Madagascar is a global biodiversity hotspot, but its biodiversity continues to be underestimated and understudied. Of raft spiders, genus Dolomedes Latreille, 1804, literature only reports two species on Madagascar. Our single expedition to humid forests of eastern and northern Madagascar, however, yielded a series of Dolomedes exemplars representing both sexes of five morphospecies. To avoid only using morphological diagnostics, we devised and tested an integrative taxonomic model for Dolomedes based on the unified species concept. The model first determines morphospecies within a morphometrics framework, then tests their validity via species delimitation using COI. It then incorporates habitat preferences, geological barriers, and dispersal related traits to form hypotheses about gene flow limitations. Our results reveal four new Dolomedes species that we describe from both sexes as Dolomedes gregoric sp. nov., D. bedjanic sp. nov., D. hydatostella sp. nov., and D. rotundus sp. nov. The range of D. kalanoro Silva & Griswold, 2013, now also known from both sexes, is expanded to eastern Madagascar. By increasing the known raft spider diversity from one valid species to five, our results merely scratch the surface of the true Dolomedes species diversity on Madagascar. Our integrative taxonomic model provides the framework for future revisions of raft spiders anywhere.

Pisauridae are a global and heterogeneous assemblage of spider genera with diverse morphologies and lifestyles. So far, the monophyly of Pisauridae and the inclusion of fishing spiders (Dolomedes) in this family have not been thoroughly tested. Here, we amend the systematics and classification of these lineages within a UCE phylogenomic framework and through a detailed morphological reappraisal. For estimations of their evolutionary age, we perform and compare outcomes from two divergence estimation approaches, an a posteriori likelihood, and an a priori Bayesian. Phylogenies reject the monophyly of both Pisauridae and Dolomedes: (1) Focal Clade I groups true Pisauridae genera including Pisaura; (2) Focal Clade II contains Blandinia and is sister to Trechaleidae and Lycosidae; (3) Focal Clade III groups Dolomedes, Megadolomedes, and Ornodolomedes, and is sister to Blandinia, Trechaleidae, and Lycosidae. We therefore propose to delimit Pisauridae by removing Dolomedidae rank resurrected (including Dolomedes, Bradystichus, Megadolomedes, Caledomedes, Mangromedes, Ornodolomedes, and Tasmomedes) and Blandinia incertae sedis. Likelihood and Bayesian time calibration approaches yield comparable divergence estimations: Pisauridae origin is estimated at 29–40 Ma; Blandinia 21–34 Ma; Dolomedidae 10–17 Ma; Dolomedes 9–16 Ma. Reconstructions suggest that the evolution of terrestrial and web‐building lifestyles from semi‐aquatic ancestors in Pisauridae coincided with cooling and drying climates during the mid‐Miocene, but this was not the case in the few recent cases of terrestrialization in Dolomedes species. This historic reconstruction illustrates how climatic changes, or rapid radiation, can drive lifestyle diversification.

Pisauridae Simon, 1890 or “nursery web spiders” are a global and heterogenous assemblage of spider genera with diverse lifestyles, containing web builders and webless species, as well as terrestrial and semi-aquatic species, notably “fishing spiders”, genus Dolomedes Latreille, 1804. Incomplete, unresolved, or conflicting phylogenies have so far hampered testing for Dolomedes and pisaurid monophyly and evolution. Here, we broadly address these questions within a phylogenomic and comparative framework. Our goals are i) reconstruction of a robust phylogeny to test the monophyly of Dolomedes and Pisauridae and to amend Dolomedes classification; ii) estimation of evolutionary shifts and trends in lifestyles and capture webs; and iii) evaluation of hypotheses of morphological trait association with a semi-aquatic lifestyle. To this end we generate subgenomic data (ultraconserved elements or UCE) for 53 Dolomedes species and 28 pisaurid genera. We analyze these data using maximum likelihood, Bayesian, and multi-species coalescence approaches, as well as using two different phylogenetic time calibration methods, RelTime and MCMCtree. Consistent across analytical approaches, our phylogenies reject the monophyly of both Pisauridae and Dolomedes . “Pisaurid” genera fall into three clades: 1) Focal Clade I groups the majority, including Pisaura Simon, 1886, hence representing true pisaurids; 2) Focal Clade II = Blandinia Tonini et al., 2016 is sister to Trechaleidae Simon, 1890 and Lycosidae Sundevall, 1833; 3) Focal Clade III with fishing and raft spiders groups Dolomedes , Megadolomedes Davies and Raven, 1980, and Ornodolomedes Raven and Hebron, 2018 and is sister to Focal Clade II, Trechaleidae, and Lycosidae. Our taxonomy, based on complementary taxa and morphological evidence, resurrects Dolomedidae Simon, 1876 to include Dolomedes and the Oceanic genera Bradystichus Simon, 1884, Megadolomedes , Caledomedes Raven and Hebron, 2018, Mangromedes Raven and Hebron, 2018, Ornodolomedes , and Tasmomedes Raven and Hebron, 2018. Both RelTime and MCMCtree analyses yield comparable divergence estimations: Pisauridae origin is estimated between 29 and 40 Ma; Blandinia between 21 and 34 Ma; Dolomedidae between 10 and 17 Ma; and Dolomedes between 9 and 16 Ma. In order to avoid misleading significant correlations and/or over-resolved ancestral states, we performed taxon sampling bias correction in all evolutionary analyses. Evolutionary analyses reconstruct semi-aquatic lifestyle as ancestral to a large clade containing pisaurids, lycosids, trechaleids, Blandinia , and dolomedids, with several reversals to terrestrial lifestyle. Capture webs evolved at least three times, with reversals. Counter to expectation, the evolution of lifestyles and capture webs are independent. Although leg and tarsus lengths do not indicate lifestyles, semi-aquatic taxa are significantly larger than terrestrial ones. We explain this pattern with a biomechanical threshold over which surface tension can be broken while spiders forage under water. Our time-calibrated analyses indicate that the evolution of terrestrial and web-building lifestyles from semi-aquatic ancestors in Pisauridae coincided with cooling and drying climates in the mid-Miocene. We therefore hypothesize that climatic changes have acted as strong selection pressures toward lifestyle diversification.

