Search

ABSTRACT The family Dysderidae is a highly diverse group of nocturnal ground‐dwelling and active‐hunter spiders. Dysderids are mostly restricted to the Western Palearctic, and particularly rich and abundant around the Mediterranean region. Interestingly, the distribution of species richness among its 24 genera and three subfamilies is highly biased—80% of its 644 documented species belong to just two genera, Dysdera (326) and Harpactea (211). Dysderidae provides an excellent study case for evolutionary and ecological research. It includes cases of trophic specialization, which are uncommon among spiders, and exhibit other remarkable biological (e.g. holocentric chromosomes), behavioural (e.g. cryptic female choice), evolutionary (e.g. adaptive radiation) and ecological features (e.g. recurrent colonization of the subterranean environment). The lack of a quantitative hypothesis on its phylogenetic structure has hampered its potential as a testing ground for evolutionary, biogeographical and ecological hypotheses. Here, we present the results of a target, multi‐locus phylogenetic analysis, using mitochondrial (cox1, 16s and 12s) and nuclear genes (h3, 28s and 18s), of the most exhaustive taxonomic sample within Dysderidae (104 spp.) to date and across related families (Synspermiata) (83 spp.). We estimate divergence times using a combination of fossil and biogeographic node calibrations and use this timeline to identify shifts in diversification rates. Our results support the monophyly of the Dysderidae subfamilies Rhodinae and Dysderinae but reject Harpacteinae as currently defined. Moreover, the clades recovered within Harpacteinae do not support its current taxonomy. The origin of the family most likely post‐dated the break‐up of Pangea, and cave colonization may be older than previously considered. After correcting for the taxonomic artefacts, we identified a significant shift in diversification rates at the base of the genus Dysdera. Although the unique coexistence of specialist and generalist diets within the lineage could be suggested as the potential driver for the rate acceleration, further quantitative analyses would be necessary to test this hypothesis. [ABSTRACT FROM AUTHOR]

This study presents the first molecular phylogenetic analysis of the Clinocerinae, challenging the traditionally accepted monophyly of this subfamily. DNA was extracted from fresh and museum specimens representing all biogeographical regions. Maximum likelihood (ML) and Bayesian inference (BI) phylogenetic analyses were performed based on sequences from two mitochondrial genes, cytochrome c oxidase subunit I (COI) and cytochrome β, and three nuclear genes, carbomoylphosphate synthase domain of rudimentary, elongation factor‐1α and isocitrate dehydrogenase. Through molecular data and morphological examination, our results reveal a division within Clinocerinae, distinguishing ‘typical’ or Clinocerinae (s.s.) from several genera, specifically Afroclinocera Sinclair, Asymphyloptera Collin and Proagomyia Collin, possibly lending support for a reclassification of these genera outside Clinocerinae. Bergenstammia Mik is proposed as a junior synonym of Phaeobalia Mik, syn. n., and the following new combinations are recognized: Phaeobalia albanica (Wagner) comb. n., Phaeobalia aurinae (Pusch & Wagner) comb. n., Phaeobalia carniolica (Horvat) comb. n., Phaeobalia frigida (Vaillant) comb. n., Phaeobalia glacialis (Palaczyk & Słowińska) comb. n., Phaeobalia multiseta (Strobl) comb. n., Phaeobalia nudimana (Vaillant) comb. n., Phaeobalia nudipes (Loew) comb. n., Phaeobalia pulla (Vaillant & Wagner) comb. n., Phaeobalia pyrenaica (Vaillant & Vinçon) comb. n., Phaeobalia slovaca (Wagner) comb. n. and Phaeobalia thomasi (Vaillant & Vinçon) comb. n. Re‐evaluation of the genus Roederiodes resulted in the following new combinations: Clinocerella macedonicus (Wagner & Horvat) comb. n. and Clinocerella montenegrinus (Wagner & Horvat) comb. n. The origins of Clinocerinae (s.s.) are traced back to the Holarctic region, Laurasian origin, with a likely complex history of dispersal events into the Southern Hemisphere. Based on current knowledge, the greatest generic and species richness is confined to the Palaearctic Region. These findings provide valuable insights into the evolutionary relationships and distribution patterns of Clinocerinae (s.s.), challenging existing taxonomic classifications and shedding light on their historical biogeography. [ABSTRACT FROM AUTHOR]

