Embryo Production in a Parthenogenetic Snail (Potamopyrgus antipodarum) is Negatively Affected by the presence of Other Parthenogenetic Females.’ Invertebrate Biology 125

Abstract. Stimuli associated with copulatory behavior are often needed to maximize repro-ductive output in internally fertilized sexual taxa. Although non-pseudogamous partheno-genetic females have no need for sperm, parthenogens descended from sexual ancestors may still require copulatory stimuli to reach their full reproductive potential. Retention of phys-iological dependence on copulation in parthenogens could facilitate the maintenance of sexual reproduction in species where sexual and parthenogenetic individuals coexist if par-thenogens do not receive enough copulatory stimuli to achieve maximal daughter production. A laboratory experiment was conducted to determine whether embryo production in par-thenogenetic female snails (Potamopyrgus antipodarum) is dependent on male presence. Rath-er than male presence, this experiment showed that embryo production is affected by the number of coexisting parthenogens. Specifically, parthenogens housed with fewer other par-thenogens produced significantly more embryos than parthenogens housed with a greater number of other parthenogens, regardless of male presence and total population size. This result indicates that copulatory dependence is not likely to contribute to the maintenance of sex in P. antipodarum. Instead, it demonstrates that females of P. antipodarum negativel