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Gregory D. Edgecombe – One of the best experts on this subject based on the ideXlab platform.
The Phylogeny and Evolutionary History of ArthropodsCurrent Biology, 2019Co-Authors: Gonzalo Giribet, Gregory D. EdgecombeAbstract:
Arthropods are the most diverse animal phylum, and their phylogenetic relationships have been debated for centuries. With the advent of molecular phylogenetics, Arthropods were found to be monophyletic and placed within a clade of molting animals, the ecdysozoans, with nematodes and six other phyla. Molecular phylogenetics also provided a new framework for relationships between the major arthropod groups, such as the clade Pancrustacea, which comprises insects and crustaceans. Phylogenomics based on second-generation genomics and transcriptomics has further resolved puzzles such as the exact position of myriapods or the closest crustacean relatives of hexapods. It is now broadly recognized that extant Arthropods are split into chelicerates and mandibulates, and relationships within the two mandibulate clades (myriapods and pancrustaceans) are stabilizing. Notably, the phylogeny of insects is now understood with considerable confidence, whereas relationships among chelicerate orders remain poorly resolved. The evolutionary history of Arthropods is illuminated by a rich record of fossils, often with exquisite preservation, but current analyses conflict over whether certain fossil groups are stem- or crown-group Arthropods. Molecular time-trees calibrated with fossils estimate the origins of Arthropods to be in the Ediacaran, while most other deep nodes date to the Cambrian. The earliest stem-group Arthropods were lobopodians, worm-like animals with annulated appendages. Confidently placing some key extinct clades on the arthropod tree of life may require less ambiguous interpretation of fossil structures and better integration of morphological data into the phylogeny.
Origins and early evolution of ArthropodsPalaeontology, 2014Co-Authors: Gregory D. Edgecombe, David A. LeggAbstract:
Phylogenomics reconstructs an arthropod tree in which a monophyletic Arthropoda splits into Pycnogonida + Euchelicerata and Myriapoda + Pancrustacea. The same chelicerate–mandibulate groups are retrieved with morphological data sets, including those encompassing most taxa known from Palaeozoic Konservat-Lagerstatten. With respect to the interrelationships of the three extant clades of Panarthropoda, a sister group relationship between Onychophora and Arthropoda is endorsed by transcriptomics and microRNAs, although this hypothesis forces homoplasy in characters of the segmental ganglia that are shared by tardigrades and Arthropods. Cambrian lobopodians, dinocaridids, bivalved Arthropods and fuxianhuiids document the successive appearance of characteristic arthropod features in the stem lineage of Euarthropoda (crown-group Arthropods). Molecular dating suggests that Arthropods had their origin and initial diversification in the Ediacaran, but no convincing palaeontological evidence for Panarthropoda is available until the earliest Cambrian.
chelicerate neural ground pattern in a cambrian great appendage arthropodNature, 2013Co-Authors: Gengo Tanaka, Gregory D. Edgecombe, Nicholas J. StrausfeldAbstract:
Cambrian great appendage Arthropods had heads that bore a claw-like appendage pair; neuroanatomical and phylogenetic analysis of a well-preserved Alalcomenaeus fossil reveals the relationship of great appendage Arthropods to Chelicerata. ‘Great appendage’ Arthropods are extinct jointed-legged creatures from the Cambrian period equipped with often large claw-like appendages of an arrangement not seen in modern Arthropods. Their evolutionary relationships are much debated. Gregory Edgecombe and colleagues use micro-computed tomography to reconstruct the neuroanatomy of Alalcomenaeus, an exquisitely preserved great-appendage arthropod from China. Several characters of the nervous system are uniquely shared with the chelicerates — spiders, scorpions, mites and horseshoe crabs — placing the fossils firmly on the arthropod tree and demonstrating that chelicerate neuroanatomy had evolved by 520 million years ago. Preservation of neural tissue in early Cambrian Arthropods has recently been demonstrated1, to a degree that segmental structures of the head can be associated with individual brain neuromeres. This association provides novel data for addressing long-standing controversies about the segmental identities of specialized head appendages in fossil taxa2,3. Here we document neuroanatomy in the head and trunk of a ‘great appendage’ arthropod, Alalcomenaeus sp., from the Chengjiang biota, southwest China, providing the most complete neuroanatomical profile known from a Cambrian animal. Micro-computed tomography reveals a configuration of one optic neuropil separate from a protocerebrum contiguous with four head ganglia, succeeded by eight contiguous ganglia in an eleven-segment trunk. Arrangements of optic neuropils, the brain and ganglia correspond most closely to the nervous system of Chelicerata of all extant Arthropods, supporting the assignment of ‘great appendage’ Arthropods to the chelicerate total group4,5. The position of the deutocerebral neuromere aligns with the insertion of the great appendage, indicating its deutocerebral innervation and corroborating a homology between the ‘great appendage’ and chelicera indicated by morphological similarities4,6,7. Alalcomenaeus and Fuxianhuia protensa1 demonstrate that the two main configurations of the brain observed in modern Arthropods, those of Chelicerata and Mandibulata, respectively8, had evolved by the early Cambrian.
