Ancient spiders on Moa’s Ark? - Biogeography, taxonomy and systematics of the enigmatic odd-clawed spiders
Final Report Abstract
The spider family Gradungulidae, endemic to mesic forests in Australia and New Zealand, is an enigmatic lineage with morphological features reminiscent of both, basal branching and modern spiders. This understudied family is a living relict of spider evolution, including both cribellate web builders and cursorial species without capture webs, and as such fascinated evolutionary biologists since their discovery in the 1950s for their systematics, morphology, and biogeography. In this project, we investigated the evolutionary history and taxonomic diversity of Gradungulidae with a focus on the subfamily Gradungulinae, the so-called odd clawed spiders. Despite substantial hurdles, including the catastrophic Australian bushfires (2019-2020) and the subsequent COVID-19 pandemic, we were able to collect a sufficient number of specimens across most of the distribution range representing the most comprehensive taxon sampling including all genera and most species to provide the first detailed insight into the diversity of this enigmatic group. Based on our integrative approach using molecular and morphological data, we can show that the Australian gradunguline fauna is paraphyletic, comprising the basal branching cribellate genera Progradungula and Macrogradungula as sistergroup to the two ecribellate genera (Kaiya and Tarlina), which are the sister-group to the monophyletic New Zealand fauna (Spelungula, Pianoa and Gradungula). This suggests that the ability to produce cribellate capture webs is a plesiomorphic condition in gradungulids, which was lost once in the evolution of this lineage. Furthermore, these data imply that New Zealand was colonized only once, likely from Australia suggesting a Goodbye Gondwana scenario. With regard to the different genera, our phylogenetic analyses highlight the high genetic diversity of some genera including the Australian genus Tarlina and New Zealand genus Gradungula. In total, we discovered five new gradungulid species in New Zealand and at least five new species in Australia. This is remarkable considering that only 17 species were described since this family was first discovered in 1955, which is further evidence on the difficulty to find these rather cryptic animals. However, a formal description is only possible based on adult specimen, which are only rarely found and also extremely scarce in collection worldwide often only represented by the type specimen. Thus, only half of our newly discovered species can be formally described. Among them, we could already describe a new species of Progradungula, which is highly endemic and an extremely rare find due to its very small distribution range and cryptic lifestyle. The restriction to ancient cool-temperate Nothofagus forests makes this species an important asset for conservation measures similar to the Nelson cave spider Spelungula cavernicola, which is the only New Zealand spider listed in the IUCN Red List of Threatened Species. Overall, it can be concluded that despite the tremendous obstacles mentioned above, our project provides substantial new insights into the evolution and systematics of odd-clawed spiders. Furthermore, we can provide a more differentiated view regarding the implication for future conservation measures, with some species being very restricted and locally endemic, and others with a wider distribution and less dependent on a specific habitat type.
Publications
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Functional trade-offs in cribellate silk mediated by spinning behavior. Scientific Reports, 9(1).
Michalik, Peter; Piorkowski, Dakota; Blackledge, Todd A. & Ramírez, Martín J.
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Web-building behavior of the odd-clawed spider Progradungula otwayensis (Araneae: Gradungulidae) and implications for the evolution of combing behavior in spiders. The Journal of Arachnology, 47(3), 299.
Ramírez, Martín J. & Michalik, Peter
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Another ghost of Gondwana—Progradungula barringtonensis Michalik & Smith, sp. nov., a new species of the relict spider genus Progradungula (Araneae: Gradungulidae) from a temperate rainforest in eastern Australia. Austral Entomology, 63(1), 72-81.
Michalik, Peter; Smith, Helen M.; Milledge, Graham & Harms, Danilo
