A nudibranch removes rival sperm with a disposable spiny penis

Ayami Sekizawa, Shin G. Goto, Yasuhiro Nakashima

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Simultaneous hermaphroditism is, at least initially, favoured by selection under low density — and therefore it can be assumed that sperm competition has little importance in this sexual system. However, many simultaneously hermaphroditic nudibranchs have both an allo-sperm storage organ (the seminal receptacle) and an allo-sperm digesting organ (the copulatory bursa), suggesting the possibility of the occurrence of sperm competition. A nudibranch, Chromodoris reticulata, autotomizes its penis after every copulation and replenishes it within about 24 h to perform another copulation. We observed that the surface of the autotomized penis was covered with many backward-pointing spines and that a sperm mass was often entangled on the spines. This suggests that the nudibranch removes sperm that is already stored in a mating partner’s sperm storage organ(s) with its thorny penis. Using six microsatellite markers, we determined that the sperm mass attached to the penis were allo-sperm originating from individual(s) that had participated in prior copulations. We revealed that C. reticulata performed sperm removal using the thorny penis. These results suggest that competition in fertilization is quite intense and mating frequency in the wild is relatively high in this species.

Original languageEnglish
Pages (from-to)21-29
Number of pages9
JournalJournal of Ethology
Issue number1
Publication statusPublished - 2019 Jan 22


  • Nudibranch
  • Sexual selection
  • Simultaneous hermaphrodite
  • Sperm competition
  • Sperm removal

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology


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