinae is a group of small to tiny short-legged spiders largely restricted to arid habitats. Among daddy-long-legs spiders (Pholcidae) this is by far the least diverse subfamily but this may partly be a result of inadequate collecting, poor representation in collections or scientific neglect. We build on a large recent collection of the ninetine genus Papiamenta Huber, 2000 from the Leeward Antilles and use cytochrome oxidase 1 (COI ) sequences, extensive scanning electron microscopy data, transmission electron microscopy data and karyotyping to analyse this geographically isolated and poorly known island genus. COI sequences support the split between the two morphologically distinct species on Curaçao but genetic distances between these are surprisingly low (7.4-9.8%; mean 8.6%). The type species P. levii (Gertsch, 1982) may include more than one species but COI and morphology suggest conflicting clade limits. A third species, P. bonay Huber sp. nov. is newly described from Bonaire. Our data on sperm ultrastructure and karyology are puzzling as these suggest different phylogenetic affinities of Papiamenta to other genera. Males transfer sperm as individual sperm (cleistosperm), agreeing with the putative closest relatives as suggested by molecular data, the North American genera Pholcophora and Tolteca . The sex chromosome system (X 1 X 2 X 3 Y ) of P. levii , however, is as in the South American Ninetinae genera Gertschiola and Nerudia but different from the putative closest relatives. ZooBank: urn:lsid:zoobank.org:pub:7A6A2E84-3A61-4637-AF6F-0E31A9FA79A8.

To be or not to be… Integrative taxonomy and species delimitation in the daddy long-legs spiders of the genus Physocyclus (Araneae, Pholcidae) using DNA barcoding and morphology

Integrative taxonomy is crucial for discovery, recognition, and species delimitation, especially in underestimated species complex or cryptic species, by incorporating different sources of evidence to construct rigorous species hypotheses. The spider genus Physocyclus Simon, 1893 (Pholcidae, Arteminae) is composed of 37 species, mainly from North America. In this study, traditional morphology was compared with three DNA barcoding markers regarding their utility in species delimitation within the genus: 1) Cytochrome c Oxidase subunit 1 (CO1), 2) Internal Transcribed Spacer 2 (ITS2), and 3) Ribosomal large subunit (28S). The molecular species delimitation analyses were carried out using four methods under the corrected p-distances Neighbor-Joining (NJ) criteria: 1) Automatic Barcode Gap Discovery (ABGD), 2) Assemble Species by Automatic Partitioning (ASAP), 3) General Mixed Yule Coalescent model (GMYC), and 4) Bayesian Poisson Tree Processes (bPTP). The analyses incorporated 75 terminals from 22 putative species of Physocyclus. The average intraspecific genetic distance (p-distance) was found to be < 2%, whereas the average interspecific genetic distance was 20.6%. The ABGD, ASAP, and GMYC methods were the most congruent, delimiting 26 or 27 species, while the bPTP method delimited 33 species. The use of traditional morphology for species delimitation was congruent with most molecular methods, with the male palp, male chelicerae, and female genitalia shown to be robust characters that support species-level identification. The barcoding with CO1 and 28S had better resolution for species delimitation in comparison with ITS2. The concatenated matrix and traditional morphology were found to be more robust and informative for species delimitation within Physocyclus.

Phylogeography of the ‘cosmopolitan’ orb-weaver Argiope trifasciata (Araneae: Araneidae)

Few spider species show truly cosmopolitan distributions. Among them is the banded garden spider Argiope trifasciata, which is reported from six continents across major climatic gradients and geographical boundaries. In orb-weaver spiders, such global distributions might be a result of lively dispersal via ballooning. However, wide distributions might also be artefactual, owing to our limited understanding of species taxonomy. To test the hypothesis that A. trifasciata might be a complex of cryptic species with more limited geographical ranges, we investigated the biogeographical structure and evolutionary history of A. trifasciata through a combination of time-calibrated phylogenetic analyses (57 terminals and three genes), ancestral range reconstruction and species delimitation methods. Our results strongly suggest that A. trifasciata as currently defined is not a single species. Its populations fall into five reciprocally monophyletic clades that are genetically distinct and have evolutionary origins in the Plio-Pleistocene. These clades are confined to East Asia, temperate Australia, Hawaii, the New World and the Old World (Africa and most of the Palaearctic). Our results provide the basis for future investigation of morphological and/or ecological disparity between the populations that are likely to represent species, in addition to examinations of the attributes and dispersal modes of these species.

