Devoramascles i transvestits: la vida sexual secreta de les aranyes

Resum: Les aranyes han desenvolupat un seguit de pràctiques sexuals sorprenents i uns caràcters mor- fològics extrems que les han convertides en les amants més estrambòtiques i imaginatives del planeta. Al llarg de més de 400 milions d'anys, aquests trets han estat seleccionats per tal de garantir el major nombre de descendents amb la millor aptitud possible, majoritàriament sota la direcció de la selecció sexual i mit- jançant processos com la coevolució antagonista o la selecció per part de la femella. Els mascles d'aranyes posseeixen unes estructures copuladores secundàries situades a l'extrem dels pedipalps amb diferents nivells de complexitat, que constitueixen el principal caràcter per a la identi cació de les diferents espècies d'aranyes, a causa del seu paper cabdal en l'establiment de barreres reproductives. Aquesta complexitat troba el seu paral·lelisme en les estructures genitals femenines que han evolucionat per tal de permetre a la femella seleccionar el company sexual que la fecundarà. En les aranyes es troben alguns dels exemples més extrems de dimor sme sexual en animals terrestres i l'evidència apunta que aquest és, en part, responsable de l'aparició del canibalisme sexual característic d'algunes espècies, tal i com ho con rmen els interessants casos d'inversió de rols sexuals observats en aquest grup. Els mascles d'aranya han desenvolupat un seguit d'estratègies per tal d'escapar d'aquest destí fatal, tot i que en alguns casos el sacri ci del mascle es veu recompensat pel fet d'assegurar-se la paternitat de la descendència. Les aranyes són elements fonamen- tals de les xarxes trò ques, imprescindibles per al funcionament dels ecosistemes. Enginyeres incansables i perfeccionistes que construeixen algunes de les estructures més elegants i intricades de la natura, les teranyines, i, com descobrim en aquest article, models experimentals ideals per entendre els mecanismes evolutius que han modelat els trets i els comportaments sexuals en el món animal. Summary: Male-eaters and transvestites: the secret sexual life of spiders. - Over more than 400 million years, spiders have developed a series of surprising sexual behaviours and extreme morphological characters that have turned them into the most bizarre and inventive lovers. These traits have been selected to guarantee the greatest number of ttest descendants, mostly under the direction of sexual selection and through processes such as antagonistic co-evolution or female choice. Male spiders have secondary copulatory structures located at the tip of their palps. The di erent levels of complexity of these structures are the key characters for identifying spider species because of their important role in the establishment of reproductive barriers. The genital structures of females are also complex, having evolved to allow them to select the sexual companion that will fertilize them. Some of the most extreme examples of sexual dimor- phism in terrestrial animals have been reported in spiders, and the evidence indicates that this feature is partly responsible for the appearance of the characteristic sexual cannibalism of some species, as con rmed by the interesting cases of inversion of sexual roles observed in this group. Male spiders have developed a series of strategies to escape this fatal destiny, although in some cases the sacri ce of the male is rewarded by an increase in his chances of ensuring the paternity of the o spring. Spiders are key elements in trophic networks and are essential for the functioning of the ecosystems. They are perfectionist engineers that build some of the most elegant and intricate structures of nature, silk webs, and¿as we discover in this article¿ are ideal experimental models for understanding the evolutionary mechanisms that have shaped sexual traits and behaviours across the animal world

Spiders on a Hot Volcanic Roof: Colonisation Pathways and Phylogeography of the Canary Islands Endemic Trap-Door Spider Titanidiops canariensis (Araneae, Idiopidae)

