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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: 123; 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: Instances of sexual size dimorphism (SSD) provide the context for rigorous tests of biological rules of size evolution, such as Cope’s rule (phyletic size increase), Rensch’s rule (allometric patterns of male and female size), as well as male and female body size optima. In certain spider groups, such as the golden orbweavers (Nephilidae), extreme female-biased SSD (eSSD, female:male body length 2) is the norm. Nephilid genera construct webs of exaggerated proportions, which can be aerial, arboricolous, or intermediate (hybrid). First, we established the backbone phylogeny of Nephilidae using 367 anchored hybrid enrichment markers, then combined these data with classical markers for a reference species-level phylogeny. Second, we used the phylogeny to test Cope and Rensch’s rules, sex specific size optima, and the coevolution of web size, type, and features with female and male body size and their ratio, SSD. Male, but not female, size increases significantly over time, and refutes Cope’s rule. Allometric analyses reject the converse, Rensch’s rule. Male and female body sizes are uncorrelated. Female size evolution is random, but males evolve toward an optimum size (3.2–4.9 mm). Overall, female body size correlates positively with absolute web size. However, intermediate sized females build the largest webs (of the hybrid type), giant female Nephila and Trichonephila build smaller webs (of the aerial type), and the smallest females build the smallest webs (of the arboricolous type). We propose taxonomic changes based on the criteria of clade age, monophyly and exclusivity, classification information content, and diagnosability. Spider families, as currently defined, tend to be between 37 million years old and 98 million years old, and Nephilidae is estimated at 133 Ma (97–146), thus deserving family status. We, therefore, resurrect the family Nephilidae Simon 1894 that contains Clitaetra Simon 1889, the Cretaceous GeratonephilaPoinar and Buckley (2012), Herennia Thorell 1877, IndoetraKuntner 2006, new rank, Nephila Leach 1815, Nephilengys L. Koch 1872, Nephilingis Kuntner 2013, Palaeonephila Wunderlich 2004 from Tertiary Baltic amber, and TrichonephilaDahl 1911, new rank. We propose the new clade Orbipurae to contain Araneidae Clerck 1757, Phonognathidae Simon 1894, new rank, and Nephilidae. Nephilid female gigantism is a phylogenetically ancient phenotype (over 100 Ma), as is eSSD, though their magnitudes vary by lineage.
Keywords: spiders, evolution of sexual size dimorphism, golden orbweavers, analyses
Published in DiRROS: 24.07.2024; Views: 1574; Downloads: 849
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Abstract: Higher-level classifications often must account for monotypic taxa representing depauperate evolutionary lineages and lacking synapomorphies of their better-known, well-defined sister clades. In a ranked (Linnean) or unranked (phylogenetic) classification system, discovering such a depauperate taxon does not necessarily invalidate the rank classification of sister clades. Named higher taxa must be monophyletic to be phylogenetically valid. Ranked taxa above the species level should also maximize information content, diagnosability, and utility (e.g., in biodiversity conservation). In spider classification, families are the highest rank that is systematically catalogued, and incertae sedis is not allowed. Consequently, it is important that family level taxa be well defined and informative. We revisit the classification problem of Orbipurae, an unranked suprafamilial clade containing the spider families Nephilidae, Phonognathidae, and Araneidae sensu stricto. We argue that, to maximize diagnosability, information content, conservation utility, and practical taxonomic considerations, this “splitting” scheme is superior to its recently proposed alternative, which lumps these families together as Araneidae sensu lato. We propose to redefine Araneidae and recognize a monogeneric spider family, Paraplectanoididae fam. nov. to accommodate the depauperate lineage Paraplectanoides. We present new subgenomic data to stabilize Orbipurae topology which also supports our proposed family-level classification. Our example from spiders demonstrates why classifications must be able to accommodate depauperate evolutionary lineages, e.g., Paraplectanoides. Finally, although clade age should not be a criterion to determine rank, other things being equal, comparable ages of similarly ranked taxa do benefit comparative biology.
Keywords: classification, family rank, phylogenomics, systematics, monophyly, spider phylogeny, zoology
Published in DiRROS: 12.07.2024; Views: 1422; Downloads: 942
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