Fig. 3. Model of the two-dimensional transmission pattern.

Circles represent all individuals seen moss-sponging at least once between 2011 and 2014. The eight original moss-spongers from Hobaiter et al.’s study (2) are represented in gray. The arrows represent the social transmission found by Hobaiter et al. (2). The rectangles represent matrilines in which vertical social learning took place, the main transmission mechanism involved in the spread. The dashed lines represent the possible learning path of the cases (n = 7) in which individuals acquired the behavior in the absence of vertical transmission because individuals did not have moss-sponging kin, suggesting learning from individuals that they were highly associated with (linked with the individual with the highest association index).