Receiver female body size and distances affect the claw-waving rate of signaller males in fiddler crabs (Brachyura, Ocypodidae)

We tested for the first time how Austruca bengali Crane, 1975 signaller males adjusted their waving rates based on receiver female body sizes and their distances. We video recorded the waving display of 46 males (9-12 mm carapace width) for 30 s, and counted their waving rate. Receiver females were categorised as small (8-10 mm carapace width) and large (>10 mm). Distances between males and females were categorised as short (<= 12 cm) and long (>12 cm) distances. Our results indicate that males are able to measure distances and female sizes, and adjust their waving display by actively reducing waving rate (1) towards small females, as usually small females have lower fecundity compared to large ones and (2) towards females at very close distance because at this point, the females would make their mating decision, and thus males start to lead/hit the females towards their burrow rather than waving vigorously.