New species of Idris Förster (Hymenoptera, Platygastroidea) from southeast Asia, parasitoids of the eggs of pholcid spiders (Araneae, Pholcidae)

Four new species of the genus Idris Förster (Hymenoptera: Platygastroidea), reared from the eggs of pholcid spiders (Araneae: Pholcidae) in southeast Asia are described on the basis of external morphology and the barcode region of the mitochondrial COI gene. The new species and their hosts are: I.badius Johnson & Chen, sp. n. (ex Nipisaphyllicola (Deeleman-Reinhold), Panjangehamiguitan Huber), I.balteus Johnson & Chen, sp. n. (ex Panjangecamiguin Huber), I.curtus Johnson & Chen, sp. n. (ex Calapnitanunezae Huber, Panjangecamiguin Huber, Tissahamiabukittimah (Huber), Uthinaluzonica Simon), and I.fusciceps (ex Belisanakhaosok Huber).

Microhabitat change drives diversification in pholcid spiders

BACKGROUND

Microhabitat changes are thought to be among the main drivers of diversification. However, this conclusion is mostly based on studies on vertebrates. Here, we investigate the influence of microhabitat on diversification rates in pholcid spiders (Araneae, Pholcidae). Diversification analyses were conducted in the framework of the largest molecular phylogeny of pholcid spiders to date based on three nuclear and three mitochondrial loci from 600 species representing more than 85% of the currently described pholcid genera.

RESULTS

Assessments of ancestral microhabitat revealed frequent evolutionary change. In particular, within the largest subfamily Pholcinae, numerous changes from near-ground habitats towards leaves and back were found. In general, taxa occupying leaves and large sheltered spaces had higher diversification rates than ground-dwelling taxa. Shifts in speciation rate were found in leaf- and space-dwelling taxa.

CONCLUSIONS

Our analyses result in one of the most comprehensive phylogenies available for a major spider family and provide a framework for any subsequent studies of pholcid spider biology. Diversification analyses strongly suggest that microhabitat is an important factor influencing diversification patterns in pholcid spiders.

Assessing the effectiveness of mitochondrial COI and 16S rRNA genes for DNA barcoding of farmland spiders in China

DNA barcoding has been widely used to identify and discover new species in a wide range of taxa. In order to assess the effectiveness of COI (cytochrome C oxidase subunit I) and 16S (16S ribosomal RNA) in the discrimination of spiders, we have generated 289 barcodes for a total of 56 farmland spider species from 14 different families for the first time in China. Our results reveal that the standard barcoding marker COI can be used to distinguish the farmland spiders both in species and family level by NJ tree-based method, despite the absence of a barcode gap between the intra- and inter-specific genetic divergences. 16S has a lower species identification success as compared with COI. However, almost 98% of the species can be correctly distinguished for both COI and 16S when a threshold of 3% nucleotide divergence was used for species discrimination. Our study significantly improves the barcode reference sequence library for Chinese farmland spiders, and will be very useful in pest management and eco-environmental monitoring and protection.

