Variation in juvenile stages and success of male acquisition in Danish and French populations of the parasitic barnacle Sacculina carcini (Cirripedia: Rhizocephala) parasitizing the shore crab Carcinus maenas

Population and developmental characteristics of the rhizocephalan parasite Sacculina carcini were studied in the Limfjord, Denmark and at Roscoff, France. The frequency of juvenile externae in the Limfjord was higher during summer (69.8% of all externae) than during winter (43%). At Roscoff, 62.6% of externae were juvenile in May-June, but only 8.4% in September. The percentage of juveniles with settled males in the Limfjord was higher in summer (20.7% of all juveniles) compared to winter (6.7%). Juveniles at Roscoff in summer had less success in male acquisition (18.0%). The mean number of settled male cyprids per juvenile externa was 0.56 in summer and 0.12 during winter in the Limfjord, but only 0.27 in the summer at Roscoff. Laboratory kept virgin externae invaded by male cyprids ceased to attract additional males within 5–6 days after the first male settlement and then grew into adults within 3 weeks. Externae without males, kept in isolation, did not grow or show any other signs of maturation. Our results confirm and extend previous data on the role of males and their effect on externa development in S. carcini, and show that the success of male acquisition is susceptible to both seasonal and regional variation.

本研究针对丹麦利姆峡湾（Limfjord）与法国罗斯科夫（Roscoff）海域的根头目寄生虫（rhizocephalan parasite）蟹奴（Sacculina carcini）的种群特征与发育特性展开调查。利姆峡湾的幼体外突（externae）占比在夏季达所有外突的69.8%，显著高于冬季的43.0%；罗斯科夫海域则在5-6月有62.6%的外突为幼体，而9月该占比仅为8.4%。利姆峡湾中，携有定居雄体的幼体占所有幼体的比例在夏季为20.7%，高于冬季的6.7%；罗斯科夫夏季的幼体雄体定殖成功率仅为18.0%，相对偏低。利姆峡湾夏季每枚幼体外突的定居雄性腺介幼体（cyprids）平均数量为0.56，冬季为0.12；而罗斯科夫夏季该数值仅为0.27。实验室饲养的未交配外突在首次有雄性腺介幼体定殖后的5至6天内，便会停止吸引其他雄体，并于3周内发育为成体；单独饲养且未接触雄体的外突则无法生长，也未出现任何成熟相关的迹象。本研究结果验证并拓展了此前关于蟹奴（Sacculina carcini）雄体作用及其对外突发育影响的相关数据，同时证实雄体定殖成功率易受季节与区域差异的影响。