Aim: To disentangle the role of evolutionary history, competition and environmental filtering in driving the niche evolution of four closely related subterranean spiders, with the overarching goal of obtaining a mechanistic description of the factors that determine species' realized distribution in simplified ecological settings. Location: Dinaric karst, Balkans, Europe. Taxon: Dysderidae spiders (Stalita taenaria, S. pretneri, S. hadzii and Parastalita stygia). Methods: We resolved phylogenetic relationships among species and modelled each species' distribution using a set of climatic and habitat variables. We explored the climatic niche differentiation among species with n‐dimensional hypervolumes and shifts in their trophic niche using morphological traits related to feeding specialization. Results: Climate was the primary abiotic factor explaining our species' distributions, while karstic and soil features were less important. Generally, there was a high niche overlap among species, reflecting their phylogenetic relatedness, but on a finer scale, niche shifts explained the realized distribution patterns. Trophic interaction was another important factor influencing species distributions – the non‐overlapping distributions of three morphologically indistinguishable Stalita species is seemingly the outcome of competitive exclusion dynamics. The distribution of the fourth species, Parastalita stygia, overlaps with that of the other species, with several instances of coexistence within caves. As inferred from the morphology of the mouthparts, the mechanism that minimizes interspecific competition is the shift in the trophic niche of P. stygia towards a more specialized diet. Main conclusions: We showed that similarity in niches only partly correlated with the phylogenetic distance among species, and that overlaps in species distributions are possible only when a parallel shift in diet occurs. Our work emphasized how even simplified environments still maintain the potential for diversification via niche differentiation. Ultimately, we provide an ecological explanation for the diversification of life in an important hotspot of subterranean diversity. [ABSTRACT FROM AUTHOR]

The genus Harpactea Bristowe, 1939 (Araneae, Dysderidae) is one of the most diverse and abundant components of the Mediterranean ground-dwelling spider fauna. However, the taxonomic boundaries of the genus are unclear and its monophyly has been questioned, yet never tested, in a quantitative framework. The only taxonomic revisions in the genus trace back to the 1960s–1990s, and most subsequent work has consisted of single species descriptions. Part of the confusion surrounding the genus and species groups delimitations have to do with the lack of a standardized nomenclature for diagnostic structures based on explicit homology statements. Here we use the description of new species of Harpactea to propose a set of homologies in the male and female genitalia and a standardized nomenclature for those structures. We formally describe three new Harpactea species: H. salvatorei sp. nov., from a cave in the north-eastern Italian Alps, and H. damini sp. nov. and H. mateparlovi sp. nov. from different caves on the Biokovo Mountain and surroundings in Croatia. All the new taxa belong to the lepida species group. In addition, we use a multilocus target gene approach to provide the first hypothesis on the internal phylogenetic structure of the genus Harpactea and the subfamily Harpacteinae, which includes representatives of all currently accepted species groups in the genus and genera in the subfamily. Our results support the close affinities of the species here described but reject the monophyly of both Harpactea and some of the species groups proposed in the literature. [ABSTRACT FROM AUTHOR]

Tandemly arrayed non-coding sequences or satellite DNAs (satDNAs) are rapidly evolving segments of eukaryotic genomes, including the centromere, and may raise a genetic barrier that leads to speciation. However, determinants and mechanisms of satDNA sequence dynamics are only partially understood. Sequence analyses of a library of five satDNAs common to the root-knot nematodes Meloidogyne chitwoodi and M. fallax together with a satDNA, which is specific for M. chitwoodi only revealed low sequence identity (32–64%) among them. However, despite sequence differences, two conserved motifs were recovered. One of them turned out to be highly similar to the CENP-B box of human alpha satDNA, identical in 10–12 out of 17 nucleotides. In addition, organization of nematode satDNAs was comparable to that found in alpha satDNA of human and primates, characterized by monomers concurrently arranged in simple and higher-order repeat (HOR) arrays. In contrast to alpha satDNA, phylogenetic clustering of nematode satDNA monomers extracted either from simple or from HOR array indicated frequent shuffling between these two organizational forms. Comparison of homogeneous simple arrays and complex HORs composed of different satDNAs, enabled, for the first time, the identification of conserved motifs as obligatory components of monomer junctions. This observation highlights the role of short motifs in rearrangements, even among highly divergent sequences. Two mechanisms are proposed to be involved in this process, i.e., putative transposition-related cut-and-paste insertions and/or illegitimate recombination. Possibility for involvement of the nematode CENP-B box-like sequence in the transposition-related mechanism and together with previously established similarity of the human CENP-B protein and pogo-like transposases implicate a novel role of the CENP-B box and related sequence motifs in addition to the known function in centromere protein binding. [ABSTRACT FROM AUTHOR]