Studies conducted on volcanic islands have greatly contributed to our current understanding of how organisms diversify. The Canary Islands archipelago, located northwest of the coast of northern Africa, harbours a large number of endemic taxa. Because of their low vagility, mygalomorph spiders are usually absent from oceanic islands. The spider Titanidiops canariensis, which inhabits the easternmost islands of the archipelago, constitutes an exception to this rule. Here, we use a multi-locus approach that combines three mitochondrial and four nuclear genes to investigate the origins and phylogeography of this remarkable trap-door spider. We provide a timeframe for the colonisation of the Canary Islands using two alternative approaches: concatenation and species tree inference in a Bayesian relaxed clock framework. Additionally, we investigate the existence of cryptic species on the islands by means of a Bayesian multi-locus species delimitation method. Our results indicate that T. canariensis colonised the Canary Islands once, most likely during the Miocene, although discrepancies between the timeframes from different approaches make the exact timing uncertain. A complex evolutionary history for the species in the archipelago is revealed, which involves two independent colonisations of Fuerteventura from the ancestral range of T. canariensis in northern Lanzarote and a possible back colonisation of southern Lanzarote. The data further corroborate a previously proposed volcanic refugium, highlighting the impact of the dynamic volcanic history of the island on the phylogeographic patterns of the endemic taxa. T. canariensis includes at least two different species, one inhabiting the Jandia peninsula and central Fuerteventura and one spanning from central Fuerteventura to Lanzarote. Our data suggest that the extant northern African Titanidiops lineages may have expanded to the region after the islands were colonised and, hence, are not the source of colonisation. In addition, T. maroccanus may harbour several cryptic species

Alpine endemic spiders shed light on the origin and evolution of subterranean species

We designed a comparative study to unravel the phylogeography of two Alpine endemic spiders characterized by a different degree of adaptation to subterranean life: Troglohyphantes vignai (Araneae, Linyphiidae) and Pimoa rupicola (Araneae, Pimoidae), the latter showing minor adaptation to hypogean life. We sampled populations of the model species in caves and other subterranean habitats across their known geographical range in the Western Alps. By combining phylogeographic inferences and Ecological Niche Modeling techniques, we inferred the biogeographic scenario that led to the present day population structure of the two species. According to our divergent time estimates and relative uncertainties, the isolation of T. vignai and P. rupicola from their northern sister groups was tracked back to Middle-Late Miocene. Furthermore, the fingerprint left by Pleistocene glaciations on the population structure revealed by the genetic data, led to the hypothesis that a progressive adaptation to subterranean habitats occurred in T. vignai, followed by strong population isolation. On the other hand, P. rupicola underwent a remarkable genetic bottleneck during the Pleistocene glaciations, that shaped its present population structure. It seems likely that such shallow population structure is both the result of the minor degree of specialization to hypogean life and the higher dispersal ability characterizing this species. The simultaneous study of overlapping spider species showing different levels of adaptation to hypogean life, disclosed a new way to clarify patterns of biological diversification and to understand the effects of past climatic shift on the subterranean biodiversity

Arm-less mitochondrial tRNAs conserved for over 30 millions of years in spiders

Background: In recent years, Next Generation Sequencing (NGS) has accelerated the generation of full mitogenomes, providing abundant material for studying different aspects of molecular evolution. Some mitogenomes have been observed to harbor atypical sequences with bizarre secondary structures, which origins and significance could only be fully understood in an evolutionary framework. Results: Here we report and analyze the mitochondrial sequences and gene arrangements of six closely related spiders in the sister genera Parachtes and Harpactocrates, which belong to the nocturnal, ground dwelling family Dysderidae. Species of both genera have compacted mitogenomes with many overlapping genes and strikingly reduced tRNAs that are among the shortest described within metazoans. Thanks to the conservation of the gene order and the nucleotide identity across close relatives, we were able to predict the secondary structures even on arm-less tRNAs, which would be otherwise unattainable for a single species. They exhibit aberrant secondary structures with the lack of either DHU or TΨC arms and many miss-pairings in the acceptor arm but this degeneracy trend goes even further since at least four tRNAs are arm-less in the six spider species studied. Conclusions: The conservation of at least four arm-less tRNA genes in two sister spider genera for about 30 myr suggest that these genes are still encoding fully functional tRNAs though they may be post-transcriptionally edited to be fully functional as previously described in other species. We suggest that the presence of overlapping and truncated tRNA genes may be related and explains why spider mitogenomes are smaller than those of other invertebrates

