Potential long-distance dispersal of freshwater diatoms adhering to waterfowl plumage

Abstract

Waterfowl are potential long-distance dispersal vectors for aquatic microbes such as diatoms, but experimental evidence is scarce. We conducted an experiment designed to emulate diatom dispersal via adherence to waterfowl, and to evaluate the effects of humidity and transport duration on potential dispersal success. We dipped individual mallard breast feathers in a pure benthic diatom culture (Nitzschia pusilla Grunow), then subjected them to one of four relative humidity levels (RH; from ca. 8% to 88%) crossed with one of four transport durations (10, 60, 120, 240 minutes) within a chamber through which air was passed continuously, mimicking light wind. We then placed the feather on sterile growth medium. After two weeks we used spectrofluorometry to detect diatom growth and thus diatom viability. A logistic regression on viability revealed a significant interaction between transport duration and RH: the negative effect of duration was strongest under lower RH conditions, but under high RH (88%) the probability of being viable was moderate to high regardless of transport duration. Importantly, even after 4 hours, the probability of being viable was predicted to be 0.45 (95% confidence interval: 0.18 to 0.75). We then placed our findings in the geographic context of the central waterfowl migration flyway in North America, and specifically Nebraska, South Dakota, and North Dakota, for which sufficient data were available to enable geospatial predictions of potential mallard-borne diatom dispersal. Combined with published data about (i) mallard flight speeds, (ii) the geographic distribution of surface waters and of N. pusilla, and (iii) daytime RH during the months of April through June, our model predicted high probabilities of potential dispersal among the region’s suitable water bodies.

Extinction of austral diatoms in response to large-scale climate dynamics in Antarctica

“…For example, direct terrestrial connections with lower latitudes must have allowed for stepwise short-distance dispersal, which is expected to be more effective for survival than long-distance dispersal over large maritime barriers. In that sense, migration of freshwater diatom species in the Arctic has likely been facilitated by both aeolian pathways and animal vectors ( 42 ). This includes the Arctic’s avian fauna, which is far richer than in Antarctica.…”

Dispersal of aquatic and terrestrial organisms by waterbirds: A review of current knowledge and future priorities

“…Both epizoochory and endozoochory are important for microbial dispersal by waterbirds, but it is unclear which mechanism is dominant. Manning et al (2021) investigated the potential of epizoochory by dipping breast feathers from mallards Anas platyrhynchos in cultures of diatoms and showed that their survival when stuck to feathers increases with relative air humidity. Tesson et al (2018) used in vitro gut‐simulation to investigate the endozoochory potential of dinoflagellates, confirming that resting cysts survived gut conditions.…”

“…Sensitivity analysis for wintering waterbirds suggests that maximum gut retention times have less influence on seed dispersal kernels than the nature of bird movements per se, reinforcing the need to include quality tracking data to obtain valid predictions (Martín‐Vélez, Leeuwen, et al, 2021). Some studies of endozoochory have made unrealistic estimates of the scale of dispersal, as they fail to accurately account for waterbird movement, and make simple extrapolations from a retention time curve by assuming propagule ingestion is followed by non‐stop flights (e.g., Manning et al, 2021; Raulings et al, 2011). However, ringing recoveries have been used to make general predictions for kernels during seasonal migration, and have shown that migrating ducks can facilitate dispersal on a very large scale, predicting dispersal of over 3.5% of seeds to be over 100 km and up to 1,600 km, although maximum dispersal distances for Artemia cysts were about half that of seeds (Viana et al, 2013).…”