Muschiol Daniel, Schroeder Fabian, Traunspurger Walter
Animal Ecology, University Bielefeld, Morgenbreede 45, 33615 Bielefeld, Germany.
BMC Ecol. 2009 May 16;9:14. doi: 10.1186/1472-6785-9-14.
The free-living nematode Caenorhabditis elegans is the predominant model organism in biological research, being used by a huge number of laboratories worldwide. Many researchers have evaluated life-history traits of C. elegans in investigations covering quite different aspects such as ecotoxicology, inbreeding depression and heterosis, dietary restriction/supplement, mutations, and ageing. Such traits include juvenile growth rates, age at sexual maturity, adult body size, age-specific fecundity/mortality, total reproduction, mean and maximum lifespan, and intrinsic population growth rates. However, we found that in life-cycle experiments care is needed regarding protocol design. Here, we test a recently developed method that overcomes some problems associated with traditional cultivation techniques. In this fast and yet precise approach, single individuals are maintained within hanging drops of semi-fluid culture medium, allowing the simultaneous investigation of various life-history traits at any desired degree of accuracy. Here, the life cycles of wild-type C. elegans strains N2 (Bristol, UK) and MY6 (Münster, Germany) were compared at 20 degrees C with 5 x 10(9) Escherichia coli ml-1 as food source.
High-resolution life tables and fecundity schedules of the two strains are presented. Though isolated 700 km and 60 years apart from each other, the two strains barely differed in life-cycle parameters. For strain N2 (n = 69), the intrinsic rate of natural increase (r m d(-1)), calculated according to the Lotka equation, was 1.375, the net reproductive rate (R 0) 291, the mean generation time (T) 90 h, and the minimum generation time (T min) 73.0 h. The corresponding values for strain MY6 (n = 72) were r m = 1.460, R0 = 289, T = 84 h, and T min = 67.3 h. Peak egg-laying rates in both strains exceeded 140 eggs d(-1). Juvenile and early adulthood mortality was negligible. Strain N2 lived, on average, for 16.7 d, while strain MY6 died 2 days earlier; however, differences in survivorship curves were statistically non-significant.
We found no evidence that adaptation to the laboratory altered the life history traits of C. elegans strain N2. Our results, discussed in the light of earlier studies on C. elegans, demonstrate certain advantages of the hanging drop method in investigations of nematode life cycles. Assuming that its reproducibility is validated in further studies, the method will reduce the inter-laboratory variability of life-history estimates and may ultimately prove to be more convenient than the current standard methods used by C. elegans researchers.
自由生活的线虫秀丽隐杆线虫是生物学研究中的主要模式生物，被全球众多实验室所使用。许多研究人员在涵盖生态毒理学、近亲繁殖衰退与杂种优势、饮食限制/补充、突变和衰老等截然不同方面的研究中评估了秀丽隐杆线虫的生活史特征。这些特征包括幼虫生长速率、性成熟年龄、成虫体型、特定年龄的繁殖力/死亡率、总繁殖量、平均和最大寿命以及内在种群增长率。然而，我们发现，在生命周期实验中，方案设计需要谨慎。在此，我们测试了一种最近开发的方法，该方法克服了一些与传统培养技术相关的问题。在这种快速且精确的方法中，单个个体被维持在半流体培养基的悬滴中，从而能够以任何所需的精度同时研究各种生活史特征。在此，在20摄氏度下，以每毫升5×10⁹个大肠杆菌作为食物来源，比较了野生型秀丽隐杆线虫品系N2（英国布里斯托尔）和MY6（德国明斯特）的生命周期。
呈现了两个品系的高分辨率生命表和繁殖力时间表。尽管这两个品系彼此相隔700公里且分离了60年，但它们在生命周期参数上几乎没有差异。对于品系N2（n = 69），根据洛特卡方程计算的自然增长内在速率（rm d⁻¹）为1.375，净繁殖率（R₀）为291，平均世代时间（T）为90小时，最小世代时间（Tmin）为73.0小时。品系MY6（n = 72）的相应值为rm = 1.460，R₀ = 289，T = 84小时，Tmin = 67.3小时。两个品系的产卵峰值速率均超过140个卵/天。幼虫和成年早期的死亡率可忽略不计。品系N2平均存活16.7天，而品系MY6提前2天死亡；然而，存活曲线的差异在统计学上不显著。
我们没有发现证据表明适应实验室环境改变了秀丽隐杆线虫品系N2的生活史特征。我们根据早期对秀丽隐杆线虫的研究讨论了我们的结果，证明了悬滴法在研究线虫生命周期方面的某些优势。假设其可重复性在进一步研究中得到验证，该方法将减少实验室间生活史估计的变异性，并且最终可能被证明比秀丽隐杆线虫研究人员目前使用的标准方法更方便。