5S ribosomal DNAs (rDNAs) are arranged in tandem and are often under-represented in genome assemblies. In the present study, we performed a global and in-depth analysis of the 5S rDNAs in the model insect Tribolium castaneum and its closely related species Tribolium freemani. To accomplish this goal, we used our recently published genome assemblies based on Nanopore and PacBio long-read sequencing. Although these closely related species share the 5S rRNA gene sequence with high homology, they show a different organization of the 5S rDNA locus. Analysis of 5S rDNA arrays in T. castaneum revealed a typical tandemly repeated organization characterized by repeat units consisting of the 121 bp long 5S rRNA gene and the 71 bp long nontranscribed spacer (NTS). In contrast, T. freemani showed a much more complex organization of 5S rDNA arrays characterized by two patterns. The first is based on the association of 5S rRNA gene with arrays of a satellite DNA, representing the NTS sequence of the 5S rDNA genes in T. freemani. The second, more complex type is characterized by a somewhat less frequent occurrence of the 5S rRNA gene and its association with longer satellite DNA arrays that are regularly interrupted by Jockey-like retrotransposons. This organization, in which the ribosomal gene is associated with two completely different repetitive elements such as satellite DNAs and retrotransposons, suggests that the 5S rRNA gene, regardless of its crucial function in the genome, could be a subject of extremely dynamic genomic rearrangements. [ABSTRACT FROM AUTHOR]

Aim: Quantifying the relative contribution of environmental filtering versus limiting similarity in shaping communities is challenging because these processes often act simultaneously and their effect is scale‐dependent. Focusing on caves, island‐like natural laboratories with limited environmental variability and species diversity, we tested: (i) the relative contribution of environmental filtering and limiting similarity in determining community assembly in caves; (ii) how the relative contribution of these driving forces changes along environmental gradients. Location: Europe. Time period: Present. Major taxa studied: Subterranean spiders. Methods: We used data on distribution and traits for European cave spiders (n = 475 communities). We estimated the trait space of each community using probabilistic hypervolumes, and obtained estimations of functional richness independent of the species richness of each community via null modelling. We model functional diversity change along environmental gradients using generalized dissimilarity modelling. Results: Sixty‐three percent of subterranean spider communities exhibited a prevalence of trait underdispersion. However, most communities displayed trait dispersion that did not depart significantly from random, suggesting that environmental filtering and limiting similarity were both exerting equally weak or strong, yet opposing influences. Overdispersed communities were primarily concentrated in southern latitudes, particularly in the Dinaric karst, where there is greater subterranean habitat availability. Pairwise comparisons of functional richness across caves revealed these effects to be strongly scale‐dependent, largely varying across gradients of cave development, elevation, precipitation, entrance size and annual temperature range. Conversely, geographical distance weakly affected trait composition, suggesting convergence in traits among communities that are far apart. Main conclusions: Even systems with stringent environmental conditions maintain the potential for trait differentiation, especially in areas of greater habitat availability. Yet, the relative influence of environmental filtering and limiting similarity change with scale, along clear environmental gradients. The interplay of these processes may explain the assembly of species‐poor subterranean communities displaying high functional specialization. [ABSTRACT FROM AUTHOR]

Satellite DNAs (satDNAs) are long arrays of tandem repeats typically located in heterochromatin and span the centromeres of eukaryotic chromosomes. Despite the wealth of knowledge about satDNAs, little is known about a fraction of short, satDNA-like arrays dispersed throughout the genome. Our survey of the Pacific oyster Crassostrea gigas sequenced genome revealed genome assembly replete with satDNA-like tandem repeats. We focused on the most abundant arrays, grouped according to sequence similarity into 13 clusters, and explored their flanking sequences. Structural analysis showed that arrays of all 13 clusters represent central repeats of 11 non-autonomous elements named Cg_HINE, which are classified into the Helentron superfamily of DNA transposons. Each of the described elements is formed by a unique combination of flanking sequences and satDNA-like central repeats, coming from one, exceptionally two clusters in a consecutive order. While some of the detected Cg_HINE elements are related according to sequence similarities in flanking and repetitive modules, others evidently arose in independent events. In addition, some of the Cg_HINE's central repeats are related to the classical C. gigas satDNA, interconnecting mobile elements and satDNAs. Genome-wide distribution of Cg_HINE implies non-autonomous Helentrons as a dynamic system prone to efficiently propagate tandem repeats in the C. gigas genome. [ABSTRACT FROM AUTHOR]