Bark spiders (Caerostris Thorell, 1868, Araneidae Clerck, 1757) are large spiders distributed across the Old-World tropics. This genus was understudied until recently, but received more attention following the discovery of unique web evolution and biomaterial properties of its species. Caerostris are characterized by web gigantism, reaching extremes in Darwin’s Bark spider (C. darwini Kuntner & Agnarsson, 2010), which employs the toughest known silk. Due to the exceptional silk of C. darwini, recent research provided whole-genome sequencing and silk-gene mapping for C. darwini and a sympatric congener misassigned, due to cryptic diversity, to C. extrusa Butler, 1882. We describe a case of convergent evolution in somatic morphology that further hinders species identification in the field. Conducting a morphological and molecular investigation of exemplars that share the “C. extrusa morphotype”, we conclude they belong to four distinct species. We redescribe the two valid ones, C. extrusa and C. hirsuta (Simon, 1895), elevate the previously synonymized C. bankana Strand, 1915 to species level, and newly describe C. kuntneri sp. nov., the species used in the assembly of its genome. We argue this to be an example of how the global taxonomic impediment can lead to errors in rapidly advancing fields such as genomics.

Raft spiders, family Dolomedidae, represent a group of spiders with 7 genera distributed near globally well known for a semi-aquatic lifestyle. One of the iconic genera representing such a unique lifestyle is the largest and diverse dolomedid genus Dolomedes. Although Dolomedes is well surveyed in parts of its distribution, its diversity in the tropics remains largely unknown, such as the western Indian Ocean region with most of the islands unsurveyed. Recent expeditions to Madagascar and La Réunion Island discovered a series of specimens that appear to belong to an unknown morphospecies of Dolomedes, exhibiting varying degrees of differences in the diagnostic characteristics. To further test and define their species boundaries, we include molecular evidence followed by species delimitation analyses. Our findings indicate that specimens from both islands are conspecific. Consequently, we introduce a new species to science, Dolomedes reuniascar sp. nov., providing detailed illustrations, descriptions of its variations and ecological characteristics. Based on our observations and existing literature, we speculate that the presence of this species on the two isolated islands could be attributed to either highly efficient dispersal abilities, such as ballooning of spiderlings, or human-mediated introduction events.

Ants and termites are insect groups that make up most of the insect biomass in tropical ecosystems. Due to their social structure and abundance, they are some of the most bountiful prey available to other invertebrates such as spiders. However, ants and termites possess dangerous defense strategies, thus limiting their accessibility to general predators. Here, we report on an unexpected finding of a three‐way predator‐prey‐kleptoparasite interaction in Madagascar among a termite Nasutitermes sp. (prey), a previously unknown theridiid spider Vigdisia praesidens gen. nov., sp. nov. (predator), and an ant Pheidole spinosa (kleptoparasite). Our field observations suggest that the spiders are able to detect a damaged termite nest from a distance to disperse onto it and prey on its residents. Kleptoparasitic ants also arrive on the scene to steal from the spiders their termite prey. Both the spider and the ant seem to possess some degree of behavioural prey specialisation for Nasutitermes termites. The here described ecological interaction warrants further study to better understand the exploitation of signals by such phylogenetically diverse arthropods.