Nuria Macías-Hernández

The dark side of an island radiation: systematics and evolution of troglobitic spiders of the genus Dysdera Latreille (Araneae : Dysderidae) in the Canary Islands

The spider genus Dysdera Latreille is an excellent model for the study of the evolution of cave life: ten species are known to exist exclusively in the subterranean environment of the Canary Islands, where the genus has undergone local diversification. In the present paper, two new troglobitic species (Dysdera madai, sp. nov. and D. sibyllina, sp. nov.) and the previously unknown sex of five additional species are described and illustrated: the males of D. gollumi Ribera & Arnedo, 1994, D. hernandezi Arnedo & Ribera, 1999 and D. labradaensis Wunderlich, 1991; and the females of D. andamanae Arnedo & Ribera, 1997 and D. gibbifera Wunderlich, 1991. The first direct evidence of troglobitic members of Dysdera in micro- and mesocaverns are reported. The evolution of cave life as hypothesised following a combined morphological and molecular phylogeny is investigated. Troglobitic Canarian Dysdera species have colonised the under- ground on eight independent occasions. The Dysderidae groundplan represents a preadaptation to cave life and has facil- itated the colonisation of caves. Canarian members of Dysdera have a predominantly parapatric mode of speciation, although postspeciation changes in distribution may have obscured allopatric processes. Eye regression and, to a lesser extent, larger body size and appendage elongation characterise troglobitic species. The different levels of troglobiomor- phism are interpreted as local adaptations to heterogeneous subterranean conditions. The high levels of sympatry among troglobites are explained by trophic segregation and changes in prey capture strategy were involved in the single identi- fied case of subterranean speciation in the group.

Living on the edge: demographic and phylogeographical patterns in the woodlouse-hunter spider Dysdera lancerotensis Simon, 1907 on the eastern volcanic ridge of the Canary Islands

The Eastern Canary Islands are the emerged tips of a continuous volcanic ridge running parallel to the northeastern African coast, originated by episodic volcanic eruptions that can be traced back to the Miocene and that, following a major period of quiescence and erosion, continued from the Pliocene to the present day. The islands have been periodically connected by eustatic sea‐level changes resulting from Pleistocene glacial cycles. The ground‐dwelling spider Dysdera lancerotensis Simon, 1907 occurs along the entire ridge, except on recent barren lavas and sand dunes, and is therefore an ideal model for studying the effect of episodic geological processes on terrestrial organisms. Nested clade and population genetic analyses using 39 haplotypes from 605 base pairs of mitochondrial DNA cytochrome c oxidase I sequence data, along with phylogenetic analyses including two additional mitochondrial genes, uncover complex phylogeographical and demographic patterns. Our results indicate that D. lancerotensis colonized the ridge from north to south, in contrast to what had been expected given the SSW‐NNE trend of volcanism and to what had been reported for other terrestrial arthropods. The occurrence of several episodes of extinction, recolonization and expansion are hypothesized for this species, and areas that act as refugia during volcanic cycles are identified. Relaxed molecular clock methods reveal divergence times between main haplotype lineages that suggest an older origin of the northern islets than anticipated based on geological evidence. This study supports the key role of volcanism in shaping the distribution of terrestrial organisms on oceanic islands and generates phylogeographical predictions that warrant further research into other terrestrial endemisms of this fascinating region.

The Imprint of Geologic History on Within-Island Diversification of Woodlouse-Hunter Spiders (Araneae, Dysderidae) in the Canary Islands

Geological processes and ecological adaptation are major drivers of diversification on oceanic islands. Although diversification in these islands is often interpreted as resulting from dispersal or island hopping rather than vicariance, this may not be the case in islands with complex geological histories. The island of Tenerife, in the Canary Islands, emerged in the late Miocene as 3 precursor islands that were subsequently connected and reisolated by volcanic cycles. The spider Dysdera verneaui is endemic to the island of Tenerife, where it is widely distributed throughout most island habitats, providing an excellent model to investigate the role of physical barriers and ecological adaptation in shaping within-island diversity. Here, we present evidence that the phylogeographic patterns of this species trace back to the independent emergence of the protoislands. Molecular markers (mitochondrial genes cox1, 16S, and nad1 and the nuclear genes ITS-2 and 28S) analyzed from 100 specimens (including a thorough sampling of D. verneaui populations and additional outgroups) identify 2 distinct evolutionary lineages that correspond to 2 precursor islands, each with diagnostic genital characters indicative of separate species status. Episodic introgression events between these 2 main evolutionary lineages explain the observed incongruence between mitochondrial and nuclear markers, probably as a result of the homogenization of their ITS-2 sequence types. The most widespread lineage exhibits a complex population structure, which is compatible with either secondary contact, following connection of deeply divergent lineages, or alternatively, a back colonization from 1 precursor island to another.