Advances in the systematics of the spider genus Troglohyphantes (Araneae, Linyphiidae)

With 128 described species and five subspecies, the spider genus Troglohyphantes (Araneae, Linyphiidae) is a remarkable example of species diversification in the subterranean environment. In this paper, we conducted a systematic revision of the Troglohyphantes species of the Italian Alps, with a special focus on the Lucifuga complex, including the description of two new species (T. lucifer sp. nov. and T. apenninicus n. sp.). In addition, we provided new diagnostic drawings of the holotype of T. henroti (Henroti complex) and established three new synonymies within the genus. The molecular analysis of the animal DNA barcode confirms the validity of this method of identification of the Alpine Troglohyphantes and provides additional support for the morphology based species complexes. Finally, we revised the known distribution range of additional Troglohyphantes species, as well as other poorly known alpine cave-dwelling spiders

Monophyly, taxon sampling, and the nature of ranks in the classification of orb-weaving spiders (Araneae: Araneoidea)

We address some of the taxonomic and classification changes proposed by Kuntner et al. (2019) in a comparative study on the evolution of sexual size dimorphism in nephiline spiders. Their proposal to recircumscribe araneids and to rank the subfamily Nephilinae as a family is fundamentally flawed as it renders the family Araneidae paraphyletic. We discuss the importance of monophyly, outgroup selection, and taxon sampling, the subjectivity of ranks, and the implications of the age of origin criterion to assign categorical ranks in biological classifications. We explore the outcome of applying the approach of Kuntner et al. (2019) to the classification of spiders with emphasis on the ecribellate orb-weavers (Araneoidea) using a recently published dated phylogeny. We discuss the implications of including the putative sister group of Nephilinae (the sexually dimorphic genus Paraplectanoides) and the putative sister group of Araneidae (the miniature, monomorphic family Theridiosomatidae). We propose continuation of the phylogenetic classification put forth by Dimitrov et al. (2017), and we formally rank Nephilinae and Phonognathinae as subfamilies of Araneidae. Our classification better reflects the understanding of the phylogenetic placement and evolutionary history of nephilines and phonognathines while maintaining the diagnosability of Nephilinae. It also fulfills the fundamental requirement that taxa must be monophyletic, and thus avoids the paraphyly of Araneidae implied by Kuntner et al. (2019)

Taxonomic revision and insights into the speciation mode of the spider Dysdera erythrina species-complex (Araneae : Dysderidae): sibling species with sympatric distributions

The genus Dysdera, a species-rich group of spiders that includes specialised predators of woodlice, contains several complexes of morphologically similar sibling species. Here we investigate species limits in the D. erythrina (Walckenaer, 1802) complex by integrating phenotypic, cytogenetic and molecular data, and use this information to gain further knowledge on its origin and evolution. We describe 16 new species and redescribe four poorly known species belonging to this clade. The distribution of most of the species in the complex is limited to southern France and the north-eastern Iberian Peninsula. The species studied do not show any obvious differences in habitat preference, and some of them even occur sympatrically at certain sites. They probably feed on the same type of prey as they readily capture woodlice. On the other hand, they differ in body size, mouthparts shape, sculpturing of carapace, morphology of the copulatory organs, karyotype and DNA sequences. Experimental interspecific mating showed a partial precopulatory behavioural barrier between D. erythrina and D. cechica, sp. nov. Our data suggest that karyotype evolution of the complex included chromosome fusions and fissions as well as translocations (between autosomes as well as autosomes and sex chromosomes). We hypothesise that chromosome rearrangements generating reproductive incompatibility played a primary role in speciation within Dysdera complexes. Dysdera spiders are poor dispersers, and their original distribution areas (forested areas in the Mediterranean) were repeatedly fragmented during Quarternary climatic oscillations, facilitating integration of chromosome rearrangements into karyotypes by genetic drift. Sympatric occurrence of closely related species may have been promoted by prey segregation as suggested by differentiation in body size in co-occurring species. The following new species are described: D. catalonica, sp. nov., D. cechica, D. dolanskyi, sp. nov., D. fabrorum, sp. nov., D. garrafensis, sp. nov., D. graia, sp. nov., D. kropfi, sp. nov., D. minairo, sp. nov., D. portsensis, sp. nov., D. pradesensis, sp. nov., D. pyrenaica, sp. nov., D. quindecima, sp. nov., D. septima, sp. nov., D. stahlavskyi, sp. nov., D. tredecima, sp. nov. and D. undecimal, sp. nov

