休眠卵孵化对策与食物浓度对萼花臂尾轮虫(Brachionus calyciflorus)两品系干雌体种群增长的影响

周期性孤雌繁殖的轮虫靠休眠卵度过不良环境，等环境适宜时休眠卵孵化出干雌体，再次通过孤雌繁殖建立种群。通常休眠卵要经历一段休眠期再孵化，但也有些休眠卵生成后很快孵化，称为早孵化现象。有关休眠卵不同孵化对策如何影响其干雌体克隆种群的增长，目前尚不清楚。分别观测了萼花臂尾轮虫（Brachionus calyciflorus）的两个品系H1（窄温度生态位）和D1（宽温度生态位）的休眠卵在不同孵化对策和不同食物浓度下所生产的干雌体克隆群的种群增长差异。孵化对策包括早孵化（early hatching，EH）和晚孵化（late hatching，LH）；食物浓度包括高食物浓度（high food concentration，HF：2×10⁶个细胞/mL）和低食物浓度（low food concentration，LF：5×10⁵个细胞/mL），每个品系下各设置4个实验组（LH-HF、LH-LF、EH-HF、EH-LF），每组10个重复。结果发现，对D1品系来说：孵化对策和食物浓度对最大种群数量具有显著的综合影响（P=0.002），但两因素间不存在交互作用（P=0.911）；早孵化的干雌体种群在最大种群数量上显著高于晚孵化的干雌体种群（P=0.001）。对H1品系：孵化对策和食物浓度对最大种群数量综合影响显著（P<0.001），且两个因素之间存在交互作用（P<0.001）；高食物浓度下，EH干雌体克隆群的最大种群数量显著低于LH干雌体克隆群（P<0.001）。高食物浓度下干雌体克隆群开始有性生殖的密度阈值，D1品系EH组显著高于LH组（P=0.041）；而H1品系EH组却显著低于LH组（P=0.022）。最高种群密度下，H1品系的有性生殖率在两种孵化对策之间存在显著差异（P=0.044），EH种群的有性生殖率低于LH种群，而D品系却未见有性生殖率在不同孵化对策间存在明显差异。本研究结果显示休眠卵的孵化对策会影响其后代干雌体种群的增长特性，其影响的结果可能与种群的生境适应相关。

Effect of hatching strategy and food concentration on the stem female's population growth in two strains of the rotifer Brachionus calyciflorus

Rotifers with cyclical parthenogenesis produce resting eggs to cope with adverse environments. It is generally assumed that resting eggs remain in dormancy until the environment is suitable, and then the hatched stem females establish new populations through parthenogenetic reproduction. However, it has been noticed that some resting eggs hatch soon after being produced, known as early hatching phenomenon. It remains unclear if different hatching strategies may affect growth of the stem female''s clone populations. This study investigated the effect of hatching strategy and food concentration on growth of the stem female''s clone populations generated from strain D1 (strain with wide temperature niche) and H1 (strain with narrow temperature niche), of the rotifer Brachionus calyciflorus. We set two hatching strategies (early hatching (EH) vs. late hatching (LH)) and two food concentrations (high food concentration (HF, 2×10⁶ cells/mL) vs. low food concentration (LF, 5×10⁵ cells/mL))in the treatment, generated four experimental groups (LH-HF, LH-LF, EH-HF, and EH-LF) for each strain. Each experimental group included ten replicates. Two way ANOVA results showed that in D1 strain, hatching strategy and food concentration had significant impacts on the maximum population size (P=0.002), but there was no interaction between the two factors (P=0.911). The maximum population number of EH group was significantly higher than that of LH group (P=0.001). In H1 strain, the above two factors also showed significant influence on the maximum population number (P<0.001), but there existed interaction between the two factors (P<0.001). In HF groups that food concentration was not the limiting factor, the maximum population number of group EH was significantly lower than that of LH (P<0.001), which differed with D1. Under high food concentration, the population density threshold for trigging sexual reproduction in D1 EH group was significantly higher than that in LH group (P=0.041). In H1, however, it was on the contrary (P=0.022). In H1, the sexual reproduction rate under peak population density of EH group was significantly lower than that of LH group (P=0.044), while no such difference was observed in D1. In brief, hatching strategy of resting eggs affected growth of the stem female clone population in different ways, which may due to adaptation to their natural habitats.