Data from: Sperm competition, but not major histocompatibility divergence, drives differential fertilization success between alternative reproductive tactics in Chinook salmon

Post-copulatory sexual selection processes, including sperm competition and cryptic female choice (CFC), can operate based on major histocompatibility (MH) genes. We investigated sperm competition between male alternative reproductive tactics [jack (sneaker) and hooknose (guard)] of Chinook salmon (Oncorhynchus tshawytscha). Using a full factorial design, we examined in vitro competitive fertilization success of paired jack and hooknose males at three time points after sperm activation (0, 15 and 60 s) to test for male competition, CFC and time effects on male fertilization success. We also examined egg-mediated CFC at two MH genes by examining both the relationship between competitive fertilization success and MH divergence as well as inheritance patterns of MH alleles in resulting offspring. We found that jacks sired more offspring than hooknose males at 0 s post-activation; however, jack fertilization success declined over time post-activation, suggesting a trade-off between sperm speed and longevity. Enhanced fertilization success of jacks (presumably via higher sperm quality) may serve to increase sneaker tactic competitiveness relative to dominant hooknose males. We also found evidence of egg-mediated CFC (i.e. female × male interaction) influencing competitive fertilization success; however, CFC was not acting on the MH genes as we found no relationship between fertilization success and MH II β1 or MH I α1 divergence and we found no deviations from Mendelian inheritance of MH alleles in the offspring. Our study provides insight into evolutionary mechanisms influencing variation in male mating success within alternative reproductive tactics, thus underscoring different strategies that males can adopt to attain success.

交配后性选择过程，包括精子竞争与隐性雌性选择（cryptic female choice, CFC），可基于主要组织相容性（major histocompatibility, MH）基因发挥作用。本研究针对奇努克鲑（Oncorhynchus tshawytscha）的两类雄性替代生殖策略个体——偷精雄鱼（jack，sneaker）与护巢雄鱼（hooknose，guard）——之间的精子竞争展开了研究。本研究采用完全析因设计，在精子激活后的三个时间节点（0秒、15秒与60秒）下，检测配对的偷精雄鱼与护巢雄鱼的体外竞争性受精成功率，以此检验雄性竞争、隐性雌性选择以及时间效应对雄性受精成功率的影响。我们还通过分析竞争性受精成功率与MH基因分化程度之间的关联，以及子代中MH等位基因的遗传模式，探究了卵介导的隐性雌性选择在两类MH基因上的作用。研究结果显示，在精子激活后0秒时，偷精雄鱼产下的子代数量多于护巢雄鱼；但随着激活后时间推移，偷精雄鱼的受精成功率逐渐下降，这表明精子速度与寿命之间存在权衡关系。偷精雄鱼受精成功率的提升（推测源于更高的精子质量），或可增强其相较于优势护巢雄鱼的偷精策略竞争力。我们还发现了卵介导的隐性雌性选择（即雌性×雄性互作）影响竞争性受精成功率的证据；但隐性雌性选择并未作用于MH基因：我们未发现受精成功率与MH II β1或MH I α1基因分化程度之间存在关联，且子代中MH等位基因的遗传模式未偏离孟德尔遗传规律。本研究揭示了影响雄性替代生殖策略内交配成功率变异的进化机制，从而凸显了雄性为达成繁殖成功可采取的不同策略。