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PubMed | Central Michigan University, Zoological Research Museum Alexander Koenig, University of Western Australia, Alfred Wegener Institute for Polar and Marine Research and 6 more.
Type: Journal Article | Journal: Royal Society open science | Year: 2015

Assessing the enormous diversity of Southern Ocean benthic species and their evolutionary histories is a central task in the era of global climate change. Based on mitochondrial markers, it was recently suggested that the circumpolar giant sea spider Colossendeis megalonyx comprises a complex of at least six cryptic species with mostly small and non-overlapping distribution ranges. Here, we expand the sampling to include over 500 mitochondrial COI sequences of specimens from around the Antarctic. Using multiple species delimitation approaches, the number of distinct mitochondrial OTUs increased from six to 15-20 with our larger dataset. In contrast to earlier studies, many of these clades show almost circumpolar distributions. Additionally, analysis of the nuclear internal transcribed spacer region for a subset of these specimens showed incongruence between nuclear and mitochondrial results. These mito-nuclear discordances suggest that several of the divergent mitochondrial lineages can hybridize and should not be interpreted as cryptic species. Our results suggest survival of C. megalonyx during Pleistocene glaciations in multiple refugia, some of them probably located on the Antarctic shelf, and emphasize the importance of multi-gene datasets to detect the presence of cryptic species, rather than their inference based on mitochondrial data alone.


Lehmann T.,Bavarian State Collection of Zoology SNSB | Lehmann T.,Ludwig Maximilians University of Munich | Hess M.,Ludwig Maximilians University of Munich | Hess M.,GeoBio Center | And 3 more authors.
Zoosystematics and Evolution | Year: 2014

In the present study 21 littoral pycnogonid species from 5 families are analysed: Ammotheidae (9 species), Callipallenidae (5 species), Endeidae (2 species), Phoxichilidiidae (3 species), and Pycnogonidae (2 species). The material was mainly taken from Mediterranean pycnogonid collections housed in the Bavarian State Collection of Zoology. Additional material was collected during field trips. Altogether the material was obtained from six different locations: Banyuls-sur-Mer (France), Tavolara Island (Italy), Elba Island (Italy), Giglio Island (Italy), Sicily Island (Italy), and Istria Peninsula (Croatia). The animals were studied in detail with a scanning electron microscope (SEM). Additionally series of light microscopic pictures were made to generate extended depth of field pictures of whole animals. The observed features are compared with previous literature. © A. B. Onadeko et al.


Lehmann T.,Bavarian State Collection of Zoology SNSB | Lehmann T.,Ludwig Maximilians University of Munich | Hess M.,Ludwig Maximilians University of Munich | Hess M.,GeoBio Center | And 4 more authors.
BMC Biology | Year: 2014

Background: The research field of connectomics arose just recently with the development of new three-dimensional-electron microscopy (EM) techniques and increasing computing power. So far, only a few model species (for example, mouse, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster) have been studied using this approach. Here, we present a first attempt to expand this circle to include pycnogonids, which hold a key position for the understanding of arthropod evolution. The visual neuropils in Achelia langi are studied using a focused ion beam-scanning electron microscope (FIB-SEM) crossbeam-workstation, and a three-dimensional serial reconstruction of the connectome is presented.Results: The two eyes of each hemisphere of the sea spider's eye tubercle are connected to a first and a second visual neuropil. The first visual neuropil is subdivided in two hemineuropils, each responsible for one eye and stratified into three layers. Six different neuron types postsynaptic to the retinula (R-cells) axons are characterized by their morphology: five types of descending unipolar neurons and one type of ascending neurons. These cell types are also identified by Golgi impregnations. Mapping of all identifiable chemical synapses indicates that the descending unipolar neurons are postsynaptic to the R-cells and, hence, are second-order neurons. The ascending neurons are predominantly presynaptic and sometimes postsynaptic to the R-cells and may play a feedback role.Conclusions: Comparing these results with the compound eye visual system of crustaceans and insects - the only arthropod visual system studied so far in such detail - we found striking similarities in the morphology and synaptic organization of the different neuron types. Hence, the visual system of pycnogonids shows features of both chelicerate median and mandibulate lateral eyes. © 2014 Lehmann et al.


The research field of connectomics arose just recently with the development of new three-dimensional-electron microscopy (EM) techniques and increasing computing power. So far, only a few model species (for example, mouse, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster) have been studied using this approach. Here, we present a first attempt to expand this circle to include pycnogonids, which hold a key position for the understanding of arthropod evolution. The visual neuropils in Achelia langi are studied using a focused ion beam-scanning electron microscope (FIB-SEM) crossbeam-workstation, and a three-dimensional serial reconstruction of the connectome is presented.The two eyes of each hemisphere of the sea spiders eye tubercle are connected to a first and a second visual neuropil. The first visual neuropil is subdivided in two hemineuropils, each responsible for one eye and stratified into three layers. Six different neuron types postsynaptic to the retinula (R-cells) axons are characterized by their morphology: five types of descending unipolar neurons and one type of ascending neurons. These cell types are also identified by Golgi impregnations. Mapping of all identifiable chemical synapses indicates that the descending unipolar neurons are postsynaptic to the R-cells and, hence, are second-order neurons. The ascending neurons are predominantly presynaptic and sometimes postsynaptic to the R-cells and may play a feedback role.Comparing these results with the compound eye visual system of crustaceans and insects - the only arthropod visual system studied so far in such detail - we found striking similarities in the morphology and synaptic organization of the different neuron types. Hence, the visual system of pycnogonids shows features of both chelicerate median and mandibulate lateral eyes.

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