Towards a DNA Barcode Reference Database for Spiders and Harvestmen of Germany

As part of the German Barcode of Life campaign, over 3500 arachnid specimens have been collected and analyzed: ca. 3300 Araneae and 200 Opiliones, belonging to almost 600 species (median: 4 individuals/species). This covers about 60% of the spider fauna and more than 70% of the harvestmen fauna recorded for Germany. The overwhelming majority of species could be readily identified through DNA barcoding: median distances between closest species lay around 9% in spiders and 13% in harvestmen, while in 95% of the cases, intraspecific distances were below 2.5% and 8% respectively, with intraspecific medians at 0.3% and 0.2%. However, almost 20 spider species, most notably in the family Lycosidae, could not be separated through DNA barcoding (although many of them present discrete morphological differences). Conspicuously high interspecific distances were found in even more cases, hinting at cryptic species in some instances. A new program is presented: DiStats calculates the statistics needed to meet DNA barcode release criteria. Furthermore, new generic COI primers useful for a wide range of taxa (also other than arachnids) are introduced.

Spider Web DNA: A New Spin on Noninvasive Genetics of Predator and Prey

Noninvasive genetic sampling enables biomonitoring without the need to directly observe or disturb target organisms. This paper describes a novel and promising source of noninvasive spider and insect DNA from spider webs. Using black widow spiders (Latrodectus spp.) fed with house crickets (Acheta domesticus), we successfully extracted, amplified, and sequenced mitochondrial DNA from spider web samples that identified both spider and prey to species. Detectability of spider DNA did not differ between assays with amplicon sizes from 135 to 497 base pairs. Spider and prey DNA remained detectable at least 88 days after living organisms were no longer present on the web. Spider web DNA as a proof-of-concept may open doors to other practical applications in conservation research, pest management, biogeography studies, and biodiversity assessments.

Testing mitochondrial marker efficacy for DNA barcoding in spiders: a test case using the dwarf spider genus Oedothorax (Araneae : Linyphiidae : Erigoninae)

The present study focusses on comparatively assessing the efficacy for DNA barcoding of the two most commonly used mitochondrial markers (cox1 and 16S) in a genus of erigonine spiders. In total, 53 specimens representing five species, including four multi-sampled species, were sampled from several European localities. Initial evaluation of species monophyly was performed through parsimony and Bayesian phylogenetic analyses. Efficacy of mitochondrial markers was tested using operational (including distance-, tree-based measures and Barcode Gap) and evolutionary criteria (using the General Mixed Yule-coalescent Model) for species delimitation. We propose that the cox1 marker can potentially overestimate analyses of biodiversity and thus might not be the preferred marker for DNA species identification and delimitation methods in Oedothorax. Instead, our results suggest that the 16S marker appears to be a promising candidate for such endeavour. Evaluating the contribution and suitability of markers to the re-identification of species, measured by their recovery of well established morphological species, is critical for future studies and for reliable results in species identification in spiders.

Exploring species level taxonomy and species delimitation methods in the facultatively self-fertilizing land snail genus Rumina (gastropoda: pulmonata)

Delimiting species in facultatively selfing taxa is a challenging problem of which the terrestrial pulmonate snail genus Rumina is a good example. These snails have a mixed breeding system and show a high degree of shell and color variation. Three nominal species (R. decollata, R. saharica and R. paivae) and two color morphs within R. decollata (dark and light) are currently recognized. The present study aims at evaluating to what extent these entities reflect evolutionary diverging taxonomic units, rather than fixed polymorphisms due to sustained selfing. Therefore, a phylogenetic analysis of nuclear (ITS1, ITS2) and mitochondrial DNA (COI, CytB, 12S rDNA, 16S rDNA) sequences was performed. Putative species in Rumina, inferred from the mitochondrial DNA phylogeny, were compared with those proposed on the basis of the COI gene by (1) DNA barcoding gap analysis, (2) Automatic Barcode Gap Discovery, (3) the species delimitation plug-in of the Geneious software, (4) the Genealogical Sorting Index, and (5) the General Mixed Yule Coalescent model. It is shown that these methods produce a variety of different species hypotheses and as such one may wonder to what extent species delimitation methods are really useful. With respect to Rumina, the data suggest at least seven species, one corresponding to R. saharica and six that are currently grouped under the name R. decollata. The species-level status of R. paivae is rejected.

