1. Waterfowl are potential long‐distance dispersal vectors for aquatic microbes such as diatoms, but supporting empirical data are scarce, especially concerning external transport on feathers.
2. We conducted an experiment designed to partially emulate diatom dispersal via adherence to waterfowl, and to evaluate the effects of relative humidity (RH) and exposure time on viability. We dipped individual breast feathers from mallards (Anas platyrhynchos) in a pure culture of the freshwater diatom Nitzschia pusilla Grunow, then, at room temperature (22.7°C), subjected them to one of four contrasting levels of RH (c. 8%, 35%, 70%, 88%) crossed with one of four exposure times (10, 60, 120, 240 min) within a chamber through which air was passed continuously, mimicking light wind that might be experienced by diatoms adhered to subsurface feathers. We then gently placed the feather on sterile growth medium. After 2 weeks, we used spectrofluorometry to detect diatom growth and thus diatom viability.
3. We found that exposure time and RH interacted significantly to affect diatom viability: the negative effect of exposure time was strongest under low RH conditions, but under high RH (88%) the probability of being viable was 0.84 for a 10‐min exposure (95% confidence interval: 0.64–0.94), and 0.45 for 4 hr of exposure (95% confidence interval: 0.18–0.75).
4. We combined our experimental findings with geospatial data to predict the probability of potential dispersal via adherence to mallards throughout Nebraska, South Dakota, and North Dakota, which are situated within the central waterfowl migration flyway in North America, and host important mallard breeding grounds. Using published data about: (1) mallard flight speeds; (2) the geographic distribution of surface waters and of N. pusilla; and (3) vapour pressure deficit (calculated using RH and air temperature) during the months of April and May, our geospatial model predicted high probabilities of potential dispersal, over tens to hundreds of kilometres, among water bodies of the central migration flyway.
5. Taken together, the results of our experiment and geospatial models provide novel insights into ectozoochory of freshwater diatoms, specifically that long‐distance dispersal of diatoms via adherence to waterfowl feathers is highly plausible, particularly during the near‐dawn hours when waterfowl flight activity peaks and vapour pressure deficit is low. Considered alongside previous evidence suggesting successful internal transport by waterfowl, we conclude that, for freshwater diatoms, ectozoochory is likely to be commonplace among waterbodies frequented by waterfowl.

中文翻译：

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附着在水禽羽毛上的淡水硅藻的长距离分散

1. 水禽是硅藻等水生微生物的潜在长距离传播媒介，但缺乏经验数据，尤其是关于羽毛的外部运输。
2. 我们进行了一项实验，旨在通过附着在水禽上来部分模拟硅藻的扩散，并评估相对湿度（RH）和暴露时间对生存力的影响。我们将野鸭（Anas platyrhynchos）的单个胸羽毛浸入淡水硅藻Nitzschia pusilla Grunow的纯培养物中，然后在室温（22.7°C）下对它们进行四个相对湿度的RH（c。8％，35％，70％，88％）在连续让空气通过的室内进行四个暴露时间之一（10、60、120、240分钟）中的一个，模仿附着在其上的硅藻可能遇到的轻风地下羽毛。然后，我们将羽毛轻轻放在无菌生长培养基上。2周后，我们使用荧光分光光度法检测硅藻的生长，从而检测硅藻的生存能力。
3. 我们发现暴露时间和相对湿度会显着影响硅藻的活力：在较低的相对湿度条件下，暴露时间的负面影响最明显，但是在较高的相对湿度（88％）下，暴露10分钟的存活概率为0.84（95 ％置信区间：0.64–0.94），以及4小时暴露时间为0.45（95％置信区间：0.18–0.75）。
4. 我们将我们的实验结果与地理空间数据相结合，以预测遵守内布拉斯加州，南达科他州和北达科他州（位于北美中部水禽迁徙路线内）的野鸭的潜在扩散可能性，这些野鸭是重要的野鸭繁殖地。使用有关以下方面的公开数据：（1）绿头鸭的飞行速度；（2）地表水和普斯猪笼草的地理分布；（3）在4月和5月的蒸气压赤字（使用相对湿度和气温计算），我们的地理空间模型预测了在中央迁徙航道的水体中潜在扩散的可能性很高，超过几十至数百公里。
5. 总之，我们的实验结果和地理空间模型为淡水硅藻的形态学提供了新的见解，特别是通过附着水禽羽毛进行硅藻的长距离扩散是很可能的，尤其是在水禽飞行活动高峰和蒸气压不足。与先前的证据表明水禽能够成功进行内部运输一起考虑，我们得出结论，对于淡水硅藻，在动物经常使用的水体中，外生极动物很可能司空见惯。