What DNA barcodes reveal: microhabitat preference, hunting strategy and dispersal ability drive genetic variation across Iberian spider species

1. The current rate of species loss calls for immediate actions to preserve biodiversity and ecosystem functioning. Cataloguing species richness and composition, and revealing how diversity is geographically distributed are the first steps towards designing efficient conservation strategies. 2. Here, we aim to determine diversity patterns and potential drivers of taxonomic and genetic diversity and population structure of Iberian spiders. We used a community level perspective, analysing more than 3000 DNA barcode sequences representing 370 spider species dwelling in white-oak forest habitats across the Spanish National Park network. 3. By combining and comparing morphological and DNA barcode-based species delimitation methods, we assessed their performance and identified putative factors behind cases of incongruence. Our findings uncovered potential overlooked diversity as suggested by the geographic patterns of genetic variation and put a red flag on those taxa that may be undergoing overlooked evolutionary or ecological processes. 4. Spider functional traits associated with foraging strategy, microhabitat preference, ballooning ability and circadian activity explained the observed patterns of population structure across species but did not explain variation in genetic diversity. Overall, our study represents a major step forward in the understanding of large-scale diversity patterns in Iberian spiders at the community level and provides relevant information to guide future conservation strategies of the so-far largely overlooked invertebrate diversit

Environmental filtering and convergent evolution determine the ecological specialisation of subterranean spiders

Ecological specialization is an important mechanism enhancing species coexistence within a given community. Yet, unravelling the effect of multiple selective evolutionary and ecological factors leading the process of specialization remains a key challenge in ecology. Subterranean habitats provide highly replicated experimental arenas in which to disentangle the relative contribution of evolutionary history (convergent evolution vs. character displacement) and ecological setting (environmental filtering vs. competitive exclusion) in driving community assembly. We tested alternative hypotheses about the emergence of ecological specialization using the radiation of a lineage of sheet‐weaver cave‐dwelling spiders as model system. We observed that at the local scale, a differential specialization to cave microhabitats generally parallels moderate levels of morphological similarity and close phylogenetic relatedness among species. Conversely, geographic distance contributed little in explaining microhabitat occupation, possibly mirroring a limited role of competitive exclusion. Yet, compared to non‐coexisting species, co‐occurring species adapted to different microhabitats showed lower morphological niche overlap (i.e. higher dissimilarity) and deeper genetic distance. The framework here developed suggests that in the subterranean domain, habitat specialization is primarily driven by environmental filtering, secondarily by convergent evolution, and only marginally by character displacement or competitive exclusion. This pattern results in the establishment of replicated communities across geographical space, composed by ecologically equivalent species. Such process of community assembly well explains the numerous adaptive radiations observed in subterranean habitats, an eco‐evolutionary pattern well documented in oceanic islands or mountain summit communities

A geographical distribution database of the genus Dysdera in the Canary Islands (Araneae, Dysderidae)

The ground-dweller spider genus Dysdera shows very high species richness on the oceanic archipelago of the Canary Islands, providing one of the most outstanding examples of island radiation among spiders, only paralleled by Tetragnatha spiders on the Hawaiian archipelago. A georeferenced database of the 48 Dysdera species occurring in the Canary Islands was assembled to facilitate ongoing and future research on this remarkable lineage. All species are endemic to the archipelago except for the cosmopolitan Dysdera crocata. The dataset consists of 794 distributional records documented from 1971 to 2015, each locality being represented only once per species. Distribution maps are provided for each species, along with basic diversity and distribution information. The database and geographical maps included in this article stand for the most updated, accurate and complete information on the distribution of the spider genus Dysdera in the Canary Islands