Sex-role reversal of a monogamous pipefish without higher potential reproductive rate in females

Atsushi Sogabe, Yasunobu Yanagisawa

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19 Citations (Scopus)


In monogamous animals, males are usually the predominant competitors for mates. However, a strictly monogamous pipefish Corythoichthys haematopterus exceptionally exhibits a reversed sex role. To understand why its sex role is reversed, we measured the adult sex ratio and the potential reproductive rate (PRR), two principal factors influencing the operational sex ratio (OSR), in a natural population of southern Japan. The adult sex ratio was biased towards females throughout the breeding season, but the PRR, which increased with water temperature, did not show sexual difference. We found that an alternative index of the OSR (Sf/Sm: sex ratio of 'time in') calculated from the monthly data was consistently biased towards females. The female-biased OSR associated with sex-role reversal has been reported in some polyandrous or promiscuous pipefish, but factors biasing the OSR differed between these pipefish and C. haematopterus. We concluded that the similar PRR between the sexes in C. haematopterus does not confer reproductive benefit of polygamous mating on either sex, resulting in strict monogamous mating, and its female-biased adult sex ratio promotes female-female competition for a mate, resulting in sex-role reversal.

Original languageEnglish
Pages (from-to)2959-2963
Number of pages5
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1628
Publication statusPublished - 2007 Dec 7
Externally publishedYes


  • Corythoichthys haematopterus
  • Monogamy
  • Operational sex ratio
  • Potential reproductive rate
  • Sex-role reversal
  • Syngnathidae

ASJC Scopus subject areas

  • Immunology and Microbiology(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Environmental Science(all)
  • Agricultural and Biological Sciences(all)


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