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Abstract: 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.
Keywords: classification, climate change, divergence time estimation, Dolomedes, fishing spiders, lifestyle evolution, MCMCtree, RelTime
Published in DiRROS: 13.04.2026; Views: 43; Downloads: 39
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Abstract: Madagascar is a biodiversity hotspot with high endemism and ancient phylogenetic diversity. We here report the discovery of Osmooka aphana gen. nov., sp. nov. from Marojejy National Park. Phylogenomic analyses place Osmooka as sister to the Australian Paraplectanoides Keyserling, 1886, and this doublet is sister to Nephilidae Simon, 1894. When proposed, Paraplectanoididae Kuntner, Coddington, Agnarsson & Bond, 2023 was exclusively Australian and monogeneric, but was predicted to contain additional, undescribed taxa. The discovery of Osmooka and its phylogenetic placement in Paraplectanoididae supports this prediction. We present a taxonomic treatment of Osmooka and Paraplectanoides, and a reappraisal of Orbipurae morphological homologies. With this new discovery, we revalidate Paraplectanoididae, Nephilidae, and Phonognathidae Simon, 1894, ranks resurrected as exclusive, monophyletic, and well-diagnosed families, whereas Araneidae Clerck, 1757 requires further redefinition. Finally, we test the hypothesis of East Gondwanan vicariant origin of Osmooka and Paraplectanoides. This scenario would predict an ancient age of their ancestor, predating the 130 Ma breakup of Gondwana. Divergence dating refutes this hypothesis by estimating their common ancestor at 57 Ma. Rather than through vicariance, the disjunct distribution of Osmooka and Paraplectanoides is best explained through Cenozoic intercontinental dispersal and/or extinctions. Potential discovery of additional paraplectanoidid diversity might better elucidate the timing, modes, and trajectories of historic dispersal and extinction events.
Keywords: Madagascar, biodiversity, Osmooka aphana gen. nov., sp. nov., Paraplectanoididae, spiders
Published in DiRROS: 23.03.2026; Views: 124; Downloads: 101
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Abstract: Madagascar is a biodiversity hotspot with high endemism and ancient phylogenetic diversity. We here report the discovery of Osmooka aphana gen. nov., sp. nov. from Marojejy National Park. Phylogenomic analyses place Osmooka as sister to the Australian Paraplectanoides Keyserling, 1886 and this doublet is sister to Nephilidae Simon, 1894. When proposed, Paraplectanoididae Kuntner, Coddington, Agnarsson & Bond, 2023 was exclusively Australian and monogeneric, but was predicted to contain additional, undescribed taxa. The discovery of Osmooka and its phylogenetic placement in Paraplectanoididae support this prediction. We present a taxonomic treatment of Osmooka and Paraplectanoides, and a reappraisal of Orbipurae morphological homologies. With this new discovery, we revalidate Paraplectanoididae, Nephilidae, and Phonognathidae Simon, 1894 ranks resurrected as exclusive, monophyletic, and well-diagnosed families, whereas Araneidae Clerck, 1757 requires further redefinition. Finally, we test the hypothesis of East Gondwanan vicariant origin of Osmooka and Paraplectanoides. This scenario would predict an ancient age of their ancestor, predating the 130 Ma breakup of Gondwana. Divergence dating refutes this hypothesis by estimating their common ancestor at 57 Ma. Rather than through vicariance, the disjunct distribution of Osmooka and Paraplectanoides is best explained through Cenozoic intercontinental dispersal and/or extinctions. Potential discovery of additional paraplectanoidid diversity might better elucidate the timing, modes, and trajectories of historic dispersal and extinction events.
Keywords: phylogenomics, classification, palpal homology, arachnology, zoology
Published in DiRROS: 22.01.2026; Views: 369; Downloads: 280
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Abstract: 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.
Keywords: fishing spider, phylogeny, taxonomy, Madagascar, Réunion
Published in DiRROS: 20.06.2025; Views: 671; Downloads: 646
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Abstract: Dolomedes may easily be considered to be among the most charismatic spider taxa. Known colloquially as fishing or raft spiders, this clade of dolomedid cursorial hunters is speciose with about 100 valid species names. Most Dolomedes are large spiders that inhabit water bodies across all continents except Antarctica and, interestingly, South America. Dolomedes have captured the attention of researchers and the public alike for their ability to walk on and submerge under water, fish for prey (including small vertebrates), and for their often-bizarre mating behavior that includes examples of male spontaneous death and sexual cannibalism. In this review, we critically evaluate what is known of Dolomedes biology, focusing on their systematics and morphology, ecology, behavior, and conservation. Given their close association with water, Dolomedes may be particularly vulnerable to the impacts of anthropogenic change and provide an important group of indicator species for understanding the effect of pollution, habitat loss and climate change. We outline a roadmap for future studies that, in our view, will consolidate Dolomedes as an ideal model lineage among spiders for addressing a vast array of questions across multiple fields of biology.
Keywords: raft spiders, behavioral ecology, diversity, physiology, evolution, conservation, Dolomedidae
Published in DiRROS: 28.03.2025; Views: 969; Downloads: 554
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