One of the most striking features of obligate subterranean species is their narrow distribution ranges. These prevail not only at specific, but often also at generic level. However, some subterranean genera have continental scale and disjunct distribution, which challenges their monophyly and questions the scenarios of their origin and colonization. In our study, we investigated the subterranean collembolan genus Verhoeffiella, currently known from five remote karst regions of Europe. Four nuclear and one mitochondrial genes were assembled to reveal the evolutionary history of the genus. We tested the monophyly of the genus, explored its relationship with putative surface relatives, and its temporal patterns of molecular diversification. The phylogeny revealed a complex relationship of Verhoeffiella with surface species Heteromurus nitidus and partially disentangled the biogeographical question of its disjunct distribution. Further on, several lineages of Verhoeffiella were recognized in the Dinarides, showing highly underestimated diversity and, compared with the number of described species, a sevenfold increase in the number of MOTUs. The radiation is relatively recent, with the events triggering the diversification linked to the Messinian salinity crisis and Pleistocene climatic shifts. The combination of this extensive subterranean radiation and close evolutionary links with epigean relatives makes Verhoeffiella an exceptional case within the subterranean fauna of temperate areas, which significantly contributes to our understanding of subterranean colonization and diversification patterns. [ABSTRACT FROM AUTHOR]

Climate change affects all ecosystems, but subterranean ecosystems are repeatedly neglected from political and public agendas. Cave habitats are home to unknown and endangered species, with low trait variability and intrinsic vulnerability to recover from human-induced disturbances. We studied the annual variability and cyclicity of temperatures in caves vis-à-vis surface in different climatic areas. We hypothesize that cave temperatures follow the average temperature pattern at the surface for each location with a slight delay in the signal, but we found three different thermal patterns occurring in caves: (1) high positive correlation and a similar thermal pattern to the surface, (2) low correlation and a slight thermal delay of the signal from the surface, and (3) high negative correlation with an extreme delay from the surface. We found daily thermal cycles in some caves, which may potentially control the circadian rhythms of cave organisms. Our results show that caves had lower thermal amplitude than the surface, and that thermal averages within caves approximately correspond to the to the annual average of surface temperature. Caves buffer external temperature and act as refugia for biota in extreme climatic events. Likewise, temperature increases at surface will lead to increment in caves, threatening subterranean biota and ecosystem services. [ABSTRACT FROM AUTHOR]

The Dinaric Karst is a global hotspot for subterranean diversity, with two distinct peaks of species richness in the northwest and southeast, and an area of a lower species richness in the central part. In this article, we present a species list and describe the ecological conditions of the Lukina jama–Trojama cave system, located in the central part of the Dinaric Karst. This cave system is the deepest and one of the most logistically challenging cave systems sampled so far in the Dinaric Karst. Repeated sampling resulted in a list of 45 species, including 25 troglobionts, 3 troglophiles, 16 stygobionts, and 1 stygophile. Most of the recorded species are endemic to the Velebit Mountain, while three species are endemic to the Lukina jama–Trojama cave system. Within the system, species richness peaks in the deepest third of the cave, most likely reflecting the harsh ecological conditions in the upper parts, including ice, cold winds, and occasional waterfalls. Milder and more stable deeper parts of the cave contain a rich subterranean species community, part of which is associated with two very distinct aquatic habitats, the cave hygropetric and the phreatic zone. The newly recognized hotspot of subterranean biodiversity in the central Dinaric Karst, which has emerged between the two known centers of biodiversity, further highlights the species richness in large cave systems, but also challenges the diversity patterns in the Dinaric Karst overall. [ABSTRACT FROM AUTHOR]

