Olsen Kevin C, Escareno Medina Luis D, Barreto Felipe S, Edmands Suzanne, Burton Ronald S
Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, United States.
Department of Integrative Biology, Oregon State University, Corvallis, OR, United States.
J Hered. 2025 Mar 1;116(2):159-169. doi: 10.1093/jhered/esae039.
Inbreeding and outbreeding depression are dynamic forms of selection critical to mating system evolution and the efficacy of conservation biology. Most evidence on how the relative severity and timing of these forces are shaped is confined to self-fertilization, distant outcrossing, and intermediate "optimal outcrossing" in hermaphrodites. We tested the notion that closed population demographics may reduce and delay the costs of inbreeding relative to distant outbreeding in an intertidal copepod with separate sexes and a biphasic larval/post-metamorphic life history (Tigriopus californicus). At three lifecycle stages (fecundity, metamorphosis, and post-metamorphosis), we quantified the effects of inbreeding and outbreeding in crosses with varying degrees of recent common ancestry. Although inbreeding and outbreeding depression have distinct genetic mechanisms, both manifested the same stage-specific consequences for fitness. Inbreeding and outbreeding depression were not apparent for fecundity, post-metamorphic survival, sex ratio, or the ability to acquire mates, but inbreeding between full siblings and outbreeding between interpopulation hybrids reduced the fraction of offspring that completed metamorphosis by 32% and 47%, respectively. On average, the effects of inbreeding on metamorphic rate were weaker and nearly twice as variable among families than those of outbreeding, suggesting genetic load was less pervasive than the incompatibilities accrued between divergent populations. Overall, our results indicate the transition from larval to juvenile life stages is markedly susceptible to both inbreeding and outbreeding depression in T. californicus. We suggest stage-specific selection acting concurrently with the timing of metamorphosis may be an instrumental factor in shaping reproductive optima in species with complex life histories.
近亲繁殖衰退和远交衰退是对交配系统进化和保护生物学功效至关重要的动态选择形式。关于这些作用力的相对严重程度和发生时间是如何形成的，大多数证据仅限于雌雄同体生物中的自花受精、远缘杂交和中间的“最佳异交”。我们测试了这样一种观点，即在具有雌雄异体和双相幼体/变态后生活史的潮间带桡足类动物（加州虎斑猛水蚤）中，封闭种群的种群统计学特征可能会降低并延迟近亲繁殖相对于远缘杂交的成本。在三个生命周期阶段（繁殖力、变态和变态后），我们量化了不同程度近期共同祖先的杂交中近亲繁殖和远缘杂交的影响。尽管近亲繁殖衰退和远交衰退有不同的遗传机制，但两者对适合度都表现出相同的阶段特异性后果。繁殖力、变态后存活率、性别比例或获取配偶的能力方面，近亲繁殖衰退和远交衰退并不明显，但全同胞之间的近亲繁殖和种群间杂种之间的远缘杂交分别使完成变态的后代比例降低了32%和47%。平均而言，近亲繁殖对变态率的影响较弱，且在不同家族间的变异性几乎是远缘杂交的两倍，这表明遗传负荷不如不同种群间积累的不相容性普遍。总体而言，我们的结果表明，在加州虎斑猛水蚤中，从幼体到幼年期的转变对近亲繁殖衰退和远交衰退都非常敏感。我们认为，与变态时间同时起作用的阶段特异性选择可能是塑造具有复杂生活史物种繁殖最优策略的一个重要因素。
