The Oldest Horseshoe Crab: A New Xiphosurid From Late Ordovician Konservat‐lagerstätten Deposits, Manitoba, Canada

Rudkin, David M.; Young, Graham; Nowlan, Godfrey S.

doi:10.1111/j.1475-4983.2007.00746.x

Cited by 144 publications

(89 citation statements)

References 35 publications

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“…The animal is identified as a "living fossil" because anatomically similar forms have been found as fossils from 445 million years ago 27 . The horseshoe crab represents a long-lived animal, requiring 10 -13 years to reach maturity and living at least 20 years 28 .…”

Section: Discussionmentioning

confidence: 99%

Blood collection from the American Horseshoe Crab, Limulus polyphemus

Armstrong

Conrad

2008

JoVE

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The horseshoe crab has the best-characterized immune system of any long-lived invertebrate. The study of immunity in horseshoe crabs has been facilitated by the ease in collecting large volumes of blood and from the simplicity of the blood. Horseshoe crabs show only a single cell type in the general circulation, the granular amebocyte. The plasma has the salt content of sea water and only three abundant proteins, hemocyanin, the respiratory protein, the C-reactive proteins, which function in the cytolytic destruction of foreign cells, including bacterial cells, and α2-macroglobulin, which inhibits the proteases of invading pathogens. Blood is collected by direct cardiac puncture under conditions that minimize contamination by lipopolysaccharide (a.k.a., endotoxin, LPS), a product of the Gram-negative bacteria. A large animal can yield 200 -400 mL of blood. For the study of the plasma, blood cells are immediately removed from the plasma by centrifugation and the plasma can then be fractionated into its constituent proteins. The blood cells are conveniently studied microscopically by collecting small volumes of blood into LPS-free isotonic saline (0.5 M NaCl) under conditions that permit direct microscopic examination by placing one of more LPS-free coverglasses on the culture dish surface, then mounting those coverglasses in simple observation chambers following cell attachment. A second preparation for direct observation is to collect 3 -5 mL of blood in a LPS-free embryo dish and then explanting fragments of aggregated amebocytes to a chamber that sandwiches the tissue between a slide and a coverglass. In this preparation, the motile amebocytes migrate onto the coverglass surface, where they can readily be observed. The blood clotting system involves aggregation of amebocytes and the formation of an extracellular clot of a protein, coagulin, which is released from the secretory granules of the blood cells. Biochemical analysis of washed blood cells requires that aggregation and degranulation does not occur, which can be accomplished by collecting blood into 0.1 volumes of 2% Tween-20, 0.5 M LPS-free NaCl, followed by centrifugation of the cells and washing with 0.5 M NaCl.

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Section: Discussionmentioning

confidence: 99%

Blood collection from the American Horseshoe Crab, Limulus polyphemus

Armstrong

Conrad

2008

JoVE

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“…Therefore, although the existence of a cumulus in myriapods continues to be unresolved (Brena and Akam, 2011), currently the most parsimonious explanation is that the cumulus evolved after the chelicerate-mandibulate split. However, as a migrating cumulus has also been described in a horseshoe crab (a marine group of chelicerates) (Sekiguchi, 1973), it is likely that this mode of development evolved very early in the chelicerate lineage (Redkin et al, 2008).…”

Section: The Segment Addition Zone: Insights Into Segmentationmentioning

confidence: 99%

Evolutionary crossroads in developmental biology: the spiderParasteatoda tepidariorum

2012

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SummarySpiders belong to the chelicerates, which is an arthropod group that branches basally from myriapods, crustaceans and insects. Spiders are thus useful models with which to investigate whether aspects of development are ancestral or derived with respect to the arthropod common ancestor. Moreover, they serve as an important reference point for comparison with the development of other metazoans. Therefore, studies of spider development have made a major contribution to advancing our understanding of the evolution of development. Much of this knowledge has come from studies of the common house spider, Parasteatoda tepidariorum. Here, we describe how the growing number of experimental tools and resources available to study Parasteatoda development have provided novel insights into the evolution of developmental regulation and have furthered our understanding of metazoan body plan evolution.

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“…385-392 Ma) to calibrate the origin of Amblypygi (i.e., the split from Uropygi), based on limb and cuticle fragments that include a patella with trichobothria, a character that occurs uniquely on legs 2-4 of modern amblypygids [34]; we employed a normal prior with a mean of 385 Ma and a standard deviation of 10 Myr. The origin of Xiphosura was calibrated using a normal prior with a mean of 445 Ma and a standard deviation of 10 Mya, based on the clear morphology of the Ordovician xiphosuran Lunataspis aurora [72]. The origin of spiders was calibrated with a normal prior with a mean of 386 Ma and a standard deviation of 10 Myr, based on recent reassessment of spigot morphology in the Middle Devonian fossil Attercopus fimbriunguis [43,44].…”

Section: Estimation Of Divergence Timesmentioning

confidence: 99%

Cross-bracing uncalibrated nodes in molecular dating improves congruence of fossil and molecular age estimates

Sharma

Wheeler

2014

Front Zool

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Introduction: The practice of molecular dating is an essential tool for hypothesis testing in evolutionary biology. Vagaries of fossilization and taphonomic bias commonly engender high uncertainty in molecular dating in taxonomic groups wherein few fossils can be unambiguously assigned to phylogenetic nodes. A recent and novel implementation in molecular dating, "cross-bracing", exploits gene duplications by formally linking calibrated node dates throughout the paralogous subtrees through hierarchical Bayesian models. An unexplored refinement of this method is cross-bracing nodes with unknown dates, in addition to calibrated nodes, such that all nodes representing the same cladogenetic events have linked priors. We applied such a refinement to molecular dating in chelicerates, one of the earliest groups of arthropods present in the fossil record, but whose molecular dating has been greatly inconsistent in the literature. We inferred divergence times using hemocyanin paralogs isolated from de novo assembled transcriptomic libraries, and multiple fossil calibrations. Results: We show that extending cross-bracing to uncalibrated nodes greatly reduced variance in estimates of divergence times throughout the phylogeny, particularly for estimated diversification ages of spiders and scorpions, whereas cross-bracing calibrated nodes alone did not affect age estimation for uncalibrated, derived clades. Comparing ages inferred with extended cross-bracing to the fossil record, we observe smaller gaps between diversification and the first appearance of crown group fossils than have previously been inferred, particularly for spiders. Our dating indicates that scorpions have a Silurian origin, but diversification of extant lineages occurred near the Triassic-Jurassic boundary, falsifying previous inference of Permian diversification age based on extant distribution alone. Conclusion: The significant reduction of variance in divergence time estimates upon extending cross-bracing to uncalibrated nodes makes this approach greatly suited for evolutionary inference in groups with poor fossil records, with particular reference to terrestrial arthropods.

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The Oldest Horseshoe Crab: A New Xiphosurid From Late Ordovician Konservat‐lagerstätten Deposits, Manitoba, Canada

Cited by 144 publications

References 35 publications

Blood collection from the American Horseshoe Crab, Limulus polyphemus

Blood collection from the American Horseshoe Crab, Limulus polyphemus

Evolutionary crossroads in developmental biology: the spiderParasteatoda tepidariorum

Cross-bracing uncalibrated nodes in molecular dating improves congruence of fossil and molecular age estimates

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