Data from: Save your host, save yourself? caste-ratio adjustment in a parasite with division of labor and snail host survival following shell damage

Shell damage and parasitic infections are frequent in gastropods, influencing key snail host life-history traits such as survival, growth, and reproduction. However, their interactions and potential effects on hosts and parasites have never been tested. Host–parasite interactions are particularly interesting in the context of the recently discovered division of labor in trematodes infecting marine snails. Some species have colonies consisting of two different castes present at varying ratios; reproductive members and nonreproductive soldiers specialized in defending the colony. We assessed snail host survival, growth, and shell regeneration in interaction with infections by two trematode species, Philophthalmus sp. and Maritrema novaezealandense, following damage to the shell in the New Zealand mud snail Zeacumantus subcarinatus. We concomitantly assessed caste-ratio adjustment between nonreproductive soldiers and reproductive members in colonies of the trematode Philophthalmus sp. in response to interspecific competition and shell damage to its snail host. Shell damage, but not parasitic infection, significantly increased snail mortality, likely due to secondary infections by pathogens. However, trematode infection and shell damage did not negatively affect shell regeneration or growth in Z. subcarinatus; infected snails actually produced more new shell than their uninfected counterparts. Both interspecific competition and shell damage to the snail host induced caste-ratio adjustment in Philophthalmus sp. colonies. The proportion of nonreproductive soldiers increased in response to interspecific competition and host shell damage, likely to defend the parasite colony and potentially the snail host against increasing threats. These results indicate that secondary infections by pathogens following shell damage to snails both significantly increased snail mortality and induced caste-ratio adjustments in parasites. This is the first evidence that parasites with a division of labor may be able to produce nonreproductive soldiers according to environmental factors other than interspecific competition with other parasites.腹足类（gastropods）常出现壳体损伤与寄生虫感染，这类因素会影响宿主蜗牛关键的生活史性状，包括存活率、生长与繁殖能力。然而，二者的交互作用及其对宿主与寄生虫的潜在影响尚未得到验证。宿主-寄生虫交互作用在近期发现的寄生于海洋蜗牛的吸虫（trematodes）劳动分工这一背景下尤为引人关注。部分吸虫物种形成的群落存在两种不同品级，且二者占比存在差异：生殖个体与特化用于防御群落的非生殖兵个体。本研究以新西兰泥螺（Zeacumantus subcarinatus）为对象，针对其壳体受损后分别感染两种吸虫——嗜眼吸虫属未定种（Philophthalmus sp.）与新西兰微茎吸虫（Maritrema novaezealandense）——的情况，评估了宿主蜗牛的存活率、生长速率与壳体再生能力。同时，本研究还探究了在种间竞争与宿主壳体受损的刺激下，嗜眼吸虫属未定种群落中非生殖兵个体与生殖个体的品级比例调控情况。研究结果显示，仅壳体损伤（而非寄生虫感染）会显著提升蜗牛的死亡率，这一现象可能由病原体引发的继发感染所致。不过，吸虫感染与壳体损伤并未对新西兰泥螺的壳体再生或生长造成负面影响；受感染的蜗牛实际较未感染个体产生了更多的新生壳体。无论是种间竞争还是宿主壳体受损，均会诱导嗜眼吸虫属未定种群落发生品级比例调整：非生殖兵个体的占比显著升高，以应对日益加剧的威胁，从而保护寄生虫群落乃至其蜗牛宿主。本研究结果表明，蜗牛壳体受损后引发的病原体继发感染，既显著提升了宿主蜗牛的死亡率，同时也诱导了寄生虫的品级比例调控。这是首个证据表明，具备劳动分工的寄生虫可依据除种间竞争之外的环境因素，生成非生殖兵个体。