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Related Experiment Videos

Evolution: One Penis After All.

Patricia L R Brennan1

  • 1Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, and Division of Organismal and Evolutionary Biology, University of Massachusetts Amherst, Amherst, MA 01003, USA.

Current Biology : CB
|January 15, 2016
PubMed
Summary
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The tuatara, a reptile lacking a penis, shows embryonic genital swellings. This discovery suggests a single evolutionary origin for amniote penises, challenging previous theories of multiple origins.

Area of Science:

  • Evolutionary biology
  • Comparative anatomy
  • Herpetology

Background:

  • Amniote reproductive anatomy exhibits diverse penile structures.
  • The absence of a penis in the basal tuatara (Sphenodon) has historically suggested multiple independent evolutionary origins.
  • Understanding the evolutionary trajectory of reproductive organs is crucial for amniote phylogeny.

Purpose of the Study:

  • To investigate the embryonic development of reproductive structures in the tuatara.
  • To re-evaluate the evolutionary history of the amniote penis based on new developmental data.
  • To determine if the tuatara's reproductive morphology supports a single or multiple origins of the penis.

Main Methods:

  • Embryonic examination of tuatara (Sphenodon) specimens.

Related Experiment Videos

  • Comparative analysis of reproductive tissue development across amniote groups.
  • Histological and morphological assessment of embryonic genital structures.

    • Main Results:

    • Genital swellings, precursors to phallic structures, were identified in tuatara embryos.
    • These embryonic structures indicate a conserved developmental pathway for amniote reproductive organs.
    • The presence of these swellings challenges the notion that tuatara represent a lineage that completely lost the penis.

    Conclusions:

    • The findings support a single, ancestral origin for the amniote penis.
    • The tuatara's reproductive morphology is consistent with a secondary loss or significant modification rather than a complete absence from the evolutionary lineage.
    • This study provides critical evidence for the unified evolutionary history of amniote reproductive organs.