Kilroy Cathy, Novis Phil
National Institute of Water and Atmospheric Research Ltd Christchurch New Zealand.
Landcare Research Lincoln New Zealand.
Ecol Evol. 2017 Dec 12;8(2):904-919. doi: 10.1002/ece3.3572. eCollection 2018 Jan.
Defining the geographic origins of free-living aquatic microorganisms can be problematic because many such organisms have ubiquitous distributions, and proving absence from a region is practically impossible. Geographic origins become important if microorganisms have invasive characteristics. The freshwater diatom is a potentially ubiquitous microorganism for which the recent global expansion of nuisance proliferations has been attributed to environmental change. The changes may include declines in dissolved reactive phosphorus (DRP) to low levels (e.g., <2 mg/m) and increases in dissolved inorganic nitrogen (DIN) to >10 mg/m because both these nutrient conditions are associated with nuisance proliferations of . Proliferations of have been observed in South Island, New Zealand, since 2004. We aimed to address the ubiquity hypothesis for in New Zealand using historical river water nutrient data and new molecular analyses. We used 15 years of data at 77 river sites to assess whether trends in DRP or DIN prior to the spread of were consistent with a transition from a rare, undetected, species to a nuisance species. We used new sequences of chloroplast regions to examine the genetic similarity of populations from New Zealand and six overseas locations. We found no evidence for declines in DRP concentrations since 1989 that could explain the spread of proliferations since 2004. At some affected sites, lowest DRP occurred before 2004. Trends in DIN also did not indicate enhanced suitability for . Lack of diversity in the chloroplast intergenic regions of New Zealand populations and populations from western North America is consistent with recent dispersal to New Zealand. Our analyses did not support the proposal that was historically present in New Zealand rivers. These results provide further evidence countering proposals of general ubiquity in freshwater diatoms and indicate that, as assumed in 2004, is a recent arrival in New Zealand.
确定自由生活的水生微生物的地理起源可能存在问题，因为许多这类生物分布广泛，而且要证明某个地区不存在某种微生物实际上是不可能的。如果微生物具有入侵特性，那么地理起源就变得很重要。淡水硅藻是一种可能广泛分布的微生物，其近期在全球范围内令人讨厌的大量繁殖被归因于环境变化。这些变化可能包括溶解活性磷（DRP）降至低水平（例如，<2毫克/立方米）以及溶解无机氮（DIN）增至>10毫克/立方米，因为这两种营养条件都与硅藻的大量繁殖有关。自2004年以来，在新西兰南岛已观察到硅藻的大量繁殖。我们旨在利用历史河水营养数据和新的分子分析来探讨新西兰硅藻广泛分布的假设。我们使用了77个河流站点的15年数据，以评估在硅藻扩散之前DRP或DIN的趋势是否与从一种罕见、未被检测到的物种向令人讨厌的物种的转变相一致。我们使用叶绿体区域的新序列来检验来自新西兰和六个海外地点的硅藻种群的遗传相似性。我们没有发现自1989年以来DRP浓度下降的证据，而这种下降本可解释2004年以来的大量繁殖扩散情况。在一些受影响的站点，最低的DRP出现在2004年之前。DIN的趋势也未表明对硅藻更适宜。新西兰种群以及北美西部种群的叶绿体基因间隔区缺乏多样性，这与近期扩散到新西兰的情况相符。我们的分析不支持新西兰河流中历史上就存在硅藻的说法。这些结果提供了进一步的证据，反驳了淡水硅藻普遍广泛分布的提议，并表明，正如2004年所假设的那样，硅藻是最近才来到新西兰的。
