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Female adders are known to mate with several males during the mating season. The presence of a copulatory plug, permitting only the first male to fertilize the eggs, has been reported. To test this paradox, female adders were mated under laboratory conditions with males carrying different, electrophoretically detectable markers. Females mated twice do produce bipaternal broods. Furthermore, single mated females can also produce multipaternal broods, showing that sperm from previous year(s) can be used.
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Stille et al. (1986) studied this question.
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