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Double spermatogenesis in Chelicerata.

Gerd Alberti1

  • 1Zoological Institute and Museum, University of Greifswald, Germany. alberti@uni-greifswald.de

Journal of Morphology
|November 19, 2004
PubMed
Summary
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Sperm dimorphism, involving fertilizing (eusperm) and nonfertilizing (parasperm) cells, is rare in Chelicerata, found in the opilionid genus Siro. These aflagellate sperm cells form ordered sperm balls, offering insights into arachnid reproductive biology.

Area of Science:

  • Arachnology
  • Reproductive Biology
  • Cell Biology

Background:

  • Sperm dimorphism is a rare phenomenon in Chelicerata, previously documented only in three species of the opilionid genus Siro.
  • Fertilizing (eusperm) and nonfertilizing (parasperm) spermatozoa develop as sister cells within the same cyst.

Purpose of the Study:

  • To examine and compare the fine structure of spermatozoa in two species of the genus Siro.
  • To investigate the implications of sperm dimorphism in Siro for understanding other enigmatic morphological characters in arachnids, such as accessory genital glands.

Main Methods:

  • Transmission electron microscopy was used to examine the fine structure of Siro spermatozoa.
  • Comparative analysis of sperm morphology between Siro rubens and Siro duricorius.

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  • Review of existing literature and integration of new findings on sperm dimorphism in Chelicerata.

    • Main Results:

    • Spermatozoa of Siro species are aflagellate, lacking a typical flagellum and acrosomal complex (notably in S. duricorius).
    • Both eusperm and parasperm develop a transient transitional process before becoming aflagellate.
    • Highly ordered sperm balls composed of both sperm types are formed and stored in the deferent duct.

    Conclusions:

    • Sperm dimorphism in Siro provides a model for understanding germ cell development dichotomy.
    • Accessory genital glands in Uropygi and Amblypygi may represent modified, degenerated germ cell derivatives, analogous to parasperm.
    • This study contributes to the ongoing debate on the phylogenetic relationships between Uropygi, Amblypygi, and Araneae.