Exploring diversity in cryptorhynchine weevils (Coleoptera) using distance-, character- and tree-based species delineation

Species boundaries are studied in a group of beetles, the western Palaearctic Cryptorhynchinae. We test for congruence of 'traditionally' identified morphospecies with species inferred through parsimony networks, distance-based clustering and the ultrametric tree-based generalized mixed yule-coalescent (GMYC) approach. For that purpose, we sequenced two variable fragments of mitochondrial DNA (CO1 and 16S) for a total of 791 specimens in 217 species of Cryptorhynchinae. Parsimony networks, morphology-calibrated distance clusters and the different tree-based species inferences all achieved low congruence with morphospecies, at best 60%. Although the degree of match with morphospecies was often similar for the different approaches, the composition of clusters partially varied. A barcoding gap was absent in morphospecies-oriented distances as well as for GMYC species clusters. This demonstrates that not only erroneous taxonomic assignments, incomplete lineage sorting, hybridization, or insufficient sampling can compromise distance-based identification, but also differences in speciation rates and uneven tree structure. The initially low match between morphospecies and the different molecular species delineation methods in this case study shows the necessity of combining the output of various methods in an integrative approach. Thereby we obtain an idea about the reliability of the different results and signals, which enables us to fine-tune sampling, delineation technique and data collection, and to identify species that require taxonomic revision.

Species delimitation and phylogeography of Aphonopelma hentzi (Araneae, Mygalomorphae, Theraphosidae): cryptic diversity in North American tarantulas

BACKGROUND

The primary objective of this study is to reconstruct the phylogeny of the hentzi species group and sister species in the North American tarantula genus, Aphonopelma, using a set of mitochondrial DNA markers that include the animal "barcoding gene". An mtDNA genealogy is used to consider questions regarding species boundary delimitation and to evaluate timing of divergence to infer historical biogeographic events that played a role in shaping the present-day diversity and distribution. We aimed to identify potential refugial locations, directionality of range expansion, and test whether A. hentzi post-glacial expansion fit a predicted time frame.

METHODS AND FINDINGS

A Bayesian phylogenetic approach was used to analyze a 2051 base pair (bp) mtDNA data matrix comprising aligned fragments of the gene regions CO1 (1165 bp) and ND1-16S (886 bp). Multiple species delimitation techniques (DNA tree-based methods, a "barcode gap" using percent of pairwise sequence divergence (uncorrected p-distances), and the GMYC method) consistently recognized a number of divergent and genealogically exclusive groups.

CONCLUSIONS

The use of numerous species delimitation methods, in concert, provide an effective approach to dissecting species boundaries in this spider group; as well they seem to provide strong evidence for a number of nominal, previously undiscovered, and cryptic species. Our data also indicate that Pleistocene habitat fragmentation and subsequent range expansion events may have shaped contemporary phylogeographic patterns of Aphonopelma diversity in the southwestern United States, particularly for the A. hentzi species group. These findings indicate that future species delimitation approaches need to be analyzed in context of a number of factors, such as the sampling distribution, loci used, biogeographic history, breadth of morphological variation, ecological factors, and behavioral data, to make truly integrative decisions about what constitutes an evolutionary lineage recognized as a "species".

Karyotype, sex determination, and meiotic chromosome behavior in two pholcid (Araneomorphae, Pholcidae) spiders: implications for karyotype evolution

There are 1,111 species of pholcid spiders, of which less than 2% have published karyotypes. Our aim in this study was to determine the karyotypes and sex determination mechanisms of two species of pholcids: Physocyclus mexicanus (Banks, 1898) and Holocnemus pluchei (Scopoli, 1763), and to observe sex chromosome behavior during meiosis. We constructed karyotypes for P. mexicanus and H. pluchei using information from both living and fixed cells. We found that P. mexicanus has a chromosome number of 2n = 15 in males and 2n = 16 in females with X0-XX sex determination, like other members of the genus Physocyclus. H. pluchei has a chromosome number of 2n = 28 in males and 2n = 28 in females with XY-XX sex determination, which is substantially different from its closest relatives. These data contribute to our knowledge of the evolution of this large and geographically ubiquitous family, and are the first evidence of XY-XX sex determination in pholcids.

