RESUMEN
Waterfalls are conspicuous geomorphological features with heterogeneous structure, complex dynamics and multiphase flows. Swifts, dippers and starlings are well-known to nest behind waterfalls, and have been reported to fly through them. For smaller fliers, by contrast, waterfalls seem to represent impenetrable barriers, but associated physical constraints and the kinematic responses of volant animals during transit are unknown. Here, we describe the flight behaviour of hummingbirds (the sister group to the swifts) and of various insect taxa as they fly through an artificial sheet waterfall. We additionally launched plastic balls at different speeds at the waterfall so as to assess the inertial dependence of sheet penetration. Hummingbirds were able to penetrate the waterfall with reductions in both their translational speed, and stroke amplitude. The body tilted more vertically and exhibited greater rotations in roll, pitch and yaw, along with increases in tail spread and pitch. The much smaller plastic balls and some flies moving at speeds greater than 2.3 m s-1 and 1.6 m s-1, respectively, also overcame effects of surface tension and water momentum and passed through the waterfall; objects with lower momentum, by contrast, entered the sheet but then fell along with the moving water. Waterfalls can thus represent impenetrable physical barriers for small and slow animal fliers, and may also serve to exclude both predators and parasites from nests of some avian taxa.
RESUMEN
Interactions between bacteria and bacteriophage viruses (phages) are known to influence pathogen growth and virulence, microbial diversity and even biogeochemical cycling. Lytic phages in particular infect and lyse their host cells, and can therefore have significant effects on cell densities as well as competitive dynamics within microbial communities. Despite the known impacts of lytic phages on the ecology and evolution of bacteria in free-living communities, little is known about the role of lytic phages in host-associated microbiomes. We set out to characterize the impact of phages in the tomato phyllosphere, that is the bacteria associated with above-ground plant tissues, by transferring microbial communities from field-grown tomato plants to juvenile plants grown under mostly sterile conditions in either the presence or absence of their associated phage community. In three separate experiments, we found that the presence of phages affects overall bacterial abundance during colonization of new host plants. Furthermore, bacterial community analysis using 16S rRNA amplicon sequencing shows that phages significantly alter the relative abundance of dominant community members and can influence both within- and among-host diversity. These results underscore the importance of lytic phages in host-associated microbiomes and are relevant to microbiome transplantation approaches, as they suggest transferring nonbacterial components of the microbiome among hosts is likely to have a strong impact on growth of both the resident and colonizing microbiota.
