Fossil amber reveals springtails’ longstanding dispersal by social insects

International audienceBackground: Dispersal is essential for terrestrial organisms living in disjunct habitats and constitutes a significant challenge for the evolution of wingless taxa. Springtails (Collembola), the sister-group of all insects (with Diplura), are reported since the Lower Devonian and are thought to have originally been subterranean. The order Symphypleona is reported since the early Cretaceous with genera distributed on every continent. This distribution implies an ability to disperse over oceans, however symphypleonan Collembola have never been reported in marine water contrary to other springtail orders. Despite being highly widespread, modern springtails are rarely reported in any kind of biotic association. Interestingly, the fossil record has provided occasional occurrences of Symphypleona attached by the antennae onto the bodies of larger arthropods.Results: Here, we document the case of a ~ 16 Ma old fossil association: a winged termite and ant displaying not some, but 25 springtails attached or in close proximity to the body. The collembola exhibit rare features for fossils, reflecting their courtship and phoretic behaviours. By observing the modes of attachment of springtails on different arthropods, the sex representation and ratios in springtail antennal anatomies in new and previously reported cases, we infer a likely mechanism for dispersal in Symphypleona. By revealing hidden evidence of modern springtail associations with other invertebrates such as ants and termites, new compelling assemblages of fossil springtails, and the drastic increase of eusocial insects? abundance during the Cenozoic (ants/termites comprising more than a third of insects in Miocene amber), we stress that attachment on winged castes of ants and termites may have been a mechanism for the worldwide dispersal of this significant springtail lineage. Moreover, by comparing the general constraints applying to the other wingless soil-dwelling arthropods known to disperse through phoresy, we suggest biases in the collection and observation of phoretic Symphypleona related to their reflexive detachment and infer that this behaviour continues today.Conclusions: The specific case of tree resin entrapment represents the (so far) only condition uncovering the phoretic dispersal mechanism of springtails - one of the oldest terrestrial arthropod lineages living today

Phylogénie des Hexapodes et implications pour l’hypothèse de leur origine aquatique

L’émergence du milieu aquatique pour coloniser le milieu terrestre est une des transitions majeures au sein des Arthropodes. Il est souvent considéré que les premiers Hexapodes, et plus particulièrement les premiers Collemboles, étaient semi-aquatiques, sortant du milieu marin en passant par un environnement d’eau douce pour finalement coloniser le milieu terrestre. La question de l’origine écologique des Hexapodes est traitée à travers un cadre phylogénétique. En optimisant les attributs écologiques sur la phylogénie, il est montré que les Hexapodes ont colonisé le milieu terrestre directement à partir du milieu marin sans transition par le milieu dulçaquicole. Un mode de vie édaphique est inféré comme étant le mode de vie ancestral des Collemboles, et plus généralement des Hexapodes dans leur ensemble. Le mode de vie aquatique est un changement évolutif secondaire acquis indépendamment dans plusieurs lignées, en particulier dans certains groupes de Collemboles et de Ptérygotes. La réponse est ambiguë pour les Ptérygotes : soit les premiers Ptérygotes ont eu des larves aquatiques et auraient réversé vers une vie pleinement terrestre chez les Néoptères, soit des larves aquatiques sont apparues indépendamment chez les Odonates et les Ephéméroptères. Dans les deux cas, différents groupes ont acquis des larves aquatiques secondairement (par exemple les Plécoptères, les Trichoptères et les Coléoptères)

Species diversity in Friesea (Neanuridae) reveals similar biogeographic patterns among Antarctic Collembola

The pan-Antarctic distributions of several collembolan species have been supported by morphology for over 120 years. However, for most species where molecular data are available, these are now known to belong instead to several species, and most classified as short-range endemics. One such species, Friesea grisea, had a pan-Antarctic distribution that has been in question, but until recently, specimens of F. grisea from the type locality on South Georgia have not been included in any molecular appraisal. Here, we compare the molecular identity of specimens of F. grisea, from South Georgia, with other Antarctic and sub-Antarctic species using the mitochondrial COI gene. A Bayesian phylogenetic analysis for 14 species of Friesea from southern regions, including F. grisea sensu stricto with species previously identified as ‘F. grisea’ (F. antarctica, F. gretae and F. propria) confirms the distinctness of the South Georgian specimens based on molecular data, and these results are confirmed morphologically. The genus Friesea is one of the most speciose genera of Collembola known in the Antarctic region, and we provide an annotated key (dichotomous and interactive versions) to all Friesea species in the sub-Antarctic and Antarctica. We compare the biogeography of Friesea to other Collembola from the region to highlight our current understanding of species boundaries and island linkages. © 2021 Royal Swedish Academy of Sciences

Islands in ice: isolated populations of <i>Cryptopygus sverdrupi</i> (Collembola) among nunataks in the Sør Rondane Mountains, Dronning Maud Land, Antarctica

<div><p>Molecular variation among Antarctic Collembola has been well appreciated over the last decade. The majority of studies have focussed on the Transantarctic Mountains and Antarctic Peninsula, and more recently Dronning Maud Land, which now accounts for all known continental species. Within most species, mean mitochondrial DNA (mtDNA) sequence divergence has not been more than around 2%, but in 2010 far greater levels of infraspecific sequence divergence (9.2–10.9%) were discovered in three species: <i>Friesea grisea</i> (10.2%), <i>Gressittacantha terranova</i> (10.4%) and <i>Cryptopygus antarcticus</i> (9.2%). Here, we present the first phylogeographic study on <i>Cryptopygus sverdrupi</i> from Dronning Maud Land. We found that mtDNA <i>COI</i> and <i>16S</i> haplotypes clustered into two lineages with a mean <i>COI</i> sequence divergence of around 7.1%. The mixing of haplotypes between nearby nunataks separated by up to 15 km revealed support for ongoing (but rare) dispersal, although a single site, the most geographically isolated (by 40–58 km) was also the most genetically divergent. These levels of sequence divergence indicate persistence of biota throughout the Miocene and Pliocene isolated in glacial refugia. Expanding sampling of <i>C. sverdrupi</i> from additional ice-free refugia throughout Dronning Maud Land will be important to further our understanding of the evolutionary processes that have influenced the Antarctic continent, its landscape and biota.</p></div

Reply to Hörnschemeyer et al. "Is Strudiella a Devonian insect?"

International audienceSince the nineteenth century, Devonian insects have repeatedly proven to be something else1–5, the sole exception being Rhyniognatha. Recently the Devonian insect Strudiella devonica6 has been denied by Hörnschemeyer et al.7, who could not ‘‘confirm the presence of a mandible or of mandibular teeth’’