Phylogeny and classification of the trapdoor spider genus Myrmekiaphila: an integrative approach to evaluating taxonomic hypotheses

BACKGROUND

Revised by Bond and Platnick in 2007, the trapdoor spider genus Myrmekiaphila comprises 11 species. Species delimitation and placement within one of three species groups was based on modifications of the male copulatory device. Because a phylogeny of the group was not available these species groups might not represent monophyletic lineages; species definitions likewise were untested hypotheses. The purpose of this study is to reconstruct the phylogeny of Myrmekiaphila species using molecular data to formally test the delimitation of species and species-groups. We seek to refine a set of established systematic hypotheses by integrating across molecular and morphological data sets.

METHODS AND FINDINGS

Phylogenetic analyses comprising Bayesian searches were conducted for a mtDNA matrix composed of contiguous 12S rRNA, tRNA-val, and 16S rRNA genes and a nuclear DNA matrix comprising the glutamyl and prolyl tRNA synthetase gene each consisting of 1348 and 481 bp, respectively. Separate analyses of the mitochondrial and nuclear genome data and a concatenated data set yield M. torreya and M. millerae paraphyletic with respect to M. coreyi and M. howelli and polyphyletic fluviatilis and foliata species groups.

CONCLUSIONS

Despite the perception that molecular data present a solution to a crisis in taxonomy, studies like this demonstrate the efficacy of an approach that considers data from multiple sources. A DNA barcoding approach during the species discovery process would fail to recognize at least two species (M. coreyi and M. howelli) whereas a combined approach more accurately assesses species diversity and illuminates speciation pattern and process. Concomitantly these data also demonstrate that morphological characters likewise fail in their ability to recover monophyletic species groups and result in an unnatural classification. Optimizations of these characters demonstrate a pattern of "Dollo evolution" wherein a complex character evolves only once but is lost multiple times throughout the group's history.

Molecular phylogeny of Echinodera and Ruteria (Coleoptera:Curculionidae:Cryptorhynchinae) and the parallel speciation of Canary Island weevils along replicate environmental gradients

A molecular phylogeny for the western Palaearctic weevil genus Echinodera Wollaston, 1863 and the former genus Ruteria Roudier, 1954 is presented, combining two mitochondrial genes (CO1 and 16S) in a Bayesian analysis. Special consideration is given to the species of Echinodera from the Canary Islands. Between islands, these are represented by multiple vicariant species that have undergone parallel speciation along replicate environmental gradients on the respective islands. Based on the phylogenetic tree and further data, a number of taxonomic changes is presented: two new species are described, Echinodera montana, sp. nov. from the Canaries (Fuerteventura) and Echinodera bargouensis, sp. nov. from Tunisia. Five species are declared to be synonyms: Echinodera gomerensis Stüben, 2000, syn. nov. = Echinodera praedicta Germann & Stüben, 2006, syn. nov. = Echinodera pseudohystrix Stüben, 2000; Ruteria bellieri epirica Wolf, 2001, syn. nov. = Echinodera tyrrhenica Caldara, 1978, syn. nov. = Acalles bellieri Reiche, 1860; Echindera troodosi Wolf, 2010, syn. nov. = Echinodera cyprica Stüben, 2010. The subgenus Echinodera (Dieckmannia) Stüben, 1998 is a synonym of Echinodera s. str. The genus Ruteria is again declared a subgenus of Echinodera: Echinodera (Ruteria) Roudier, 1954 stat. rev. Two species are transferred to a different subgenus: Echinodera (Ruteria) incognita (Hoffmann, 1956) and Echinodera (Ruteria) cognita Stüben, 2006 (both formerly Echinodera s. str.).