Yves Basset – One of the best experts on this subject based on the ideXlab platform.
arthropod distribution in a tropical rainforest tackling a four dimensional puzzlePLOS ONE, 2015Co-Authors: Yves Basset, Lukáš Čížek, Philippe Cuenoud, Raphael K Didham, Vojtech Novotny, Frode Odegaard, Tomas Roslin, Alexey K TishechkinAbstract:
Quantifying the spatio-temporal distribution of Arthropods in tropical rainforests represents a first step towards scrutinizing the global distribution of biodiversity on Earth. To date most studies have focused on narrow taxonomic groups or lack a design that allows partitioning of the components of diversity. Here, we consider an exceptionally large dataset (113,952 individuals representing 5,858 species), obtained from the San Lorenzo forest in Panama, where the phylogenetic breadth of arthropod taxa was surveyed using 14 protocols targeting the soil, litter, understory, lower and upper canopy habitats, replicated across seasons in 2003 and 2004. This dataset is used to explore the relative influence of horizontal, vertical and seasonal drivers of arthropod distribution in this forest. We considered arthropod abundance, observed and estimated species richness, additive decomposition of species richness, multiplicative partitioning of species diversity, variation in species composition, species turnover and guild structure as components of diversity. At the scale of our study (2km of distance, 40m in height and 400 days), the effects related to the vertical and seasonal dimensions were most important. Most adult Arthropods were collected from the soil/litter or the upper canopy and species richness was highest in the canopy. We compared the distribution of Arthropods and trees within our study system. Effects related to the seasonal dimension were stronger for Arthropods than for trees. We conclude that: (1) models of beta diversity developed for tropical trees are unlikely to be applicable to tropical Arthropods; (2) it is imperative that estimates of global biodiversity derived from mass collecting of Arthropods in tropical rainforests embrace the strong vertical and seasonal partitioning observed here; and (3) given the high species turnover observed between seasons, global climate change may have severe consequences for rainforest Arthropods.
arthropod diversity in a tropical forestScience, 2012Co-Authors: Yves Basset, Lukáš Čížek, Philippe Cuenoud, Raphael K Didham, Francois Guilhaumon, Olivier Missa, Vojtech Novotny, Frode Odegaard, Tomas Roslin, Juergen SchmidlAbstract:
Most eukaryotic organisms are Arthropods. Yet, their diversity in rich terrestrial ecosystems is still unknown. Here we produce tangible estimates of the total species richness of Arthropods in a tropical rainforest. Using a comprehensive range of structured protocols, we sampled the phylogenetic breadth of arthropod taxa from the soil to the forest canopy in the San Lorenzo forest, Panama. We collected 6144 arthropod species from 0.48 hectare and extrapolated total species richness to larger areas on the basis of competing models. The whole 6000-hectare forest reserve most likely sustains 25,000 arthropod species. Notably, just 1 hectare of rainforest yields >60% of the arthropod biodiversity held in the wider landscape. Models based on plant diversity fitted the accumulated species richness of both herbivore and nonherbivore taxa exceptionally well. This lends credence to global estimates of arthropod biodiversity developed from plant models.
Russell Greenberg – One of the best experts on this subject based on the ideXlab platform.
interactions among predators and the cascading effects of vertebrate insectivores on arthropod communities and plantsProceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Kailen A Mooney, Daniel S Gruner, Nicholas A Barber, Sunshine A. Van Bael, Stacy M Philpott, Russell GreenbergAbstract:
Theory on trophic interactions predicts that predators increase plant biomass by feeding on herbivores, an indirect interaction called a trophic cascade. Theory also predicts that predators feeding on predators, or intraguild predation, will weaken trophic cascades. Although past syntheses have confirmed cascading effects of terrestrial arthropod predators, we lack a comprehensive analysis for vertebrate insectivores—which by virtue of their body size and feeding habits are often top predators in these systems—and of how intraguild predation mediates trophic cascade strength. We report here on a meta-analysis of 113 experiments documenting the effects of insectivorous birds, bats, or lizards on predaceous Arthropods, herbivorous Arthropods, and plants. Although vertebrate insectivores fed as intraguild predators, strongly reducing predaceous Arthropods (38%), they nevertheless suppressed herbivores (39%), indirectly reduced plant damage (40%), and increased plant biomass (14%). Furthermore, effects of vertebrate insectivores on predatory and herbivorous Arthropods were positively correlated. Effects were strongest on Arthropods and plants in communities with abundant predaceous Arthropods and strong intraguild predation, but weak in communities depauperate in arthropod predators and intraguild predation. The naturally occurring ratio of arthropod predators relative to herbivores varied tremendously among the studied communities, and the skew to predators increased with site primary productivity and in trees relative to shrubs. Although intraguild predation among arthropod predators has been shown to weaken herbivore suppression, we find this paradigm does not extend to vertebrate insectivores in these communities. Instead, vertebrate intraguild preda-tion is associated with strengthened trophic cascades, and insectivores function as dominant predators in terrestrial plant-arthropod communities.