Striking parallels between dorsoventral patterning in and reveal a complex evolutionary history behind a model gene regulatory network.

Dorsoventral pattering relies on Toll and BMP signalling in all insects studied so far, with variations in the relative contributions of both pathways. and the beetle share extensive dependence on Toll, while representatives of more distantly related lineages like the wasp and bug rely more strongly on BMP signalling. Here, we show that in the cricket , an evolutionarily distant outgroup, Toll has, like in , a direct patterning role for the ventral half of the embryo. In addition, Toll polarises BMP signalling, although this does not involve the conserved BMP inhibitor Sog/Chordin. Finally, Toll activation relies on ovarian patterning mechanisms with striking similarity to . Our data suggest two surprising hypotheses: (1) that Toll's patterning function in and is the result of convergent evolution or (2) a system arose early in insect evolution and was extensively altered in multiple independent lineages.