Al-Jahdali Mohammed O
Biological Sciences Department, Rabigh-Faculty of Science and Arts, King Abdulaziz University, Rabigh 21911, Saudi Arabia.
J Helminthol. 2012 Sep;86(3):378-85. doi: 10.1017/S0022149X11000551. Epub 2011 Sep 26.
Factors regulating gastrointestinal nematode infrapopulations are to a great extent density-dependent. Here, 23 natural infrapopulations (41-281 individuals) of the viviparous nematode Procamallanus elatensis (Camallanidae) from the fish Siganus rivulatus were found distributed in a well-defined fundamental niche (posterior 55% of the intestine). Immature worms were mostly found in the anterior third of this niche, while mature worms were found in aggregations posterior to them and followed by gravid females in the posterior 20% of the intestine. This distribution strongly suggests that worms migrate towards the posterior intestine while they mature, copulate and reproduce. In small infrapopulations, the sex ratios were distinctly female-biased and the number of gravid females was low. In large infrapopulations, the sex ratios were distinctly male-biased and the number of gravid females was high. However, the mean lengths of both immature males and females and mature females decreased dramatically as the infrapopulation size increased, while those of mature males increased significantly. These results strongly suggest intraspecific competition and density-dependent regulation of mean worm length, and the increase in the mean length of mature males strongly suggests intense sexual selection and competition between mature males. Production of larvae by female worms decreased significantly as the infrapopulation size increased, suggesting a density-dependent reduction in female worm fertility. The results are statistically significant and strongly suggest that infrapopulation self-regulation is through density-dependent mechanisms, in which development of immature worms, infrapopulation size, sex ratio, sexual selection and carrying capacity of the fundamental niche play essential roles in shaping and regulating the infrapopulations.
调节胃肠道线虫种群内数量的因素在很大程度上是密度依赖性的。在这里，发现来自细纹篮子鱼的胎生线虫艾氏原驼形线虫（驼形科）的23个自然种群内数量（41 - 281个个体）分布在一个明确界定的基础生态位（肠道后55%）中。未成熟的线虫大多分布在该生态位的前三分之一处，而成熟线虫聚集在其后，随后是妊娠雌虫，分布在肠道的后20%处。这种分布强烈表明，线虫在成熟、交配和繁殖过程中会向后肠迁移。在小型种群内数量中，性别比例明显偏向雌性，妊娠雌虫数量较少。在大型种群内数量中，性别比例明显偏向雄性，妊娠雌虫数量较多。然而，随着种群内数量的增加，未成熟雄虫和雌虫以及成熟雌虫的平均长度都显著下降，而成熟雄虫的平均长度则显著增加。这些结果强烈表明存在种内竞争以及线虫平均长度的密度依赖性调节，成熟雄虫平均长度的增加强烈表明成熟雄虫之间存在激烈的性选择和竞争。随着种群内数量的增加，雌虫的幼虫产量显著下降，这表明雌虫的繁殖力存在密度依赖性降低。这些结果具有统计学意义，强烈表明种群内数量的自我调节是通过密度依赖性机制进行的，其中未成熟线虫的发育、种群内数量大小、性别比例、性选择以及基础生态位的承载能力在塑造和调节种群内数量方面起着至关重要的作用。
