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First published online December 1, 2006
Journal of Experimental Biology 209, 4974-4983 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02586

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Males also have their time of the month! Cyclic disposal of old spermatophores, timed by the molt cycle, in a marine shrimp

Shmuel Parnes^*, Shaul Raviv^*, Asaf Shechter and Amir Sagi

Department of Life Sciences and National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, PO Box 653, Beer-Sheva 84105, Israel

Author for correspondence (e-mail: sagia{at}bgu.ac.il)

Accepted 5 October 2006

That sexually mature females go through hormonally regulated reproductive cycles is a well-established phenomenon in sexually reproducing organisms. Males, on the other hand, are commonly regarded as being continuously ready to mate. `Programmed sperm degradation' on a periodic basis or an innate sperm `expiry date' have never been shown. This manuscript describes a newly discovered molt-dependent mechanism by which old sperm is periodically removed from the reproductive system of male Litopenaeus vannamei shrimp. Firstly, it is shown that the spermatophores of males held in captivity become progressively melanized, a process that eventually renders them impotent. Then, by using melanin specks as a color marker, it is demonstrated that this phenomenon can be delayed and even reversed as long as the males remain sexually active. Lastly and most importantly, it is shown that male shrimp go through reproductive cycles that are strictly associated with their molt cycles, which, in turn, are hormonally regulated. Intact intermolt spermatophores disappeared about 12 h premolt, and a new pair of spermatophores appeared in the ampoules the day after the males had molted. This phenomenon was observed in an almost constant portion of males, both those in an all-male population and those in mixed male/female populations, even during the times that the females of those populations were not vitellogenically active. To the best of our knowledge, this is the first report of males of any animal species exhibiting endogenous reproductive cycles, as do females, and of the finding that spermatozoa have a predetermined expiry date, a feature that may possibly contribute to male fitness.

Key words: Litopenaeus vannamei, shrimp, male, female, sperm, spermatophore, melanization, mating system, impotency, sterility, molt cycle, reproductive cycle

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