Female octopuses are thought to copulate with multiple males and store sperm for months prior to spawning, a generalization that has led to hypotheses of strong sperm competition throughout the family. Their diversity, and the difficulty in observing many octopus species in the wild, force indirect tests of this generalization. Male reproductive effort, already high in these generally semelparous animals, is predicted to increase further with sperm competition. Hypothesized functional constraints on the spermatophores that males build to transfer sperm could mean that selection impacts spermatophore number more than morphology. To test whether the number of spermatophores could indicate differences in octopodid biology, the greatest number of spermatophores carried by one individual, and longest spermatophore and mantle lengths were compiled for 74 species. Differences in number were predicted to be independent of differences in specimen availability, related species were predicted to have similar counts, and counts were predicted to be largely independent of spermatophore and mantle length. The median spermatophore count was 24; nearly one-third of the species had 60 or more spermatophores. Of these, 16 were species of Eledone, Octopus (Octopus) or Abdopus, supporting the hypothesis that related species share similar spermatophore counts; relationships of the other species are poorly known. Spermatophores of these 24 species tended to be slightly shorter relative to mantle length than in the family as a whole. Callistoctopus spp. carry nine or fewer spermatophores, as do deep-sea species of Bathypolypus, and the Southern Ocean endemic and deep-sea octopus clade. The number of specimens did not differ between species with fewer or more than the median number. Differences in spermatophore counts among species may offer insight into male response to sperm competition and the unsuspected diversity of reproductive behavior in benthic octopods.
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Vol. 51 • No. 1