A molecular palaeobiological exploration of arthropod terrestrialization

Abstract

Understanding animal terrestrialization, the process through which animals colonized the land, is crucial to clarify extant biodiversity and biological adaptation. Arthropoda (insects, spiders, centipedes and their allies) represent the largest majority of terrestrial biodiversity. Here we implemented a molecular palaeobiological approach, merging molecular and fossil evidence, to elucidate the deepest history of the terrestrial arthropods. We focused on the three independent, Palaeozoic arthropod terrestrialization events (those of Myriapoda, Hexapoda and Arachnida) and showed that a marine route to the colonization of land is the most likely scenario. Molecular clock analyses confirmed an origin for the three terrestrial lineages bracketed between the Cambrian and the Silurian. While molecular divergence times for Arachnida are consistent with the fossil record, Myriapoda are inferred to have colonized land earlier, substantially predating trace or body fossil evidence. An estimated origin of myriapods by the Early Cambrian precedes the appearance of embryophytes and perhaps even terrestrial fungi, raising the possibility that terrestrialization had independent origins in crown-group myriapod lineages, consistent with morphological arguments for convergence in tracheal systems.This article is part of the themed issue ‘Dating species divergences using rocks and clocks’.

Tying pest insects in knots: the deployment of spider‐venom‐derived knottins as bioinsecticides

“…Spiders evolved from an arachnid ancestor in the late Ordovician around 450 million years ago and they are now the most speciose invertebrates on the planet after insects and mites. About ∼48 000 species have been morphologically characterized and assigned taxonomic names, but this likely represents less than a third of all living spider species; indeed, the total number of extant species might exceed the total number of venomous animals in all other terrestrial phyla .…”

Phylogenomics illuminates the backbone of the Myriapoda Tree of Life and reconciles morphological and molecular phylogenies

“…Diversification of Dignatha is inferred to date to the latest Cambrian-Early Ordovician, Progoneata to the mid-late Cambrian, and Myriapoda to the early-middle Cambrian (auto- and uncorrelated rates, respectively). The shared terrestrial adaptations of all extant myriapods (e.g., tracheae, Malpighian tubules, uniramous trunk limbs) suggest that the common ancestor of each of these estimated Cambrian nodes was terrestrial, coinciding (although being slightly younger) with estimates of terrestrialisation for other arthropod lineages, including arachnids and hexapods [3, 5]. Although the trace fossil record is consistent with amphibious arthropods by the mid Cambrian [21, 22], these molecular estimates for early or middle Cambrian crown-group myriapods continue to pose an unanswered question in arthropod terrestrialisation.…”

The house spider genome reveals an ancient whole-genome duplication during arachnid evolution

“…The age of the duplication event identified here must predate the most recent common ancestor of spiders and scorpions. Molecular clock approaches vary widely on the age of arachnids, and have suggested that arachnids diversified in the Ordovician (Lozano-Fernandez et al, 2016;Rota-Stabelli et al, 2013) or in the Silurian (Sharma and Wheeler, 2014), with large confidence intervals on node age estimates that often span entire geological periods. However, the earliest stem-group spiders (the extinct order Uraraneida) date to the mid-Devonian (386 MYA; Selden et al (2008)), whereas discoveries of Paleozoic scorpions have extended the stratigraphic range of scorpions into the Silurian (430 MYA; Waddington et al (2015)).…”