Diversity of Loxosceles spiders in Northwestern Africa and molecular support for cryptic species in the Loxosceles rufescens lineage

Until recently, Loxosceles rufescens was the only species known from a geographic range including Northern Africa, Mediterranean Europe and the Middle East. Rich Loxosceles diversity in the New World suggests either that L. rufescens is a young lineage or that its diversity is underappreciated. We use a molecular phylogenetic and morphological approach to examine diversity in L. rufescens and other Loxosceles lineages in Northwestern Africa. Molecular analyses of one nuclear and two mitochondrial genes strongly support a monophyletic clade including L. rufescens, the Northern Brazilian L. amazonica and three other divergent Northwestern African lineages, though relationships among them remain unresolved. A genetically divergent Moroccan individual morphologically consistent with L. rufescens was strongly supported as sister to all other putative L. rufescens, consistent with the presence of at least 2 species in this lineage. COI p-distances and population structuring among remaining putative L. rufescens clades further suggest the absence of gene flow between clades and the possibility that they represent multiple species. Morphological characters of preserved Loxosceles collected in a range of African countries provide additional indication that Loxosceles are more diverse and have a deeper history in Africa than has been previously understood.

Increased sampling blurs morphological and molecular species limits: revision of the Hispaniolan endemic spider genus Tainonia (Araneae:Pholcidae)

The genus Tainonia comprises unusually large pholcids endemic to Hispaniola. Previously, only the type species had been formally described, represented in collections by no more than 12 adult specimens. However, the existence of more species has been hypothesised based on a few further individuals. The present paper is based on a sample of 205 mostly newly collected adult specimens from 18 localities in the Dominican Republic and four localities in Haiti. The increased sampling reveals a wide range of variation, including intermediate levels of divergence that often blur rather than clarify species limits. Therefore, although not all taxonomic questions can be settled here, morphological (including morphometric) and molecular (mitochondrial 16S, CO1) data strongly support two new species: one in La Visite National Park, Haiti (T. visite, sp. nov.) and another on Samaná Peninsula and parts of the eastern Dominican Republic (T. samana, sp. nov.). Species limits among the other populations are more difficult to support or reject. Specimens from Bayahibe (eastern Dominican Republic) and from La Ciénaga (Cordillera Central) are each assigned species status on the basis of consistent morphological differences (T. bayahibe, sp. nov., T. cienaga, sp. nov.), but no molecular data are available due to lack of specimens. All other specimens are provisionally assigned to a possibly paraphyletic T. serripes (Simon). There is considerable morphological variation within this widely distributed group of populations but this variation is rather continuous and molecular distances fill most of the range between morphologically unambiguous conspecifics and unambiguous heterospecifics.

Phylogeny in cryptic weevils: molecules, morphology and new genera of western Palaearctic Cryptorhynchinae (Coleoptera:Curculionidae)

A phylogeny is presented for the western Palaearctic representatives of the weevil subfamily Cryptorhynchinae using a combination of phenotypic and genotypic characters. This phylogeny is the first for the extremely species-rich Cryptorhynchinae to use molecular data (mitochondrial CO1 and 16S as well as nuclear ribosomal 28S). The results of this study show the need for molecular tools within this morphologically cryptic group of weevils and provide a scaffold based on which genus assignment can be tested. The present study mostly corroborates the current subdivision into genera (but many of the subgeneric groups are questioned). Three new genera are described: Montanacalles gen. nov. (type species: Kyklioacalles nevadaensis Stüben, 2001), Coloracalles gen. nov. (type species: Acalles humerosus Fairmaire, 1862) and Elliptacalles gen. nov. (type species: Acalles longus Desbrochers, 1892). Relevant external characters and the male genitalia of all discussed taxa are illustrated. Three species are transferred to different genera: Kyklioacalles aubei (Boheman, 1837) (formerly: Acalles), Ruteria major (Solari A. & F., 1907) and Ruteria minosi (Bahr & Bayer, 2005) (both formerly Echinodera).