Integrative taxonomy uncovers hidden species diversity in woodlouse hunter spiders (Araneae, Dysderidae) endemic to the Macaronesian archipelagos

The development of molecular techniques as a taxonomic tool and their integration with information provided by other disciplines, has enhanced species discovery, facilitated species delimitation and produced invaluable data for inferring species phylogenies. Here, we provide an example of how DNA sequence data, together with morphometric, distributional and ecological information, assist in identifying and diagnosing previously overlooked lineages. The nocturnal, ground-dwelling spider genus Dysdera has colonized all the Macaronesian archipelagos, and has undergone a major diversification in the Canary Islands. A recent molecular phylogenetic analysis of Dysdera species from the eastern Canary Islands revealed deep genetic divergences among some populations, suggesting the existence of cryptic taxa. Here, we combine data from mitochondrial and nuclear loci with morphological and ecological evidence to delimit and formally describe three previously overlooked species: D. aneris sp. nov., endemic to the Salvage Islands; D. mahan sp. nov., distributed along coastal habitats of Lanzarote, north of Fuerteventura and adjacent islets; and D. simbeque sp. nov., restricted to two valleys in northern Lanzarote. Molecular markers provide key information that allows apparent morphological polymorphisms to be used as diagnostic features of evolutionarily independent lineages. Dysdera mahan sp. nov. is unique among the Canarian Dysdera in that it is found in the intertidal zone on pebbled beaches. Low levels of genetic variability and genital differentiation associated with relatively high somatic divergence suggest that speciation in D. mahan sp. nov. was driven by a selection of phenotypic traits that are adaptive to this rare environment. Separate analyses and statistical tests revealed phylogenetic incongruence between mitochondrial and nuclear genes, probably as a result of incomplete lineage sorting. The temporal framework for the origin and diversification of the new species inferred from the molecular data corroborates former hypotheses on the late Pliocene origin of the present-day biota of the Salvage Islands.

Evolution of Chemosensory Gene Families in Arthropods: Insight from the First Inclusive Comparative Transcriptome Analysis across Spider Appendages

Unlike hexapods and vertebrates, in chelicerates, knowledge of the specific molecules involved in chemoreception comes exclusively from the comparative analysis of genome sequences. Indeed, the genomes of mites, ticks and spiders contain several genes encoding homologs of some insect membrane receptors and small soluble chemosensory proteins. Here, we conducted for the first time a comprehensive comparative RNA-Seq analysis across different body structures of a chelicerate: the nocturnal wandering hunter spider Dysdera silvatica Schmidt 1981. Specifically, we obtained the complete transcriptome of this species as well as the specific expression profile in the first pair of legs and the palps, which are thought to be the specific olfactory appendages in spiders, and in the remaining legs, which also have hairs that have been morphologically identified as chemosensory. We identified several ionotropic (Ir) and gustatory (Gr) receptor family members exclusively or differentially expressed across transcriptomes, some exhibiting a distinctive pattern in the putative olfactory appendages. Furthermore, these IRs were the only known olfactory receptors identified in such structures. These results, integrated with an extensive phylogenetic analysis across arthropods, uncover a specialization of the chemosensory gene repertoire across the body of D. silvatica and suggest that some IRs likely mediate olfactory signaling in chelicerates. Noticeably, we detected the expression of a gene family distantly related to insect odorant-binding proteins (OBPs), suggesting that this gene family is more ancient than previously believed, as well as the expression of an uncharacterized gene family encoding small globular secreted proteins, which appears to be a good chemosensory gene family candidate.

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

Abstract 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.