Geometric regularity of spider webs has been intensively studied in orb‐weaving spiders, although it is not exclusive of orb weavers. Here, we document the geometrically regular, repetitive elements in the webs of the non‐orb‐weaving groups Leptonetidae and Telemidae for the first time. Similar to orb weavers, we found areas with regularly spaced parallel lines in the webs of Calileptoneta helferi, Sulcia sp., and cf. Pinelema sp. Furthermore, we provide a detailed account of the regular webs of Ochyrocera (Ochyroceratidae). The sections of the web with regularly disposed parallel lines are built as U‐shaped modules reminiscent of orb webs. It has been suggested that the regularly spaced parallel lines in the webs of Ochyroceratidae and Psilodercidae may be produced in a single sweep of their posterior lateral spinnerets, which have regularly spaced aciniform gland spigots, perhaps involving expansion of the spinnerets. To test this hypothesis, we compared the spacing between parallel lines with the spacing between spigots, searched for expansible membranes in the spinnerets, and examined the junctions of regularly spaced lines. The distance between parallel lines was 10–20 times the distance between spigots, and we found no expansible membranes, and the intersection of parallel lines are cemented, which opposes the single sweep hypothesis. Furthermore, we found cues of viscid silk in the parallel lines of the psilodercid Althepus and broadened piriform gland spigots that may be responsible of its production. Finally, we evaluated the presence or absence of geometrically regular web elements across the spider tree of life. We found reports of regular webs in 31 spider families, including 20 families that are not orb weavers and hypothesize that the two basic aspects of regularity (parallel lines spaced at regular intervals, and radial lines spaced at regular angles) probably appeared many times in the evolution of spiders. [ABSTRACT FROM AUTHOR]

In light of recent alarming trends in human population growth, climate change, and other environmental modifications, a "Warning to humanity" manifesto was published in BioScience in 2017. This call reiterated most of the ideas originally expressed by the Union of Concerned Scientists in 1992, including the fear that we are "pushing Earth's ecosystems beyond their capacities to support the web of life." As subterranean biologists, we take this opportunity to emphasize the global importance and the conservation challenges associated with subterranean ecosystems. They likely represent the most widespread nonmarine environments on Earth, but specialized subterranean organisms remain among the least documented and studied. Largely overlooked in conservation policies, subterranean habitats play a critical role in the function of the web of life and provide important ecosystem services. We highlight the main threats to subterranean ecosystems and propose a set of effective actions to protect this globally important natural heritage. [ABSTRACT FROM AUTHOR]

Abstract: We provide the first overview on spiders living in subterranean habitats in Europe, including the first European subterranean spider checklist. In Europe, there are 486 spider species known to dwell in caves and other subterranean habitats, distributed across 22 families. Despite a few species being able to colonize caves across the whole continent, approximately 90% of the species show a restricted distribution, occurring exclusively in one or two countries. From a biogeographic perspective, southern Europe emerges as the main hot spot of subterranean spider diversity, showing the highest richness of endemic species. Compared to other temperate regions of the world, some families appear to be well represented and other poorly represented (or lacking) in European subterranean habitats. Overall, it appears that the taxonomical knowledge on subterranean spiders in Europe is sufficient, but not evenly distributed. As this checklist represents a useful baseline for advances in this field, we point out specific areas of interest for future research. [ABSTRACT FROM AUTHOR]

The genus Troglocladius Andersen, Baranov et Hagenlund, gen. n. is erected based on T. hajdi Andersen, Baranov et Hagenlund, sp. n. collected at 980 m depth in the Lukina jama—Trojama cave system in Croatia. Morphological features such as pale color, strongly reduced eyes and very long legs make it a typical cave animal. Surprisingly, it has also retained large wings and appears to be capable of flight which would make T. hajdi the first flying troglobiont worldwide, disproving previous beliefs that bats are the only animals capable of flying in complete darkness. Morphologically the new species does not readily fit within any described genus, but shares characteristics with genera both in the tribes “Metriocnemini” and “Orthocladiini”. Bayesian molecular phylogenetic analysis using the markers COI, 18S rDNAs, 28S rDNA, CADI, and CADIV groups it with the genera Tvetenia, Cardiocladius and Eukiefferiella in the tribe “Metriocnemini”. Troglocladius hajdi may be parthenogenetic, as only females were collected. The discovery confirms the position of the Dinaric arch as a highly important hotspot of subterranean biodiversity. [ABSTRACT FROM AUTHOR]