The evolution of asymmetric genitalia in spiders and insects

Asymmetries are a pervading phenomenon in otherwise bilaterally symmetric organisms and recent studies have highlighted their potential impact on our understanding of fundamental evolutionary processes like the evolution of development and the selection for morphological novelties caused by behavioural changes. One character system that is particularly promising in this respect is animal genitalia because (1) asymmetries in genitalia have evolved many times convergently, and (2) the taxonomic literature provides a tremendous amount of comparative data on these organs. This review is an attempt to focus attention on this promising but neglected topic by summarizing what we know about insect genital asymmetries, and by contrasting this with the situation in spiders, a group in which genital asymmetries are rare. In spiders, only four independent origins of genital asymmetry are known, two in Theridiidae (Tidarren/Echinotheridion, Asygyna) and two in Pholcidae (Metagonia, Kaliana). In insects, on the other hand, genital asymmetry is a widespread and common phenomenon. In some insect orders or superorders, genital asymmetry is in the groundplan (e.g. Dictyoptera, Embiidina, Phasmatodea), in others it has evolved multiple times convergently (e.g. Coleoptera, Diptera, Heteroptera, Lepidoptera). Surprisingly, the huge but widely scattered information has not been reviewed for over 70 years. We combine data from studies on taxonomy, mating behaviour, genital mechanics, and phylogeny, to explain why genital asymmetry is so common in insects but so rare in spiders. We identify further fundamental differences between spider and insect genital asymmetries: (1) in most spiders, the direction of asymmetry is random, in most insects it is fixed; (2) in most spiders, asymmetry evolved first (or only) in the female while in insects genital asymmetry is overwhelmingly limited to the male. We thus propose that sexual selection has played a crucial role in the evolution of insect genital asymmetry, via a route that is accessible to insects but not to spiders. The centerpiece in this insect route to asymmetry is changes in mating position. Available evidence strongly suggests that the plesiomorphic neopteran mating position is a female-above position. Changes to male-dominated positions have occurred frequently, and some of the resulting positions require abdominal twisting, flexing, and asymmetric contact between male and female genitalia. Insects with their median unpaired sperm transfer organ may adopt a one-sided asymmetric position and still transfer the whole amount of sperm. Spiders with their paired sperm transfer organs can only mate in symmetrical or alternating two-sided positions without foregoing transfer of half of their sperm. We propose several hypotheses regarding the evolution of genital asymmetry. One explains morphological asymmetry as a mechanical compensation for evolutionary and behavioural changes of mating position. The morphological asymmetry per se is not advantageous, but rather the newly adopted mating position is. The second hypothesis predicts a split of functions between right and left sides. In contrast to the previous hypothesis, morphological asymmetry per se is advantageous. A third hypothesis evokes internal space constraints that favour asymmetric placement and morphology of internal organs and may secondarily affect the genitalia. Further hypotheses appear supported by a few exceptional cases only.

Three new species of Mesabolivar (Aranea, Pholcidae) from leaf litter in urban environments in the city of São Paulo, São Paulo, Brazil

In this study we describe three new litter inhabiting species of Mesabolivar González-Sponga, 1998 from nine urban forest remnants in the metropolitan region of the city of São Paulo, Brazil: M. forceps, M. mairyara and M. cavicelatus. In three of these remnants, we conduced a three year sampling using pitfall traps. Mesabolivar forceps sp. nov. was the most abundant pholcid (n=273 adults), always present in the samples, but with highest numbers in spring and summer. Mesabolivar mairyara sp. nov. was the second most abundant species (n=32), but the majority of individuals were collected in March 2001. Only three individuals of M. cavicelatus sp. nov. were collected.