Data from: Tropical nematode diversity: vertical stratification of nematode communities in a Costa Rican humid lowland rainforest

Comparisons of nematode communities among ecosystems have indicated that, unlike many organisms, nematode communities have less diversity in the tropics than in temperate ecosystems. There are, however, few studies of tropical nematode diversity on which to base conclusions of global patterns of diversity. This study reports an attempt to estimate nematode diversity in the lowland tropical rainforest of La Selva Biological Research Station in Costa Rica. We suggest that one reason previous estimates of tropical nematode diversity were low is that habitats above the mineral soil are seldom sampled. As much as 62% of the overall genetic diversity, measured by an 18S ribosomal barcode, exists in litter and understory habitats and not in soil. A maximum likelihood tree of barcodes from 360 individual nematodes indicates most major terrestrial nematode lineages were represented in the samples. Estimated â speciesâ richness ranges from 464 to 502 within the four 40 by 40 m plots. Directed sampling of insects and their associated nematodes produced a second set of barcodes that were not recovered by habitat sampling, yet may constitute a major class of tropical nematode diversity. While the generation of novel nematode barcodes proved relatively easy, their identity remains obscure due to deficiencies in existing taxonomic databases. Specimens of Criconematina, a monophyletic group of soil-dwelling plant-parasitic nematodes were examined in detail to assess the steps necessary for associating barcodes with nominal species. Our results highlight the difficulties associated with studying poorly understood organisms in an understudied ecosystem using a destructive (barcode) sampling method.

不同生态系统间的线虫（nematode）群落对比研究表明，与多数生物不同，热带地区的线虫群落多样性低于温带生态系统。然而，目前鲜有针对热带线虫多样性的研究可作为全球多样性格局结论的依据。本研究尝试对哥斯达黎加拉塞尔瓦生物研究站（La Selva Biological Research Station）的低地热带雨林中的线虫多样性进行评估。我们认为，过往热带线虫多样性评估结果偏低的原因之一，是极少对矿质土壤以上的生境开展采样。通过18S核糖体条形码（18S ribosomal barcode）测定的总遗传多样性中，多达62%存在于枯落物和林下生境，而非土壤中。对360条单个线虫的条形码构建的最大似然树显示，样本中涵盖了绝大多数主要的陆生线虫演化支系。在4块40×40平方米的样地中，估算的「物种」丰富度介于464至502之间。针对昆虫及其共生线虫的针对性采样获得了第二组条形码，这类条形码未在生境采样中被检出，但可能构成热带线虫多样性的一个主要类群。尽管新线虫条形码的生成相对简便，但由于现有分类学数据库存在不足，这些条形码对应的物种身份仍不明确。本研究对环线线虫亚科（Criconematina）——一类土栖植物寄生线虫的单系群——的标本开展了详细检视，以评估将条形码与标称物种相关联所需的步骤。本研究结果凸显了在一个研究不足的生态系统中，采用破坏性（条形码）采样方法研究认知匮乏的生物所面临的诸多困难。