Webb, J. L. | bioRxiv Science

bioRxiv2026

Fires attract and fuel hunting success of Australian pyrophilic birds

Changes in fire regimes negatively impact biodiversity worldwide1,2. The immediate behavioral responses of animals to fire, however, are largely unknown. Despite presenting obvious dangers, fire can also attract animals by providing unique foraging opportunities3. Such attraction to fire (pyrophilia) has already been observed in some bird species, yet its underlying motivation remains unidentified. Here, we examined the abundance and behavior of 16 bird species before, during, and after prescribed burns in the northern Australian savanna. Eight species were on average 3 to 23 times more abundant during fires. Raptors caught on average ten times more prey per hour during burns than in the absence of fire, and their foraging success increased with fire size. Black kites, the most pyrophilic birds observed, were more numerous during larger fires and foraged more efficiently on the ground than in the air. These results underscore the importance of investigating animal behavior in response to active fire and the effects of shifting fire regimes on the foraging ecology of pyrophilic animals.

animal behavior and cognition↗

bioRxiv2025

Opsins are Phospholipid Scramblases in All Domains of Life

Opsins are highly abundant retinal proteins in the membranes of photoheterotrophic bacteria. However, some microbial genomes encode an opsin but lack the gene for the final enzyme in retinal synthesis. To account for this paradox, we hypothesized that bacterial opsins play a role in membrane structure and/or biogenesis independent from their potential for light-driven signaling or proton pumping. After purifying actinorhodopsin from a cell-free expression system and from E. coli membranes upon overexpression, we demonstrated both in vitro and in silico that actinorhodopsin from Nanopelagicus ca. is a phospholipid scramblase, serving in its pentameric state as a retinal-independent phospholipid diffusion channel. Phospholipid headgroups move along a transbilayer path between actinorhodopsin protomers, to equilibrate lipid content in the inner and outer leaflets. Two profound activities, membrane biosynthesis and capture of light energy, are thus facilitated by one ancient bacterial polypeptide. Light-dependent activity and light-independent phospholipid scrambling are shared functions of eukaryotic, archaeal, and bacterial rhodopsins. ImportanceCells are surrounded by membranes which concentrate metabolites and protect cellular contents. Most biomembranes are phospholipid bilayers, in which the phospholipids of each leaflet orient their greasy tails inward and polar groups outward. Bilayer biogenesis depends on phospholipids synthesized on the cytofacial side of the membrane reorienting to the extracellular membrane leaflet. This reorientation requires proteins, termed scramblases, and it was shown that rhodopsins -- 7-helix photoactive membrane proteins bound to the cofactor retinal -- from organisms as widely divergent as mammals and archaea possess scramblase activity. Now we conclusively demonstrate using purified proteins in laboratory membranes as well as computational approaches, that bacterial rhodopsins are also phospholipid scramblases. This work is important because it highlights a surprising commonality among bacteria, archaea and eukaryotes and because it shows that rhodopsins - ancient proteins found in the last universal common ancestor - manifest two seemingly unrelated biochemical functions in one protein.

biophysics↗