Hakoyama Hiroshi, Iwasa Yoh
Hokkaido National Fisheries Research Institute, Katsurakoi 116, Kushiro 085-0802, Japan.
J Theor Biol. 2004 Jan 21;226(2):185-94. doi: 10.1016/j.jtbi.2003.08.012.
An unisexual species (either parthenogenetic or gynogenetic form) often coexists sympatrically with a closely related anisogamous sexual species, forming a unisexual complex. This is puzzling because, all else being equal, a sexual population with the two-fold cost of sex (or the cost of producing males) cannot coexist with a unisexual population. This suggests that some ecological processes are at work to make possible the coexistence of the unisexual complex. Field and laboratory studies suggest that parasitism in a gynogenetic complex of the Japanese crucian carp (Carassius auratus) may play an important role in realizing the coexistence by giving frequency-dependent benefit to sexual population. Here, we study the simple dynamics of host-parasite interactions in which non-specific immune reaction of a sexual host is more effective than that of an unisexual host. We simply assume that the infective individuals are sterile. Stable coexistence of a unisexual species with their sexual relative is possible if pathogens are virulent and if the susceptibility of the unisexual form is more than twice as high as that of the sexual form. The coexistence is more difficult, when the fertility of males is relatively low in gynogenetic complexes. This implies that the coexistence of gynogenetic complexes is more difficult than that of parthenogenetic complexes in which parthenogenesis has no constraint on males. We conclude that parasitism is a promising candidate mechanism for the coexistence of unisexual complexes.
单性物种（孤雌生殖或雌核发育形式）通常与其密切相关的两性异体有性物种同域共存，形成单性复合体。这令人困惑，因为在其他条件相同的情况下，具有两倍性成本（或产生雄性的成本）的有性种群无法与单性种群共存。这表明一些生态过程在起作用，使得单性复合体的共存成为可能。野外和实验室研究表明，日本鲫鱼（Carassius auratus）雌核发育复合体中的寄生现象可能通过给予有性种群频率依赖的益处，在实现共存方面发挥重要作用。在这里，我们研究宿主 - 寄生虫相互作用的简单动态，其中有性宿主的非特异性免疫反应比单性宿主更有效。我们简单地假设感染个体是不育的。如果病原体具有毒性，并且单性形式的易感性比有性形式高两倍以上，单性物种与其有性近亲的稳定共存是可能的。当雌核发育复合体中雄性的繁殖力相对较低时，共存就更加困难。这意味着雌核发育复合体的共存比孤雌生殖复合体更困难，在孤雌生殖复合体中孤雌生殖对雄性没有限制。我们得出结论，寄生现象是单性复合体共存的一个有前景的候选机制。
