Figure 2.

Graphical representation of morphological/behavioural differences between species. Dendrogram resulting from cluster analysis showing the Euclidean distance based on seven morphological/behavioural characters related to the acoustic tracheal system and directional hearing (data matrix, Additional file 2). One main cluster (in blue) comprises species that use intraspecific acoustic communication in conjunction with the possession of an acoustic vesicle. The second major cluster consists of species of the family Gryllidae that secondarily lost acoustic signalling and presumably reduced the acoustic vesicle but still have tibial ears (green cluster) and species that are primarily non-hearing (orange cluster).