Beyond planktonic encounter theory: a Rotimer-based model of benthic mate search in the rotifer Euchlanis dilatata

The benthic rotifer Euchlanis dilatata produces Rotimer, a filamentous biopolymer forming persistent three-dimensional webs on substrate surfaces. Rotimer is conserved across Rotifera and serves basal functions in females, but its function in non-feeding, short-lived males remains unclear. We test whether female-produced Rotimer functions as a mate-search cue detectable by males. We propose the Benthic Rotifer Encounter Model (BREM), extending planktonic encounter theory to substrate-anchored systems by substituting the Rotimer web’s effective encounter radius for the female body radius; BREM is bidirectional in principle, though only the female-to-male direction was tested here. Consistent with BREM, female webs were structurally more complex than male webs, and males showed greater trajectory straightness in the presence of female Rotimer. Directed tracking of conspecific Rotimer to copulation was observed in both sexes. These findings support BREM’s female–male encounter pathway and generate testable predictions for mate-search dynamics in benthic microinvertebrates.