Supplementary Materials: Table S1. The morphological measurements of males of Cyclommatus mniszechi used for allometry analyses. Table S2. The behavioural sequence data used for sequential analyses of size-matched contests in major males of Cyclommatus mniszechi. Table S3. The behavioural sequence data used for sequential analyses of size-matched contests in minor males of Cyclommatus mniszechi. Video S1. The behavioural sequence of males of Cyclommatus mniszechi in fighting contests under the laboratory setups. One of the opponents walked to the other and touched it (00:07), and then both of them displayed ‘defensive posture’ (00:08) after ‘touch’. Once both individuals approached each other, they accelerated antennation and raised their mandibles and prothoracic parts. The contest then progressed into ‘body raising’ (00:14). They then performed ‘attack’ and ‘push’ to each other several times and then escalated to ‘tussle’ (00:20) and interlocked their mandibles until one of the contestants was clamped (‘clamp1’) in the air by the other for a second and flipped (00:50). The winner dropped the loser and kept attacking and pushing the loser while the loser retreated and moved backwards (00:51).