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Appendage patterning in Acanthoscurria geniculata

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  • Appendage patterning in Acanthoscurria geniculata

    An interesting one

    Pechmann, M. & Nikola-Michael Prpic (2009) Appendage patterning in the South American bird spider Acanthoscurria geniculata (Araneae: Mygalomorphae), Development Genes and Evolution, Electronically published 6th March 2009 [ahead of print].

    Abstract :
    Pattern formation by the genes dachshund (dac), Distal-less (Dll), extradenticle (exd) and homothorax (hth) in spider appendages has been studied previously only in members of the higher spiders (Araneomorphae). In order to study the diversity and conservation of pattern formation in spiders as a whole, we studied homologs of these genes in embryos of the bird spider Acanthoscurria geniculata, which belongs to the Mygalomorphae, a more primitive spider group. We show that the patterns of dac and Dll are largely conserved in all spiders studied so far. We find a duplication of hth and exd genes as previously identified in the higher spider Cupiennius salei. These data suggest that pattern formation shows little diversity in all spiders, including the duplication of hth and exd that likely occurred before the split of Mygalomorphae and Araneomorphae. We also find that the legs and pedipalps bear endites of which only the pedipalpal endite expresses Dll and is retained in the adult. Similarly, the limb buds of the posterior spinnerets express Dll and become segmented appendages in the adult, whereas the anterior spinnerets lack Dll expression and are absent in postembryonic stages. In both cases, the expression of Dll or the lack of it indicates structures which will be retained as adult traits or rudimentary structures that degenerate, respectively. The presence of embryonic rudiments of leg endites in Acanthoscurria and the leg-like pattern formation in the posterior spinnerets are interpreted as primitive traits that have been lost in the Araneomorphae.

    Open access and freely available here

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  • #2
    The term "conserved" would have been better than "primitive" [grhh pet hate time...]

    Theraphosids and mygalomorphs are no more primitive than any other extant species on the tree of life.

    By that reasoning we're all primitive to a chromosomally well-endowed waterlily

    Richard

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    • #3
      Puts a bit of a damper on Myrmecia pilosula too, bearing in mind that females have only one pair of chromosomes (males in common with other Hymenoptera are haploid)

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