The Middle Cambrian fossil Pikaia and the evolution of chordate swimming

Conway Morris and Caron (2012) have recently published an account of virtually all the available information on Pikaia gracilens, a well-known Cambrian fossil and supposed basal chordate, and propose on this basis some new ideas about Pikaia’s anatomy and evolutionary significance. Chief among its chordate-like features are the putative myomeres, a regular series of vertical bands that extends the length of the body. These differ from the myomeres of living chordates in that boundaries between them (the myosepta) are gently curved, with minimal overlap, whereas amphioxus and vertebrates have strongly overlapping V- and W-shaped myomeres. The implication, on biomechanical grounds, is that myomeres in Pikaia exerted much less tension on the myosepta, so the animal would have been incapable of swimming as rapidly as living chordates operating in the fast-twitch mode used for escape and attack. Pikaia either lacked the fast-twitch fibers necessary for such speeds, having instead only slow-twitch fibers, or it had an ancestral fiber type with functional capabilities more like modern slow fibers than fast ones. The first option is supported by the sequence of development in zebrafish, where both myoseptum formation and fast fiber deployment show a dependence on slow fibers, which develop first. For Pikaia, the absence of fast fibers has both behavioral and anatomical implications, which are discussed. Among the latter is the possibility that a notochord may not have been needed as a primary stiffening device if other structures (for example, the dorsal organ) could perform that role

Phased Helical Antenna Array for CubeSat Application

CubeSats communication links are typically slow due to their power and size restrictions. However, a low power, high speed down link connection can allow for greater data collection and relaying, pushing the capability of 1U CubeSats beyond what is traditionally thought possible. Investigated here is the feasibility of a 11 Mb/s down link connection on a 1U CubeSat, accomplished via 2x2 helical antenna phased array operating on the 802.11 standard. Using a phased array also allows for beam steering to secure connection with the ground station when the on board ADCS may not provide precise pointing capability of the CubeSat, as 1U systems often do not

Community Property—Characterization of the Inflationary Increase in the Value of Separate Property Improved by Community Funds—In re Marriage of Elam, 97 Wn. 2d 811, 650 P.2d 213 (1982)

The Washington Supreme Court held that: (1) the increase in value of separate property is presumptively separate, unless the community claimant rebuts the presumption by direct and positive proof that community contributions caused the increase, and (2) the community is entitled to a share of the inflationary increase in the value of the separate property proportionate to the community contributions

A hexamer origin of the echinoderms' five rays

Of the major deuterostome groups, the echinoderms with their multiple forms and complex development are arguably the most mysterious. Although larval echinoderms are bilaterally symmetric, the adult body seems to abandon the larval body plan and to develop independently a new structure with different symmetries. The prevalent pentamer structure, the asymmetry of Loven's rule and the variable location of the periproct and madrepore present enormous difficulties in homologizing structures across the major clades, despite the excellent fossil record. This irregularity in body forms seems to place echinoderms outside the other deuterostomes. Here I propose that the predominant five-ray structure is derived from a hexamer structure that is grounded directly in the structure of the bilaterally symmetric larva. This hypothesis implies that the adult echinoderm body can be derived directly from the larval bilateral symmetry and thus firmly ranks even the adult echinoderms among the bilaterians. In order to test the hypothesis rigorously, a model is developed in which one ray is missing between rays IV-V (Loven's schema) or rays C-D (Carpenter's schema). The model is used to make predictions, which are tested and verified for the process of metamorphosis and for the morphology of recent and fossil forms. The theory provides fundamental insight into the M-plane and the Ubisch', Loven's and Carpenter's planes and generalizes them for all echinoderms. The theory also makes robust predictions about the evolution of the pentamer structure and its developmental basis. *** including corrections (see footnotes) ***Comment: 10 pages, 6 figure

Spatial and spatiotemporal pattern formation in generalised Turing systems

Reaction-diffusion, or Turing, models have been proposed to account for a number of pattern formation phenomena in early development. However, there are a number of crucial morphogenetic phenomena that contradict the standard Turing model. Here we review three generalisations of the Turing model and show how they can be applied to two such phenomena. We discuss how these generalisations can provide insight to the processes underlying patterning in these cases

On the Origin and Evolution of Vertebrate Olfactory Receptor Genes: Comparative Genome Analysis Among 23 Chordate Species

Olfaction is a primitive sense in organisms. Both vertebrates and insects have receptors for detecting odor molecules in the environment, but the evolutionary origins of these genes are different. Among studied vertebrates, mammals have ∼1,000 olfactory receptor (OR) genes, whereas teleost fishes have much smaller (∼100) numbers of OR genes. To investigate the origin and evolution of vertebrate OR genes, I attempted to determine near-complete OR gene repertoires by searching whole-genome sequences of 14 nonmammalian chordates, including cephalochordates (amphioxus), urochordates (ascidian and larvacean), and vertebrates (sea lamprey, elephant shark, five teleost fishes, frog, lizard, and chicken), followed by a large-scale phylogenetic analysis in conjunction with mammalian OR genes identified from nine species. This analysis showed that the amphioxus has >30 vertebrate-type OR genes though it lacks distinctive olfactory organs, whereas all OR genes appear to have been lost in the urochordate lineage. Some groups of genes (θ, κ, and λ) that are phylogenetically nested within vertebrate OR genes showed few gene gains and losses, which is in sharp contrast to the evolutionary pattern of OR genes, suggesting that they are actually non-OR genes. Moreover, the analysis demonstrated a great difference in OR gene repertoires between aquatic and terrestrial vertebrates, reflecting the necessity for the detection of water-soluble and airborne odorants, respectively. However, a minor group (β) of genes that are atypically present in both aquatic and terrestrial vertebrates was also found. These findings should provide a critical foundation for further physiological, behavioral, and evolutionary studies of olfaction in various organisms